SUMMARY

Generators /Auxiliary Engines1. How to Synchronize Generators on a Ship?2. Important Points to Consider While Carrying out Alternator Maintenance

of Ship’s Generator3. Procedure for Starting and Stopping Generators on a Ship4. Procedure for D’carb of Ship’s Generator5. Hydraulic Starting of Emergency Generator

Air Compressor1. Procedure for Starting Breathing Air Compressor On a Ship2. What is Clearance Volume or Bumping Clearance in Air Compressors?3. The Basics of Air Compressor On a Ship4. Troubleshooting Air Compressors on a Ship: The Ultimate Guide5. Efficiency of Air Compressor and Uses of Compressed Air on a Ship6. Air Compressor on a Ship: Checks for Starting and Stopping a Compressor7. Safety Features and Maintenance Procedure for Air Compressor on a Ship8. Different Parts of a Marine Air Compressor Used on a Ship9. Air bottle or Air receiver On board Ship

Oil Water Separator1. How to Operate an Oily Water Separator (OWS) on Ship?2. Oily Water Separator: Construction and Working

Sewage Treatment Plant1. Sewage Treatment Plant on a Ship Explained2. Procedure for Starting and Stopping of Sewage Treatment Plant on a Ship3. Maintenance and Checks for Sewage Treatment Plant on Ship4. 4 Important Terms Related to Sewage Treatment Plant

Fresh Water Generator1. Converting Seawater to Freshwater on a Ship: Fresh Water Generator

Explained2. Reverse Osmosis: Modern Alternative for Shipboard Water Production

Heat Exchanger1. Types of Heat Exchangers on a Ship2. Heat Exchangers on Ship Explained3. How to do Maintenance of Marine Heat Exchangers on Ships?

Propulsion System1. Understanding Nuclear Marine Propulsion2. Starting Procedure for Turbine Generator on Ship3. An Introduction to Ship’s Turbine Generator4. What is Azipod Propulsion System on Ship?5. Nuclear Ship Propulsion: Is it the Future of the Shipping Industry?6. Different Types of Marine Propulsion Systems Used in the Shipping World

Marine Growth Prevention1. 4 Types of Anti-fouling Systems Used on Board Ships to Prevent Marine

Growth2. What is Marine Growth Preventive System (MGPS) On a Ship?3. Learn About Fatal Bacteria that Grow in Ship’s Air-Con System

Pumps / Valves / Pipes and Bends1. Pipes and Bends – An Essential Guide for Second Engineers: Part 12. Pipes and Bends – An Essential Guide for Second Engineers: Part 23. Pipes and Bends – An Essential Guide for Second Engineers – Part 34. Pipes and Bends: An Essential Guide for Second Engineers – Part 45. General Overview of Types of Pumps on Ship6. What is a Metering Pump On board a Ship?

Other Auxiliaries / Equipment1. Viscosity Meter and Viscosity Controller Used on Ships2. Understanding Stern Tube Arrangement on Ships3. General Overview of Central Cooling System on Ships4. Life Raft Release System and Launching Procedure5. High Speed Centrifuge on Ship: Construction and Working6. Bow Thrusters: Construction and Working7. The Green Source of Power On Ship – Shaft Generator

Slow Steaming1. A Chief Engineer’s Concern Regarding Slow Steaming of Ships2. Slow Steaming of Ships: Optimization of Ship’s Main Engine

Efficiency / Performance / Workshop Tools

1. List of Processes Used in Marine Workshop of Ships2. Different Types of Mechanical Measuring Tools and Gauges Used on Ships3. A Guide to Welding Electrodes on Ships – Part 14. A Guide to Welding Electrodes on Ships – Part 25. Energy Audit on Ships: Part 16. The Urgent Need to Reduce Nitrogen Oxide (NOx) Emissions from Ships7. Condition Monitoring Techniques – What is Shock Pulse Monitoring

(SPM)?

How to Synchronize Generators on a Ship?Synchronizing of an incoming generator or alternator is very important before paralleling it with another generator. The synchronizing of the generator is done with the help of synchroscope or with three bulb method in case of emergency. It is of utmost importance that before paralleling the generators the frequency and voltage of the generators need to be matched. In this article we will describe the method for synchronizing generators on a ship.

There are two methods to synchronize generators on a ship – one is the normal and other is the emergency method.

Synchroscope method

 

1. Ÿ  The synchroscope consists of a small motor with coils on the two poles connected across two phases. Let’s say it is connected in red and yellow phases of the incoming machine and armature windings supplied from red and yellow phases from the switchboard bus bars.

2. Ÿ   The bus bar circuit consists of an inductance and resistance connected in parallel.

3. Ÿ  The inductor circuit has the delaying current effect by 90 degrees relative to current in resistance.

4. Ÿ  These dual currents are fed into the synchroscope with the help of slip rings to the armature windings which produces a rotating magnetic field.

5. Ÿ  The polarity of the poles will change alternatively in north/south direction with changes in red and yellow phases of the incoming machine.

6. Ÿ  The rotating field will react with the poles by turning the rotor either in clockwise or anticlockwise direction.

7. Ÿ  If the rotor is moving in clockwise direction this means that the incoming machine is running faster than the bus bar and slower when running in anticlockwise direction.

8. Ÿ  Generally, it is preferred to adjust the alternator speed slightly higher, which will move the pointer on synchroscope is in clockwise direction.

9. Ÿ  The breaker is closed just before the pointer reaches 12 o clock position, at which the incoming machine is in phase with the bus bar

Emergency synchronizing lamps or three bulb method

This method is generally used when there is a failure of synchroscope. In case of failure a standby method should be available to synchronize the alternator, and thus the emergency lamp method is used.

Three lamps should be connected between three phases of the bus bar and the incoming generator should be connected as shown in the diagram:-

1. Ÿ  The lamps are connected only in this manner because if they are connected across, the same phase lamps will go on and off together when the incoming machine is out of phase with the switchboard .

2. Ÿ  In this method as per the diagram the two lamps will be bright and one lamp will be dark when incoming machine is coming in phase with the bus bar.

3. Ÿ  The movement of these bright and dark lamps indicates whether the incoming machine is running faster or slower.

4. Ÿ  For e.g. there is a moment when lamp A will be dark and lamp B & C will be bright, similarly there will be instance when B is dark and others are bright and C is dark and other two are bright. This example indicates that machine is running fast and the  movement of the lamps from dark and bright gives an clockwise movement

5. Ÿ  Clockwise movement indicates fast and  anti clockwise direction indicates slow running of incoming generator.

Important Points to Consider While Carrying out Alternator Maintenance of Ship’s GeneratorA ship cannot remain “Live” without a Generator – the lifeline and power production plant of the vessel. A generator on ship is a combination of two separate systems – an alternator and a prime mover whose capacity depends upon the number of machinery or power consuming items fitted on the ship.

What is Alternator?

An alternator is an electro-mechanical device comprising of stator, rotor winding and an external exciter for supplying excitation voltage. Alternator generates electricity when coupled with a prime mover.

Alternator on a ship is exposed to harsh weather and sea conditions, due to which, its capacity and efficiency tends to reduce. It is very important to have proper maintenance on the alternator part of the generator as per planned maintenance or as and when required.

 

Following Points are to be considered while Carrying Out Maintenance on Alternators:

Before starting any maintenance work on the alternator, all safety precaution should be taken and the alternator should be shut and locked down. Also, post notice and ply cards on relevant places and alternator heater to be isolated.

Clean the alternator ventilation passage and air filter.

Check the Insulation resistance of stator and rotor winding.

Air gap between stator and rotor to be checked and maintained between 1.5 to 2 mm.

Slip rings to be checked for even wear down to be renewed if required.

Carbon brushes to be clean and checked for free movement.

The brush contacting pressure to be checked by spring balance.

Automatic Voltage Regulator to be checked and cleaned off oil and dust.

The lube oil level of pedestal bearing to be maintained and renewed as per planned maintenance.

A vacuum cleaner can be used to remove dust accumulated in the inner parts of alternator.

The terminal box cover gasket to be checked for proper oil and water tightness.

All the connection in the terminal box to be tightened properly.

Cable gland to be checked for integrity.

Forced Ventilation around alternator must be maintained all the time.

Check heater for proper operation.

The foundation bolts of the alternator to be checked for tightness.

 

After maintenance is performed, a no load test should be carried out and general condition such as noise, temperature, voltage generated etc. of the alternator should be observed and noted.

Procedure for Starting and Stopping Generators on a ShipA generator on a ship is known as the heart of the ship. It is that life-line which supports each and every function of the ship. Generator of the ship requires special care, attention, and maintenance for its effective and economic running. Moreover, when it comes to operating a generator on a ship, it’s a totally different ball game.

Unlike the conventional generators that we use on land, a ship’s generator requires a special procedure for starting and stopping it. Though not a very complex one, the process demands a step-by-step system to be followed. Missing even a single step might lead to failure in starting or stopping the generator and can even lead to “black-out”, a situation which everyone on ship tries their best to stay away from. In this article, we bring to you an accurate, step by step procedure for starting and stopping a generator on a ship.

 

Generator starting procedure

Automatic Start

1. Ÿ  This method is only possible if sufficient amount of starting air is available. The air valves and interlocks are operated like in the turning gear operation.

2. Ÿ  In this method the operator has nothing to do, for the generator starts itself depending on the load requirement.

3. Ÿ  However during the Maneuvering process and in restricted areas, the operator has to start by going into the computer based Power Management System (pms). Once inside the system, the operator needs to go to the generator page and click start.

4. Ÿ  In PMS system, the automation follows sequence of starting, matching voltage and frequency of the incoming generator and the generator comes on load automatically.

5. Ÿ  In case of a blackout condition or a dead ship condition, the operator might have to start the generator manually.

Manual start

The manual process is totally different from the automatic start system. The following steps need to be followed.

 

1. Ÿ  Check that all the necessary valves and lines are open and no interlock is active on the generator before operating.

2. Ÿ  Generally before starting the generator the indicator cocks are opened and small air kick is given with the help of the starting lever. After this, the lever is brought back to the zero position, which ensures there is no water leakage in the generator. The leakage can be from cylinder head, liner or from the turbocharger .

3. Ÿ  The step is performed by putting the control to local position and then the generator is started locally.

4. Ÿ  In case any water leakage is found, it is to be reported to a senior officer or chief engineer and further actions are to be taken.

5. Ÿ  It is to note that this manual starting procedure is not followed generally on Ums ships, but it is a common procedure on manned engine room.

6. Ÿ  In engine rooms, which have water mist fire fighting system installed, this procedure is not followed because when the engine is given a manual kick with open indicator cocks, small amount of smoke comes out of the heads which can lead to false fire alarm, resulting in release of water mist in the specified area.

7. Ÿ  After checking the leakage, in case of any, the indicator cocks are closed and generator is started again from the local panel.

8. Ÿ  The generator is then allowed to run on zero or no load condition for some time for about 5 minutes.

9. Ÿ  After this the generator control is put to the remote mode.10. Ÿ  If the automation of the ship is in working after putting in remote mode the

generator will come on load automatically after checking voltage and frequency parameters.

11. Ÿ  If  this doesn’t happen automatically, then one has to go to the generator panel in Engine control room and check the parameters.

12. Ÿ  The parameters checked are voltage and the frequency of the incoming generator.

13. Ÿ  The frequency can be increased or decreased by the frequency controller or governor control on the panel.

14. Ÿ  The incoming generator is checked in synchroscope to see if it’s running fast or slow, which means if frequency is high or low.

15. Ÿ  In synchroscope, it is checked that the needle moves in clockwise and anticlockwise direction.

16. Ÿ  Clockwise direction means it is running fast and anti-clockwise means it is running slow.

17. Ÿ  Generally the breaker is pressed when the needle moves in clockwise direction very slowly and when it comes in 11’o clock position.

18. Ÿ  This process is to be done in supervision of experienced officer if someone is doing for the first time, for  if this is done incorrectly the blackout can happen which can lead to accidents, if the ship is operating in restricted areas.

19. Ÿ  Once this is done, the generator load will be shared almost equally by the number of generators running.

20. After this the parameters of the generator are checked for any abnormalities.

Stopping procedure

 

Automatic Procedure

Ÿ  In this procedure the generator is stopped by going into the PMS system in the computer and pressing the stop button to bring stop the generator.

1. Ÿ  This is to be followed only when two or more generators are running.2. Ÿ  Even if you trying to stop the only running generator it will not stop due to

inbuilt safety. The safety system thus prevents a blackout.3. Ÿ  When the stop button is pressed the load is gradually reduced by the PMS

and after following the procedure the generator is stopped.

Manual Procedure

1. Ÿ  In this procedure the generator to be stopped, is put off load from the generator panel in the Engine control room.

2. Ÿ  The load is reduced slowly by the governor control on the panel.3. Ÿ  The load is reduced until the load comes on the panel below 100 kw.4. Ÿ  When the load is below 100kw the breaker is pressed and the generator is

taken off-load.5. Ÿ  The generator is allowed to run for 5 minutes in idle condition and the stop

button is pressed on the panel.6. Ÿ  The generator is then stopped

Procedure for D’carb of Ship’s GeneratorGenerator is one of the prime machinery on board a ship. Ship’s generator supplies power to all other machines and acts like the lifeline of the ship. Like other machinery, generator’s on board routine maintenance is also done by the engineers. One of the important procedures of generator maintenance is d’carb, which is carried out by qualified engineers within the time limit set by the makers and technical department.

D’carb or de-carbonisation of generator not only means cleaning and removing carbon from parts and spaces involved in combustion of fuel but also includes checking, overhauling and renewal of parts involved in power transmission like connecting rods, con-rod bearings, main bearings etc.

Before d’carb of any of the generators onboard ship, preparation has to be done by management and operational level engineers, and the management level engineers will decide in consent with the office ashore, whether to proceed with the process or not.

Following preparations and checks are to be done before doing d’carb of auxiliary generator onboard vessel:

General Preparations

Make sure that other generators are available for taking up the load of the ship at all times, in case one or more generators are lined up for d’carb.

The d’carb of the generator should be planned with such time interval so that during d’carb operation, if any one of the running generator has a breakdown, other generators or means must be available to propel the ship.

Make sure all the special tools of auxiliary generator are available onboard and are in sound condition.

Check with the engine stores that all the spares that are required for d’carb are available.

Raise the requisition for all spare parts required for the d’carb operation.

Before D’carb

Brief discussion with the team about the procedure as per the manuals is to be done.

Isolate the given generator from the main switch board and auto start panel.

Close all the systems attached with the generator like sea water system, fuel oil system, air system, lube oil system etc.

Inform every one by putting placards and posters of “MEN AT WORK” and “DO NOT START” etc.

Have a look on the previous d’carb report and fill the pre d’carb checklist.

If the d’carb includes crank shaft and bearings, record crank shaft deflection prior to the start of the same.

Tool box meeting to be carried out and risk assessment form to be filled and signed by all the personnel involved in the operation.

During d’carb

Safety should be the primary concern and personal protective equipment should be donned by all individuals.

Make sure all the tools, hydraulic jack and lifting devices are placed at safe position before the work begins.

All the removed parts should be kept in a secured place and in sequential manners.

Cleaning, checking and measuring should be done and worn out parts are to be replaced as directed by the manual.

Lifting of all the heavy parts by crane or chain block should be supervised by experienced engineers.

Care should be taken not to drop any small parts, nut-bolts, tools etc. inside the jacket passage or in the crankcase.

Clearances and other measurements are should be recorded.

All the parts should be fitted back under supervision of senior engineer.

After D’carb

Crank shaft deflection should be taken and recorded.

Crank case oil should be removed and sump be cleaned.

Crank case inspection should be done so that nothing is left inside.

Make sure all the parts are fitted and tightened as per the manual.

All the isolated systems are put back into operation one by one, starting from the fresh water system. Leaks should be checked thoroughly.

Fresh oil should be taken and lube oil system should be put back in use followed by fuel oil system.

Turning gear should be rotated by tommy bar to ensure free movement of crank shaft.

Hydraulic Starting of Emergency GeneratorMaintaining continuous power on the ship is one of the most important tasks while sailing. However, sometimes accidents are inevitable and due to some reason such as breakdown of machinery, technical snag etc. there can be a power failure on the ship.

During such conditions, emergency equipments like life boat, navigation lights etc. should be in operating conditions so that they can be used in case of emergencies.  As we all know that a ship is built under class regulations and all the necessary regulation described by SOLAS and IMO have to be followed during the construction of the ship.

In case of blackout there should be an alternate source of power available and which should come on load automatically. Alternate source of power are taken from batteries and emergency generators to provide power to critical equipments. As batteries cannot provide power for a longer period of time, emergency generators are preferred.

Understanding Emergency Power System

As per SOLAS regulation the emergency power equipments should come on load within 45 seconds of the power failure. When the power failure takes place the emergency generator is normally started by a small electric motor which cranks the engine for starting. This motor gets power from the battery which is being charged by emergency switchboard.  Also in case the equipment or emergency generator is unable to start due to any reason, there should be an alternate method or manual starting available in hand. As per Solas regulation the secondary means of starting should be able to provide additional three starts within 30 minutes.

One of the most common methods for starting emergency generator is hydraulic starting. Options other than hydraulic start are:

1) By compressed air.

2) Inertia starters.

3) Hand cranking

Construction and Working Principle

Hydraulic system for starting works on the principle of hydraulic and pneumatic, in which, the energy is first stored and then supplied or released for the starting of the engine.

The main components of this system are:

1) Feed tank and hand pump

The feed tank is provided with hydraulic oil which is pumped by the hand pump to the accumulator which helps in starting the engine.

2) Hydraulic Accumulator

This is the most important component of the system. It is the heart of the system where the energy is stored. It consists of a cylinder in which there is a leak proof sliding piston. Above this piston the cylinder is pre charged with the nitrogen gas to about a pressure of 200 bars. The oil is pressed against this piston and necessary pressure of oil is stored inside the accumulator.

3) Pressure Gauge

This is to check the pressure inside the accumulator.

4) Relay valve lever

The operation of this lever will release the energy stored in the accumulator to the starter unit.

5) Starter unit and engine dog

The starter unit is attached to the free end of the engine with the help of a bracket and the engine dog is attached to the engine crankshaft with the help of a suitable adapter. This starter unit consists of two opposed cylinders with rack and pinion arrangement. The pinion arrangement has teeth on one end which drives the dog having the corresponding teeth. Two helical grooves are formed inside the periphery of the pinion which is engaged by spring loaded balls inside the starter housing which helps in engaging and disengaging by the axial movement. The positive engagement is maintained by the helical tooth-form of the pinion and racks.

How to Operate the Hydraulic Starter?

1) Check whether all the valves for fuel, cooling water etc. are open to the generator.

2) Check the level of the feed tank. Fill it if necessary. Please see that if the level in the gauge glass is low and the pressure in the accumulator is ok as per manufacturer recommendation then do not fill the tank as the oil will return from the starter after starting.

3) Check the pressure in the accumulator. Raise pressure if required. Pressurize the accumulator as per OEM recommendations.

4) Operate the relay valve lever. The relay valve lever operates in two stages. Move the relay valve to an angle of 45 degrees, at this position the resistance is felt. In this stage a small bleed is given to the starter causing a slow rotation, engaging the dog. When the dog gets engaged operate the lever fully. This releases the pressure in the starter and engine starts. Sudden jerk of relay lever is avoided so as to prevent damage to the gears and the clutching arrangement.

5) When the engine starts turning, release the lever and the lever goes back to normal position. The oil used for starting the engines comes back to the feed tank after starting.

6) Check the pressure in the accumulator. It should be enough for two additional starts.

7) Raise the pressure again for the next emergency.

Procedure for Starting Breathing Air Compressor On a ShipA breathing air compressor is used to fill up the oxygen bottles used for fire fighting or entering enclosed spaces. The breathing air compressors, as they are known, needs to be operated in a special way. They are smaller than the conventional compressors found on ship. 

While operating the breathing air compressor, there are certain points that should be followed in order to ensure smooth starting and operation of the compressor. The article describes the procedure for starting a breathing air compressor on a ship.

Pre- Starting Procedure

Follow the below step-by-step procedure before starting the compressor.

Fill water in the filling tank to keep the bottles cooled as heat is generated while filling the air.

Check oil level in compressor-sump through indicator glass fixed on the side of the compressor.

Check O-ring is placed in DIN-coupling male part and is in good condition and also no O-ring is there in the female-part of the valve on the bottle.

Place bottle in water tank. Connect hose to the bottle and do not tighten too firmly as the pressure will

ensure a proper fit. Open the valve on the hose by turning counter clockwise. Open the valve on the bottle by turning it counter clockwise.

Procedure for starting the compressor

Following steps are to be followed for starting the compressor:

Even though the unit has automatic condensate draining you should drain the condensate frequently while filling by turning the knob.

The compressor will stop on reaching 300Bar. If not you must stop it immediately.

Close the bottle valve (1) by turning clockwise. Close the hose valve (2) by turning anticlockwise. After filling all bottles open the hose valve carefully to relieve pressure from

hose. Drain condensate from the compressor and water from the filling tank.

What is Clearance Volume or Bumping Clearance in Air Compressors?Clearance volume or bumping clearance is the space between the top of the piston and the cylinder head of an air compressor. This clearance is an important aspect of the compressors and should be as less as practically possible to improve the volumetric efficiency of the compressor. The clearance volume should not be too less or too more. Moreover, it affects the efficiency of the machinery and thus should be checked at regular intervals of time.

Significance and Effects of Bumping Clearance

In an air compressor, when the discharge valve closes in the end of the compression cycle, a small amount of high pressure air is trapped in the clearance volume.

Before again taking suction, the air trapped in the clearance volume must expand below the suction pressure i.e. below the atmospheric pressure.

The expansion of this trapped air in the clearance volume causes effective loss of stroke due to which the volumetric efficiency of compressor drops. Therefore, the clearance volume has a significant effect on the efficiency of the compressor.

Effects Due to Less Clearance

Small clearance volume may result in piston banging or colliding to the cylinder head.This is dangerous when the compressor when is running in unloaded condition without any resistance to the movement of the piston.

Effects Due to Large Clearance

Large bumping clearance retards the formation of vacuum on the suction stroke and thus less air is drawn inside for compression and accordingly the weight of the air delivered is reduced proportional to the clearance volume.

Compressor has to run for a longer period to provide the necessary compression pressure.

Reasons for Change in Clearance Volume

During overhauls of the air compressor, if the gasket fitted between the cylinder head joints is of the wrong type, then the bumping clearance will increase, resulting in wear down of bottom bearings or wrong bearings are put in place.

How Bumping Clearance is checked?

Bumping clearance is checked by putting a lead ball or plastic gauges over the piston and then turning the compressor one revolution by hand.

By doing this the lead ball will compress and the thickness obtained is the clearance volume.

This thickness is measured with vernier caliper or micrometer and is then compared with the manufacturer’s value. Adjustments are made in case there is an offset in the value.

Adjustment of bumping clearance

Bumping clearance can be adjusted with the help of inserting shims (thin metallic plates) in the bottom bearings. Inserting shims will move the connecting rod and the piston which will change the clearance.

What should be the Bumping Clearance?

Generally bumping clearance depends on the manufacturer but as a thumb rule it should be between 0.5% to 1% of the bore of the cylinder.

The Basics of Air Compressor On a ShipCompressor is one such device which is used for several purposes on a ship. As the main aim of the compressor, as the name suggests, is to compress air or any fluid in order to reduce its volume. Some of the main applications of compressors are main air compressor, deck air compressor, AC compressor and refrigeration compressor. In this article we will learn about air compressors and its types. 

 

Air Compressor produces pressurized air by decreasing the volume of air and in turn increasing its pressure. Different types of air compressors are used according to the usage.

 

Types of Air Compressors

There are mainly four types of compressors:

1)Centrifugal compressor

2)Rotary vane compressor

3)Rotary screw compressor

4)Reciprocating air compressor.

However, on ship reciprocating air compressor is widely used.

Uses of Air Compressor on Ship:

On board a ship, compressed air is used for several purposes. On the basis of application, different air compressors are kept for a particular usage. Normally, air compressors on board ships are:

-main air compressor,

-topping up compressor

-deck air compressor

-Emergency air compressor

Main air compressor

Main air compressor is used for supplying high pressurised air for starting of main and auxiliary engines. The pressurised air generated by the air compressor is stored in air storage bottle. These are high capacity compressors and the air pressure that is required from these compressors to start the main engine is 30 bars.

Control air is also supplied from air bottle through a pressure reducing valve and a control air filter. Normally they are twice in number and can be more than that for redundancy.

Topping up compressor

Topping up compressor takes up the lead to cover up for the leakage in the system. This means that as soon as the air pressure in the system goes below a particular level, the topping up compressor replenished the system with pressurized air.

Deck air compressor

Deck air compressor is used for deck use and as service air compressor and might have a separate service air bottle for the same. These are lower capacity pressure compressors as pressure required for service air is in between the range of 6 to 8 bar.

Emergency air compressor

Emergency air compressor is used for starting auxiliary engine at the time of an emergency or when the main air compressor has failed for filling up the main air receiver. This type of compressor can be motor driven or engine driven. If motor driven, it should be supplied from emergency source of power.

Troubleshooting Air Compressors on a Ship: The Ultimate Guide

Air compressors on a ship require special attention and care for their smooth running. It is only through routine maintenance and checkups that you can expect smooth and efficient running of the compressors. 

However, compressor is a peculiar equipment which tends to get some or the other problem while working. In this article, we will go through each and every problem that can arise in an air compressor and also enumerate ways to troubleshoot that problem.

This is the ultimate guide for troubleshooting air compressors on a ship

1)Lube Oil Pressure Low

The following can be the reasons for lube oil pressure low in the air compressor:

Faulty pressure gauge. Cock to pressure gauge in closed position. Low oil level in the sump. Leakage in supply pipe. Suction filter is choked. Oil grade in the crank case is not compatible. Attached Lube oil gear pump is faulty.

Worn out Bearing, clearance is more.

 

 

2)  Abnormal noise during operation

If you get any abnormal noise during operation, the following can be the reasons:

Loose foundation bolts. Worn out bearings, clearance is high. Imbalance crankshaft resulting in high-end play. Valve plate broken or faulty. Relief valve lifting below setting pressure. Bumping clearance is less. Piston worn-out, broken piston ring.

3)Vibration in the machinery:

In case of vibrations, the following reasons are to be considered and checked.

Foundation bolts are loose.

Discharge pressure high, faulty discharge valve plates. Liner and piston worn out. Small bumping clearance.

4)Cooling water temperature is high

Cooling water temperature can go high because of the following reasons: 

Inlet or outlet valve for cooling water is closed. Inter-cooler is chocked. Cooling water in the expansion tank is low. Pipe passage becomes narrow due to scale formation. Water-pump belt or gear drive broken. Pump not working.

 

5)First stage discharge pressure high

In case the first stage discharge pressure is high, it must be because of :

Pressure gauge is faulty. Inter-cooler air passage is chocked. Second stage suction valve is not closing properly, allowing air to escape

from 2nd to 1st stage. Discharge valve of first stage is malfunctioning, and remains in closed

position. Spring of discharge valve is malfunctioning.

 

6)  First stage discharge pressure low

In case the first stage discharge pressure is low, it must be because of :

Pressure gauge is faulty. Suction filter is choked. Unloader of first stage is leaking. First stage suction valve is not closing properly, resulting in compressed air

leakage. First stage suction valve is not opening fully, leading to less intake of air. Discharge valve is faulty and remains open permanently. Relief valve after first stage is leaking. Piston ring of first stage is badly worn out, allowing air to pass.

7)Second stage discharge pressure high:

In case of high discharge pressure in the second stage, the reasons can be:

Faulty pressure gauge. Discharge valve to air bottle is shut. Second stage discharge valve plate worn out, and even the spring worn out. Valve is stuck in closed position. After cooler air passage choked.

Air bottle is over pressurized.

8 )Second stage discharge pressure low:

When second stage discharge pressure is low, it could be because  of:

Pressure gauge is faulty. Suction valve for second stage is malfunctioning, in open position. Suction valve for second stage is not opening fully, and thus less intake of

air. Discharge valve is faulty and remains open during operation. Piston rings of second stage are worn out, leaking out compressed air. Relief valve of second stage is leaking. Un-loader of second stage is leaking.

9)Relief valve of first stage lifting

If relief valve of the first stage is lifting, it can be because of

Spring of relief valve is malfunctioning, thus lifting at less pressure. Discharge valve of first stage is not opening. Intercooler air passage is blocked. Suction valve of second stage is in stuck position. Water inside the compression chamber due to crack in the jacket and water

is leaking inside.

10)Relief valve of second stage is lifting

If relief valve of the second stage is lifting, look for the following reasons:

Relief valve is malfunctioning, lifting at lower then setting pressure. Main discharge valve to the air bottle is closed. Discharge valve plates and spring are worn out, valve in closed position. Blockage in the after cooler air passage. Water inside the compression chamber due to crack jacket.

The above mentioned points are just a brief explanation to the problems of the air compressor tackled on board. However, they   serve as a guiding light for finding the right fault in the compressor.

Efficiency of Air Compressor and Uses of Compressed Air on a ShipThe Efficiency of an air compressor on a ship depends on several factors. A compressor provides highly pressurized air which increases the temperature to exceptionally high levels. In order to get quality performance out of air compressors, it is important to check and control the pressure and temperature within optimum range. In this article we will learn as to what it takes for efficient running of an air compressor on a ship. 

 

Efficient working of Air Compressor

An air compressor is to provide air at high pressure. The temperature during the compression process is known as the compression temperature. The compression temperature that is generated is enough to ignite vaporized oil if present in the system. Moreover, in the process, a lot of energy is also wasted in the form of heat.

 

To avoid the loss of heat and overheating of internal parts, inter-coolers are fitted in the air compressor. With the help of inter-coolers, it is possible to approach the ideal isothermal compression to achieve maximum volumetric efficiency.

Sea water is commonly used for the cooling purpose in air compressor. Sea water is circulated in the system using an attached pump or by using main or auxiliary sea water circulating system. It is to note that sea water causes scale deposits in cooling passages. Sometimes, fresh water from a closed loop system is also used to avoid scale deposit problems.

Graph showing saved work due to inter cooling

Uses of Compressed Air on Ship

Compressed air is used for the following purposes on a ship.

For starting of main engine, auxiliary engine, emergency generator and emergency fire pump.

For automation and control air for main and auxiliary engine. For different application on the deck side and in engine room such as

chipping, drilling, buffing, pressurized water jet cleaning etc. by use of pneumatic tools and machinery.

For overhauling machinery by use of pneumatic tools and hydraulic jack. For pressure testing of different machinery parts, pipeline etc. Compressed air is also used for ships whistle and fog horn. It is used in life boat for heaving up the later, if air motor is attached as a

heaving provision. For supplying water to accommodation and various parts of the ship through

hydrophore by keeping the later pressurized with air. For conducting aerobic breakdowns of the on board sewage in sewage plant. For pressurized spray painting. Used in soot blowing of boiler and economizer. Used in portable pneumatic pumps like Weldon pumps for oil, water and

bilge transfer. For general cleaning and services.

The above mentioned are the most common purposes for which compressed air is used. The application and uses may differ from ship to ship.

Air Compressor on a Ship: Checks for Starting and Stopping a CompressorCertain steps and systematic procedure need to be followed in order to start or stop an air compressor on a ship. In this article, we will learn how to start and stop an air compressor and also find out checks that are need to be made before starting the air compressor and also during its operation.

 Checks before Starting the Air Compressor

The following steps are to be followed before starting an air compressor on a ship.

1) Check the lube oil in the crankcase sump by means of dipstick or sight glass.

2) All the valves of compressor discharge must be in normally open condition.

3) If any manual valve is present in un-loader line, it must always be kept open.

4) All alarms and trips- Lube oil low pressure, water high temperature, over load trip etc. must be checked for operation.

5) All valves in cooling water line must be in normally open position.

6) Cocks for all the pressure gauges must be in open position.

7) Air intake filter should be clean.

8 ) If compressor has not been started from long time than it should be turned on manually with a tommy-bar to check for the free movement of its parts.

 

Starting and Stopping procedure: What is Unloading the compressor?

Unloading is a normal procedure during the starting and stopping of the compressor. It is carried out due to following reasons:

1) When starting a compressor motor, since the load on the motor is very high the starting current is also high. In order to avoid further loading of the compressor an un-loader arrangement is provided which is normally pneumatic or solenoid control and which releases the pressure during the starting of the compressor. Once the current comes down to the running value, the un-loader closes automatically. Normally a timer function is used for opening and closing of un-loader.

2) Air contains moisture and during the compression process some amount of moisture gets released. Liquid in any form is incompressible and if some amount of oily water mixture is present inside the cylinder then it will damage the compressor. To overcome this problem un-loader is used. During starting un-loader comes in action and releases all the moisture accumulated inside the cylinder.

3) Intermediate operation of un-loader is also selected so that during the process of compression any moisture or oil accumulation cannot take place inside it.

4) During stopping the compressor un-loader is operated so that for the next starting the cylinder will remain moisture free.

Checks during the Operation of Compressor:

1) Check if all the pressure gauges are showing correct readings of lube oil pressure, water pressure etc.

2) Check for any abnormal sound like knocking etc.

3) Check for any lube oil or water leakages.

4) If cylinder lubrication is provided, check the supply from sight glass.

5) Check if the discharge pressure for all units is normal.

6) Check air temperature after the final stage is under limit.

7) Check the flow of cooling water from sight glass.

8 ) If attached cooling water pump is provided check for its free rotation.

9) Check the relief valve of all units for leakage. In some compressor, provision is given to check the relief valve with hand lever, if provided check all units.

Safety Features and Maintenance Procedure for Air Compressor on a ShipEvery Air compressor on a ship is fitted with several safety features to avoid abnormal and dangerous operational errors of the equipment. If safety, alarms and trips are not present on the air compressor, abnormal operation may lead to breakdown of the compressor and may also injure a person working on or around it.

 

 

Different safety features on an air compressor are

 

Relief valve:

Fitted after every stage to release excess pressure developed inside it. The setting of the lifting pressure increases after every ascending stage. Normally fitted between 1st stage and intercooler and 2nd stage – aftercooler.Bursting disc:

A bursting disc is a copper disc provided at the air cooler of the compressor. It is a safety disc which bursts when the pressure exceeds over the pre-determined value due to leaky air tubes of the cooler (intercooler or aftercooler).

Fusible plug:

Generally located on the discharge side of the compressor, it fuses if the air temperature is higher than the operational temperature. The fusible plug is made up of material which melts at high temperature.

Lube Oil low pressure alarm and trip:

If the lube oil pressure goes lower than the normal, the alarm is sounded followed by a cut out trip signal to avoid damage to bearings and crank shaft.

Water high temperature trip:

If the intercoolers are choked or the flow of water is less, then the air compressor will get over heated. To avoid this situation high water temperature trip is activated which cut offs the compressor.

Water no-flow trip:

If the attached pump is not working or the flow of water inside the intercooler is not enough to cool the compressor then moving part inside the compressor will get seized due to overheating. A no flow trip is provided which continuously monitor the flow of water and trips the compressor when there is none.

Motor Overload trip:

If the current taken by motor during running or starting is very high then there is a possibility of damage to the motor. An overload trip is thus fitted to avoid such situation.

Maintenance

A compressor requires a proper planned routine maintenance for safe and efficient operation and to avoid breakdown maintenance. Routine for maintenance depends on the manufacturer’s advice given in the manual. The following are the maintenance checks that should be carried out after the mentioned running hours.

@ 250hrs:

1) Clean air filter.2) Check un-loader operation.3) If belt is provided for driving cooling water pump, check its tightness.

@ 500hrs:

1) Change lube oil and clean sump.2) Clean lube oil filter.3) Check and renew suction and discharge valves with overhauled one.

@ 1000 hrs:

1) Crankcase inspection, main and big end bearing inspection.2) Relief valve overhauling.

@ 4000 hrs:

1) Piston and big end bearing overhauling, piston ring renewal.2) Intercooler cleaning.3) Motor overhauling.

Running hour may differ from maker to maker. The above description is a rough idea for a general maintenance of marine air compressor.

Without the supply of air, a ship will soon be termed as a dead ship. It is very important for a marine engineer to understand the importance of the compressor; hence it’s the responsibility of the engineer onboard to maintain the compressor, the air receiver and the air pipe line and the overall system in the proper condition.

Different Parts of a Marine Air Compressor Used on a ShipA marine air compressor provides compressed air for various purposes on a ship. An air compressor is one of the most important equipments on a ship which needs special care and routine maintenance. In this article we will know the basics of the marine air compressor by first getting familiarized with the different parts of the same. 

The main parts of the marine air compressor are:

1) Cylinder liner:

It is made of graded cast iron and is accompanied with water jacket around it to absorb heat produced during compression process. It is designed so as to give a streamline passage to the pressurized air resulting in minimum pressure drop.

2) Piston:

For a non-lubricating type compressor, light weight aluminum alloy piston are used and for lubricating type graded, cast iron piston are used with piston rings for sealing and scrapping off excess oil.

3) Piston Rod:

In high capacity compressor which is normally big in size, piston is attached to piston rod made up of alloy steel. They are fitted with anti friction packing ring to avoid chances of compressed air leakage.

4) Connecting rod:

Connecting rod plays its role to minimize thrust to the bearing surface. It is made up of forged alloy steel.

5) Big end bearing and Main bearing:

They are constructed to give rigidity to the running rotational mechanism. They are made up of copper lead alloy and have a long operational life if proper lube oil and lubrication is provided.

6) Crank shaft:

It is a one piece designed part, using counterweights for dynamic balancing during high speed of rotation to avoid twisting due to torsion forces. Connecting rod big end bearing and main bearing are connected to crank shaft at crank pin and journal pin which are polished to ensure long working life of bearings.

7) Frame and crankcase:

Normally they have rectangular shape and accommodate all the moving parts and that’s why are made up of rigid cast iron. Main bearing housing is fitted on a bore in crank case and is made with highest precision to avoid eccentricity or misalignment.

8 ) Oil pump:

A lubricating oil pump is fitted to supply lube oil to all the bearings, which can be chain or gear driven, through crank shaft. Pressure of oil can be regulated by means of regulating screw provided in the pump. A filter in the inlet of the pump is also attached to supply clean and particle free oil to the bearings.

9) Water pump:

Some compressor may have attached water cooling pump driven by crankshaft through chain or gear. Some system does not use attached pump as they use water supply from main or auxiliary system for cooling.

10) Suction and Discharge valve:

These are multi-plate valves made up of stainless steel and are used to suck and to discharge air from one stage to another and to the air bottle. Proper assembling of valves is very important for efficient operation of the compressor.

11) Suction Filter:

It is a air filter made up of copper or soft steel with a paper material to absorb oil and wire mesh to avoid any metal or dust particle to go inside compression chamber.

12) Inter-coolers:

Inter-coolers are normally fitted in between two stages to cool down the air temperature and to increase the volumetric efficiency of compressor. Some compressor have inbuilt attached copper tubes for cooling and some have outside assembly of copper tube inter-coolers.

13) Driving Motor:

An Electrical motor is attached to the compressor for making it operational and is connected to the compressor through the flywheel.

There are the main parts of a marine air compressor. The parts may vary according to the requirement of the system or ship.

Air bottle or Air receiver On board ShipMain engine and auxiliary engine are the two prime components in a ship’s engine room, on which, the entire operation of the vessel is dependent. There are several other important machineries that are necessary to support these two main components; however, one equipment without which any of the above mentioned machines cannot do away with is an air bottle or air receiver.

 

What is an Air bottle or Receiver?

The air bottle or air receiver is a large container acting as a reservoir to store compressed air supplied by the main air compressor of the ship at high pressure. This compressed air is very important to start main engine or auxiliary engine.

Purpose of Air Bottle

The high pressure is used for initial starting of the marine I.C engines present onboard vessel.

It also supplies control air to the marine engines.

Service air is supplied from the air bottle.

If the quick closing valves are air operated, safety air is supplied through air bottle.

Spring air for exhaust valve is supplied through air bottle.

Apart from above mentioned ones, there are several other uses as well.

 

What are the Air Bottle Mountings and Connections?

The general mountings and connection present on air bottle of a ship are:

Filling valve: This is a valve fitted in the supply connection from main air compressor to the air bottle.

Outlet to Main engine: An outlet valve and pipe is fitted for connection from air bottle to main engine for supplying air during starting.

Outlet to auxiliary engine: An outlet valve and pipe is fitted for connection from air bottle to auxiliary engines for supplying air during starting.

Auxiliary connection: Other auxiliary supplies connections such as service air, safety air etc. is also provided with isolating valve.

Relief valve: A relief valve is fitted on the air bottle to relieve excess pressure inside the bottle.

Drain valve: A drain valve is fitted at the bottom of the bottle to drain accumulated condensate from the receiver.

Fusible plug: A fusible plug is fitted in the bottle with a separate connection leading out of the engine room so that in the event of fire, this plug will melt and relieve all the air to the outside atmosphere.

Manhole door: A manhole door is fitted in the bottle to carry out inspection of the same.

How to Operate an Oily Water Separator (OWS) on Ship?An oily water separator clears the bilge water of oily content to bring it inside the acceptable range to discharge it overboard. An oily water separator is machinery for such importance that it is handled by only the 2nd or chief engineer. (However, the duty engineer might also be asked to operate under supervision)

Operating an Oily Water Separator

An oily water separatorcan only be operated when the ship is sailing and en route. According to MARPOL, the oil content of the effluent must be less than 15 ppm andthe ship has in operation an oil discharge monitoring and control system and oily-water separating/filtering equipment.

In case of failure to follow any of the above mentioned rules, the ship will be fined and stopped, and the chief or 2nd engineer can even be imprisoned.

Because of such high risks, operating an oily water separator should be done with utmost precision to minimize the risks of marine pollution. Though a “How to Operate?” guide is always posted near the oily water separator, there are few points to be kept in mind and followed to prevent any mistake.

Operating Procedure

The following points are to be followed while operating OWS.

1) OWS overboard manual discharge valve is to be kept locked and keys are to be kept with the chief engineer. Open the lock and overboard valve. Open all the other valves of the system.

2) Open the desired bilge tank valve from which the oily water mixture is to be discharged from OWS.

3) Open air if the control valves are air operated.

4) Switch on the power supply of the control panel and OCM unit.

5) Fill the separator and filter unit with fresh or sea water to clean up and prime the system till the water comes out from vent of second stage.

6) Start the OWS supply pump which is a laminar flow pump and one that will supply the oily water mixture to OWS.

7) Observe the OCM for ppm value and keep checking sounding of bilge tank from where OWS is taking suction and of the OWS sludge tank.

8 ) A skin valve/sample valve is provided just before overboard valve and after the 3-way valve. Keep a check on the sample for any effluent and clarity.

9) Keep a watch on the ship side at the overboard discharge valve.

10) After the operation, Switch off the power and shut and lock the overboard valve. Keys to be handed over to the chief engineer.

11) Entry to be made by chief engineer in the Oil Record Book (ORB) with signature of operating officer, chief engineer and the master.

Oily Water Separator: Construction and WorkingTo minimize the oily content in bilge water, which can be discharged from the ship, MARPOL has a regulation under ANNEX I which limits the oil content in the bilge water that vessel can legitimately discharge into the sea. It is now a requirement for all vessels to have an oil discharge monitoring and control system along with an oil filtering equipment known as the Oily Water Separator (OWS).

As the name indicates, the function of oily water separator is to separate maximum amount of oil particles from the water to be discharged overboard from engine room or cargo hold bilges, oil tanks and oil contaminated spaces. As per the regulation, the oil content in the water processed from the OWS must be less then 15 parts per million of oil.

Construction and Working of OWS

OWS consists of mainly three segments:

Separator unit

This unit consists of catch plates which are inside a coarse separating compartment and an oil collecting chamber.

Here the oil having a density which is lower than that of the water, which makes the former rise into the oil collecting compartment and the rest of the non-flowing oil mixture settle down into fine settling compartment after passing between the catch plates.

After a period of time more oil will separate and collect in the oil collecting chamber. The oil content of water which passes through this unit is around 100 parts per million of oil.

A control valve (pneumatic or electronic) releases the separated oil in to the designated OWS sludge tank.

Heater may be incorporated in this unit for smooth flow and separation of oil and water.

First stage helps in removing some physical impurities to achieve fine filtration in the later stage.

The Filter unit

This is a separate unit whose input comes from the discharge of the first unit. This unit consists of three stages – filter stage, coalescer stage and collecting chamber. The impurities and particles are separated by the filter and are settled at the bottom

for removal. In second stage, coalescer induces coalescence process in which oil droplets are joined

to increase the size by breaking down the surface tension between oil droplets in the mixture.

These large oil molecules rise above the mixture in the collecting chamber and are removed when required.

The output from this unit should be less than 15 ppm to fulfil legal discharge criteria. If the oil content in water is more than 15 ppm then maintenance work such as filter

cleaning or renewal of filters is to be done as required.

Oil Content Monitor and Control Unit

This unit functions together in two parts – monitoring and controlling. The ppm of oil is continuously monitored by Oil Content Monitor (OCM); if the ppm is

high it will give alarm and feed data to the control unit. The control unit continuously monitors the output signal of OCM and if alarm arises, it

will not allow the oily water to go overboard by means of operating 3 way solenoid valve.

There are normally 3 solenoid valves commanded by control unit. These are located in the first unit oil collecting chamber, second unit oil collecting chamber and one in discharge side of the oily water separator which is a 3 way valve.

The 3 way valve inlet is from the OWS discharge, where one outlet is to overboard and second outlet is to OWS sludge tank.

When OCM gives alarm, 3 way valve discharges oily mixture in the sludge tank.

Sewage Treatment Plant on a Ship ExplainedDiscarding sewage produced onboard on a ship is one of the few tasks on a ship which should be taken utmost care of if one wants to same him and his shipping company from heavy fine. The sewage generated on the ship cannot be stored on the ship for a very long time and it for this reason it has to be discharged into the sea.

 

Though sewage can be discharged into the sea, we cannot discharge it directly overboard as there are some regulations regarding discharging of sewage that needs to be followed. Sewage on sea is generally the waste produced from toilets, urinals and WC scuppers. The rules say that the sewage can be discharged into the sea water only after it is treated and the distance of the ship is 4 nautical miles from the nearest land.

But if the sewage is not treated this can be discharged 12 nautical miles away from the nearest land. Also the discharged sewage should not produce any visible floating solids nor should it cause any discoloration of surrounding water.

Generally, ships prefer treating sewage before discharging to save themselves from any type of embarrassment. There are different methods of treating sewage available in the market, but the most common of them is the biological type for it occupies less space for holding tank, unlike those of the other methods. Moreover, the discharge generated from this plant is eco

friendly. It is to not that each sewage treatment system installed onboard has to be certified by classification society and should perform as per their requirement and regulations.

 

Working of a Biological Sewage Plant

The basic principle of the working of a biological treatment plant is decomposition of the raw sewage. This process is done by aerating the sewage chamber with fresh air. The aerobic bacteria survive on this fresh air and decompose the raw sewage which can be disposed off in the sea. Air is a very important criterion in the functioning of the biological sewage plant because if air is not present, it will lead to growth of anaerobic bacteria, which produces toxic gases that are hazardous to health.Also, after decomposition of the sewage with anaerobic bacteria, a dark black liquid causes discoloration of water which is not accepted for discharging. Thus in a biological sewage treatment plant the main aim is to maintain the flow of fresh air.

 

Division of Processes 

The biological sewage plant is divides into three chambers:-

 

Aeration chamber

 This chamber is fed with raw sewage which has been grinded to form small particles. The advantage of breaking sewage in small particles is that it increases the area and high number of bacteria can attack simultaneously to decompose the sewage. The sewage is decomposed into carbon dioxide, water and inorganic sewage. The air is forced through diffuser into the air chamber. The pressure of air flow also plays an important role in decomposition of the sewage. If pressure is kept high then the mixture of air and sewage will not take place properly and it will escape without doing any work required for decomposition. It is for this reason; controlled pressure is important inside the sewage treatment plant as this will help in proper mixing and decomposition by the agitation caused by air bubbles. Generally the pressure is kept around 0.3-0.4 bars.

 

Settling tank

The mixture of liquid and sludge is passed to settling tank from the aeration chamber. In the settling tank the sludge settles at the bottom and clear liquid on the top. The sludge present at the bottom is not allowed to be kept inside the settling tank as this will lead to growth of anaerobic bacteria and foul gases will be produced.The sludge formed is recycled with the incoming sludge where it will mixes with the later and assist in the breakdown of sewage.

 

Chlorination and Collection

In this chamber the clear liquid produced from the settling tank is over flown and the liquid is disinfected with the help of chlorine. This is done because of the presence of the e-coli bacteria present in the liquid. To reduce these bacteria to acceptable level chlorination is done. Moreover, to reduce the e-coli, the treated liquid is kept for a period of at least 60 minutes. In some plants disinfection is also done with the help of ultra violet radiation. The collected liquid is discharged to overboard or settling tank depending on the geological position of the ship. If the ship is in restricted or near coastline then the sewage will be discharged into the holding tank; otherwise, the sewage is discharged directly into the sea when high level is reached and is disposed automatically until low level switch activates.

Procedure for Starting and Stopping of Sewage Treatment Plant on a ShipAny machine on the ship requires a proper procedure to be followed for starting and stopping it. Failure to follow this step-by-step procedure will lead to either failure in starting or stopping the machine or lead to some fault.

Sewage treatment plant is one such equipment on the ship which requires a step-by-step procedure to be followed for starting and stopping it. In this article we will go through the procedure of starting and stopping a sewage treatment plant.

Starting of a Sewage Plant

Sewage plant is generally running all the time during sailing, but it might need to be started when the ship is installed with a new sewage treat plant which needs to be stopped at regular interval of time for improving its performance and maintenance procedures. Below are the points that need to be followed for starting a sewage treatment plant.

1. Make sure if any maintenance is carried out on the sewage treatment system, all the openings have been closed properly before starting.

2. The sewage plant is be filled with fresh water inside the chamber.

3. At this stage, there are no aerobic bacteria inside the chamber, but the sewage has started coming to the plant. Thus, in order to increase efficiency and starting rate of the plant bio pac is added to the plant by flushing the amount specified in the manual.  This bio pac is mixed with warm water which helps in growth of these bacteria and also efficient functioning of the plant.

4. If the bio pac is not added, the plant might take up to 5 to 7 days to be completely functional. However, with the bio pac it becomes functional within 24 hours.

5. Start the air compressor or open the air valve as per the design of the plant. The pressure is maintained as per the manual. Generally 0.3-0.4 bars.

6. Open the sewage overboard valve and close holding tank valve when the ship is out of restricted waters.

7. The plant is continuously monitored and checked for the flow through the transparent plastic tubes.

8. The sample is taken for checking for suspended solids and chlorine content.

Stopping of the plant

Stopping of the sewage treatment plant is generally done either before entering the dry dock or in case some maintenance has to be carried out inside the treatment plant.

1. For stopping the system, close the inlet valve to the sewage plant and close the overboard valve and let the sewage go overboard.

2. Empty all the three chambers of the plant i.e. aeration, settling and chlorination chambers. If the chambers are not emptied, it will lead to growth of anaerobic bacteria which forms the toxic H2S gas.

3. If entry has to be made inside the tank, the later should be checked for hydrogen sulphide gas H2S with the help of dragor tube by taking a continuous sample from the plant. Entry is made with the help of mask and rubber gloves should be put on.

4. In case the ship is going to dry dock the overboard should be connected to shore reception facilities.

Maintenance and Checks for Sewage Treatment Plant on ShipAn efficient running of a sewage treatment plant on a ship requires periodic maintenance and daily checks of the system. Failure to do so can lead to an output that cannot be discharged into the sea, blockage of pipelines, and even failure of some parts.

 There are several factors that results in smooth working of a sewage treatment plant on a ship and this article enumerates all the maintenance and checks for that smooth running.

Routine Checks

1. During daily rounds the pressure of the system should be checked and should be within the limits.

2. The air lift return should be checked to make sure the system is working properly. This is usually checked by the flow through the clear plastic pipe present on the installation. A clear sludge can be seen flowing through the tubes back to the aeration chamber.

3. Over a period of time, the sludge content in the aeration tank due to the recycling of the sludge from settling tank and fresh sewage increases. This sludge content or suspended solid particle is measured in mg/liter. The method of checking it is to take sample in a conical flask provided by the manufacturer and filling it up to 1000ml mark. The sample is then allowed to be settled and reading of sludge content is checked.

The sludge content should not be above the 200 mark, but if it is above the 200 mark, the tank has to be emptied for increasing the performance. In some ships this is checked by filtering the sample through a pre-weighed pad which is dried and re-weighed. This also depends from manufacturer to manufacturer, but is done every week.

4. Also the bio-pac is added every week to the plant to increase efficiency. The bio-pac contains aerobic bacteria which get activated when mixed with hot water.

5. The chlorination of the sample should be between 1-5 ppm and accordingly the dosing has to be increased or decreased.

6. The level of biological oxygen demand (BOD) is also checked and it should not be above 50 mg/liter. The sample is checked by incubating the sample at 20 degrees and well oxygenating the same. The amount of oxygen absorbed over a period of five days is measured. This is done to check the oxygen required for full breakdown of sewage after it has been treated by aerobic bacteria.

7. The internal coating of the sewage treatment plant should be checked for cracking and blistering. If any kind of damage is found then we first need to empty the tanks and then necessary repairs to be performed. Special precautions should be taken before entering the tank as it may contain toxic gases that cause suffocation. The gases should

be checked by dragor tube, a special tube in which samples of various gases are taken before entering.

When it is made sure of the absence of toxic gases, entry is made with the mask and gloves. After completion of work the area has to be disinfected. Later, hands should be properly scrubbed and overalls be thoroughly washed.

8. If the sewage treatment plant is fitted with UV disinfectant system instead of the chlorination system, the UV lamp has to be changed as recommended by the manufacturer.

9. High and low level limit switches should be checked for auto cut-in and cut-out of the discharge to over-board pump.

10. Make sure the stand-by sewage discharge pump is put on auto during the working of the sewage treatment plant.

Maintenance

In case of a blockage of the sewage line there is a connection for back flushing which uses sea water. This is to be used to unclog the sewage pipelines; however, it is to note that all valves are closed and only the necessary valves are open, for it might back flush from WC of the cabins.

Generally, stewards are instructed for using chemicals provided by various manufacturers such as Drew Marine and Unitor during washing so that no blockages of lines are caused. However, there shouldn’t be any overuse of these chemical as it would lead to killing of aerobic bacteria which will decrease the efficiency of the plant and other problems.  The amount of chemicals is to be as per manufacturer recommendation.

4 Important Terms Related to Sewage Treatment Plant on ShipsSewage on board ships needs to be treated before it is discharged to the sea. Sewage treatment plant is used to treat the sewage and make it less harmful for the sea.

Marine engineers must know the operation of the sewage plant before using the same in order to comply with the rules and regulations of discarding sewage.While operating the sewage plant, engineer must know:

Procedure for starting and stopping sewage treatment plant

Maintenance and checks for sewage treatment plant

However, apart from the above mentioned aspects, marine engineers should also know four important terms while dealing with sewage treatment plants on ships. They are:

1. Biochemical Oxygen Demand (BOD)2. Coliform Count3. Recommended levels of pumping out solids4. Bio-chemical digestion of sewage

1. Biochemical Oxygen Demand

Biochemical oxygen demand is a test to identify biological decomposable substances and to test the strength of the sewage. BOD

depends on the activity of bacteria in the sewage. These bacteria feed on and consume organic matter in the presence of oxygen.

BOD can also be defined as the amount of oxygen required by the micro-organisms in the stabilization of organic matter. The results are generally expressed as the amount of oxygen taken by one litre sample (diluted with aerated water) when incubated at 20 degree for five days.

BOD of raw sewage is 300-600 mg/litre. IMO recommends BOD of less than 50 mg/litre after treatment through sewage treatment plant.

2. Coliform Count

Coliform is a type of organism which is present in human intestine and is recognized as indicator organisms of sewage pollution. Presence of these organisms in water is an indication of pathogen (pathogen count), which are diseases causing bacteria responsible for cholera, dysentery, typhoid etc.

The number of coliform organisms present in sewage on ship is very large, with each person contributing around 125 billion in winters and 400 billion in summer.

IMO recommends faecal coliform count of less than 250 faecal/100 ml. of affluent after treatment.

3. Recommended levels of pumping out solids

Dissolved solids – Solids which are dissolved in the solution

Suspended solids – Solids physically suspended in sewage that can be removed by laboratory filtration and are relatively high in organic matter.

Settle able solids – Suspended solids that will subside in quiescent liquid in a reasonable period of time (usually around an hour)

Suspended level of raw sewage – Around 300-400 mg/litre; IMO recommends 50 mg/ litre after treatment.

Residual disinfectant – After treatment residual disinfectant should be as low as possible. IMO recommends use of ultra violet exposure for chlorination method.

4. Biochemical digestion of sewage:

Anaerobic process

Anaerobic bacteria can only multiply in the absence of free oxygen as they utilize chemically bound oxygen to survive. Anaerobic bacteria break down the organic matter into water, carbon dioxide, methane, hydrogen sulphide and ammonia. This process is called putrefaction.

The products thus produced out of this process are noxious and toxic. The effluent is of poor quality and by-products are highly corrosive.

Aerobic process

Aerobic bacteria require free oxygen to survive. They break down the organic matter to produce safe products such as water, carbon dioxide, inert residue, and energy to synthesize new bacteria.

Converting Seawater to Freshwater on a Ship: Fresh Water Generator ExplainedFresh water generator, one of the important machinery on board a ship, is something that cannot be done without. Fresh water produced from fresh water generator is used for drinking, cooking, washing and even running other important machinery which use fresh water as a cooling medium. Fresh water is generally produced on board using the evaporation method. There are two things that are available in plenty on ship to produce fresh water –Seawater and heat. Thus fresh water is produced by evaporating sea water using heat from any of the heat source. The evaporated sea water is then again cooled by the sea water and the cycle repeats.

Generally the heat source available is taken from the main engine jacket water, which is used for cooling the main engine components such as cylinder head, liner etc. The temperature available from this jacket water is about 70 deg. centigrade. But at this temperature the evaporation of water is not possible as we all know that the evaporation of water takes place at 100 deg centigrade under atmospheric pressure.

Thus in order to produce fresh water at 70 degrees we need to reduce the atmospheric pressure, which is done by creating a vacuum inside the chamber where the evaporation is taking place. Also, as a result of the vacuum the cooling of the evaporated sea water will also take place at lower temperature. This cooled water is collected and transferred to the tank.

Nowadays, reverse osmosis is one of the methods which are used on board for generating fresh water. Generally this is used on passenger vessels wherein there is a large requirement of fresh water production. However, in merchant ships the evaporation method is used as reverse osmosis is costly and includes large maintenance cost for membrane.

Fresh Water Generator Arrangement

The main body of a fresh water generator on the ship consists of a large cylindrical body with two compartments. One of the compartments is the condenser and the other is the evaporator. The fresh water generator also consists of an educator which helps in generating the required vacuum. The fresh water pump and ejector pump helps in transfer of water to and from the fresh water generator.

 

Starting the Fresh Water Generator

1.       Before starting the fresh water generator we have to check that the ship is not in congested water, canals and is 20 nautical miles away from the shore. This is done because near the shore the effluents from factories and sewage are discharged into the sea can get into the fresh water generator.

2.       Check whether engine is running above 50 rpm, the reason for this is that at low rpm the temperature of jacket water which is around 60 degrees and not sufficient for evaporation of water.

3.       Check the drain valve present at the bottom of the generator is in close position.

4.       Now open suction and discharge valves of the sea water pump which will provide water for evaporation, cooling and to the eductor for creating vacuum.

5.       Open the sea water discharge valve from where the water is sent back to the sea after circulating inside the fresh water generator.

6.       Close the vacuum valve situated on top of the generator.

7.       Now start the sea water pump and check the pressure of the pump. The pressure is generally 3-4 bars.

8.       Wait for the vacuum to build up. Vacuum should be at least 90% which can be seen on the gauge present on the generator. Generally the time taken for the generation of vacuum is about 10 minutes.

9.       When vacuum is achieved open the valve for feed water treatment, this is to prevent scale formation inside the plates.

10.    Now open hot water (jacket water) inlet and outlet valves slowly to about half. Always open the outlet valve first and then inlet valve. Slowly start to increase the opening of the valves to full open.

11.    Now we can see that the boiling temperature starts increasing and the vacuum starts dropping.

12.    The vacuum drop to about 85% which is an indication that evaporation is started.

13.    Open the valve from fresh water pump to drain.

14.    Switch on the salinometer if it has to be started manually. Generally it is on auto start.

15.    Now start fresh water pump and taste the water coming out of the drain.

16.    When fresh water starts producing it is seen that the boiling temperature drops again slightly and vacuum comes back to the normal value.

17.    Check the water coming out of the salinometer is not salty and also check the reading of the salinometer. This is done to see if the salinometer is working properly or not and to prevent the whole fresh water from getting contaminated with salt water. The value of salinometer is kept below 10ppm.

18.    After checking the taste of the water coming out of the salinometer, open valve for tank from the pump and close drain valve.

 

Stopping the Fresh water Generator

 

1.       Close the jacket water inlet valves. Generally inlet is closed first and then the outlet valve.

2.       Close the valve for feed water treatment.

3.       Stop fresh water pump.

4.       Switch off the salinometer.

5.       Stop sea water pump (also known as ejector pump).

6.       Open vacuum valve.

7.       Close sea water suction valve and overboard valve. This is generally not required as they are non- return valves. However, in case of valve leaking or damage, these valves are to be closed without fail.

Reverse Osmosis: Modern Alternative for Shipboard Water ProductionEvery ship is installed with fresh water production unit which produces fresh water from sea water. The efficient water production unit of the ship helps the vessel owner to save on additional fresh water expenses that are incurred by purchasing water from port suppliers.

Two popular methods for production of fresh water on ships include:

Fresh water generator

Reverse osmosis process.

Reverse osmosis is one of the modern methods used by the shipping industry to produce fresh water from sea water. This method of water production does not use waste heat source, unlike fresh water generator, to desalinate the sea water to convert it into fresh water with low salt ppm.

Principle of Reverse Osmosis

As the name suggest, this methods works on reversing the osmosis principle.

When a chemical solution is separated from pure water by a semi permeable membrane (allowing passage of water not salt) then the pure water flows through the membrane

until all the pure water has passed through or until the hydrostatic pressure head of the salt solution is sufficiently big enough to arrest or stop the process.

Reverse osmosis is the use of this phenomenon in reverse direction. This results in water being forced through the membrane from the concentrated solution toward the more dilute one. This is achieved by applying pressure of the osmotic pressure of the concentrated solution.

Working

The osmotic pressure of sea water is 28 bars but to overcome system losses and the fact that the sea water concentration increases as it passes through the length of the membrane, much higher pressure around 40-70 bar, depending upon the plant size, is required.

A triplex plunger pump is popularly used to produce high pressure across the membrane. The membrane used has a very fine barrier of dense holes which only allows water and gases to pass through, while preventing the passage of solutes such as salt and other impurities.

The fresh water produced after this stage is treated with chemicals and ultraviolet treatment to make it drinkable and useful for other purpose.

Types of Heat Exchangers on a ShipDifferent types of heat exchangers are used on board a ship. The type of heat exchange used for a particular usage depends on the application and requirement. In this article we talk about different types of heat exchangers used on a ship.

The types of exchangers are mainly defined by their construction and are as follows:

1)      Shell and Tube Type Heat Exchanger

This is the most popular type design with a shell accompanying several tubes and the flow of liquid to be cooled is mainly through tubes, whereas the secondary liquid flows over the tube inside shell.

Shell and tube type heat exchanger is extremely economical to install and easy to clean; however the frequency of maintenance is higher than other types.

2)      Plate Type Heat Exchanger

Plate type exchanger consists of thin corrugated plates joined parallel together, creating cavity for fluid flow inside it. Alternate sides of the plate carries two different fluids, between which, heat transfer is carried out.

Installation of this type of heat exchanger is expensive than shell and tube type, but maintenance cost is much lower.

Efficiency of plate type is higher than shell and tube type for same size of unit and can withstand high pressure.

3)      Plate Fin Heat Exchanger

Plate and fin type heat exchanger is constructed similar to a plate type exchanger but also contains fins to increase the efficiency of the system. Aluminium alloy is used as it gives higher heat transfer efficiency and lowers the weight of the unit.

Fins can be fixed in perpendicular to the direction of flow and are known as offset fins. Fins fixed in parallel to the direction of flow are straight fins. Fins can be fixed in curvature form to increase the heat exchanging effect and are thus known as wavy fins. Efficiency of this heat exchanger is slightly higher than plate type unit but installation and maintenance cost is higher

4)      Dynamic Scrapped Surface Heat Exchanger

In this heat exchanger because of the continuous scrapping of the surface long running time is achieved which helps in better heat transfer efficiency and decrease in the fouling of the system.

The scrapping is done by a blade unit operated by a motor driven shaft with timer moving inside the frame. This heat exchanger is normally used for heat transfer of highly viscous fluid by increasing the turbulence of the fluid. Maintenance cost is less as compare to other types because of the auto cleaning process.

5)      Phase Change Heat Exchanger

As the name suggests, this type of heat exchanger is used to change the phase of a medium from solid to liquid or liquid to gas by principle of heat transfer. This type is normally operated in freeze cycle and melts cycle for change in phase to happen.

The heat exchanger is normally constructed like a shell and tube type exchanger, but consists of at least two divider walls to construct upper and lower annular space for flow passage. It also consists of fins in both passage ways for efficient heat transfer.

6)     Spiral Heat Exchanger

This type of heat exchanger consists of concentric shape flow passages which help in creating a turbulence flow of a fluid which in turns increases the heat transfer efficiency. Initial installation cost is higher but highly efficient as compare to other types as space saving is much more because of the compact size. Maintenance cost is lowest as compare to other types for the same size of the unit.

The Flow of fluid in spiral type is rotary current flow which itself possesses the property of self cleaning of fouling inside the spiral body.

7)      Direct Contact Heat Exchanger

In this type of heat exchanger, there is no separating wall inside the unit. Both the mediums are in direct contact for heat transfer process.

Direct contact type heat exchangers can be further classified as

1.      Gas – liquid

2.      Immiscible liquid- liquid

3.      Solid- liquid or solid- gas

Heat Exchangers on Ship ExplainedHeat exchanger is an equipment which reduces the temperature of a medium by transferring temperature of that medium to another, when both the mediums are separated by a solid membrane or wall like structure. For efficient operation, the surface area of the wall which separates the two mediums is maximized, simultaneously minimizing the flow resistance of the fluid.

Exchanging of heat in a heat exchanger can be in between- liquid and liquid, gas and liquid, liquid and gas etc. For heat transfer basically three patterns of flow are used for construction of a heat exchanger.

Opposite flow : Primary medium (to be cooled) and secondary medium (which is cooling the primary medium) enters in the heat exchanger in opposite direction to each other.

Cross flow : Primary and secondary medium enters in an exchanger perpendicular to each other.

Parallel flow : Primary and secondary medium both enter the heat exchanger parallel to each other.

Where are Heat Exchangers Used Onboard Ship?

Each and every system in a ship is interlinked with each other in some way or the other. Even if one system fails, vessel can come to a standstill.

Heat exchanger plays an important role for efficient working of different systems, which include-

1) Propulsion Plant:

-  Main propulsion plant consists of different sub system for running of main engine like lube oil system, jacket water system (open or closed system), fuel system etc.

-  While generating energy all these systems gets heated up and the temperatures are controlled by the use of heat exchanger in the system.

-   Heat exchangers normally used in main propulsion system are – Shell and tube type and plate type heat exchanger.

2) Auxiliary Power Generation System:

- Auxiliary power generation system is similar to the main propulsion system, except that the power is generated in terms of output.

- Shell and tube type, plate type and plate fin type heat exchanger are generally used

3) Starting Air System:

- High pressure air is produced in the compressor which is further cooled in inter-cooler, which acts as a heat exchanger

-  Shell and tube type exchanger is popularly used for this purpose.

4) Fuel injection system:

-  For proper atomization, fuel is heated up in a heater with heating medium as steam. Shell and tube type heater is used for this purpose.

-  For reducing Sox emission from propulsion plant, combustible fuel is mixed with spray of water, for this direct contact heat exchanger is used.

5) Refrigeration System:

-   In refrigeration system, for meat room, fish room and vegetable room, evaporator acts as phase change heat exchanger.

-    Shell and tube type unit is used for condenser unit in refrigeration system.

6)  A.C system:

-   For maintaining the temperature, phase change heat exchanger unit is installed as evaporator.

-   Condenser unit is normally shell and tube type exchanger.

7)  Fresh Water System:

-   For generating fresh water, sea water condenser and jacket water evaporator is used. Both are types of heat exchangers.

-    Shell and tube type and plate type heat exchangers are normally used for this.

8)  Steam Turbine Unit:

-   If a ship consists of stem turbine or turbine generator, normally spiral heat exchanger is used for heat transfer.

Apart from the above mentioned places, there are several other applications where heat exchangers are effectively used for smooth running of the ship.

How to do Maintenance of Marine Heat Exchangers on Ships?Marine heat exchangers play an important role of removing the heat produced by a running machinery to ensure smooth functioning of the equipment. It is also necessary to enhance the heat exchanging ability which would reduce after certain amount of time of operation.

 

The cooling medium used in the heat exchanger depends on the medium used, including other factors.

Along with mediums such as fresh water, air and oil, sea water is also used abundantly in marine heat exchangers as an important cooling source. However, because of the presence of dissolved salts in sea water, corrosion and scale deposits is a common condition in heat exchangers. Maintenance of marine heat exchangers is therefore necessary at regular intervals of time to prevent reduction of heat transfer or failure of equipment.

The method of maintenance used depends on the type of heat exchanger and type of deposits, but the general aim of every heat exchanger maintenance procedure remains the same – cleaning of heat transfer surfaces to prevent any kind of obstruction in the flow process.

The main reason for fouling of heat exchanger surface is the increase in temperature difference between the two fluids and change in pressure. But it is the sea water side of the heat exchanger which suffers the most as a result of corrosion and scale deposits.

 

Methods of marine heat exchanger maintenance

Note: Prior to Maintenance, isolate the heat exchanger by shutting off the line valves for both medium and media; and drain the remaining liquid using the drain cock. The Vent must be open to ensure everything is drained from the heat exchanger.

If the deposits on the heat exchanger are not so hard, then they can be removed using a wire brush.

If the deposits are stubborn, chemical cleaning should be used by emersion of the part in chemical solution.

Depending on the type of the heat exchanger, there are tools provided by the manufacturers for the cleaning purpose. For e.g. there are special tools for cleaning shell and tube type heat exchangers.

Once the cleaning is done, the heat exchanger must be flushed with fresh water to remove any remaining chemical or dirt from the surface.

In sea water cooled heat exchanger, anodes are fitted on the cover to prevent it from galvanic corrosion. Anodes must be checked and changed if required.

Always renew the cover gasket if it is damaged during opening of heat exchanger.

In oil coolers and heaters, fouling can take place on the outside of the tubes as well. This can be removed by chemical flushing.

In plate type heat exchangers, the stack of plates is removed to expose the surface. The plate surface is then cleaned with brush or by the methods suggested by the manufacturer. (Sharp tools should be avoided). Cleaning should be done in such a way that it does not damage the plate seals. However, if a replacement of the seal is necessary, it must be done before putting the plates back.

While tightening the plates together, care must be taken for even tightening of all the exchanger studs and bolts or else leak will occur.

Excessive corrosion of the heat exchanger surface can also lead to perforation of the surface, resulting in mixing of one liquid with another. Minor leakage detection is not easy especially when the header tanks are automatically toped or if there is no proper manual record maintained. However, major leakages can be easily detected as a result of sudden loss of lubricating oil or jacket water. Low level alarms are also useful in detecting major leaks.

Another way to prevent mixing of two liquids because of perforation is by keeping the sea water at a pressure lower than the jacket water or any other liquid used. This reduces the risk of sea water entering into other mediums.

 

How leaks are detected?

Shell and tube type heat exchangers

If it’s a shell and tube type heat exchanger, leaks can be detected by following the procedure below:

Isolating the heat exchanger from the system and draining the sea water

Removing the end covers or headers to expose the tubes or plates

If the surface is clean and dry, inspection of the liquid flow is made from around the tube ends and through the perforations. However, in large coolers it is difficult to get the coolers extremely dry to visualize any perforation. In such cases special fluorescent dye is added to the shell side of the cooler. The dye glows when an ultraviolet light is shone on the tube, revealing the tube leaks.

Plate Type Heat Exchangers

Similarly in plate type heat exchangers, visual inspection or fluorescent dye penetrate is used to find any defeats. (Dye penetrate is used on one side, followed by ultraviolet rays on the other side)

Air coolers

When it comes to air coolers, leakages can be dangerous as they allow sea water to pass through to the engine cylinder. This can lead to formation of scales on air inlet valves’ spindle.

In such cases, location of the leaks can be detected by allowing low air pressure on the air side and checking the flooded sea water side for air bubbles. For better results, soapy water can be used for sea water side flooding.

 

Apart from the above mentioned methods, there are other ways as well to carry of marine heat exchanger maintenance. However, these are the most commonly used ones.

Understanding Nuclear Marine PropulsionNuclear ships are rapidly gaining popularity in the maritime industry for the myriad advantages they offers. Nuclear ships use atomic engines which have lower fuel costs and last for many years and have practically zero emissions. The working of a Nuclear Ship is based on the simple nuclear fission reaction.

Working of a Nuclear Ship

The working of Nuclear ships basically depends on the nuclear fission reactions taking place in the nuclear reactors. A nuclear fission reaction involves splitting of the nucleus of an atom to produce smaller nuclei, i.e. free neutrons and photons. The atoms once split result in a huge amount of heat-emission and gamma radiation. Usually, elements having long core lives are used as they would then require refuelling only once in 10 years or so. Nuclear fission reactions produce a lot of heat and this is the driving force for the working of a nuclear ship.

Nuclear Marine Propulsion

The nuclear plant of the ship requires constant recirculation of water. The reactor, pumps, and steam generators are initially circulated with water. The heat emitted from the nuclear reactor is used to heat water, which is circulated in hollow coils surrounding the reactors. This is done at a very high pressure to prevent the boiling of water at this stage.

The hot water is then transferred to another hollow coil that has water at normal temperature. This produces enormous amounts of steam .The steam generated from the generator is the source of energy for the turbine generators, which make the ship move forward by rotating the propeller of the ship. The steam, after passing through the turbines, is cooled, condensed and then re-circulated to the steam generators by pumps. The enormous amount of heat emitted in the process is the main reason for the nuclear propulsion. Surplus electricity generated in the process is stored in batteries for emergency use and also to meet the electricity requirements on board.

The reducing availability of fossil fuels may cause widespread use of marine nuclear propulsion in near future. Nuclear Ships have also received criticism as any fault in the working of a nuclear ship can cause unimaginable amount of contamination in the sea and danger to the human life on board. Therefore, modern day nuclear ships are more safe and advanced. They have large protective castings to protect the reactors.

The quality and durability of parts of the reactors are a very importing factor in the efficient working of a nuclear ship reactor as the components are not open for inspection for very long durations of time.  The fears about crew safety, maintenance, disposal costs and quality are now being condensed slowly as there is a greater pressure to have improved performance efficiency in naval ships.

Starting Procedure for Turbine Generator on ShipLike every other machinery, the turbine generator of the ship also needs to start under sequential starting procedure to avoid trouble free operation of the whole system. The correct procedure ensures that no part of the machinery goes through any kind of stress- thermal or mechanical. It also helps the ship to operate without wasting any extra time.

The correct starting procedure for steam Turbine Generator onboard ship is as follows:

-Check turbo generator lube oil sump level and drain it for water. Replenish it if level is less than normal.

-Start the lube oil priming pump from the local station and check the lube oil pressure. Put the priming pump on auto.

-Check and fill up the Turbine Generator vacuum pump operating water tank to normal level.

-Check vacuum condenser condensate level from the condensate pump. Put the pump on auto so that the level is maintained all the time.

-Operate the steam drain valve to drain any condensed water from the steam line to avoid excessive hammering and vibration while starting turbo generator.

-Open the main steam inlet valve for turbo generator.

-Adjust the gland steam pressure to normal level.

-Check and open the sea water valves for vacuum pump cooler, T/G lube oil cooler and vacuum condenser are opened.

-Start the vacuum pump and bring up the vacuum in the condenser.

-Open condensate pump valves and switch on the pump.

-Check whether the condensate vacuum, gland steam pressure, steam inlet pressure, and lube oil pressure are normal.

-Start turbo generator from the local station and close the drain in the steam line.

-Check first and second stage steam pressure.

-Check condenser vacuum and water level.

-Check lube oil pressure and vibration levels.

-Check turbo generator speed, voltage, frequency, vacuum, condenser level and other parameters.

-Give control to remote station from the local control and take the TG on load.

An Introduction to Ship’s Turbine GeneratorTurbine generator is a popular source of clean power generation on ships as they don’t use any type of fuel i.e. heavy or diesel oil. Steam is used for power production in case of turbine generators. Steam is an easy, environmental friendly and cheap form of fuel on ships. For turbine generators, the steam comes from the ship’s steam boiler plant.

In turbine generator, steam is used with high pressure to rotate turbine wherein the thermal energy of the steam gets converted into rotary motion. The turbine is connected to the alternator’s rotor; hence the rotary notion of the turbine is utilized to generate electric power.

Alternate Uses of Steam Turbine

On ships, the steam turbine can also be used as a direct propulsion plant, in which, the turbine shaft is connected to propeller shaft of the ship. Since the speed will be in thousand rpm, reduction gears and reduction systems are used to get a drop in propeller rpm.

The propelling plant of the ship can be driven by steam turbine through a slow speed motor. The turbine generator directly supplies power to these slow speed motors which are connected to the propeller shaft of the ship.

 

Understanding the Construction of Turbine Generator system:

Turbine Prime Mover

A turbine will act as a prime mover in turbo generator and is fitted on the same shaft as of the alternator’s rotor.

Alternator

The alternator is used to convert the rotary motion of the turbine to electrical energy and its output is supplied to the main switch board of the ship.

Steam Control Governor

The governor is used to control the speed of the turbine generator during starting, normal operation and shutting down. It controls the quantity of the steam inlet to the turbine generator.

Steam Control Valve

Different pressure control valves are fitted in the steam line and are controlled using governor for the flow of steam from the ship’s boiler system.

Condensate pump

The condensed steam, after the turbine is further cooled down, is pumped back to the cascade tank by condensate pump.

Vacuum pump for glands

The steam turbine shaft is provided with glands wherein steam is sprayed at a pressure of 0.3~ 0.5 bar so that the vacuum inside the turbine casing doesn’t drop.

Condenser

The heat exchanger acts as a condenser to cool down and condense all the steam from the turbine into water so that it can be pumped back to the hot well.

Vacuum pump header tank

A vacuum pump header tank is provided to cool down the vacuum pump as the later deals with high temperature steam.

What is Azipod Propulsion System on Ship?Azipod system used on ships is combination of both propulsion and steering systems. In conventional propulsion system, a large two stroke engine is connected to a shaft, which passes through shaft tunnel and stern tube and connects to the propeller outside the hull in the aft part of the ship. The steering of such system is done with the help of a rudder placed in the aft of the propeller.

However, in azipod arrangement, the propulsion and steering systems are combined and made into one part. The system consists of a propeller which is driven by an electrical motor and the propeller is turned by the rudder which is connected to the system.

The motor is placed inside the sealed pod and is connected to the propeller. It should be noted that the sealing of the pod should be perfect otherwise it can damage the whole motor and make the ship handicap from maneuvering. The motor used for this system is variable frequency electric motor. Using variable frequency, the rotational speed of the propeller can be controlled i.e. the speed can be increased or decreased.

The azipod system is also known as POD drive system, where POD stands for Propulsion with Outboard Electric motor. The whole azipod system is situated outside the hull in the aft of the ship. The azipod can turn in all the directions i.e. 360 degrees with the help of a rudder, and thus provides a thrust in any direction which is not possible in the conventional system. The propeller in the pod system is moved by the rudder which is placed in the steering flat, also the power module for the system.

Understanding the Azipod System

The azipod system is a type of electric propulsion system which consists of three main components:

1) Supply Transformer

The power produced from the generators is as high as 6600 KV, which is stepped down to the necessary voltage by the supply transformer required and is provided to the motor placed in the pod.

2) Propulsion motor

Propulsion motor is used to drive or to produce thrust. The system needs some method for rotating the propeller and this is done with the help of electric motor.

3) Frequency Controller/converter

This is used to change the frequency of the supplied power so that the rotating speed of the motor can be controlled depending on the requirement.

Advantages of Azipod System

1) Greater maneuverability as the propeller can be turned in all directions. This enables better stop distance during crash maneuvering than that provided by the conventional system.

2) In case of ships having large breadth, two or more azipods which are independent of each other can be used. This provides subtle maneuvering.

3) It saves a lot of space in the engine room as there is no engine, propeller, shafting and other arrangements. The saved space can thus be used for storing more cargo.

4) The system can be placed below the ship’s height thus providing more efficiency than the conventional system.

5) Use of side thruster is eliminated as the pods can be used for providing the side thrust.

6) Low noise and vibrations than the conventional system.

7) Low fuel and lube oil consumption.

8) Environment friendly as emissions are extremely low.

Disadvantages

1) Azipod system requires massive initial cost.

2) A large number of diesel generators are required for producing power.

3) There is a limitation to the power produced by the motor. As of now the maximum power available is 21 MW.

4) Cannot be installed in large ships with heavy cargo which need a lot of power and large motors.

Nuclear Ship Propulsion: Is it the Future of the Shipping Industry?Marine industry, like other fuel dependent enterprises, faces a danger of fuel shortage. At present fossil fuels feature at top on list of fuels used in this industry. Of these, diesel is the one used most frequently under various names such as gas oil, marine gas oil (DMX, DMB), intermediate fuel oil (IFO), residual fuel oil (RMA, RML) etc. 

But they are under immediate danger of exhaustion. In this scenario, marine nuclear propulsion steps in as the savior. However, how much can the shipping industry rely on this new technology?

What is nuclear marine propulsion?

For those who don’t know much about it, nuclear marine propulsion refers to use of nuclear energy for purpose of propulsion of ships. It makes use of a nuclear reactor where a nuclear reaction can be carried out under controlled conditions. Such reaction produces immense energy which can be tapped and used to power anything from small vessels to a cruise ship.

The nuclear reaction carried out is a fission reaction wherein a heavier molecule splits into smaller ones producing energy along with the products. This energy produced is

mainly used to heat water that can be further used to produce steam for the purpose of nuclear ship propulsion.

Status of nuclear marine propulsion

Use of nuclear ships is increasing gradually though this idea has been present for long. Nuclear reactions have been used to produce energy for other commercial purposes mainly electricity production for some time now. But idea of marine propulsion using this energy was proposed somewhere in 1940s when the first design for a nuclear marine propulsion engine was made. Since then, nuclear ships have become designed and used. Right now, the marine propulsion dependent on nuclear energy is found mainly in armed forces and navy but soon commercial and domestic nuclear ships will also become just as common.

Mostly merchant cargo ships like American NS Savannah (1962-1972) and German NA Otto Hahn (1968- 1972) or nuclear powered ice breakers have been in use for brief periods. At present, only few ships based on nuclear marine propulsion are in use on experimental basis.

Why is nuclear marine propulsion a good idea?

Amongst all the speculations and standing doubts about use of marine propulsion system based on nuclear energy, there are some key factors that make this a good idea, whatever way you look at it.

In the current scenario of extreme fuel shortage, nuclear ships are the answer that everyone has been looking for. Energy produced from nuclear reactions is immense which can be used easily.

Since amount of energy produced in every reaction is quite large, a single time energy production can be used for a propulsion ship for a long time. Nuclear ships offer a refilling solution of as less as once a month. This could make shipping a speedy and hassle free process.

A nuclear reactor is designed to produce energy under controlled conditions. It is compact and can be moved around easily. So apprehensions about practicality of a nuclear reactor on ships, boats and vessels can be put to a rest.

Nuclear military ships like submarines can survive for months underwater without feeling the need to resurface for refueling. This can make combative forces much more efficient.

Fuel efficiency of nuclear propulsion engines is more than most of the fuels currently in use. This means that amount of energy derived from nuclear reactions per unit weight is more than any other fuel.

The better power to weight ratio means that nuclear ships can have better weight carrying capacity than other ships, offering quicker traveling over longer distances with greater load.

Nuclear ships tackle problem of air pollution too as there is no production of undesirable smoke or particular pollutants that have become a menace all over the world.

 

Why can’t we trust this technology much right now?

The picture of a nuclear energy powered propulsion ship seems very rosy. However, there is a downside with this whole scenario. Some of the points not so good with this technology are:

Nuclear reactions produce immense energy, which if not controlled can lead to disastrous results. As such, even a minor fault can lead to accidents with massive implications all over the world.

Most apprehensions lie with use of something as dynamic as nuclear energy on ships which can be occupied by thousands of people at sometimes.

In case of accidents of nuclear ships, there is a huge chance of contamination of water bodies with nuclear fuels that can damage marine life and human population both. During the brief usage of such ships, the number of accidents due to minor technical faults has been proportionately large.

Due to the need for ships to travel across the world, there is a need for nuclear reactors to be able to bear that sort of wear and tear. The nuclear reactor should be secured to prevent its undesirable movement on the ship.

The major problem faced by every nuclear ship would be of disposal of nuclear waste. With increasing use of nuclear fuel all over the world, there is an increasing stack of nuclear waste that humans are still struggling to dispose of. In absence of a practical solution to dispose of excessive amount of nuclear wastes that will be produced due to such ships, there could be more problems in long run.

At last, one major apprehension with this energy is its political and moral implications. There will always be fear of this energy being misused which remains one of the major political reasons to be cautious about this energy.

 

There is a future in nuclear energy for marine propulsion but still there is a long way to go before we can see a fully fledged ship running on nuclear marine propulsion system.

Different Types of Marine Propulsion Systems Used in the Shipping WorldUsing propulsion forces, ships are able to manoeuvre themselves in the water. Initially while there were limited number of ship propulsion systems, in the present era there are several innovative ones with which a vessel can be fitted with.

Today ship propulsion is not just about successful movement of the ship in the water. It also includes using the best mode of propulsion to ensure a better safety standard for the marine ecosystem along with cost efficiency.

Some of the various types of propulsion systems used in ships can be enumerated as follows:

Diesel Propulsion: Diesel propulsion system is the most commonly used marine propulsion system converting mechanical energy from thermal forces. Diesel propulsion systems are mainly used in almost all types of vessels along with small boats and recreational vessels.

Wind Propulsion:  Wind propulsion emerged as an alternative to those systems which emit huge quantities of CO2 gases in the marine atmosphere. However, the usage of wind turbine marine propulsion has not started extensively in large commercial ships because of a requirement of constant windiness. Two wind propulsion systems for ships that have become lately are- kite propulsion and sail propulsion for merchant ships.

Nuclear Propulsion: Naval vessels incorporate the usage of nuclear maritime propulsion. Using the nuclear fission process, nuclear propulsion is a highly complex system consisting of water reactors and other equipments to fuel the vessel. The nuclear reactors in the ships are also used to generate electricity for the ship. Several merchant ships are also being planned to be constructed with this propulsion system

 

Gas Turbine Propulsion: Gas turbine propulsion is used for naval as well as non-naval ships. In case of naval ships, the gas turbine propulsion system aids in faster movement of the ships which is necessary in case of the ship coming under attack.

Fuel Cell Propulsion: Fuel cell propulsion systems use hydrogen as the main fuel component. Electricity is created in the fuel cell without any combustion whatsoever. The process is clean and therefore has been regarded as a very important alternative marine propulsion system. There are various types of propulsion under the fuel cell propulsion head like PEM (Photon-Exchange-Membrane) and the molten-carbonate systems.

Biodiesel Fuel Propulsion: Biodiesel propulsion has been deemed as a potential marine propulsion system for the future. Currently tests are being carried out to find out about the viability of this propulsion system which is expected to be in full operation by the year 2017.

 

Solar Propulsion:  Solar propulsion for ships was utilised for the first time in the year 2008. Solar propulsion benefits include a high reduction in the poisonous carbon dioxide emissions. Solar propulsions are capable of generating a capacitance as high as 40 kilowatts (kW).

Steam Turbine Propulsion: Steam turbine propulsion involves the usage of coal or other steam-generating fuels to propel the vessel. Steam turbine maritime propulsion system was highly utilised between the late 19th and the early 20th century.

Diesel-Electric Propulsion: In simple terms, diesel-electric ship propulsion systems use a combination of a generator operated by electricity attached to a diesel motor. The technology has been in use since the early 1900s. In today’s times, submarines and merchant ships incorporate the diesel-electric propulsion system to propel themselves.

Water-Jet Propulsion: Water-jet propulsion has been used since the year 1954. The most important advantage of water-jet propulsion is that it does not cause noise pollution and offers a high speed to the vessels. In contrast the water-jet propulsion as a ship propulsion system is costlier to maintain which can cause problems to the user.

Gas fuel or Tri Fuel Propulsion: LNG fuel is now utilised to be burnt in the Main Engine after adopting some modification in the propulsion engine to reduce emission from the ship. It is known as tri fuel because it can burn gas fuel, diesel and heavy fuel.

 

The various types of propulsion systems offer their own unique advantages to a vessel. Depending on the necessity and the requirement, the best type of ship propulsion system needs to be fitted. Only then the vessel will be able to offer its optimum service capacitance.

4 Types of Anti-fouling Systems Used on Board Ships to Prevent Marine GrowthBiofouling is one of the main problems faced by every type of ship at the sea. Marine growth such as barnacles and mussels have been the reason for problems such as decreased ship efficiency, corrosion etc.

 

Biofouling not only sticks to the external surface of the ships but also gets into the water intakes and sticks to the surface of the pipes leading to problems such as blockage and corrosion.

Though mechanical removing tools can be used to get rid of such marine growth, this is not always possible. For this reason, different types of marine growth prevent systems are used on board ships, along with anti-fouling paints.

The main types of preventive measures used on ships are:

1.   Electrolytic system

2.   Chemical dosing

3.   Ultrasonic system

4.   Electro-chlorination

1.   Electrolytic system

This is one of the most commonly used systems to fight biofouling on ships.

The electrolytic system consists of pairs of anodes, mostly copper and aluminum (or iron). The anodes are mounted in the sea chest or the strainer.

DC current is passed through the copper anodes, which produce ions that are carried with the seawater in the whole piping network. These copper ions in the seawater prevent marine organisms from settling down and multiplying on the surface of the pipes.

The second anode is used to prevent corrosion of the metal surface. The iron anodes help in preventing layers of oxide films of the metals from breaking down by the corrosive agents (sulphur) of seawater. This system also gives protection to valves, condensers, engine cooling systems and ancillary equipment.

A control panel measures and monitors the output of each of the anodes.

2.      Chemical Dosing

Chemical dosing is also a common method which is used to prevent marine growth in piping network. Anti-fouling chemical such as ferrous chloride is used to dose sea water boxes. The chemical coats the pipework with a protective ferrous layer to prevent corrosion.

3.      Ultrasonic

High frequency waves are also used as a method to prevent marine growth in piping systems. Ultrasonic system is supposed to be known as one of the most highly effective methods to prevent biofouling. A reduction in biofouling of as much as 80% is claimed by this method.

According to research, ultrasonics is supposed to have two types of effects on anti-fouling.

1. A disturbance action because of the high frequency waves which renders the habitat unacceptable

2. A mechanical action on the organisms which are trying to deposit adhesive. It not only helps in preventing it from solidifying but also acts on 4-5mm organisms which are already anchored.

In the ultrasonic method, a wave generator produces and sends electrical impulses at high frequency. These waves are passed through a coaxial cable to transducers which are mounted externally to the sea chests or strainers.

The transducers contain piezoelectric ceramic crystals, which when excited by electrical impulses, generate an ultrasonic beam.

The main advantage of this system is that it is non-invasive and no parts are in contact with sea water. Moreover, no toxic substances are produced.

4.      Electro-chlorination

Electro-chlorination is a method in which chlorine is generated to produce sodium hypochlorite, which is used to prevent fouling.

Titanium is used as the cathode material whereas titanium coated with 100 micro-inches of platinum is used as anodes. Titanium is an electrochemically inert element at positive voltages less than 9 volts. The anode/cathode voltage is kept 7 volts.

Chlorine is generated at the anodes along with other elements to form sodium hyperchlorite. A large amount of hydrogen gas is also produced which should be evacuated safely.

The layer at the anode in consumed at a rate of 6 mg/ampere per year. However, it depends on the unit voltages and currents supplied. The total output of chlorine is a function of current rather than flow through the unit. Thus adequate flow is required to ensure cooling and to prevent calcareous deposits.

10pp chlorine in sea water would kill all marine life quickly, whereas 1 PPM will prevent fouling. This can be tested on board.

It is to note that this system is designed to be used only in sea water and not in fresh water.

Biofouling is one of those problems which have been bothering the shipping industry since the start. Project such as AMBIO has been implemented to find solid solutions to this problem.

Advances have already been made in the field of anti-fouling paints and anti-marine growth systems. Some innovative techniques that can be used to prevent biofouling in the future are anti-fouling system inspired from floating seeds and special molecules of bacteria.

What is Marine Growth Preventive System (MGPS) On a Ship?Ships while sailing use seawater for several purposes. The seawater is used in the ship’s system and discharged after the use. However, seawater contains several marine organisms which enter the ship along with the seawater and deposit and flourish on the parts of the ship’s system.  If preventive measures are not taken, the marine growth can cause damage to the particular part in the long run. In this article we will learn about the causes and effects of marine growth in a ship’s system along with the measures to fight it.

 

What Causes Marine Growth?

Sea water contains both macro and micro marine organisms such as sea worm, molluscs, barnacles, algae, hard shells like acorn barnades etc. These organisms stick to the surface of the ship and flourish over there, resulting in marine growth.

Marine fouling can form huge clusters of marine growth inside the piping system of the ship. This is mainly caused because of the entering of the seawater into the seawater system. The organisms find the perfect spot inside the system wherein the environmental conditions and other relevant factors such as temperature, ph, nutrients etc are appropriate for them to breed and disseminate.

Effects of Marine Growth

As the marine organisms flourish they block and narrow the passage of cooling water in the ship’s system resulting in the following factors:

-  Impairing the heat transfer system.

-   Overheating of several water-cooled machineries.

-  Increase in the rate of corrosion and thinning of pipes.

-  Reduced efficiency which can lead to loss of vessel speed and loss of time.

Fighting Marine Growth

To avoid formation of marine growth MGPS or marine growth preventive system is used onboard ship. Description and working of MGPS is as follows.

Basic principle on which MGPS runs is electrolysis. The process involves usage of copper, aluminum and ferrous anodes. The anodes are normally fixed in pairs in the main sea chest or in such place where they are in the direction of the flow of water.

The system consists of a control unit which supplies impressed current to anodes and monitors the same. While in operation, the copper anode produces ions, which are

carried away by water into the piping and machinery system. Concentration of copper in the solution is less then 2 parts per billion but enough to prevent marine life from settling.

Due to the impressed current, the aluminum/ferrous anode produces ions, which spread over the system and produce a anti corrosive film over the pipes, heat exchanger, valves, refrigeration and ac unit etc, internally.

MGPS anodes are fitted with specially designed safety cap which helps in removing the anode for replacement on board ship. Normally MGPS have a design life which coincides with the dry dock of the vessel.

Learn About Fatal Bacteria that Grow in Ship’s Air-Con SystemIt is a known fact that there are certain types of bacteria which flourish in the air conditioning system of a ship. These organisms or bacteria flourish or increase in number in stagnant water or in wet deposits of slime or sludge. If these bacteria multiply exponentially and are not removed then they spoil the living condition on ship, making it harmful for the crew.

The most common locations where these bacteria colonies are found are at the inlet areas and filters of the cooler, humidifiers of the water spray type air-con, and inside damaged insulations.

This specific type of bacteria is known as legionella bacteria, which cause a disease known as Legionnaire disease. It is a type of Pneumonia which can be fatal to people, especially to the elder ones.

How to Prevent Growth of Such Bacteria?

Growth of bacteria can be prevented by removing stagnant water from different areas of the ship. Also, follow the steps mentioned below.

Growth of legionella bacteria can be prevented with the help of proper provision of adequate drainage to remove the stagnant water.

Regular inspection and cleaning of the filters and similar parts using 50 ppm super chlorinated solution used as a sterilizing agent.

The super chlorinated solution is also to be used on the cooler drain area at not more than three months intervals.

This sterilization is necessary for water spray type humidifier in air conditioning system.

Steam spray humidifiers are to be preferred over water spray humidifiers.

Pipes and Bends – An Essential Guide for Second Engineers: Part 1Becoming a second engineer is a big responsibility as the person is no longer just an engineer officer but a management level officer who has to look after the affairs of the engine room and also share the burden of the chief engineer.

A 2nd engineer has to look after his own machinery, assign work to junior engineers, and attend to other important machinery.

There are several important aspects of the duties of second engineer as he is someone who s in charge of all the operations of the engine room. In this series of articles, we will be discussing an important aspect of the engine room – pipes and bends. This is the first part of an essential series for second engineers.

In case of new fabrication of a pipe line, repair work, or making dry dock specification, the second engineer must have good knowledge of piping and fittings in the engine room of the ship.

Pipes vs. Tubes – What is the Difference?

There is always a doubt among several marine engineers about difference between pipes and tubes. Several consider them as synonyms and even think that they are interchangeable.

However, it is to note that there is a difference and it is based primarily on the rules of nomenclature of the pipes and the tubes.  In the following points we endeavor to clarify the issue.

1. Pipe is rigid and resistant to bending whereas some tubes such as copper tubes and brass tubes can be flexible. However, in structural projects tubes are rigid.

2. Pipes are classified by schedule and nominal diameter. For example, a 250mm nominal diameter and schedule 80 pipe.

3. Tubes are classified by outside diameter and thickness. For example 10mm copper tube 2 mm thickness.

4. In pipes, all the fittings can be matched by nominal size and schedule. For example a schedule 40 one inch pipe will have fittings specified by same name. These pipe fittings would not fit a 1” tube.

5. Pipe is always round or cylindrical. Tubes may be square, rectangular and cylindrical.6. Pipes generally start from ½ inch to very large sizes. However, tubes are generally of

small diameter only. We use a 10 inch pipe but not 10 inch tube.7. Tubes are used in applications where the outside diameter must be precise, like in

cooler tubes, heat exchanger tubes, boiler tubes etc.8. Pipes are generally used to carry fluids and must contain them and have pressure

rating and hence are scheduled.9. In tubes the thickness increases in standard steps like 1 mm thick, 2 mm thick etc. In

pipes however the thickness depends on schedule of the pipe and there is no fixed step.

10. Pipe joining is more time consuming like welding, threading, flanges with bolts etc. The tubes joining are faster like flaring, brazing, couplings etc.

11. Tube dimensions are actual dimensions. Whereas the pipe dimensions are only nominal. That means that a 1” tube will have actually OD as 1”. The pipes on the other hand are named nominally, which means only for name. The 1” schedule 40 Nominal size pipe has an ID of 1.049”, OD of 1.32” and a wall thickness of 0.133”.

12. Tube fittings are compression fittings like ferrule and union nut, flared fittings, biting fittings, mechanical grip type fittings. The pipe fittings on the other hand are pipe to pipe butt welding, threaded pipe fitting connectors, flange to flange bolted fittings etc.

What is Nominal Diameter?

The dictionary meaning of nominal is, “existing in name only”. For example a 250 A nominal size pipe has an ID of 242.8 mm and OD of 273 mm and as per schedule 80. But instead of saying 242.8 mm IDF pipe with wall thickness of 15.1 mm, we say 250A, SH80. It is easier to say and easier to remember.

Nominal diameter is the approximate inner diameter of the pipe it is a rounded figure easier to use and remember. By prescribing the nominal size of the pipe all the different fittings can be selected based on the same nominal diameter, without physically checking the dimensions and compatibility of each component.

Nominal diameter is not internal diameter but similar to it. With reference to the above example the nominal bore of the pipe is 250 mm, but the ID varies from 266.2 mm to 222.3 mm depending on schedule of the pipe.

Schedule of Pipes: What does it mean?

In marine field we generally use schedule 40 for light duty and schedule 80 for heavy duty. There are however many other schedules which have been incorporated due to improvement in metallurgy and requirements due to increased pressure demands.

Basically the schedule of a pipe refers to its pressure rating. The higher the schedule the higher pressure it can contain. The schedules are normally 5S, 10S, 10, 20, 30, 40S, 40, 60, 80 100, 120, 140 and 160.  As the schedule increases the wall thickness increases and the ID deceases.

Pipes and Bends – An Essential Guide for Second Engineers: Part 2In our previous article (Pipes and Bends –Part 1) we discussed about the difference between a pipe and a tube, meaning of nominal diameter and schedule of a pipe. In this article we will discuss bends, elbows and miter bends.

 

Bend or Elbow

pipe bend

There is always a doubt about the terms bends and elbows on ships. They are frequently used as synonyms.   The difference between them is as follows:

1. Bend is a generic term for any offset or change of direction in the piping. It is a vague term that also includes elbows.

2. An elbow is an engineering term and they are classified as 90 deg or 45 deg, short or long radius.

3. Elbows have industrial standards and have limitations to size, bend radius and angle. The angles are usually 45 deg or 90 degrees. All others offsets are classified as pipe bends.

4. Bends are generally made or fabricated as per the need of the piping; however elbows are pre fabricated and standard, and are available off the shelf.

5. Bends are never sharp corners but elbows are. Pipe bending techniques have constraint as to how much material thinning can be allowed to safely contain the pressure of the fluid to be contained. As elbows are pre fabricated, cast or butt welded, they can be sharp like right angles and return elbows which are 180 degrees.

6. Elbow is a standard fitting but bends are custom fabricated.7. In bends as the pipe is bent and there is no welding involved, there is less pipe friction

and flow is smoother. In elbows, the welding can create some friction.8. All elbows are bends but all bends are not elbows.9. Bend has a larger radius then elbows.10. Generally the most basic difference is the radius of curvature. Elbows generally have

radius of curvature between one to twice the diameter of the pipe. Bends have a radius of curvature more than twice the diameter.

Short Radius and Long Radius

Elbows are again classified as long radius or short radius elbows. The difference between them is the length and curvature. A short radius elbow will be giving the piping a sharper turn than a long radius elbow.

90 degree short radius elbow

 

1. In a long radius elbow the radius of curvature is 1.5 times the nominal diameter. In a standard elbow the radius of curvature is 1.0 times the nominal diameter of the pipe.

2. Long radius elbows give less frictional resistance to the fluid than the short elbows.3. Long radius elbows create lesser pressure drop than short radius elbows.4. Short radius is less costly than long radius elbows.5. The short radius elbows are used where there is scarcity of space.

90 degree stainless long radius elbow

In addition to this classification the elbows are 45 degrees, 90 degrees and 180 degrees also called as a return elbow.

180-Degree Elbow

The 45 degrees elbow turns the fluid /piping at 45 degrees and so on.

45 deg short radius elbow

Miter bends

Another type of bend is a Miter bend. A Miter bend is a bend which is made by cutting pipe ends at an angle and joining the pipe ends. A true miter bend is a 90 degree bend made by cutting two pipes at 45 degrees and joining them by welding.  Similarly three pipes cut at 22.5 degrees will give a 90 degree miter bend.

miter bend

In the next article we will discuss about various pipe fittings.

Pipes and Bends – An Essential Guide for Second Engineers – Part 3In our last article Pipes and Bends – An Essential Guide for Second Engineers – Part 2 we discussed about bends, elbows and miter bends.  In this article we will discuss about different types of pipe fittings found on ships.

Pipe Fittings

Pipe fittings are special parts that are used for joining two pipes together, to join a different size pipe to the existing piping, to regulate flow of fluid, etc.

Different types of pipe fittings are nipples, coupling, adapter, plugs, elbows, tees, valves etc. All the fittings are discussed below.

Nipple

A nipple is basically a pipe with male threads on each side to facilitate joining two pipes or fittings with similar female threads.

It is made by cutting threads on both sides of a pipe by die or a suitable process. The nipples may be short or long.

Long Pipe Nipple

A long pipe nipple is similar to a standard nipple but longer in length.

It is used when there is more distance between the fittings or when a fitting like a valve is to be put at a distance.

Hexagonal Nipple

A hexagonal nipple is a pipe connector with male threads on both sides and a hexagonal nut in between for easy installation and screwing.

Both sides are to be screwed in pipe or fitting having reciprocating female threads.

Hexagonal Reducer Nipple

A hexagonal reducer nipple is a hexagonal shaped nipple with two different sizes of threads on each side.

The purpose of the hexagonal reducer nipple is to connect the pipes of two different sizes together

Hexagonal Long Nipple

A hexagonal long nipple is used where the distance between the pipe and the fittings is to be joined.

They are otherwise similar to the hexagonal nipples apart from the length.

Close Nipple

A close nipple is completely threaded and there is no unthreaded area.

This means that there is no hexagonal nut of plain pipe for putting the wrench. These can be damaged by using wrenches. Therefore, a special tool called nipple wrench, which holds the nipple from inside, is used for fitting.

Coupling

A pipe coupling is a connector with female threads on both sides that allows two pipes or fittings with male threads to join together.

Coupling can be a normal pipe coupling or a hexagonal coupling. Pipe couplings are fittings that help to extend or terminate pipes.

Reducing Coupling

A reducer coupling is a coupling with two different sizes of threads on each side.

They also can be plain reducer coupling and hexagonal reducer coupling. They are used to connect two different sizes of pipes or fittings and sometimes also for flow control.

Adapter

Pipe adapters are fittings that have to adapt to changes and are therefore used for joining different types of pipes such as a pipe to a hose. Adapters are used to extend or terminate the piping. They are also used to connect dissimilar pipes.

There are male to female adapters, parallel to taper thread adapters, and pipe to hose adapters etc.  Pipe adapters have a male or female thread on one side and an opposite gender thread on the other side.

Reducing Adapter

A reducing adapter is used for joining a pipe to a hose or tube as well as to help in flow control.

In doing so it controls the pressure acting on the hose at the end. It is used in applications where a copper tube is joined to the main steam pipe for trace heating.

These are the main types of pipe fittings. However, there are many more types. In the next article we shall continue discussing about various pipe fittings.

Pipes and Bends: An Essential Guide for Second Engineers – Part 4This article is a continuation of the series of articles which explains piping engineering as practically required on ships. The article discusses various types of pipe fittings used on board ships.

For those who have not read earlier articles of the series, here are the links:

Pipes and Bends – An Essential Guide for Second Engineers – Part1

Pipes and Bends – An Essential Guide for Second Engineers – Part2

Pipes and Bends – An Essential Guide for Second Engineers – Part3

Gauge Adapter

A gauge adapter is used for fitting pressure gauges and instrumentation fittings.  They are used for the fitting of pressure measuring instrument such as pressure gauges, gauge cocks, shut off valves etc. The different types of gauge adapters are male – female adapters, female – female adapters,  male – male adapters, self sealing nipples, LH-RH unions, union nut with nipple, compression fitting with ferrule, swivel adapters etc.

Hose Adapter

A hose adapter is used where a hose is connected to a pipe. It may be the termination of the piping like a garden hose at the end or a high rating hydraulic hose used to give flexibility and movability to the system

 

Reducing Bushing

A reducing bushing is a pipe fitting with both male and female threads that joins two pipes of different diameters.

Pipe Cap

A pipe cap is a fitting that seals the end of the pipe. It is like a plug but it has female threads and screws on the male threads on the end of a pipe or adapter

Pipe Plug

A pipe plug is a fitting to close or seal the end of a pipe. A plug has male threads and screws on to the female threads on a fitting.

 

Female Elbow

A female elbow is a pipe fitting that is used to change the direction of the piping and has female threads on both sides that allows for fixing pipes or fittings with male threads. They come in various angles like 45 degrees and 90 degrees.

 

Male Elbow

A male elbow is a fitting with male threads on both sides and is used for changing the direction of the piping. They fix on to female threads of the fittings on both sides. They come in various angles like 45 degrees and 90 degrees.

Street Elbow

A street elbow is different from the male and female elbows in the respect that it has a male thread on one side and a female thread on other side. The advantage of using the street elbow is that it can directly fix to the pipe without connecting a nipple. They come in various angles like 45 degrees and 90 degrees.

Reducing Street Elbow

A reducing street elbow is a pipe fitting that has male thread on one side and unequal female threads on other side. They are used for altering the direction of flow as well as joining pipes of two different sizes. They come in various angles like 45 degrees and 90 degrees.

Female Tee

A female tee is a pipe fitting that joins one pipe to another pipe in a perpendicular direction. The female tee is having female threads on all ends and pipes or fittings with male threads fix into it.

Male Tee

A male tee is a pipe fitting that joins two perpendicular pipes together or makes a “tee”. It is similar to a female tee but has male threads on all ends and joins to fittings with female threads.

Street Tee

A street tee is a pipe fitting which joins one pipe to another, perpendicular to it. In addition it has male threads on one end and female threads on other two.

Reducing Tee

A reducing tee has two openings of same size and one of different size. These are also used to join two pipes perpendicular to each other as well as to obtain flow control.

Cross Tee

A cross tee is a pipe fitting that joins four pipes at 90 degrees each. There is either one inlet or three outlets or vice versa.

 

General Overview of Types of Pumps on ShipA ship consists of various types of fluids moving inside different machinery and systems for the purpose of cooling, heating, lubrication, and as fuels. These liquids are circulated by different types of pumps, which can be independently driven by ship power supply or attached to the machinery itself. All the systems on board ship require proper operational and compatible pump and pumping system so that ship can run on its voyage smoothly.

The selection of a type of pump for a system depends on the characteristics of the fluid to be pumped or circulated. Characteristics such as viscosity, density, surface tension and compressibility, along with characteristics of the system such as require rate of fluid, head to which the fluid is to be pumped, temperature encountered in the system, and pressure tackled by the fluid in the system, are taken into account.

Types of Pumps

The pumps used on board are broadly classified into two types:

Positive Displacement Pump

Positive displacement pumps are self priming pumps and are normally used as priming devices.

They consist of one or more chamber, depending upon the construction, and the chambers are alternatively filled and emptied.

The positive displacement pumps are normally used where the discharge rate is small to medium.

They are popularly used where the viscosity of the fluid is high. They are generally used to produce high pressure in the pumping system.

Dynamic Pressure or Roto-Dynamic Pump.

In dynamic pressure pump, during pumping action, tangential force is imparted which accelerates the fluid normally by rotation of impeller.

Some systems which contain dynamic pump may require positive displacement pump for priming.

They are normally used for moderate to high discharge rate.

The pressure differential range for this type of pumps is in a range of low to moderate. They are popularly used in a system where low viscosity fluids are used.

These broad classification of pumps are further differentiates by their constructional properties and popularity of usage onboard ship;Positive Displacement pump:

Reciprocating Pump Screw pump Gear pump Piston pump Ram type pump Vane pump

Dynamic pressure pumps:

Centrifugal pumps Axial flow pumps Submersible pump Centrifugal-axial (mixed) pump.

What is a Metering Pump On board a Ship?Metering pump, as the name suggests, is a type of pump which is used on ship to pump a precise volume of liquid. Metering pump can be adjusted to provide different flow rates. They are generally used when the precision of volume to be delivered is very important.

The marine application of metering pump is in the form of chemical dosing pumps, which is used to transfer precise amount of dosing chemicals, especially in boilers. They are also used for dosing chemical additives to protect corrosion in the cooling water system. It is to note that the amount of dosing has to be precise. Over dosing or under dosing may cause corrosion and other damages inside the boiler, which may end up in heavy repairs.

The metering pump is connected to the system in which the chemicals are injected with the help of valve in the pipeline. The pressure produced by this pump should be higher than the pressure in the pipeline, or else there will not be any dosing and the level of chemicals in the dosing tank will be the same.

The metering pumps consist of a small motor which moves the plunger, in and out of the barrel, to provide pressure in the system. The check valves are provided in the suction and discharge side of the pump. Since the pump is of the plunger type, metering pump is a positive displacement pump.

Points to Note

For a positive displacement pump, the relief valve has to be provided in the discharge line. The reason for this is that the liquid is incompressible and there is no space in the barrel to accommodate the pressed liquid. A high pressure is created if the discharge valve is closed or if there is any other restriction/blockage in the system. The high pressure might completely damage the pipes connected. For this reason a relief valve is connected in the discharge line and is set at a particular pressure. When the pressure rises, the relief valve opens and relieves the extra pressure, thus protecting the pipes.

Generally metering pumps are connected to the dosing pumps and the whole unit is known as the dosing unit. The relief valve is connected to the dosing pump, which releases the excess pressure back to the dosing tank.

Working of Metering Pump

As the plunger moves away from the suction valve, a vacuum is created inside the pump because of which makes liquid flow inside the pump. This closes the check valve closes and the plunger again starts moving towards the valves. The discharge valve then opens and supplies the liquid to the system.

The seal arrangement is provided at the end of the plunger i.e. towards the motor side so that no leak should take place.The volume of the liquid supplied can be altered by altering the movement of the plunger inside the barrel. This is generally done by a small knob provided on the pump and which thus allows adjusting the percentage of liquid supplied.When the knob is turned to increase or decrease the flow rate, it alters the movement of the plunger, which means that it moves less in the plunger rather than along the full length of the plunger. Because of this the liquid enters the chamber and changes the plunger position along with the flow rate.

Viscosity Meter and Viscosity Controller Used on ShipsAs the fuel prices go sky high, ships are using lower grades of fuel for saving its operational cost. The fuel used for burning in auxiliary engine and main propulsion plant is normally heavy fuel oil. Along with other properties, viscosity is an important property which determines the efficiency of fuel combustion and of the marine engine.

Viscosity of fuel oil depends on the grade of oil. If the viscosity of the fuel oil and its viscosity index are on the higher side, it would lead to more difficulty in achieving atomization state and poor combustion inside the engine cylinder.

Understanding the Important Definitions

Viscosity

In simple term, it can be defines as ‘resistance to the flow of the fluid offered by its internal layers due to internal frictions’. It is measured in centi-stokes (cst).

Less the viscosity, lesser the resistance to flow and the fuel can be easily atomized.

Viscosity index

It is an important factor in selecting any kind of oil, fuel or lube oil. It’s the measure of change of viscosity of oil with variation in temperature.

Since fuel oil is heated to achieve proper atomization, it should have proper VI. If it’s on the higher side, it will be difficult to alter the viscosity of oil by heater.

Atomisation

It is the process of breaking the fuel particle into fine mist spray under high pressure to improve the surface area of contact of fuel and air for proper combustion.

 

Viscometer or Viscotherm

The viscosity of the marine bunker HFO fuel when supplied at 50 Odeg C varies from 180cst to 380 cst. The fuel is heated and the viscosity of the fuel is reduced to 13~15 cst at the time of injection in the engine by means of electrical or steam heaters or both.

The viscosity to the high pressure fuel oil pump has to be maintained approximately at 13 cst to achieve efficient combustion.

A viscotherm or viscometer is used to measure the viscosity of fuel oil at the fuel injection system of the engine.

 

Construction and Working of Viscosity meter

It consists of a capillary tube inside of which a gear pump is fitted which rotates at very slow rpm (say 40 rpm). There is an out side casing provided for the capillary tube.

When the oil passes through the casing, some part of the oil pass through the gear pump and its capillary, and some part of the oil passes over the capillary tube. Hence a flow difference occurs inside the casing. The oil inside the tube maintains a laminar flow and outside the tube maintains a turbulent flow.

The pressure difference between outside and inside of the tube is measured which is directly proportional to the viscosity of the oil. Hence oil viscosity is maintained.

 

Viscosity Controller

The viscosity controllers acts as the controller of the 3 way valve from which steam is passed into the heater or bypassed from the heater as per the position of the control valve.

Construction and working

Normally pneumatic control system is used with bellows, flapper and nozzle. The output signal from the viscometer is connected to measured value bellow of the viscosity controller.

Another bellow is supplied with set point of the required viscosity and both the bellows are connected opposite to each other to complete a flapper nozzle control system. The output of flapper nozzle is the controlling signal of fuel oil heater 3 way valve.

A 3-way valve has 2 openings in which one is inlet and 2 are outlet. One outlet goes through the heater and one outlet is connected to a bypass line of heater.

When the set value and measured values are same, no signal is given to control valve and valve position remains same. More of the steam bypasses the heater.

When the measured value decreases, the output signal opens the control valve to steam side so that more steam is supplied and viscosity can be brought down.

 

It is important to have a better grade of marine fuel oil with proper viscosity index for maintaining proper efficiency of engine and to reduce wear down of the fuel injection parts.

Understanding Stern Tube Arrangement on ShipsThe propeller of the ship is fitted at the aft and attached to a crankshaft coming from the main engine. This is done so that the rotating motion of the Main Engine can be converted into thrust to propel the ship. The propeller shaft or tail shaft is supported by a bearing arrangement which acts as an intermediate phase between the sea and the ship.

The stern tube is a hollow tube passing at the lower stern part of the ship carrying tail shaft and connecting it to the propeller out at sea, bearing for the tail shaft, lubrication arrangement and most importantly the sealing arrangements.

The stern tube bearing arrangement and sealing plays a vital part in ship’s operation and pollution prevention. The two main purpose of the stern tube bearing are:

Withstand load

The propeller which hangs at the aft end exerts load on the shaft, which is supported and withstand by the stern bearing. The bearing is a cast iron bush lined with a white metal having excellent load handling and lubricating property.

The stern tube is fitted at the stern frame and internal framing of vessel’s hull at aft peak.This allows the tail shaft to rotate smoothly in the bearing area for uninterrupted propulsion.

Sealing

The stern tube bearing consists of sealing arrangement to prevent ingress of water and to avoid the lubricating oil to escape into the sea.

Sealing arrangement

The lubrication system for ships with variable draught (due to loading and unloading of cargo) consists of header tanks located at around 2 to 3 meters above the water line so that the differential pressure ensures no water ingress.

Different sealing arrangements are used to prevent water ingress and oil leakage. They are as follows:

Stuffing boxes consisting of packing material. Lip seals in contact with shaft to prevent passage of oil or water along the shaft. Radial face seals supported with springs fitted radially around the shaft, aft bulkheads

and after end of the stern tube.

Out of these, the lip seal arrangement is most popularly used. Read more about Lip seals here.

General Overview of Central Cooling System on ShipsThe machineries fitted on board ships are designed to work with maximum efficiency and run for long running hours. The most common and maximum energy loss from machineries is in the form of heat energy. This loss of heat energy has to be reduced or carried away by a cooling media to avoid malfunctioning or breakdown in the machinery. For this reason, cooling water systems are fitted on board ships.

Types of Cooling Systems

There are two cooling systems used on board for the cooling purpose:

1. Sea Water cooling system: Sea water is directly used in the machinery systems as a cooling media for heat exchangers.

2. Fresh water or central cooling system: Fresh water is used in a closed circuit to cool down the engine room machineries. The fresh water returning from the heat exchanger after cooling the machineries is further cooled by sea water in a sea water cooler.

Understanding Central Cooling System

As discussed above, in central cooling system, all the working machineries on ships are cooled down using circulating fresh water. This system comprises of three different circuits:

1. Sea water circuit: The sea water is used as a cooling media in large sea water cooled heat exchangers to cool the fresh water of the closed circuit. They are the central coolers of the system and are normally installed in duplex.

2. Low temperature circuit: The low temperature circuit is used for low temperature zone machineries and this circuit is directly connected to the main sea water central cooler; hence its temperature is low than that of high temperature (H.T circuit). The L.T circuit comprises of all auxiliary systems.

3. High temperature circuit (H.T): The H.T circuit mainly comprises of jacket water system of the main engine where the temperature is quite high. The H.T water temperature is maintained by low  temperature fresh water.

4. Expansion tank: The loss in the closed circuit of fresh water is continuously compensated by the expansion tank which also absorbs the increase in pressure due to thermal expansion.

Advantages of central cooling System

-Low maintenance cost:  As the system runs with fresh water, the cleaning, maintenance and component replacement reduces.

-Less corrosion: Since the sea water system is only in the central part, the corrosion of pipes and valves decreases.

-Higher speed of fluid hence better heat exchange: Higher speed is possible in the fresh water system which results in reduced piping and low installation cost.

-Use of cheaper materials: Since the corrosion factor decreases, expansive materials are not required for valves and pipelines.

-Constant temperature level maintained: Since the temperature controlled is irrespective of sea water temperature, stable temperature is maintained which helps in reducing machinery wear down.

Life Raft Release System and Launching ProcedureAs discussed in the previous article, life raft has an advantage over life boat as they are easy to launch and during emergencies, the life raft inflates itself automatically as soon as it comes in contact with seawater. In this article, we will discuss the life raft release system and launching procedure.

The life raft on board ship are released or launched in to the water by three different methods:

1)      Auto release with Hydrostatic Release Unit (HRU).

2)      Manually launching.

3)      Launching by Davits.

Auto Release with Hydrostatic Release Unit (HRU):

The life raft HRU plays an important role when it comes to saving life during abandon ship situation. SOLAS 74 clearly specify the requirements for construction and positioning of the HRU at the life raft.

The Working of HRU:

HRU acts as a connecting media between life raft container and ship deck, where it is stored.

The HRU comes in action under the pressure of water exerted on HRU when the ship sinks below 4m of water level.

The HRU consists of a sharp knife or chisel which is used to cut the strap lashed over the container carrying life raft, but it still holds the painter at the weak link.

The HRU is connected to the container through a lashing arrangement which can be disengaged quickly by means of slip hook when launching the raft manually.

The HRU is connected to a strong point on deck through a weak link. When vessel sinks, the HRU cuts the rope and the container floats to the surface of

water. As vessel sinks further, the tension in the painter causes the life raft to inflate out of

the container. The tension acting on the weak link will cause it to break making the life raft free from

the ship. When vessel sinks, the HRU cuts the rope and the container floats to the surface of

water.

Manual Launching Procedure of Life raft:

Check that one end of the painter of the raft is well secured to a strong point on ship’s deck or structure.

Remove the lashing from the container of the raft and open the way to portable rail if available.

Check the ship side where the raft to be launched is clear. Two people should lift the container from both sides horizontally and throw the

container. Make sure the painter is still fixed at a strong point so that the raft should not be

waved away by waters. Pull the painter with a hard jerk to fire the gas bottle to inflate the raft. The life raft will take 20-30 sec to inflate. Board the life raft one by one using ladder or rope. Avoid sharp objects like knives, shoes and other sharp objects etc which may damage

the raft surface.

When everybody is aboard, after a headcount, cut the painter with a sharp knife.

Launching Raft by Davit:

Open the lashing and remove the raft container from HRU by opening the manual slip hook or bottle screw arrangement. 

Tie up the one end of the painter of raft into a strong point at deck.  Keep the container in the open and attach the davit hook to the given eye in the

canister/ container  Take up the raft load by davit and keep the container hanging at embarkation deck

area.  Pull the painter and inflate the raft. Have a thorough check on the inflated raft.  Start boarding the raft without the shoes and other sharp object.  After the boarding is completed, check the bottom is clear and release the securing

lines, if any.

Someone inside the raft will detach the hook of the davit from the raft when tha raft is just above the water.

The davit operating person will board the raft either by jumping in to the sea, raft or by other boarding means if provided. 

Cut the painter and cast away the raft from ship.

High Speed Centrifuge on Ship: Construction and WorkingA high speed centrifuge is a type of separator which is used on ship to remove contamination from liquids such as fuel and lube oils. It is imperative to carry out this treatment in order to remove solid impurities and water before they are supplied to the marine engine. Thus, the task of centrifuge is to remove solid contamination from liquid and to remove undesirable liquid (water) from useful liquids (fuel).

Principle of Working

The separation principle of high speed centrifuge depends on the difference in the specific gravity of two different liquids. To understand, let’s take a settling tank where fuel is stored and because of the difference in the gravity of water and fuel (water is heavier) the water gets collected at the bottom part of the due to the effect of gravity. Mathematically this process can be represented by:

Fs = ∏/6x D3 (ρw-ρo) g

Where Fs is the separating force, ρw is density of water, ρo is density of oil and “g” is gravitational force.

Now if we convert the tank into a conical rotating object, then the gravitational factor g will be replaced by the centrifugal force ω2 r, where ω2 is angular velocity of rotation and r is effective radius.

Fs = ∏/6x D3 (ρw-ρo) ω2 r.

Now the separating force will be much higher in centrifuge as compare to settling tank.

Construction of High Speed Centrifuge:

Basic components of the centrifuge are as follows:

Exterior framework:

The exterior frame work is normally made up of caste iron which supports the internal bowl and disk parts and carries water line, feed line and outlet line connections.

Bowl and disk:

There are bowls inside the frame, which can be a solid assembly operating non continuous and have space enough to retain the separated sludge. There can also be an

arrangement in which the upper and lower parts are separate for discharging the accumulated sludge by a continuous operation. These parts are normally made up of high tension stainless steel.

Vertical shaft:

The Vertical shaft is used to transform the electrical motor output into rotational motion for rotating the bowl in high speed through spur gear and horizontal shaft or belt. The material used for vertical shaft construction is an alloy of steel.

Horizontal shaft or belt drive:

The electrical motor drives the horizontal shaft through clutch pads and is used for transmitting the rotational motion to bowl assembly. A special belt having elastic character is used in some models in place of horizontal shaft, thus removing the use of the gear assembly. The horizontal shaft material is a special alloy of steel.

Spur gear:

A spur gear is placed between the horizontal and vertical shafts for the transfer of rotational motion. These gears are manufactured by special aluminum bronze material.

Clutch or friction pads:

An electric motor will get overloaded if it is connected directly to the bowl assembly for the rotation of the same as the complete assembly is very heavier. To avoid this, clutch or friction pads and drum assembly are installed on the horizontal shaft. Normally the number of pads varies from 2 to 4 depending upon the frequency supply to the motor.

As the motor starts, the pads inside the drum moves out gradually due to centrifugal force and cause friction in the internal wall of the drum resulting in rotation of the shaft and the bowl gradually without overloading and damaging the motor and gears.

Attached Gear pump:

A general construction of centrifuge consists of a horizontal shaft driven attached supply or discharge gear pump. In some system an external supply pump may be installed in place of the attached pump.

Types of Centrifuge:

There are normally two types based on the application:

1)     Purifier: When a centrifuge is arranged for separating two liquids of different densities, for e.g. water from oil, it is known as a purifier. The main component of purifier is correct size gravity disc or dam ring which is responsible to create interface between the oil and water.

2)     Clarifier:  When a centrifugal is arranged to remove only impurities and small amount of water, it is called as clarifier. Since it is used mainly for that fluid where mostly solid impurities are to be removed, gravity disc is not used in clarifier; instead a sealing ring is used to keep the impurities intact unless desludged.

The basic operations of clarifier and purifier are:

-   It contains stack of disk numbering up to 150 and are separated from each other by very small gap. A series of holes are aligned in each disk near the outside edge which permits the entry of dirty oil.

-    Due to difference in gravity and centrifugal force, the heavier impure liquid (water) and particles moves outside and lighter clean oil flows inwards and get separated.

-   The collected sludge and impurity can be discharged continuously or at a time intervals, depending upon the construction, automation and system incorporated.

Bow Thrusters: Construction and WorkingBow thrusters are type of propellers, which are smaller in size and which help in better maneuverability of the ships at lower speeds. They are generally used for maneuvering the vessel near the coastal waters or while entering or leaving a port. Bow thrusters help in assisting tug boats in berthing the ship without wasting time. This saves a lot of money for the shipping company because of lesser stay of the ships in the ports. Moreover, presence of bow thrusters on a vessel eradicates the need of two tugs while leaving and entering the port, and thus saves more money.

Generally, bow thrusters are transverse thrusters placed at the forward and aft end of the ship. The thruster placed in the forward end is known as the bow thruster and the one placed in the aft is known as the stern thruster. The requirement for the number of thrusters to be installed depends on the length of the ship.

Construction and Working of Bow Thrusters

The bow and stern thrusters are placed in the through-and-through tunnels which open at both sides of the ship. There are two such tunnels – at forward and aft ends of the ship. The thruster takes suction from one side and throws it out at the other side of the ship, thus moving the ship in the opposite direction. This can be operated in both the directions i.e. port to starboard and starboard to port. The bow thrusters are placed below the water line of the ship. For this reason, the bow thruster room should be checked for water accumulation at regular intervals of time.

The bow and the stern thrusters can be electric driven or hydraulic driven or diesel driven. However, the most commonly used are electric driven, as in hydraulic driven thrusters there occur many leakage problems. Also, with diesel driven bow thrusters, the amount of maintenance required is more and every time before starting someone needs to go to the thruster room to check the thrusters.

Bow thruster consists of an electric motor which is mounted directly over the thruster using a worm gear arrangement. The motor runs at a constant speed, and whenever there is a change required in the thrust or direction, the controllable pitch blades are adjusted. These blades are moved and the pitch is changed with the help of hydraulic oil which moves the hub on which the blades are mounted. As the thruster is of controllable pitch type, it can be run continuously, and when no thrust is required the pitch can be made to zero.

The thruster is controlled from the bridge and the directions are given remotely. In case of remote failure, a manual method for changing the pitch is provided in the thruster room and can be operated from there.

Maintenance Required

1) The insulation needs to be checked regularly and should be kept dry. This is done because bow thrusters are not used frequently and thus there are chances of damages by moisture. Moreover, because of the frequent idle state of the bow thrusters, there can be reduction in the insulation resistance especially in colder regions.

2) The space heater is checked for working condition so that the insulation can be kept dry.

3) The bearings of the motor and the links are to be greased every month.

4) The condition of hydraulic oil is to be checked every month for water in oil and samples should be sent for lab analysis for further checking.

5) The thickness of the contactors is to be checked from time to time.

6) Checks are to be made for any water leakages in the bow thruster room which is indication of seal leaking.

7) The flexible coupling between the motor and thruster should also be checked.

Advantages

1) Better maneuverability at low speeds of the ship.

2) Safety of the ship increases when berthing in bad weather.

3) Saves money due to reduction of stay in port and less usage of tug boats.

Disadvantages

1) A very large induction motor is required, which takes a lot of current and load, and thus large generator capacity is required.

2) Initial investment is high.

3) Maintenance and repairs are costly when there is damage.

The Green Source of Power On Ship – Shaft GeneratorA ship consist of a power plant system which generates enough power for the propulsion plant machines, engine room and deck machines, and navigation equipment of the ship, along with daily life demands of the crew onboard which includes galley, lift and cabin power supply etc. For this, large quantities of fuel are burned within the prime mover which in turns rotates the rotator in the alternator and generates power. The burning of fuel increases the operational cost for owner, burdens the engine crew with maintenance of the generator and the most importantly, it causes air pollution.

To eliminate the usage of independently driven generators when the ship is sailing in the mid sea, shaft generator concept is used. Shaft generator is a clean source of power, which means it does not burn any fuel to generate power, and for the same reason it is also called the green source of power.

Shat Generator: Principle of Working

In an A.C generator, in order to produce power, the stationary armature conductors are cut by the rotating magnetic field, produced by the rotation taken from the propeller shaft of the main propulsion plant or main engine.

The running machinery’s power is supplied through main switch board with constant voltage and frequency by diesel generator. In case of shaft generator, which is driven by

main engine, the speed of the former may vary at different situations like ship sailing in traffic water and crossing canals, resulting in variation in voltage and frequency of shaft generator.

To overcome this deficiency, two systems are used Onboard ship

a)       Power take off (PTO) system is incorporated with different kinds of frequency control system which makes sure of producing power with constant frequency.

b)       Hybrid system consisting of an advanced power electric system for conditioning the power generated from shaft generator so that the supply to the switchboard always remains constant at any engine speed.

The modern application of the shaft generator includes its functioning as a motor by taking power from the electrical plant of the ship to drive the propeller at reduced speed.

This application is expensive to install and is used for vessels which moves very slowly or vessel which stays still most of the time.

Advantages of Shaft generator system:

1)       The biggest advantage- it dose not cause air pollution unlike other traditional methods of power production in ship. Moreover, noise level is also low.

2)       It is more cost effective as it dose not requires expensive fuel for power generation as main engine itself is a prime mover.

3)       The wear and tear and hence the maintenance schedule and costs for the same reduces for independent driven generator.

4)       Installation space is less as it is installed close or in line with the shaft of the main engine.

5)       The investment cost depends on the type and system of the shaft generator but for a basic designed shaft generator it is low.

6)       The installation cost for shaft generator is also low as it doesn’t require separate foundation, prime mover or exhaust system. Even time for installation is also less.

7)       Low spare parts cost and man – hour cost as the schedule maintenance period for shaft generator has larger time gap as compared to diesel generator.

Disadvantages of Shaft generator:

1)       For a basic shaft generator system, the efficiency of propeller and engine is reduced at low propulsion power. Since the frequency requirement is constant, for a main engine with a CPP, it has to run at constant speed even at low load.

2)       No power generation in port as the prim mover is in stop condition.

3)       Due to an additional attachment to shaft of the engine, the load in the engine also increases, resulting in increase in specific fuel and cylinder oil consumption when shaft generator is used.

4)       Cannot cope up alone when the load demand is high as it may affect the main engine performance and maintenance.

5)       It requires gears, couplings and other complicated arrangement for installation in some system.

A Chief Engineer’s Concern Regarding Slow Steaming of Ships

Slow steaming has been adopted by majority of companies and ship owners in order to survive in these tough times of rising fuel prices and financial recession.

Originally started for Container Shipping by Maersk Lines and justified by the cost sheets and economics, the concept has been borrowed by other kinds of ships including the Dry Bulk ships, whose operating speeds are traditionally low.

Ship owners instruct their Chief Engineers to run the ship on economy speed also called Eco speed or slow steaming.

Long before other ship owners caught on with the concept, shipping companies like Maersk experimented with slow steaming and presented to its customers and ship owners the complete fact sheet of slow steaming along with the financial viabilities. They even requested all major engine builders to issue a no objection certificate that convinced reluctant Marine Engineers  and ship owners that slow speeding is possible and if correctly done would not jeopardize the Main Engine.

In these series of well researched articles we will discuss the technical requirements to slow steaming, various modes of slow steaming including super slow steaming, the

retrofitting, modifications with the upgrade kits and the suitability of intelligent engines for slow steaming.

Chief Engineer’s Concern

In the transient times of changing standards, stricter regulations and new emerging technology it finally translates to the ship’s Chief Engineer, along with his team of marine engineers in consultation with the technical management to  implement the changes on the ship.

As slow steaming is not a regular affair for a marine engineer nor have they been trained for it, some efforts have to be made to remove the traditional mindset and reluctance of the engine staff and retrain them. In addition they have to be instructed about additional routines and inspections of the Main Engine, which is operating outside its designed optimal range.

Marine engineers have always been advised by engine manufacturers that low load operation must be avoided.  The engines must be run close to its continuous rating for optimization of all its parameters and allowing the individual components to operate in their designed range.

A chief engineer has the following concerns with regards to slow steaming:

Frequent and thorough scavenge and under piston inspections must be carried out.

Over lubrication of the cylinder liners is as dangerous as under lubrication. Unless the engine has a load dependent cylinder lubrication system which is suited for slow steaming, the cylinder lubrication rate must be adjusted to optimal value as per manufacturer’s advice.

Slow steaming causes fouling of the turbochargers and loss of efficiency.

Turbochargers operating outside their designed range produce less air flow leading to more deposits.

Causes increased carbon deposits on the injectors compromising their performance.

Causes fouling of the exhaust gas economizer resulting in reduction of capacity as well as increased danger of soot fire.

Causes a reduction in scavenge air pressure resulting in improper combustion.

Leads to improper atomization of the fuel as well as impingement.

Causes increased carbon deposits and maintenance intervals have to be modified likewise.

Causes low exhaust gas temperatures. Running the engine with exhaust gas temperatures below 250 deg C can cause low temperature corrosion.

Causes reduced peak compression pressure.

Damage occurs and becomes imminent when engine is run at full load after long period of slow steaming.

Compromises the piston ring pack efficiency, leading to increased under piston and scavenge deposits.

Increases the risk of scavenge fires and needs extra scavenge and under piston area draining.

Cause loss of heat transfer due to carbon deposits and failure of components due to thermal stresses.

Causes reduction in the efficiency of the economizer causing the need of oil fired boiler to operate and adding to extra cost and maintenance.

Slow Steaming of Ships: Optimization of Ship’s Main EngineIn the previous article, we discussed about several concerns regarding slow steaming in the minds of marine engineers.

As the low speed marine engines are not traditionally suited for prolonged slow steaming, a number of precautions need to be taken in case slow steaming operations are adopted without modification.

In this article we shall discuss the checks to be done, additional maintenance required and the precautions to be taken so that there are no long term damages to the machinery.

Optimization of ship’s main engine

Traditionally main engines are designed to run between 70 % to 85 % load range during continuous operation. The matching and

designing of all the auxiliaries is based on this load range operation.

The exhaust boiler size (surface area) is decided based on the exhaust temperature, volume of exhaust gas flow and the waste heat recovery in this range. Low load operation makes this waste heat recovery system ineffective and there is less production of steam, which increases the load on the oil fired boiler.

The air cooler size (surface area) is selected based on the heat load of the air in this operating range. During low load operation the cooling water to the air cooler needs to be controlled by bypassing the cooler and throttling the water valves to maintain optimum scavenge air temperature. Too much throttling of the water valves reduces the flow velocity of the cooling water thereby increasing the deposit rates of the precipitants, leading to fouling and contamination of tubes.

The turbocharger selection and matching to the main engine is based on the enthalpy of the exhaust gas that needs to be extracted. The other selection criteria is the quantity of the scavenge air that needs to be supplied to the cylinders for optimum combustion. The turbocharger is selected for the normal running load range of 70 to 85 %. Low load operations of the main engine lead to lower running RPM of the turbocharger and less generation of scavenge air. This leads to ineffective and incomplete combustion, increased fouling and also makes the cleaning measures like dry grit cleaning of the turbine ineffective.

The propeller is designed to give maximum efficiency for the RPM in this range. Due to lower RPM the propeller efficiency may be affected.

The Specific fuel oil Consumption (SFOC) is optimized for running in this range. Even though the fuel consumption is lower in totality, the SFOC is higher at part loads as injection and combustion is not proper.

The fuel injectors and fuel pumps are designed for this range thus the atomization and penetration may be effected at low load operation.

The operating parameters and their alarm and monitoring system is designed for this range.

The hydrodynamic lubrication is RPM dependent and the grade of oil and its properties like oiliness are selected for this range.

The shaft generators are designed and selected based on this range. Low load operation may make shaft generators unusable.

Thus running the main engine below its normal operating range of 70 to 85 % Maximum Continuous Rating (MCR), the whole system is not optimized.

Generally is known that if engine modifications and retrofitting is done on the main engine, then it is safe for slow steaming as well as ultra slow streaming. However we limit ourselves to slow steaming without any engine modifications in this article.

Slow steaming up to 50 to 55 % load can be done generally on most engines without harm in long terms if certain precautions are taken. That generally is the point above where the auxiliary blowers cut in. In the article “How to Test Ship’s Main Engine for Slow Steaming”, the testing method for the optimum eco speed by trial has been discussed.

List of Processes Used in Marine Workshop of ShipsWorkshop technology is the back bone of any engineering industry and when it comes to shipping, it becomes the most important aspect which is responsible for planning, construction and operation of a ship and its machinery. In this article, we will discuss the most common work shop technology elements which are widely used in shipping industry, both in ship and on shore.

Any construction and operation of shipping structure or machinery is not possible without the following workshop practices:

Welding

It is the process by which metals are joined by heating and melting the metals and simultaneously adding filler material. This forms a weld pool and makes a strong joint when cooled down. It functions on the principle of coalescence. Welding is widely used for fabrication and maintenance operations. Different types of welding are electric arc, laser, electronic beam etc but the most famous out of these is electric arc welding.

Brazing

It is the process of joining metals by heating base metals at a temperature of 800°F after which a nonferrous filler metal with a melting point well below the base metal is added to form a strong joint by capillary action. When brazing is done, flux is used as it prevents the oxide formation while the metal is heated

Gas Cutting

Gas cutting is the process of cutting metals by application of high temperature flame or torch produced by combination of two gases-oxygen and acetylene. It is the most common method used on board ship. Other metals cutting procedures are carbon air cutting, plasma arc cutting etc.

Annealing

It is a heat treatment process done to induce ductility in the metal. Material is heated above its recrystallization temperature and then it is cooled down which relieves its internal stresses and refines the structure.

Riveting

It is a process of fastening a metal in another metal by the use of riveting machine and small cylindrical shaft with head in one end. It is not as strong as annealing and welding but still comes handy in different parts of the ship.

Lathe Practice

A lathe machine is one of the most important parts of the ship’s workshop as it is used for various purposes such as manufacturing, cutting, shaping and checking different spares and parts of the ship.

With number of tools different operation can be performed on lathe like, machining, surface finishing, thread making, gear making, knurling etc.

Drilling

It is a process of cutting or enlarging a cylindrical hole in a solid material. This is done by applying a rotational pressure on top of the metal through a strong drill bit.

Drill bit is a drilling tool made up of a higher strength metal like high speed steel or cobalt steel alloy.

Grinding

This process is used to smoothly cut the metal and to remove edges from the metal. In this process a grinding machine is used which rotates a highly abrasive grinding wheel acting as a cutting tool. The grains on the wheel cuts off a piece of metal by shear deformation.

Buffing

It is the process of cleaning and removing debris and hard deposits like carbon and sludge from the surface of the metals. A buffing wheel or buffing tool, which is a metal wire wheel, is attached to a portable hand driven buffing machine or an installed buffing wheel.

Tapping

It is a process of making threads in a hole of metal. Worn out threads are restructured by using taps and drills. Tapping tools are used in series to get a perfect thread. The tools are plug tap, intermediate tap and taper tap.

Thread extraction

It is the process of removing or extracting a broken part of bolt or metal which is threaded in a hole. Extracting tool is fitted after drilling a hole in the metal or bolt to be removed. It is a reverse tap and turns the thread in the direction of the drawn pitch.

Different Types of Mechanical Measuring Tools and Gauges Used on ShipsMachinery onboard ships require regular care and maintenance so that their working life and efficiency can be increased, and the cost of operation, which includes unnecessary breakdowns and spares, can be reduced. For different types of machinery and systems, different measuring tools, instruments and gauges are used on ship.

Measuring instruments and gauges are used to measure various parameters such as clearance, diameter, depth, ovality, trueness etc. These are important engineering parameters which describes the condition of the working machinery.

Popular mechanical gauges and tools used on ships are:

Ruler and scales: They are used to measure lengths and other geometrical parameters. They can be single steel plate or flexible tape type tool.

Callipers: They are normally of two types- inside and outside calliper. They are used to measure internal and external size (for e.g. diameter) of an object. It requires external scale to compare the measured value. Some callipers are provided with measuring scale. Other types are odd leg and divider calliper.

Venire calliper: It is a precision tool used to measure a small distance with high accuracy. It has got two different jaws to measure outside and inside dimension of  an object.It can be a scale, dial or digital type venire calliper.

Micrometer: It is a fine precision tool which is used to measure small distances and is more accurate than the venire calliper. Another type is a large micrometer calliper which is used to measure large outside diameter or distance.

Feeler gauge: Feelers gauges are a bunch of fine thickened steel strips with marked thickness which are used to measure gap width or clearance between surface and bearings.

Telescopic feeler gauge: It is also known as tongue gauge and it consists of long feeler gauge inside a cover with tongue or curved edge. The long feeler strips protrude out of the cover so that it can be inserted in to remote places where feeler gauge access is not possible.

Poker gauge: This gauge is used to measure propeller stern shaft clearance, also known as propeller wear down.

Bridge gauge: Bridge gauges are used to measure the amount of wear of Main engine bearing. Normally the upper bearing keep is removed and clearance is measured with respect to journal. Feeler gauge can be used to complete the process.

Liner measurement tool: Liner measurement tool is a set of straight assembled rod with marked length in each set. It is used to measure the wear down or increase in the diameter of the engine liner.

American Wire Gauge: American wire gauge or AWG is a standard tool which is circular in shape and has various slots of different diameter in its circumference. It is used to measure cross section of an electric cable or wire.

Bore Gauge: A tool to accurately measure size of any hole is known as bore gauge, It can be a scale, dial or digital type instrument.

Depth gauge: A depth gauge is used to measure the depth of a slot, hole or any other surface of an object. It can be of scale, dial or digital type.

Angle plate or tool: It is a right angle plate or tool used to measure the true right angle of two objects joined together.

Flat plate: Flat plate is a précised flat surface used to measure flatness of an object when it is kept over the flat plate.

Dial Gauge: Dial gauge is utilised in different tools as stated above and can be separately used to measure the trueness of the circular object, jumping of an object etc.

Lead Wire: It is a conventional method to used soft lead wire or lead balls to measure the wear down or clearance between two mating surfaces. The lead wire or balls of fixed dimension is kept between two surfaces and both are tightened against each just as in normal condition. The increase in the width of the lead wire or ball will shoe the clearance or wear down.

A Guide to Welding Electrodes on Ships – Part 1A Guide to Welding Electrodes on Ships – Electrode Selection and Current Setting

A ship’s engine room has machines, structural members, pipes etc. composed of different kind of metals and alloys. A second engineer should be able to guide the ship’s welder in identifying the metal of the machine or structural member that is to be repaired and suggest suitable electrode for welding the same.

Electrodes have identification numbers like E6013 and sometimes color coding which are difficult to understand.  Normally branded electrode from well known companies can be identified as there is a product guide on board. However often we discover electrodes packets in the store in unknown language and only the number is comprehendible.

This article endeavors to help the marine engineers to recognize commonly used electrodes in engine room for Manual Metal Arc Welding.

Commonly Used Welding Electrodes in Ship’s Engine Room

Every engine room has a collection of welding electrodes in the engine store. Generally there are general purpose electrodes in bulk and few kilograms of special electrodes like Low Hydrogen electrodes and Cast Iron electrodes etc.  Recognizing a few electrodes and their applications can make life easier for the second engineer. The commonly use electrodes in engine room are as follows:

E6011: All position welding electrode that can be used with both AC and DC. It is useful for pipe welding.  It produces a deep penetration weld and can weld over rust, dirt and paint also. It is also suitable for x-ray quality welding. It is a general purpose electrode for ship building.  As it has fast freezing or rapid freezing of weld metal, it is also suitable for vertical and overhead welding.

Important Characteristics : Pipe welding, vertical and overhead, rust and paint tolerant, deep penetration.

E6013: It is a general purpose electrode which can be used with both AC and DC currents and produces a medium penetrating weld with a superior weld bead appearance. It is suitable for welding medium gauge steel and sheet metal jobs.  It is also especially useful where there is poor fitting and wide gaps exist in the job piece.

Important Characteristics : General purpose, poor fitting, medium penetration.

E7014:  It is a general purpose electrode and is used where a higher efficiency than E6013 is required. It can be used with both AC and DC current. It has light to medium penetration. It is designed to give high deposit rates and is suitable for higher speeds.

Important Characteristics : High deposition, high speed, general purpose, light to medium penetration.

E7018: it is a low hydrogen electrode which can be used both with AC and DC. The flux coating of this electrode has low hydrogen content which reduces the amount of hydrogen going into the weld. The electrode is capable of producing x ray quality welds in hands of a good welder. It had a medium penetration.  It is used for welding carbon steels, low alloy steels and free machining steels.  Its other uses are cold rolled steels as in heavy machines, fired and unfired pressure vessels like air bottles and boiler tubes, cast steel and any application in ship building that needs to be subjected to x ray welding. It is used where high strength welding requirements exist.

Important Characteristics : High strength, low hydrogen, medium penetration.

 

Use of Low Hydrogen Electrodes 

Low hydrogen electrodes are those that have a low concentration of hydrogen in the flux coating. This ensures that hydrogen does not

get into the weld of the metal during welding. They are useful for metals and alloys that are susceptible to hydrogen induced cracking or cold cracks. LH electrodes can be used for welding unalloyed, low alloy and yield point controlled steel.  Yield point controlled steel is ship steel which is used in deck plates, hull plates and frames.

Hydrogen is a concern because it results in heat affected zone cracking. Hydrogen in combination with high residual stresses and crack sensitive steel may result in cracks after the welding.  As high strength steels and restrained parts are more susceptible to hydrogen cracking they must be welded by low hydrogen electrodes.

 

Selection of Correct Size of Electrode 

On board ships we generally use electrodes of 2.5 mm and 3.2 mm and sometimes 4 mm.  However commonly available electrode sizes are 2.0 mm, 2.5 mm, 3.2 mm, 4.0 mm and 5.0 mm.  For special applications we have different size electrodes also. Some manufacturers use slightly different sizes like 3.15 mm for 3.2mm and 2.4 mm for 2.5 mm etc.

Generally the size of the electrode that should be used depends on the thickness of the part to be welded.  For thin metals the electrode is only slightly larger than the metal to be welded. For example if a plate is of 2.0 mm thick the electrode of 2.5 mm should be used.

The table below shows the recommended electrode sizes for various thickness of the job piece.

 

 Current Setting

Current setting also depends upon the size of the electrode and the metal/alloy being welded. Normally the manufacturers specify the current range that must be maintained.  In over head welding the current setting is slightly less than that for flat welding.

In arc welding correct current selection is very important. If the current is set too low than there is difficulty in starting the arc and the arc will not be stable. In addition there is a tendency for the electrode to stick to the work piece and the penetration is poor.

If the current is set too high then the electrode may overheat, there is excessive splatter and undercutting and burning of the material may take place.

Optimum current is between the current ranges specified for the electrode by the manufacturer. The optimum current is one in which there is no overheating of the electrode, no burning of the work and no undercutting of the job piece.

The table below gives the recommended for E6013 electrodes based on the sizes. The range may differ from manufacturer to manufacturer and for different specification of electrode and is for general guidance.

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A Guide to Welding Electrodes on Ships – Part 2A Guide to Welding Electrodes on Ships – Electrode Nomenclature and Classification

In A Guide to Welding Electrodes on Ships- Part 1, we discussed commonly used welding electrodes in the engine room, use of low hydrogen electrodes, electrode selection based on size of the work piece and current setting. In this article we shall discuss the nomenclature and classification of the electrodes based on popular ISO 2560 and AWS standards.

Standardization of Welding Electrodes 

The standardization of welding electrodes is essential as they are as important as the parent metals and alloys in manufacturing and repair. A correctly chosen electrode, which is matched perfectly to the parent metal, assures the effectiveness and strength of the welding.

The welding electrodes are classified on the basis of the electrode metal, flux coating, current used, position of welding, performance

characteristics, chemistry and the mechanical properties of the weld metal etc.

There are various standards of nomenclature and classification of welding electrodes such as American Welding Society (AWS), Bureau of Indian Standards (BIS), British Standards Institution (BSI), Deutsches Institut für Normung (DIN) and  ISO 2560 etc.

We will discuss the two popular standards; ISO 2560 and AWS in this article.

AWS Classification 

AWS stands for American Welding Society and this classification is widely used in the merchant marine.  In this, standard electrodes for different applications are numbered such as E6010, E6011, E6013, and E7018 etc. For example let us consider the welding electrode E6013 which is a commonly used electrode on board.

E XXXX:  The first character “E” in E6013 stands for flux covered electrode as used in Metal Manual Arc Welding.

E60XX: The next two characters indicate the minimum tensile strength. The “60” in E6013 indicates that the weld metal will have a minimum tensile strength of 62000 psi. Please refer to the chart below for the other key numbers and the associated tensile strength.

EXX1X: The fourth character indicates the different positions in which welding can be done using this electrode. In this case “1” in E6013 means that the welding can be done in flat, overhead, horizontal and vertical (upwards). Please refer the table below for other key numbers and the associated welding positions.

EXXX3:  This fifth character indicates the type of flux coating used, penetration of the electrode and the type of current suitable for the electrode. In this case the “3” in E6013

tells that it has a rutile potassium based flux coating. The penetration of the electrode is light and it can be used with AC and DC currents. Please refer the table below for other key numbers and their properties.

EXXXX-X This extra character is sometimes used for additional requirements. For example in the electrode E7018-A1, the suffix “A1” in the last refers to added chemical composition of 0.5 % Mo. Please refer the table below for other suffixes. These suffixes generally differ from manufacturer to manufacturer and even though the electrodes may be belonging to the same standard they may still be slightly different as each manufacturer likes to add a personal touch.

 

 

 

 

 

 

Thus the number E6013 written on an electrode indicates that it is a rutile potassium based flux coated mild steel electrode with 62,000 psi minimum tensile strength having light penetration which can be used in all positions of welding except vertically down. This information is helpful for the marine engineer preparing for a repair / fabrication and wondering which electrode to use.

ISO Standard

ISO 2560: 2009 is the standard under ISO for the classification of welding electrodes for Manual Metal Arc Welding. It is an international standard and all other regional and domestic standards are based on it. It is more comprehensive and gives a lot more information than the AWS classification however it is not so easy to remember and recall as the American Welding Society classification.

For example under ISO 2560 a welding electrode is classified as E55 3 MnMo B T 42 H10. We shall discuss the key numbers one by one.

E55 3 MnMo B T 42 H10: The character”E” here refers to a flux covered electrode for Manual Metal Arc Welding.

E55 3 MnMo B T 42 H10: The number 55 here indicates that the weld metal will have a minimum tensile strength of 550 N/mm2. . Please refer the table below for the other key numbers and the associated tensile strength.

 

 

 

 

 

 

E55 3 MnMo B T 42 H10: The key number “3” here indicates the lowest temperature at and below which the weld will become brittle. The weld must be able to absorb 46J of energy without breaking to be considered non brittle. Thus “3” here means that at or below -30 deg C the weld will become brittle.

 

 

 

 

 

 

 

 

E55 3 MnMo B T 42 H10: This is an additional field and sometimes used. The characters “MnMo” here refers to the alloying metal present in the weld deposit. In this particular case the key character indicates that the weld deposit will have Manganese

concentration between 1.4 to 2.0 % and Molybdenum concentration between 0.3 to 0.6 %. Please refer the table below for further details.

 E55 3 MnMo B T 42 H10: The key character “B” here refers to the type of flux coating. In this case it is basic coating containing Calcium Carbonate. Please refer the table below for the other type of flux coatings.

 

 E55 3 MnMo B T 42 H10: The character “T” here is an extra designation to advice about the heat treatment of the weld. Here it indicates that the weld must be annealed to between 560 to 600 deg C for one hour then cooled in furnace to 300 deg C and thereafter cooled in air. Please refer the example below.

 

 E55 3 MnMo B T 42 H10: The key character “4” here refers to current and the deposit rate. In this case it can be used for DC only and has a deposit rate of 105 to 125 %. As it is more than the amount of metal present in the welding electrode it means that the flux coating has some iron powder. Please refer the table below for details.

E55 3 MnMo B T 42 H10: The key character “2” here refers to the welding positions the electrode can be used in. Here it means all positions except vertically down. Please refer the table below for details.

E55 3 MnMo B T 42 H10: The symbol “H10” here refers to the hydrogen content in the deposited weld metal. In this case it is 10ml/100g. Please refer the table below for other symbols.

Thus the meaning of the marking E55 3 MnMo B T 42 H10 on a welding electrode is that it is a basic flux coated welding electrode having a minimum tensile strength of 550N/mm2 which will become brittle at -30 deg C. It has an alloying Manganese concentration between 1.4 to 2.0 % and Molybdenum concentration between 0.3 to 0.6 %. It can be used with DC current and has a deposit rate between 105 to 125 %.  It can be used in all positions except vertically down. The deposited weld metal will have a hydrogen concentration of 10 ml/100g. Thus the ISO 2560 standard is more detailed and comprehensive than AWS but very difficult to remember unless proper specification tables are provided.

Energy Audit on Ships: Part 1Now days with the rising fuel prices and slack freight market, every ship-owner is seeking ways to save money and to keep his enterprise in profit.

Apart from the energy recovery systems, ships have started using several latest technologies to reduce energy consumption and to make ships greener.

As fuel accounts for the major part of the daily running cost of the ship, any reduction in the fuel consumed is lending to profitability of the establishment. It is with this sentiment that many companies have become proactive towards fuel efficiency and conservation.

Some Japanese ship owners have been running “Bunker Save Campaign” and “Cylinder Oil Save Campaign”, where they honor the Chief Engineer with a cash award for running a tight ship. Moreover, the Energy Efficiency Design Index (EEDI) to improve energy efficiency and reduce carbon emission.

In these series of articles we will look in depth into energy audit of different machineries of ships and the ways to optimize their efficiencies.

What is an Energy Audit?

An energy audit is the first step towards adopting an exercise in energy efficiency on ships and to harvest the resultant savings.  Energy audit basically consists of identifying

core areas where conservation of energy can be done and then developing a program for the same.

During new building a ship is usually at the peak of its efficiency and the guaranteed speed, SFOC etc are tested in sea trial before handing over to the buyer. However over the time as the ship ages and the machineries are no longer in their prime the efficiency starts decreasing and the FO consumption starts increasing.  An energy audit at such a stage can identify key areas where loss is taking place and help in generating great savings

Objective of Energy Audit

The objective of conducting an energy audit is as follows:

To identify areas where there is a loss of energy due to loss of efficiency or wrong operation and cost savings by correcting it.

To identify areas where new developed technology can give cost savings. To project the information in such a way without alienating any one, to the buyer so

that he can make a decision based on cost and profit. To improve energy efficiency of the ship by saving fuel and also to reduce global

warming by emission control and help go green.

Energy Audit Contents

The energy audit seeks to find information about things that are taken for granted and often ignored.  It investigates the energy being used in the ship per day while at sea and while in the port. It identifies the processes that use this energy and the ways energy saving can be achieved. It also accesses the effectiveness of the control that can be exercised by the management in carrying out these recommended changes.

The energy audit report also emphasizes that plant metering and control should be done such as the running hours of the pumps, the air compressors, the boiler firing time, and fuel used etc.  All this helps the Chief Engineer and the technical department to formulate a policy that can be incorporated into the routines of the ship and save money for the life of the ship.

By identifying the quantity of savings and thus helping the management to make a decision the energy audit also helps in allocating a budget for the company’s energy management program.

 

Energy Audit Processes 

Generally in an energy audit irrespective of the machinery or industry it is being carried out, there are the following steps:

Data collection: All relevant data for the applicable machine is collected. The collection of data can be from mechanical means like, counters, running hour indicators, event logs etc. In case these are not available, the duty engineers and operators are interviewed.

Condition Evaluation: The condition of the machinery is evaluated and it is ascertained whether any overhaul or components change can elevate its performance.

Economic Alternatives: The audit will also inform the owner of the economic alternatives available and help him to make a decision.

Audit Report: Finally the energy audit report is created.

The Urgent Need to Reduce Nitrogen Oxide (NOx) Emissions from ShipsThe continuous rise of Nitrogen Oxide (NOx) in the atmosphere is a matter of great concern. Several factors have been stated as the reason for the increase of this element in the air and toxic emission from ships is one of them.

Nitrogen Oxide (NOx) is formed in the atmosphere when fuels such as oil, gas, and coal are burned at a very high temperature. The pollution caused because of NOx is supposed to be known as one of the most dangerous forms, which eventually contributes towards global warming.

Nitrogen Oxide and its effects on the Environment

A high-level of nitrogen oxide being released into the atmosphere can result in to:

Ground Level Ozone Acid Deposition Particulate Matter Nitrification Eutrophication Indirect Effect to Global Warming

Significant contributors to this toxic oxide are factories, coal-burning plants and emissions from motor vehicles and marine diesel engines.

Studies show that shipping is the source of 18-30% of the world’s nitrogen oxides. Moreover, though several steps have been taken to reduce the emission of NOx from ships, there is still a long way to go to bring down emissions to zero or an acceptable level.

IMO’s MARPOL Annex VI

MARPOL (Marine Pollution) is one of International Maritime Organization (IMO)’s regulatory policies focuses on preventing different forms of marine pollution including oil, noxious liquid substances, harmful substances, waste water, garbage and emissions of sulphur oxides and nitrogen oxides at sea.

MARPOL Annex VI Regulation 13 sets out the mandatory limitations on NOx. The regulation affects not only ships from signatory states but also ships entering MARPOL signatory-member waters.

MARPOL Annex VI and ECAs

Apart from the mandatory NOx limitations for oceangoing vessels around waters of the member states, IMO also defines Emission Control Areas or ECAs where the MARPOL NOx emission standards will apply.

The ECAs includes:

Baltic Sea (2006) North Sea (2007) Waters in North American coasts that include waters adjacent to the Pacific coast, the

Atlantic/Gulf coast extending to 200 nautical miles from US coast (2010) Waters around Puerto Rico and the US Virgin Islands that are just recently designated

by IMO (effective 2014) Norway, Japan and Mediterranean areas are being considered for future ECA proposal.

In the past few years, IMO has become stricter in implementing norms to reduce shipping emissions and to minimize the effects of marine pollution.

Is there a way to reduce NOx emission?

In the hope of complying with IMO’s global limits on nitrogen oxides and the enforcement of more stringent standards within the three Emission Controlled Areas marine diesel engine operators, ship owners and seafarers are left with no option but to find the best technology in reducing the amount of NOx from their ship’s exhaust systems and to take steps to make their ship “greener”.

Among the various emission control applications Selective Catalytic Reduction (SCR) System comes out to be the most efficient, effectively reducing ship’s NOx emission by 90-95%. By mixing a reagent (SCR 40 – 40% Marine Urea Solution) to the exhaust gas, nitrogen oxides are converted to Nitrogen (N2), water and Carbon Dioxide (CO2).

 Global Marine Urea Solution Suppliers

Some marine SCR System providers offer the supply of urea solution with their application. A known SCR System provider in Japan is Hitachi Zosen while Miratech is from the United States. Both suppliers offer Marine SCR application that complies with Tier III NOx emission standards.

For marine urea solution requirements, there are growing urea markets in the US, China and recently in Singapore. Read here for more information regarding marine urea solutions in Singapore.

Condition Monitoring Techniques – What is Shock Pulse Monitoring (SPM)?Shock Pulse Monitoring also known as SPM is a patented technique of predictive maintenance by measuring vibration and shock pulses of bearing in motors and to identify their condition and operating life before the next overhaul procedure.

 

It was introduced in 1969 and is now a known Condition Monitoring method for monitoring of machines like electric motors using roller bearing.

Difference between SPM and other Vibration Measurement Techniques

Vibration analysis has been used for motor predictive maintenance on ships for many years. Traditionally marine engineers have been using a listening rod to listen to the sound and ascertain the condition of rotating machinery. Nowadays to avoid premature overhaul of motors many companies are supplying vibration analysis pens and SPM instruments on board ships. However there is a difference between vibration analysis and Shock Pulse Measurement.

When two metal surfaces contact each other while in motion, an impact occurs and a shock wave develops, which travels through the metal. The shock wave is in ultrasonic range and is around 36 KHz. This shock wave is utilized in the SPM.

As impact continues the metal flexes and is compressed and recoils. This second phase is called vibration. The frequency of this vibration is dependent on stiffness, shape, mass and the dampening property of the material.  In SPM this phase of collision i.e. vibration is filtered out as it is depending on the structure and the material of the machine. Thus the inaccuracies that are frequently encountered by hand held vibration analysis pens is not here, especially in machinery with flexible mountings and working in vicinity of other vibration prone machinery.

Another difference between SPM and other vibration measurement techniques is that in SPM the transducers respond and resonate to a frequency of 36 KHz only, which ensures a calibrated response and accurate measurement to the shock pulses.

How does SPM Works?

Whether new or old, any bearing generates shocks in the interface between the loaded roller element and the race way. Initially these shocks or vibrations are subtle and hardly felt till already damage is done, but these are captured routinely by the SPM machine which tells about the condition of the bearings, the state of lubrication and the maintenance interval required. This type of monitoring and maintenance based on this evaluation is called as Condition Monitoring System or Condition Based Monitoring.

The shock pulses are measured by accelerometers with filters. The accelerometers have piezoelectric crystals so designed that they resonate at a frequency of 36 KHz which corresponds to the frequency of the pure shock pulses. This helps the accelerometers to measure both shock pulse as well as vibration making other vibration pens only measuring vibration obsolete.

The amplitude of shock pulses measured by the SPM meter is due to the following factors:

Rolling velocity which is a function of speed or rotation and size of bearing. The thickness of the oil film, which in turn depends on preload and the quantity of oil

supplied as well as the viscosity of the oil. The alignment of the system. That means between the prime mover and the load. Other mechanical factors like roughness of the raceways, the stress and damages.

The shocks are received by the SPM transducer which then gives an output signal proportional to the magnitude of the shock felt.  The SPM meter measures the shock pulses per second and then lowers its threshold so that two amplitude levels are discovered, first the decibel carpet value of 200 shocks per second and secondly, the maximum level of incoming shock under 2 seconds.

The decibel carpet value gives an indication of the condition of the lubrication and the peak value gives the extent of bearing damage.

The peak value can be ascertained by increasing the threshold value till no signal is received.  In this equipment the noise generated due to the rolling velocity is negated by entering the shaft diameter and RPM of the motor. This gives an accurate condition assessment of the machine being monitored.

The amplitude of the shock is a function of the rolling element and the instrument measures the absolute value and subtracts from it the expected shock value from a good bearing at similar speed. This gives us an indication of the bearing operating condition.

There are three condition zones namely Green for Good Condition, Yellow for Caution and Red for Damaged condition. The peak value measured by the operator gives the status of the machine and the zone it belongs to.

 Uniqueness of Shock Pulse Monitoring

SPM specializes in determining accurate information on the mechanical condition of the bearing surfaces as well as the state of lubrication on the bearing throughout the life of the bearing.

SPM instrument can measure both the vibration as well as shock pulses. One additional advantage of SPM over other vibration measurement methods is that

analysis of the SPM spectrum enables to pin point the source of the trouble. This is because in case the bearings are damaged, the shocks generated by the damaged bearings have a pattern that corresponds to the frequency of the balls passing over the damaged area. In case the shocks generated are due to gears they will have a different shock pattern, while random shocks will not have a pattern and not be investigated.

As both the RPM as well as the shaft diameter are entered into the instrument evaluation can be done independent of speed in variable speed drives.

Advanced warning of lubrication problems can be given. As any machine with metal to metal contact will give shock pulses it is useful for

analysis of other machines like screw compressors, gear boxes, lobe compressors, centrifuges, purifiers, centrifugal pumps apart from motors.

SPM also gives an indication of faulty installation and alignment. In vibration analysis advanced stage of damage occurs before the vibration levels

exceed above the noise carpet. In SPM the noise carpet is eliminated and the bearing as well as the lubrication condition is continuously monitored after filtering out the vibration as well as the background noise, giving sufficient warning to avoid breakdown and plan maintenance.

SPM is not influenced by the size, speed, design, background noise or installation of the machine.