INTERNSHIP PROJECT Submitted to: Hassan Sajjad Qureshi

ABSTRACT Detailed study on

failure of Recycle Gas

Lube oil Pump Turbine

284-C1P1A-ST to

analyze its root cause

i.e. governor control,

bearings, rotor etc.

Zaid Bin Farooq Internee: 09-2014

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Table of Contents REACTION TYPE STEAM TURBINE ............................................................................................................. 2

IMPULSE TYPE STEAM TURBINE ................................................................................................................ 2

The Single-Stage Impulse Turbine ......................................................................................................... 3

Compounded-Impulse Turbine ............................................................................................................. 4

Velocity compounded impulse turbine ................................................................................................. 4

COMPONENTS .............................................................................................................................................. 6

THE STEAM STRAINER ............................................................................................................................... 6

STEAM SEPARATOR AND DRAINS ............................................................................................................. 6

THE THROTTLE VALVE ............................................................................................................................... 6

THE OPERATING GOVERNOR ................................................................................................................... 7

TG-13 and TG-17 ................................................................................................................................... 8

OVERSPEED TRIP VALVE ............................................................................................................................ 9

GOVERNOR MOUNTING HOUSING ......................................................................................................... 10

MAIN BEARINGS ..................................................................................................................................... 10

THRUST BEARINGS AND SQUEALER RINGS ......................................................................................... 10

SKF 6213C3 ......................................................................................................................................... 11

GOVERNOR BEARING HOUSING ............................................................................................................. 11

SHAFT PACKING ...................................................................................................................................... 11

SHAFT COUPLINGS .................................................................................................................................. 12

BUCKETS AND BLADES ............................................................................................................................ 12

TURBINE WHEELS .................................................................................................................................... 13

ALIGNMENT REQUIREMENTS: ................................................................................................................... 14

LUBRICATION SYSTEMS: ............................................................................................................................. 14

INSPECTION CHECKLIST .............................................................................................................................. 16

SPECIFICATIONS: ......................................................................................................................................... 17

TROUBLESHOOTING ................................................................................................................................... 18

STEAM TURBINE: ..................................................................................................................................... 18

Failure of Recycle Gas Compressor Lube oil Pump Turbine: ..................................................................... 21

CAUSE: ..................................................................................................................................................... 21

DESCRIPTION: .......................................................................................................................................... 21

CARBON RINGS ....................................................................................................................................... 23

References: ................................................................................................................................................. 24

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STEAM TURBINES

A steam turbine is a rotary type of steam engine, having a rotating wheel to which is secured a

series of buckets, blades or vanes, uniformly spaced on its periphery. Steam from nozzles or guide

passages is directed continuously against these buckets, blades or vanes, thus causing their

rotation. Expansion of steam in the nozzles or buckets converts its heat energy into energy of

motion and gives it a high velocity which is expended on the moving wheel or buckets. The

difference in the various types of steam turbines is due to different methods of using the steam

depending upon the construction and arrangement of the nozzles, steam passages and buckets.

The steam turbine is essentially a high speed machine. It is used to advantage with direct

connection to electric generators, centrifugal pumps and compressors and with geared connections

to rolling mills, fans and other machinery which are run at low speed.

The advantages of steam turbines are: comparatively low initial cost, low expense for maintenance,

small floor space, large overload capacity, exhaust steam is free of oil contamination as no internal

lubrication is needed and high efficiency over a wide range of load conditions. The steam turbine

can be built in a unit of much greater capacity than is practical with the reciprocating steam

engines.

REACTION TYPE STEAM TURBINE In the reaction type steam turbine, the expansion and consequent change in pressure of the steam

occurs entirely in the blading where the steam is directed against the moving buckets or blading

by guide valves or orifices. The expansion of the steam takes place through both the stationary and

moving guide vanes, and therefore the clearance space between the stationary and moving surfaces

is very small, to cut down on the pressure drop by leakage between stages, to a minimum.

IMPULSE TYPE STEAM TURBINE In the impulse type steam turbine, the expansion and consequent change in the pressure of the

steam occurs entirely within the nozzles which direct the steam in jets against the moving buckets.

In as much as the expansion of steam takes place in the nozzles, the clearance between the rotating

and stationary surfaces is greater than in the reaction type steam turbine.

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The Single-Stage Impulse Turbine

•It is also called the de Laval turbine after its inventor. In this type a single rotor is used to which

impulse blades are attached.

•The steam is fed through one or several nozzles which do not extended completely around the

circumference of the rotor, so only part of the blades are impinged at any one time.

•The pressure drop in this type occurs mainly in the nozzle and the velocity drops on the blades.

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Compounded-Impulse Turbine

•From the impulse principle the blade speed in a single impulse turbine is nearly half the incoming

absolute steam velocity.

•In modern plants the turbine velocity is very high which is beyond the safety limits due to

centrifugal stresses on the rotor material. Also high velocity results in high friction losses and thus

reduction in the turbine efficiency.

•To overcome these difficulties two methods have been utilized which are called compounding or

staging; 1-velocity-compounded turbine 2-pressure compounded turbine.

Velocity compounded impulse turbine

•It is called Curtis stage turbine.

•It is composed of three zones of blades, where the first and third zones are moving, while the

middle blade stage is stationary.

•This configuration results in velocity reduction.

•Any number of rows can be used. Such staging usually is built with successively increasing blade

angles and flatter and thinner blades toward the last row.

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COMPONENTS

THE STEAM STRAINER A steam strainer should be installed in the main steam line to the turbine to prevent foreign particles

from being carried into the turbine with the steam. It is therefore an important accessory. Steam

strainers are normally installed ahead of and close to the throttle valve.

Some are an integral part of the governor/throttle valve assembly. When installed as a separate

part of the unit, the grid is usually accessible for cleaning without breaking any piping connections.

STEAM SEPARATOR AND DRAINS It is unsafe to permit water to enter the steam passages of a turbine. The steam supplied to a turbine

should be reasonably dry at all times. A separator of the receiver type and having ample drains

should be installed in the steam supply line near the turbine. The drains should be located on the

boiler side of the throttle valve. In addition it is necessary to drain all portions of the turbine casing

where water from condensation may collect. Water in any pocket in a turbine casing may cause a

slug of water to be carried over in the turbine during operation, with very serious results.

THE THROTTLE VALVE The throttle valve performs the functions of controlling the quantity of steam admitted to the

turbine by throttling and acting as a quick-closing emergency valve (on some governors). It should

always be closed by means of the manual trip device. The throttle valve should receive careful

attention and all moving parts should be kept well lubricated.

At dismantled inspections the throttle valve should be examined for leakage at the disc, under the

seat and through the threads. A careful check should be made to see that no dirt, grit or metallic

particles are imbedded in the valve seat or disc and no corrosion or pitting is taking place in these

parts or in the valve body. It is important that proper repairs or replacement be made when required

for tightness and free operation.

There are various tripping mechanisms that may be used with a throttle valve. These include a

hand trip lever on the valve, a solenoid trip, a pressure trip, and a differential pressure trip. These

specially designed trips usually have separate hydraulic operating and emergency cylinders.

Certain older types of throttle valves have a steam actuated cylinder for operating the quick closing

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emergency valve. In this type, steam leakage around the piston may cause rusting and sticking of

the valve so that it becomes necessary to jar the valve to close it.

THE OPERATING GOVERNOR

All turbine governors, regardless of their design operate off of one specific principle: centrifugal

force from the main shaft acting to overcome spring tension.

Except on smaller size auxiliary turbines, where shaft governors are used, very little work is done

by the governor. It normally operates as a relay, and the mechanism upon which the governor acts

must be given the same consideration as the governor. Proper lubrication of the parts of the

governor should be carefully maintained. Any lost motion in this mechanism is of primary

importance and should be given immediate attention.

The typical shaft governor employs weights held in place by a stationary spring. Centrifugal force

tends to move the weights outward. This motion is transmitted to the governor slide and in turn

through levers, to the valve regulating admission of steam to the turbine. The weights have knife

edges that contact knife edge seats on the stationary spring, causing it to move. It is essential that

the knife edges and seats be kept in good condition.

Practically the same type governor is used on larger units, except that the motion transmitted to

the governor slide moves only a pilot valve which controls the flow of oil to an operating piston

directly attached to the steam admission valve. These governors are called oil relay governors. It

takes oil pressure, usually shaft driven off the main turbine shaft, to actuate the governor and open

the throttle valve. In this sense, they will "fail safe" on loss of the oil pump or oil pressure.

Hydraulic governors are an older type of oil relay governor taking oil pressure directly from the

main oil pump, instead of through a pilot valve, with excess oil pressure bled off back to the main

oil sump. The main drawback to this type governor is that unlike the oil relay governor that takes

oil pressure to open the throttle valve, the hydraulic governor requires oil pressure to close the

throttle valve, and therefore do not "fail safe" on loss of the main oil pump or pressure.

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TG-13 and TG-17

TG13 Governors are self-contained, mechanical-hydraulic, speed-droop governors for use on

small steam turbines driving pumps, compressors, or generators, where isochronous (constant

speed) operation is not required. These governors are directly coupled to the steam-turbine’s rotor

or auxiliary shaft to sense and control turbine speed.

Description

TG13 governors are mechanical-hydraulic speed-droop governors for controlling small steam

turbines.

These governors control turbine speed by sensing turbine rotor speed via their input drive shaft,

comparing this speed to an internal speed setpoint, then using a rotary output terminal shaft

connected to the turbine’s governor valve to control turbine inlet steam flow. This self-contained

governor utilizes an integrated drive-shaft-driven ballhead assembly to sense turbine speed, and

an integrated drive-shaft-driven oil pump to create the necessary output force to move/control the

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turbine’s governor valve. The governor output is a serrated terminal shaft that extends out each

side of the governor housing and rotates up to 40° to accurately control the turbine’s inlet steam

valve(s).

Different models are available depending on the output shaft force and input driveshaft speed range

required. The TG13 governor’s (turbine) speed set point is set and adjusted via a speed-setting

screw located on the unit’s cover plate. TG13 governors are available in two different work

outputs: 16 Nm (12 lb-ft) and 23.7 Nm (17.5 lb-ft). These governors are hydraulically powered for

a high work output, and are available for three different speed ranges.

Like most mechanical governors, the TG13 governor uses its output terminal shaft position as a

feedback signal for stability. By using this stabilizing method, turbine speed will “droop” a certain

percentage as load increases (shaft position increases).

Standard Features

Simplicity and low cost are distinct advantages of the TG13 Governor. The governor operates

with speed droop for stability of control and screw-type speed setting.

An internal oil pump, driven by the governor's drive shaft, transports oil from the self-contained

sump. Internal pressure is maintained by a relief valve-accumulator system. An oil sight-glass

provides ease in checking the oil level. The output (terminal) shaft extends out both sides of the

case, and the governor drive rotation can be in either direction.

OVERSPEED TRIP VALVE Only a relatively short period of time is required to dangerously accelerate the rotor of a steam

turbine. Therefore, when the governor fails, the rotor is subject to the danger of a "run away", or

in other words, instant over speeding. To guard against this hazard, the turbine is provided with an

overspeed trip valve which shuts off the steam to the turbine when normal speed is exceeded by

10%.

Most overspeed trip valve consist of a small piston located in a recessed opening in a collar

mounted on the main shaft of the turbine. Centrifugal force of the turbine over speeding causes the

piston to move outward where it contacts a trip lever as it emerges from the recess, which in turn,

actuates the quick closing emergency valve, shutting off the steam supply to the turbine.

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Movement of the piston is opposed by a spring, the tension of which is adjustable to obtain the

desired tripping speed.

GOVERNOR MOUNTING HOUSING It supports governor and connects it out of the governor end to the bearing end housing. Trip

collar, overspeed trip valve and governor drive coupling are on it.

MAIN BEARINGS

Various types of bearings are used by the different manufacturers. The older type bearings were

babbitt lined in cast iron shells and had water coils imbedded in the babbitt for cooling purposes.

This type used a relatively small quantity of oil, the oil being drawn under the bearings to form the

oil film. Modern bearings are generally of the oil-cooled type, where large quantities of oil are fed

into the top half of the bearing and distributed it's full length by special cut oil grooving. The oil

acts as the cooling medium as well as the lubricant. On the latest types of steam turbines, in the

larger units there are no valves in the oil lines, with the oil flow being regulated by orifices

provided at the factory before shipment. Bearing pressures per square inch of projected area have

been greatly increased in the new designs.

Bearing clearances allowed when a turbine leaves the factory are generally from .001 to .002 inch

per inch of shaft diameter, with a minimum clearance of .010 inch. In most cases this amount may

be doubled before replacement is necessary, although the running condition and load on the

bearing should be considered. When the bearings of a steam turbine need to be re-babbitted, they

should be returned to the manufacturer as the babbitt is of a special composition and have special

grooving.

THRUST BEARINGS AND SQUEALER RINGS

Thrust bearings should be checked for wear and clearance. The smaller impulse turbines have

roller thrust bearings with especially hardened steel washers. These should be very carefully

inspected as the clearance is close. Any bearings of this type which show even minute pitting or

roughness of the rollers or any cutting or galling on the hardened washers should be replaced. In

reality these are not thrust bearings, but only serve to maintain shaft position since there is not

axial thrust transmitted to the shaft on impulse turbines.

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It is the practice of certain manufacturers of the impulse type steam turbine to build into the

machine so-called squealer rings. The purpose of these rings is to give warning before a dangerous

degree of wear occurs at the thrust bearing.

They are usually either placed close to or made a part of the thrust bearing and consist of a rotating

ring mounted on the shaft and stationary rings mounted on a stationary part close thereto. The rings

are spaced with a clearance less than the clearance at the bucket wheels so as to make contact and

give warning before the wheels begin to rub, hence the squeal is easily detected.

SKF 6213C3

Single row deep groove ball bearings are versatile, self-retaining bearings with solid outer rings,

inner rings and ball and cage assemblies. These products, which are of simple design, robust in

operation and easy to maintain, are available in unsealed and sealed variants.

Due to the manufacturing processes used, unsealed bearings have turned recesses in the outer ring

for seals or shields. Due to the raceway geometry and the balls, deep groove ball bearings can

support axial forces in both directions as well as radial forces. Due to their low noise level and low

frictional torque, single row deep groove ball bearings are particularly suitable for electrical

machinery, ventilators, washing machines and power tools.

GOVERNOR BEARING HOUSING

Ball bearing supporting the shaft is contained within this housing. Oil level gauge and constant

level oiler are mounted on bearing along with oiler filter, exhaust and intake. The ball bearing in

casing end bearing also serves as thrust bearings.

SHAFT PACKING The function of the shaft packing is to prevent excessive steam leakage. The water seal method is

used in combination with packing rings of carbon or labyrinth type, affords a positive seal when

functioning properly. Where this type of seal is used careful check should be made for cracking of

blading and erosion of the stationary casings. Clearances also should be checked.

Other types of shaft packing are made in three or four segments held together by springs called

garter springs, and are self-aligning, to some extent. These types should be checked for clearance,

flexibility of springs, joint openings between sections and overall general condition. Carbon

packing will be found to have smaller clearances than most other types. Another type used is the

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bronze lead alloy, which has good wearing-in qualities without excessive overheating, so that small

clearances may be used. The diaphragm packing in the impulse type turbine usually has only one

ring of packing per diaphragm, because of the limited space and small pressure drop. Wear on

diaphragm packings is an indication of diaphragm misalignment. As the packing controls leakage

of steam between stages, wear of the packing will have a definite effect on turbine efficiency.

SHAFT COUPLINGS Shaft couplings connecting steam turbines to driven machines are usually of the flexible type.

Turbine manufacturers use several designs of flexible couplings, usually of the jaw, pin or gear

type. Lubrication is a matter of extreme importance with all flexible couplings, as lack of sufficient

and proper lubricant will cause excessive wear. Wear and the lubrication of couplings should be

checked at each inspection, and in no case less than once each year.

BUCKETS AND BLADES The term buckets and blades are often used synonymously. Although the shape and appearance

are similar, it has usually been considered that buckets are used in the impulse type turbine and

blades, both stationary and rotating, are used in the reaction type steam turbine. Buckets of impulse

turbines and blades of some reaction turbines have a shroud band, either continuous or in sections,

either welded, brazed or riveted to the blade tip, which acts as a bracing to the blades and maintains

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radial clearance with the turbine casing. One of the principal causes of blade failure is shocks due

to water being carried over with the steam. This may be due to priming of the boiler, poor

arrangement of the steam piping, resulting in pockets in the line which are insufficiently drained,

of failure of the drains to operate.

At light loads a considerable quantity of water may accumulate in these pockets and when the load

increases, the higher velocity of the steam will carry this water over into the turbine in the form of

slugs. The impact of this mass of water at the comparatively high velocity may cause serious

damage to the blading.

TURBINE WHEELS The wheels on a turbine shaft should be checked carefully at a dismantled inspection for possible

defects such as looseness on the shaft. A loose wheel is often difficult to locate as it may appear

tight when the turbine is stationary and be loose when the rotor is at normal speed.

Evidence of this is that the wheel will run untrue and can be detected by indicating the side of the

wheel at the rim. A close examination of the shaft or key may disclose traces of iron oxide deposits

adjacent to the wheel.

Cracks are sometimes difficult to discover in some parts of a wheel or disc, particularly at the

bucket or blade attachments. The majority of impulse wheels have so-called steam balance holes

drilled through them to equalize the steam pressure on both sides of the wheel. Cracks in the wheel

disc frequently start at these holes. The manufacturers carefully grind and round off all corners of

these holes to reduce the possibility of cracks starting at the holes. Where there is any suspicion

whatsoever that a wheel may be cracked, the entire wheel should be given a magnaflux test or be

x-rayed.

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ALIGNMENT REQUIREMENTS: Excessive vibration, bearing edge loading and high shaft loads can result from incorrect alignment.

Factors affecting alignment are:

Setting in the foundation growth of the shaft heights due to temperature changes.

Machine movement of either unit with respect to foundation due to vibration, worn out

bearings, distortion of casing due to loads from connecting systems and structures.

Angular misalignment occurs when shaft centerlines intersect at an angle.

Parallel misalignment occurs when shaft centerlines are parallel to each other and don’t

intersect.

LUBRICATION SYSTEMS: Oil Ring Lubrication:

Brass oil rings running on the turbine shaft pick up oil from the reservoirs in the

bearing housings. It ceases at below speeds of 900 rpm. It is an important cause of

bearing failure.

Oil Mist Lubrication:

In pure mist oil rings are omitted and a mist of oil is being supplied to the

bearing housing by oil mist generator. Turbine must be operated without it.

When purge oil mist is supplied oil rings are included and the turbine can

be operated without oil mist generator.

Lubrication Type Cooling water to Bearing

Housing Mandatory

Cooling water to Bearing

Housing Optional

Standard Oil Ring Only when inlet steam

temperature exceeds 550oF

OR when ambient

temperature exceeds 110oF

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Pure Oil Mist X

Purge Oil Mist Only when inlet steam

temperature exceeds 550oF

OR when ambient

temperature exceeds 110oF

The optional application of cooling water will assist in the maintaining recommended oil under

severe services condition such as high ambient temperature, partial load operations and frequent

shutdowns.

Cooling water for bearing houses must meet following specifications:

Flow Rate 0.5gpm

Min Inlet Pressure 690kPa

Maximum Inlet Temperature 90oF

Condition Clean, non-corrosive

Oil Temperature 100oF

Minimum Flashpoint 350oF

Viscosity Index Above 90

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INSPECTION CHECKLIST

Parts to be examined Are to be examined Inspect for Action Required

Turbine and Sector

blades

Shrouds

Blades

Cracks, poor

rivet heads

Corrosion,

erosion,

cracks

Consult

Manufacturer

File or grind

smooth

Bearings Races and balls Pitting and Corrosion Replace

Bearing Housing Oil

Seals

Seal Rings Leakage Replace

Glands Carbon Rings Breakage Wear Replace

Throttle Stern

Seal Sleeves

Valve

Scaling, wear

Wear

Wear, galling,

pitting

Remove

Replace

Replace

Governor Linkage Connecting end rods Wear, excess

clearance

Replace

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SPECIFICATIONS:

SERIAL NO: 98T4384

INLET PRESSURE NORMAL: 10.5 Kg/cm2

INLET TEMPERATURE NORMAL: 205oC

EXHAUST PRESSURE NORMAL: 3.5 Kg/cm2

CRITICAL SPEED: 8500

TRIP RPM: 3570

POWER: 30 KW

TYPE/SIZE: RLA 22L

RPM: 2950

VOLTAGE: 400 V

BEARINGS: SKF 6213C3/ SKF 6213C3

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TROUBLESHOOTING

STEAM TURBINE:

Symptom Probable Cause Corrective Action

Excessive vibration/Noise Misalignment Disconnect coupling between Turbine & Driven machine and drive turbine only

Worn Bearing Replace.

Worn coupling to driven m/c Check condition of coupling

Unbalanced coupling to driven machine

Remove coupling halves and check the balance

Unbalance Wheel Due to foul, overspeed, loss/damage to shrouds or blades. Turbine standing idle for long time, solid matter can build up in lower half.

Piping Strain Inlet and exhaust steam lines should be supported and sufficient allowance must be given for expansion.

Bearing Failure Improper Lubrication Check oil periodically that it is free from condensate

Improper cooling water Water should be adjusted to maintain bearing oil sump temp.

Misalignment Check alignment

Bearing Fit Ball bearing should fit on the turbine shaft with a light press fit. Too tight cause cramping, too lose will cause the turn on the shaft.

Excessive thrust Verify that coupling is clean and is installed so that excessive thrust is not impressed on turbine from driven.

Unbalance Can cause excessive wear and bearing failure.

Rust It may develop when the turbine is improperly stored. Also when it is out of service for long.

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Excessive Steam Leakage under carbon rings

Dirt under rings Steam may carry the scale and the dirt which foul the rings

Shaft Scored Shaft surface under carbon rings must be smooth to prevent leakages. Polish minor imperfections

Worn or broken carbon rings Entire rings must be replaced

Corroded worn out dirty partition plate surfaces

Steam will leak past the carbon ring partition surface therefore replace it.

Leak off pipe plugged Verify that all steam discharge freely.

Oil leaks past seal ring High oil level Reduce oil level to bring it to coincide with the markings on bearing housing.

Scratched or rough shaft under seal ring

Polish shaft under seal ring and install a new ring.

Washer plate too tight Polish shaft under seal ring and install a new ring if necessary.

Seal ring improperly installed Refer to manual for proper installation.

Shaft vibration Install a new seal ring if necessary.

Insufficient Power (Turbine does not run at rated speed)

Too many hand valves closed Open additional handvalves.

Oil relay governor set too low Refer to section for Speed adjustment and speed range limits.

Inlet steam pressure too low or exhaust pressure too high

Check steam pressure at the turbine inlet & exhaust pressure close to the exhaust casing, using accurate gauges. Low inlet pressure may be the result of auxiliary control equipment such as a pump governor which is too small, improper piping sizes, excessive piping length.

Load higher than turbine rating Determine actual load req. of the driven equipment. Sometimes available turbine power can be increased by modifying a few components.

Low oil level Refill.

Steam Strainer Remove all foreign matter from steam strainer.

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Speed increases excessively as load is decreased

Throttle valve not closing fully Refer to insufficient power mentioned in above.

Throttle valve and valve seats cut or worn

Replace if necessary.

Excessive speed variation Governor droop adjustment An increase in the internal droop setting will reduce speed variation or hunting.

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Failure of Recycle Gas Compressor Lube oil Pump Turbine:

CAUSE:

Excessive leakage of steam between carbon rings and shaft, due to improper

clearance between them, entering bearing housing and causing rusting of bearings

and other ferrous materials. Thus damaging the bearing structure, which in turn

damages the entire system in several ways as mentioned in Troubleshooting.1

DESCRIPTION: Water contamination of lube oil, occurring rather commonly in small or modest quantities, does

not result in apparent or immediate problems. But, in time the effects it will range from appreciable

to severe. Water contamination results in:

Rusting of ferrous components in the lube systems. This causes wear of bearings and shaft

journals, and sticking of oil lubricated mechanisms, such as mechanical trip mechanisms,

oil trip cylinders and pilot valve (governor) mechanisms. In some instances, admittedly

unusual, rusting of ferrous components has dislodged hard particles which have then

embedded in the bearings and actually machined away the shaft journals. There have been

many instances where water has been present for a long time resulting in extreme rusting

of oil drain lines and oil reservoir covers. Once this condition exists, it is virtually

impossible to get the system clean. Because of this, some users have specified stainless

steel drain lines and oil reservoirs. Small and medium (100 to 1500 hp) turbines usually

have ball thrust bearings.

In an extreme case, one might receive the report that "oil is over flowing from the

reservoir." This has happened and is often the result of sufficient water accumulating in the

oil system to displace so much oil that oil overflows from the reservoir. If continued

unchecked, the water level can rise until the oil pump picks up the water and bearing

failures with their unpleasant consequences will quickly follow.

1 Troubleshooting: Bearing Failure and Excessive Steam leakage under carbon rings.

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Most present-day lube oils contain additives which are necessary to make the oil perform

without excessive oxidation, foaming, slugging, and general deterioration. Water

contamination of the lube oil will often remove or wash out these additives.

In addition, water will promote formation of emulsions, which in turn can plug oil filters

and leave deposits in the bearings. Evidently then, water contamination of lube oil will

eventually cause serious problems and this deficiency should not be ignored.

In most cases, the moisture source is gland leakage, although water also can enter by means of a

cooler leak. Testing the water sample for dissolved solids will distinguish between the two sources

of contamination. Steam condensate gland leakage is quite low in dissolved solids, whereas

cooling water is moderate to high in dissolved solids.

As the lubricating oil leaves the bearings, the oil becomes aerated.

Some bearing designs promote greater aeration than others, but all bearings aerate the oil. This

aerated oil then flows out of the bearing housing or bearing box into the drain line and on into the

oil reservoir. Some air separates from the oil in the bearing box, some separates in the drain line,

and the rest separates from the oil in the reservoir. The air released in the reservoir then collects

above the oil and exists through the reservoir vent.

Thus the oil flow is removing air from the bearing housings or boxes, and releasing the air in the

reservoir. Air flows into the bearing boxes to replenish the air taken away by the oil. The bearing

boxes are usually tight and generally the air enters along the shaft. Quite near the place where the

air enters the bearing box is the gland case, which in many instances is leaking at least some steam.

As will be examined later, in many instances this steam leakage is normal and expected. If this

steam leakage is sufficient to raise the dew point of the air being drawn into the bearing box above

the temperature of the underside of the oil reservoir cover, then air released in the oil reservoir

causes dew to form on the underside of the oil reservoir cover. When these dew drops fall into the

oil, water contamination exists.

There are two basic types of carbon rings and labyrinths. With both types there is flow. Both types

can be likened to throttle bushings. In no instance will "NO FLO W" be achieved.

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CARBON RINGS Carbon rings are relatively inexpensive and the normal design aim is to achieve essentially line-to

line fit with the shaft at operating conditions. Because the expansion coefficient of carbon is about

half that of steel, there is a differential expansion problem to contend with that becomes

increasingly difficult as temperatures and speeds become higher. This fact, coupled with the

phenomenon that new carbon rings generate greater frictional heat for several hours until they are

run in, requires carbon rings to have greater clearances in some circumstances.

Hence, the leakage flow will be greater than that obtained under optimum conditions. The general

practice with carbon ring glands relative to removing the steam that does leak through the gland is

to bleed the leakage off the shaft through a leak off, and to depend on one (or two) carbon rings to

prevent excessive amounts of steam to get past the last ring. Anything that will elevate the pressure

in the gland at the leak off location such as, restrictive leak off piping, will increase the leakage

past the gland and raise the point where the air is drawn into the bearing housing.

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References:

WATER CONTAMINATION OF STEAM TURBINE LUBE OILS-HOW TO AVOID IT

by William L. Coleman Manager, Steam Turbine Department (Retired) Dresser-

Rand Repair.

www.woodward.com

www.schunkgraphite.com

www.dresser-rand.com/upgrades/steam/ssl-060.pdf

www.energy-tech.com

www.turbomachinerymag.com

Deep groove ball bearings www.skf.com

www.bearings-direct.com

6213/C3 SKF SKF Single Row Deep Groove Ball Bearings - Bearing King

www.bearing-king.co.uk

Fluid machinery nptel.ac.in

Bullard Industrial Technologies, Inc. www.bullardindustrialtech.com

www.FAG-GenerationC.com