3implementation of tank cleaning work - nyk training of tank cleaning work ... crude oil washing at...

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Chapter 3

Implementation of Tank Cleaning Work

§ Precautions during implementation of various tasks in the tank cleaning work are explained here.

1. Crude oil washing at the previous discharging terminal (P.3-2 to P.3-3)

2. Filling of washing water (P.3-4 to P3-8)

3. Heating of washing water (P3-9)

4. Rough washing of cargo line and cargo pump (P.3-10)

5. Line washing and valve flushing (P.3-11)

6. Tank washing work (P.3-12)

7. HC gas purging (P.3-13)

8. Airing (P.3-14)

9. Settling and discharging water (P.3-15 to P.3-16)

10. Final line washing (P.3-17)

11. Sludge removal (P.3-18 to P.3-19)

12. Slop removal (P.3-20)

13. Primary slop tank washing and HC gas purging (P.3-21)

14. Gas-freeing and sludge removal of primary slop tank (P.3-22)

15. Final line stripping (P.3-23)

16. Gas-free certificate (P.3-24)

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1. Crude oil washing at the previous discharging terminal

1.1 Precautions

The precautions below should be taken during crude oil washing (“COW” hereafter) at the previous

discharging terminal.

1) Thoroughly study the bell mouth position of the stripping line in each tank and adjust the trim and

heel of the ship to the optimum levels. 2) Ensure that the accumulation of crude oil does not become greater than the stripping capacity of the

eductor and that the “defeat of stripping capacity” does not occur when implementing COW. 3) As far as possible, consider open-cycle washing in the discharging plan.

1.1.1 Adjusting trim and heel of the ship to the optimum levels Perform trim and heel adjustments as given below.

1) Trim

A trim by the stern of about 2% (6 m to 7 m) of the ship’s length is necessary when the bell mouth

is at the aftermost part of the tank.

Examine the main engine and boiler for defects referring to past records of the ship and adjust to

obtain an appropriate trim as far as possible. 2) Heel

Stripping efficiency is generally good when the heel is about 1 to 1.5 degrees. Reports from SBT

ships indicate that the stripping efficiency was good when the heel was about 2 degrees.

If the ship is heeled when berthed at the pier, take into account the condition of the mooring lines

and give instructions to the deck watch to adjust the mooring lines suitably.

1.1.2 Measures against “defeat of stripping capacity” If COW is continued so that the “defeat of stripping capacity” is reached, there is a risk of

accumulation of a large amount of sludge near the bell mouth at the aft part of the tank. The method

described below may be adopted as a measure against the “defeat of stripping capacity.”

a) If extra time for discharging is available, use some COW machines on the aft side only at the final

state of COW, and again perform the bottom washing near the bell mouth. b) Temporarily stop the COW and assign adequate stripping time.

1.1.3 Bottom wash by open-cycle method

The sludge gathered by the eductor during the stripping can be adequately discharged to the shore tanks

if bottom wash is implemented using the open-cycle method, thereby enabling the accumulation of

sludge in the slop tank to be reduced. Wherever possible, tank bottom wash should be implemented

using the open-cycle method. In such cases, care should be taken against reduction of intake pressure

of the tank cleaning pump due to the ullage reduction of the slop tank.

1.1.4 Effective use of AUS (Automatic Unloading System) Implement sludge control according to the method given below at the final stage of discharging when

AUS has been provided.

1) Perform COW of slop tank used as the eductor gathering tank, using the fresh oil stored in the slop

tank on the opposite side of the ship. 2) At this stage, do not use the eductor at all for tank stripping. Use the cargo pump of the AUS and

directly discharge the contents of the tank. 3) This results in discharging the sludge accumulated in the eductor gathering tank directly to the

shore tank. 4) After completing COW of the eductor gathering tank, a large amount of sludge is likely to remain

in the cargo line used for discharge. By forcefully discharging the fresh oil remaining in the slop

tank on one side to the shore tank, the sludge in the cargo line can be completely removed.

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Compared to not implementing the method mentioned above, the quantity of gathered sludge in the eductor

gathering tank has reduced considerably using this method, as is evident from past records. If time permits, the

method should be incorporated in the discharging plan, explained to the terminal and their understanding

obtained.

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2. Filling of washing water

2.1 Measures to prevent accidents during work

Take the measures to prevent accidents given below before starting the filling work. 1) Keep ready the line diagram clearly showing the valve operating sequence at the operating

location. 2) To prevent errors in valve operation, frame measures that make use of valve sealing tape. 3) Confirm valve lineup by the method of pointing with the finger and repeating the actions aloud.

(promote confirmation by pointing out and repeating the actions aloud)

2.2 Work before valve lineup

Perform the tasks mentioned below before the valve lineup for filling water.

1) Start the stripping pump before starting the water filling operation, strip all the necessary lines in

the cargo line, and gather the remaining oil in the primary slop tank. Also discharge the oil on the

discharge side (riser part) of the stripping pump to the same tank. 2) Perform the leak test of the overboard sea chest valve. 3) Adjust the vent valve of the filling tank before the filling operation and reduce the tank pressure

(200 to 300 mmAq) such that this pressure does not become negative. If the IGS interlock switch

has been provided, cancel it before starting the filling operation.

2.3 Filling sea water (from the sea chest) by gravity

(Refer to "Line Diagram" in Fig. G-3-1 of P2-68 and "Line Diagram" in Fig. G-3-2 of P2-69 in

the "Documents Section”.) 1) Station a look-out carrying a portable transceiver near the overboard sea chest to monitor the sea

water level and to ensure a sound monitoring system.

2) Valve lineup (1) Take adequate care to configure the line from the overboard sea chest valve to the initial filling tank

such that the sea water does not flow in the reverse direction by the shortest distance.

5C tank valve V252 Open

Bulkhead valve V121 Open

Common line valve V152 Open

Sea chest valve (inboard side) V192 Open

3) Start of water filling

Backflow may sometimes occur due to operational errors such as error in the valve opening sequence or

opening a different valve by mistake (for instance, opening the sea chest valve first, opening a valve located

on a pipe that is higher than the sea water level). Thus, it is important that the operators be educated and

trained in the valve operating sequence such that errors are prevented in the normal course of work.

IGS interlock switch If the tank pressure in the IGS system drops below 100 mmAq, a protective device provided in the tank trips

the cargo pump and the tank cleaning pump. During tank cleaning however, the cargo pump will be operated

when the tank pressure is low. Therefore, this protective device has to be canceled to enable the pump to be

operated. The IGS control panel has a switch for key operation. The position of this switch during normal

cargo handling operation is at “INTERLOCK”, but during tank cleaning it should be set at the “CANCEL”

position.

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Sea chest valve (outboard side, adjusting

valve) V191 Open

Suction line V121, V122 Open

Riser common valve V114, V124 Open

Deck main line master valve V321, V322, V333 Open

Crossover valve V331, V332, V333 Open

Return line to 5C V144, V174, V176, V182 Open

Gradually open the overboard sea chest valve (avoid opening it suddenly) after confirming that all the

valves in the filling line, including valves of the tank to be filled, are open and start filling the water.

4) Completion of filling When the expected volume of water has been filled in the 5C tank, close the sea chest valve (outboard

side) and complete the filling operation. Take care to avoid closing first the upstream valves, such as

the tank valves .


valve) V191 Close

5) Valve lineup (2) Shift the washing water from the 5C tank to the slop tank using the cargo pump.

No. 2 COP suction valve V122 Open

Deck master valve V322 Open

Crossover valve V331,V332 Open

Direct filling valve V311 Open

Tank main valve of slop tank V274 Open

Common line valve V152 Close

Sea chest valve (inboard side) V192 Close

6) Priming Open the tank valve and pass sea water into the pump. When the pump is full of sea water, slightly

open the delivery valve and perform priming.

5C tank valve V252 Open

No. 2 COP delivery valve V123 Slightly

open

7) Close the cargo pump delivery valve and start the pump. Then slowly open the delivery valve, and

shift the washing water in the 5C tank to the slop tank. 2.4 Filling sea water from the sea using pump

(Refer to "Line Diagram" in Fig. G-3-3 of P2-70 and "Line Diagram" in Fig. G-3-4 of P2-71 in

the "Documents Section”.)

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1) Station a look-out carrying a portable transceiver near the overboard sea chest to monitor the sea

water level and to ensure a sound monitoring system.

2) Valve lineup (1)

SLOP (P) tank high suction valve V173 Open


Sea chest valve (inboard side) V192 Open

Take adequate care to configure the line from the overboard sea chest valve to the initial filling tank

such that the sea water does not flow in the reverse direction by the shortest distance.

3) Start of water filling


valve) V191 Open

Suction line V121, V122 Open

Riser common valve V114, V124 Open

Deck main line master valve V321, V322, V333 Open

Crossover valve V331, V332, V333 Open

Return line to 5C V144, V174, V176, V182 Open

Gradually open the overboard sea chest valve (avoid opening it suddenly) after confirming that all the

valves in the filling line including valves of the tank to be filled are open and start filling the water.

4) Preparations for tank cleaning pump and valve lineup (2) After the flow from the sea chest to the SLOP (P) tank is established, make preparations for starting

the tank cleaning pump. Monitor the balance between the water level in the SLOP (P) tank and the sea water level. As the flow

is established, start the tank cleaning pump and change over the line.

Riser common valve V146 Open Riser master valve V195 Open ODM line bypass valve V197 Open ODM re-circulation valve V196 Open

Tank cleaning pump suction valve V143 Open

5) Start the tank cleaning pump. 6) When the tank cleaning pump has been started and is ready for use, check the governor. 7) Gradually open the tank cleaning pump delivery valve. In this case, adjust the pump rpm such that

the pump delivery pressure becomes 0.4 Mpa to 0.5 Mpa.

Tank cleaning pump delivery valve V145 Open

8) When the flow from the tank cleaning pump is established, close the line through which water was

being filled by gravity from the sea chest, while carefully monitoring the suction pressure.

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SLOP (P) tank high suction valve V173 Close

9) Completion of water filling When the expected volume is reached, fully close the delivery valve while reducing the rpm of the

tank cleaning pump.

SLOP (P) tank high suction valve V173 Close

10) Stop the tank cleaning pump and close the sea chest valve. At this stage, make sure that you close

from the outboard side.

Sea chest valve (outboard side) V191 Close

Sea chest valve (inboard side) V192 Close

2.5 Filling water by gravity from the ballast tank

(Refer to "Line Diagram" in Fig. G-3-5 of P2-72 in the "Documents Section”.) 1) Fit the spool piece that connects the ballast line and the cargo line. 2) Valve lineup Fill washing water from the ballast tank with a high water level (advisable to select tank on forward

side considering the trim) to the slop tank through the spool piece. The hatch cover of the ballast tank at the source should be open during the valve lineup.

SLOP (P) tank stripping valve V162 Open

Common line stripping master valve V163 Open


Cargo ballast connection valve (cargo tank side) V551 Open

3) Open the valve in the ballast tank used for washing water, fill the ballast line with sea water, and

apply pressure. Station a person beforehand to monitor the ballast water surface of the said ballast

tank. 4) Passing water through the cargo line

Cargo ballast connection valve (ballast tank

side) V550 Open

Gradually open the cargo ballast connection valve and allow sea water to pass through. To be prepared

for emergencies, station a worker near the valve until the filling operation is completed. Always monitor the water level in the ballast tank at the source from the cargo control room and

confirm that reverse flow does not occur.

5) When the estimated volume is reached, close the cargo ballast connection valve (ballast tank side)

and finish the filling operation. Note that you should take care to close the cargo ballast connection

valve (on the ballast tank side) first, otherwise oil may flow back to the ballast line.

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Cargo ballast connection valve (ballast tank

side) V550 Close

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3 Heating of washing water

3.1 Heating using heating coils

Follow the procedure given below for heating the water using heating coils. 1) Open all the valves of the branch pipes. 2) Keep the steam supply valve slightly open. 3) Drain out the contents. 4) Gradually open the steam supply valve until it is fully open. 5) Wait until the setting temperature is reached while confirming the temperature (remote indication is

normally displayed on the console of the COC). 6) When the setting temperature is reached, adjust the steam supply valve and maintain the setting

temperature.

3.2 Heating using tank cleaning heater

Maintain the tank washing pressure at a constant level and ensure that the same quantity of water flows

into the heater at all times while the tank cleaning heater is being used. This is to prevent abnormalities

such as overheating that may occur when the flow rate of water through the heater changes. Take

particular care when you change over the washing water tank.

The temperature of washing water decreases when tank washing is started because the unheated washing water

on the secondary slop tank side circulates. Accordingly, the setting temperature should be maintained by

continuing to heat using the heating coils.

The cleaning records in recent days show a trend of not using the said heater. Moreover, newly-built VLCC tankers

are not being provided with heaters.

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4. Rough washing of cargo line and cargo pump

Rough washing of cargo line and cargo pump should be implemented taking the precautions mentioned

below. 1) Adequate flow should be maintained for washing each line so that washing can be performed

efficiently in a short period of time. 2) Before changing over the line, reduce the pump rpm to minimum and close the pump delivery

valve. 3) Make sure that the oil in the U-shaped tube of the surface valve is replaced by sea water (using the

fire extinguishing line or by other means).

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5. Line washing and valve flushing5. Line washing and valve flushing5. Line washing and valve flushing5. Line washing and valve flushing Perform line washing and valve flushing taking the precautions mentioned below.

1) Perform valve flushing by opening/closing all the valves 2 to 3 times during line washing. 2) To shorten the tank stripping time after washing, restrict the flushing of washing water to locations

other than the slop tank to a minimum.

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6. Tank washing work

6.1 Precautions during the work

For details of the work procedure for valve opening/closing and so on, please refer to “2. Implementing

crude oil washing work” of P4-4 in the Discharging Section. Consider the points below related to work

implementation. 1) The oxygen concentration in the tank’s atmosphere should always be less than 8% during the tank

washing work. 2) Consider the washing water stripping efficiency and adjust the ballast such that the optimum ship’s

attitude (trim greater than 6 m, heel of about 1 to 2 degrees) is maintained. 3) Perform washing speed adjustments (refer to the instruction manual of the COW machine provided

on board each ship) in parallel, if necessary. 4) If “defeat of stripping capacity” is initiated due to ship motions in rough seas, measures to raise the

stripping efficiency may be considered, such as suspending tank washing at each stage temporarily

to set adequate stripping time, or using only a few washing machines at the aft part of the tank and

removing the sludge near the bell mouth at the final stage of washing. 5) After the washing with fixed washing machine is completed, inspect the shadow areas in the tank.

If sludge and oil have accumulated, wash using the portable washing machine.

6.2 Precautions when using the tank cleaning heater

When performing hot water washing of tank using the tank cleaning heater, a constant flow of sea

water should be passed through so as to prevent overheating of the tank cleaning heater during the

washing work. For this reason, personnel should be stationed at the release valve of the slop tank when

the washing tank is to be changed over or when the tank washing is to be suspended temporarily so that

the associated valves can be closed or opened carefully, as required. Two procedures are available for

opening/closing the release valve, as given below.

1) While confirming that a steady flow rate is maintained, open/close the release valve by

opening/closing washing machine valves one by one. 2) When washing tank after tank continuously, slightly open the release valve, then open the washing

machine valve of the next tank, close the washing machine valve of the tank in which the washing

has been completed. Proceed with the work in this way carefully, one tank after another.

If there is a mistake even in one step of this series of operations, it may lead to damage to the tank

cleaning heater. Therefore, all steps of the procedure should be thoroughly explained at the meeting

before the work so that workers can perform the work skillfully.

Note that some portable machines may be provided with hoses of short length and the washing water may not

be delivered up to the desired locations.

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7. HC gas purging (Refer to Fig.4-1(A) ,Fig.4-1(B) of P1-12 and Fig.4-2 ,Fig.4-3 of P1-13 in the “Discharging

Section”)

7.1 Precautions during parallel operation of IG fans

Take adequate precautions during parallel operation in relation to the points given below.

1) Change in tank pressure 2) Allowable gas flow rate in the vent line 3) Boiler load 4) O2 concentration of supplied inert gas (maintained below 8%)

7.2 Precautions during work

The environment above deck becomes extremely dangerous because flammable and toxic HC gas is

discharged to the atmosphere from the vent riser. Accordingly, special care should be taken during HC

gas purging work, such as control of bare flames (including static electricity, lightning, etc.), ventilation

controls in accommodation spaces, and flow of air above deck (wind speed and wind intensity). SMS

regulations related to safety and prevention of oil pollution should be followed and the items below

should be implemented.

1) Restrictions on smoking and use of flames

Designate smoking places, take measures against static electricity and sources of ignition, such as

soot from the smokestack and lightning bolt. 2) Preparations for fire extinguishing equipment and rescue appliances

Keep ready fire extinguishing hoses and portable fire extinguishers so that they can be immediately

used when required. Keep ready equipment that can be used in an emergency such as breathing

apparatus, spare air cylinders, lifelines and oxygen resuscitation equipment. 3) Ventilation control of accommodation spaces

Prohibit the opening of all passage access openings and other openings in accommodation spaces.

Close mechanical vent intake openings, use internal circulation system and prevent the entry of

petroleum gases. Gases that are harmful to the human body are discharged from the cargo tanks.

Thus, ventilation controls within accommodation spaces should be continued even during the

airing operation. 4) Control of access to enclosed spaces

Perform gas detection before entering enclosed spaces for internal inspection of tank, station the

required personnel and continue with the ventilation even during the access, in accordance with

established procedures. Workers should never enter enclosed spaces for which access is not

permitted. 5) Appropriate pressure control of cargo tank

During water filling/discharging operations to/from cargo tanks, check whether the watertight

hatches and manholes are open and adopt measures to prevent damage to tanks. 6) Controlling the environment in the cargo tank

Confirm that the oxygen concentration in the tank environment is maintained below 8% during the

tank washing work.

7) Perform safety checks periodically based on the Safety Check List. 8) Check that the scupper plugs on upper deck are closed. 9) Make preparations (to check quantity) for materials required for oil removal.

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8. Airing

8.1 Precautions before airing

Perform the tasks below before implementing the airing work.

1) Inserting blind plates

Before implementing the airing work, insert blind plates in the IG branch lines of tanks to be aired

so that they can be completely isolated from tanks that are filled with inert gas. 2) Closing and confirming closure of valves in tank

Confirm that the tank main valve and the tank stripping valve in the tank are fully closed. Affix

sealing tape on the valve switches on the CCR console so that no careless mistakes are made and

gases do not enter the airing tank. 3) Double-shutting valves

Wherever possible, double-shut valves in the tanks.

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9. Settling and discharging water

9.1 Work procedure

Perform the work of settling and discharging water by the procedure described below.

1) After the cleaning of all tanks except the slop tank is completed, allow the slop water in the primary

and secondary slop tanks to settle. 2) Make preparations to discharge water from the slop during the settling operation. 3) Perform the first discharging operation. (Cut down the settling time and discharge the water from

the slop. 4) Collect all the slop water in the primary slop tank. 5) Wash the secondary slop tank which has become empty with the collected slop water. 6) Allow the primary slop to settle. 7) Perform the second discharging operation. 8) Repeat 6) and 7) above to perform settling and discharging operations two to three times.

9.2 Preparations for discharging water from slop

Before discharging water, make the preparations and perform the checks mentioned below.

1) Preparations of the IG system

During the discharging of water, inert gas needs to be supplied to the relevant tank, therefore, make

preparations of the IG system. 2) Preparations of the ODM equipment

If the sampling line and overboard line are contaminated, oil concentration cannot be measured

accurately. The ODM drain valve opens automatically to the slop tank simultaneously with the start

of the water discharging operation, which may destroy the separated layers of oil and water due to

settling. To avoid this situation, the discharging line should be washed beforehand. (See “6-2 Line

diagram” of the Documents Section.) 3) Checking the blind plates in the overboard lines

Check that the blind plates have been removed. 4) Studying the condition of separation of oil and water

Measure the overall ullage of slop water and the ullage of the oil-water interface using MMC.

Calculate the remaining quantity of water and the oil quantity to know the condition of separation

of oil and water.

9.3 First discharging operation (by TCP)

(Refer to "Line Diagram" in Fig. G-3-6 of P2-73 in the "Documents Section”.) 1) Use the normal tank cleaning pump and start discharging at a low rate during the first discharging

operation. 2) Draw out the sea water from the sea chest with TCP and check the working condition of ODM

while discharging the sea water from the sea valve. 3) Open the high suction valve of the secondary slop tank to start discharging water. Stabilize the oil

concentration (ppm) using the control monitor of the ODM equipment while throttling the sea chest

valve. 4) Fully close the sea chest valve and gradually raise the rate to the expected discharging rate. 5) While carefully noting the ullage, change over from high suction to main suction. 6) At the final state of the discharging operation, the oil concentration of the discharged water starts

becoming unstable. When this tendency is observed, decrease the discharge rate. (Take sea water

from the sea chest and reduce the instantaneous discharge rate.) 7) When discharging is completed, transfer the water remaining in the secondary slop tank to the

primary slop tank.

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9.4 Secondary slop tank washing

After the first discharge operation is completed, transfer the washing water remaining in the secondary

slop tank to the primary slop tank. Perform cleaning of the secondary slop tank using this collected

washing water. Perform the washing of the primary slop tank after discharging the slop to the barge at the anchorage

before dry-docking.

9.5 Discharging of water for the second time and later (by stripping pump)

(Refer to "Line Diagram" in Fig. G-3-7 of P2-74 in the "Documents Section”.) After the second time and later, discharge the water from the slop carefully using the stripping pump. If

a small quantity of slop water is forcibly discharged, the oil concentration rises, the drain valve opens,

the separated oil and water layers are destroyed (become mixed) and once again settling is required,

resulting in considerable waste of time and money.

9.6 Precautions

9.6.1 Settling

The precautions below should be adopted during the settling operation.

1) Although the washing water is heated during tank washing and its temperature maintained at 50 to

60 degrees, stop the heating beforehand during the settling operation so that convection of the

washing water does not occur, and maintain its temperature at 45 to 55 degrees. 2) Avoid ship motions as far as possible.

9.6.2 Discharging water from slop

During the discharge of water from slop, take the precautions given below.

1) Station a look-out for monitoring the sea water surface near the shell overboard discharge opening.

Strive to prevent pollution of the sea by monitoring the oil concentration and visually checking the

discharge condition. 2) Do not forget to check the oil content of the discharged water by appropriately sampling the water

from the pump air bleed cock in addition to the ODM equipment. 3) If the level of liquid in the slop tank is adequately high from the tank bottom, discharge the water

using the suction at the high location in the slop tank, and take care not to suck in the oily sludge

that has settled at the bottom of the tank.

Although the final volume of slop water remaining in VLCC class vessels may vary depending on conditions such

as settling time and ship motions, it is generally about 180 to 220 m3.

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10. Final line washing

10.1 Precautions

Precautions related to the implementation of final line washing are as given below.

1) If the excessive time is taken up for final line washing and the amount of water drawn in is

considerable, the settling and water discharging operations to be implemented subsequently will

require considerable time. Therefore, perform the final line washing work efficiently. 2) After washing is completed, strip the line thoroughly so that no water remains in the pump and in

the line. 3) Check the finished condition of final line washing by confirming the drain line and air bleed cock

of each manifold. If necessary, take appropriate measures to ensure proper finishing.. 4) Collect all the bilge generated in the pump room and other locations in the primary slop tank so

that it can be discharged to shore together with the slop during slop removal.

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11. Sludge removal

11.1 Communications

The sub-contractor for removing /recovering sludge and slop to the anchorage is to be arranged by the

ship owner or the ship management company. Communications with the sub-contractor will be

specified, but in general, the items listed below are necessary. These items should be studied

beforehand.

1) ETA at the slop removal anchorage 2) Estimate amount of sludge in tons in each tank (or total amount) 3) Amount of slop carried, estimate washing water quantity for slop tank and line washing quantity 4) Details of previously-loaded cargo 5) Indication of side of slop barge in contact with berth 6) Bore of slop removal line and specifications of connecting flanges

11.2 Preparatory work

1) Continuing the airing work

Continue airing the spaces even after the sludge gangs board the ship, so that they can start the

work quickly. Before starting the work, the ship should issue authorization for access in accordance

with the established procedures for access to enclosed spaces. 2) Confirming sub-contractor arrangements

Confirm that an adequate number of workers for sludge removal, adequate number of slop vessels,

work boats and work equipment and accessories for sludge removal are kept ready and available

for the estimated working days. 3) Ensuring shipboard security

Ensure that measures against robbery are taken before the workers board the ship. These measures

should include locking the cabins and stores in accommodation spaces, deck stores and lifeboat

equipment and provisions boxes, etc. After the work is completed, confirm that all workers have

disembarked and none remain on board the ship. 4) Measures to prevent oil pollution

Before starting the work, hold detailed discussions on measures to prevent oil pollution and the

work plan (including condition of accumulation of sludge in each tank, areas where workers are

prohibited from entering) with the sub-contractor’s supervisor. This is to ensure the ship’s crew and

the workers become thoroughly familiar with the work plan so that no oil pollution accidents occur,

such as leakage of oil from sludge bags to the ship’s sides since they are stacked on the deck and

work is being performed within the port premises.

11.3 Precautions

Take the precautions mentioned below during sludge removal.

1) Ensure that sludge storage bags are stacked at the appropriate locations on deck. 2) Adopt measures to prevent oil pollution ensuring that the oily sludge does not leak overboard due

to the effect of rainfall. 3) Confirm that continuous ventilation is provided during work in the tank and ensure that the

environment in the tank is checked periodically using gas detectors. 4) Ensure that measures have been adopted to prevent falls into open tank hatches and portable man

holes . 5) Patrol the deck periodically during the sludge removal work. 6) Sequentially inspect the internal parts of tanks from which sludge has been removed. If necessary,

request the workers to finish up the work. 7) After the work is completed, ensure that the workers meticulously clean and remove oil sticking to

the upper decks and to other structures.

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12. Slop removal

12.1 Work procedure

(Refer to "Line Diagram" in Fig. G-3-8 of P2-75 in the "Documents Section”.) Perform slop removal according to the procedure described below.

1) After the slop barge berths, connect the transfer hose to the ship’s line (generally MARPOL LINE). 2) Start inerting in accordance with the requirements (Part D60, D62) of Chapter 2 of SOLAS-II. 3) Start the stripping pump and transfer the slop to the barge.

12.2 Precautions

Take the precautions mentioned below during slop removal. 1) Always monitor the water level during the slop transfer and strive to prevent pollution of the sea. 2) When gas-freeing the slop tank, carefully monitor the wind direction and the wind force. If gas is

likely to accumulate above deck, consider suspending the gas-freeing work temporarily. 3) Cut off the tank from which slop is removed and other tanks using two ore more valves. 4) While the barge is being berthed, monitor the condition of the mooring ropes and the transfer hose. 5) A considerable amount of sludge collected from various tanks accumulate in the primary slop tank

during slop removal. The strainer in the stripping pump is likely to clog causing the pump to stop.

Keep ready the spare strainer (if not available, arrange to procure it), chain block and tools so that

the strainer replacement work can be performed beforehand.

To prevent clogging of the strainer, open up the strainer and wash it before starting the transfer of slop water.

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13. Primary slop tank washing and HC gas purging

13.1 Precautions

Take the precautions mentioned below related to the work implementation. 1) Measure the oxygen concentration in the tank before washing the tank and confirm that it is below

8%. 2) To prevent the “defeat of stripping capacity” during tank washing, consider suspending the tank

washing operation temporarily at each stage and perform stripping.

3) The construction within the primary slop tank differs from that of other tanks since heating coils

are installed at the bottom of the primary slop tank. Accordingly, the bottom washing should be

performed with additional care.

4) The strainer of the stripping pump used for stripping the tank clogs easily because a large amount

of sludge accumulates in the tank. Preparations should be made to allow for replacement with a

spare strainer or for opening up and cleaning the strainer. 5) Perform HC gas purging in parallel with tank washing. Measures should be considered such as

temporary suspension of work considering the effect of discharged gas on sludge removal workers

of other tanks.

Washing becomes more effective if it is implemented while passing steam through the heating coil. During the

washing operation, slightly open the steam supply valve, fully open all the branch pipes, and heat to such an

extent that the coils do not get overheated.

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14. Gas-freeing and sludge removal of primary slop tank

14.1 Precautions

1) Confirm that the HC gas concentration in the tank atmosphere is below 2% by volume and then

start airing the tank. 2) During the airing of the same tank, sludge is being removed from other tanks.

If the discharged gas has accumulated on the deck, suspend the work temporarily to prevent the

adverse affects of the gas o the human body.

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15. Final line stripping

15.1 Work procedure

Perform the final line stripping by the procedure described below.

1) Using the stripping pump and drawing sea water from the sea chest, wash the piping on the

discharge side of the stripping pump and the MARPOL line on deck. At this stage, the stripping

suction line of the primary slop tank is contaminated. Therefore, pass the washing water through

this line.

(Refer to "Line Diagram" in Fig. G-3-9 of P2-76 in the "Documents Section”.) 2) After washing the MARPOL line, close the sea chest valve. Strip the water remaining in all the

lines and finish the washing work.

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16. Gas-free certificate

16.1 Precautions

General precautions for gas inspection when the ship is to dry-dock at Singapore Dock are given below.

Note that these precautions may vary depending on the location, and should be confirmed beforehand.

1) Even if the sludge removal has not been completed, gas inspection can be received. 2) The spaces in which gas inspection is to be carried out include cargo tanks, ballast tanks, fuel oil

tanks, void spaces and cargo lines. The access to these spaces should always be kept open. Open up

the blind plate of the manifold and keep all the valves in the open condition. 3) The allowable gas concentration during inspection should be less than 3% LEL. However, when

the F.O . tank contains fuel oil, then this value should be taken as less than 30%. 4) A ship’s officer should be present during the gas inspection. 5) If the hydrostatic pressure test has been carried out during the periodic survey, more than half the

cargo tank would have been filled with water. In this condition, the gas inspection cannot be

performed.

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Line Diagram Title Page

G-3-1 Filling sea water (from the sea chest)by gravity (1/2) 2-25

G-3-2 Filling sea water (from the sea chest)by gravity (2/2) 2-26

G-3-3 Filling sea water from the sea using pump (1/2) 2-27

G-3-4 Filling sea water from the sea using pump (2/2) 2-28

G-3-5 Filling water by gravity from the ballast tank 2-29

G-3-6 First discharging operation (by TCP) 2-30

G-3-7 Discharging of water for the second time and later (by stripping

pump) 2-31

G-3-8 Slop removal 2-32

G-3-9 Final line stripping 2-33

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