20 Lubrication

Lubrication of rotating equipment

Oil characteristics and more

Ronald Bakker Shell Global Solutions

Shell Global Solutions International B.V., 2010. All rights reserved.

Contents Introduction Basic turbine lubrication system Turbine lubrication requirements What is a turbine oil & what properties does it need? How do we test and evaluate these properties? Oil and oil system cleanliness Field cases Oil Condition Monitoring Questions

Shell Global Solutions International B.V., 2008. All rights rights reserved. Shell Global Solutions International B.V., 2010. All reserved.

1

Common Turbine Lubrication System Features

Oil tank Oil pump Oil cooler Oil supply/return pipes Plain journal bearings Thrust bearing Turbine speed control system & valves Filters Gearbox in geared systems


Typical Gas Turbine Lubrication Systemcooling air

compressorair out

Power turbine

Generator

oil demister

IGV

duplex filter lube oil pump hydraulic oil pump

MOOG valves servo protection filters

extra by pass filter

Oil reservoir Either combined for bearing and control system or separated (2 tanks: 1x bearing oil & 1x hydraulic oil for control system)


2

Industrial Steam Turbine - working


Industrial Gas Turbine

Simplified turbine schematic3. Combustion chamber 4. Expansion turbine 6. Exhaust

5. Turbine outer casing

2. Compressor

1. Air intakeSiemens SGT6-6000G Gas Turbine 300 MW to 500 MW for Combined Cycle Applications

Picture courtesy of Siemens web site


3

Industrial Gas Turbine - working


Schematic of Steam Turbine Lube System

Main lube filter Main pump HP Thrust bearing Main lube oil tank Vacuum extract pump IP

To bearings Hydrogen sealing LP LP Jacking oil feed LP Generator and exciter Stator water cooling

Purifier Stages (HP, IP, LP) BearingsLube oil purifier

Control system not shown


4

Turbine Components Requiring Lubrication Journal bearings (Hydrodynamic) Used to support the weight of the turbine rotors. A journal bearing consists of two half-cylinders that enclose the shaft and are internally lined with Babbitt, a metal alloy usually consisting of tin, copper and antimony

Thrust bearings (Hydrodynamic) Axially locate the turbine rotors. A thrust bearing is made up of a series of Babbitt lined pads that run against a locating disk attached to the turbine rotor


Turbine Components Requiring Lubrication

Pocket type bearing (jacking hole in centre)

3 wedge bearing (jacking hole off centre)

Tilting pad thrust bearing Tilting pad journal bearing


5

Typical Turbine and Bearing Oil Flow

SWF File

Hydrodynamic Shell Global Solutions International B.V., 2008. All rights rights reserved. Shell Global Solutions International B.V., 2010. All reserved.

Hydrodynamic Oil Wedge Principle At rest, metal-to-metal contact, no oil film layer is present.JOURNAL

As the journal begins to rotate, it tends to climb up the bearing and onto a layer of oil. This reduces friction and allows the journal to slide. Increase in rotational speed drawns oil into the wedge-shaped clearance space, and fluid pressure is developed between the journal and bearing. At full journal speed, the converging wedge exists under the journal, and a minimum film thickness exists to one side of the bearing: Hydrodynamic lubricationPRESSURE FORCES DIAGRAM

BEARING

PRESSURE ZONE

HIGH PRESSURES ZONES

Any Deposit will reduce running clearance and increase bearing temperature.

Picture courtesy of PALL


6

Turbine Components Requiring Lubrication (cont.) Jacking Oil System: During turning, high pressure jacking oil is used to increase oil film thickness. Also to float the shaft before starting rotation from rest During start-up and shut down the rotor must be rotated slowly (barred) to avoid uneven heating or cooling which would distort or bow the shaft & to prevent them settling in the bearings, due to weight resting on one spot A barring mechanism or turning gear is used to do this

Jacking oil creates hydrostatic lubrication during turning

SWF File

Hydrodynamic Shell Global Solutions International B.V., 2008. All rights rights reserved. Shell Global Solutions International B.V., 2010. All reserved.

Steam Turbine - Control system

Steam turbines use a control system to operate the steam valves This is to control the turbine operational speed (governor) Hydraulic fluid is used to power this system High hydraulic pressures (possible leaks) Steam pipes are above auto-ignition temperature of mineral oils ( 200C


Key property #2: Air Separation and Foaming


18

Aeration and Foaming

Foaming Oil surface

> 1 mm dia. air bubbles Rise rapidly to surface Burst or produce foam

Aeration Oil Reservoir

10-3 to 1 mm air bubbles Entrained in oil Slow to rise to surface


Aeration and foaming

Oil condition invariably diagnosed as foaming problem Majority of cases actually caused by entrained air & poor ARV Addition of silicone anti-foamer seriously worsens aeration Silicones cannot be easily removed once added

REPLACE ENTIRE OIL CHARGE Shell Global Solutions International B.V., 2008. All rights rights reserved. Shell Global Solutions International B.V., 2010. All reserved.

19

Effect of silicone anti-foam agents on ARV

Air content (% vol)

10 8 6 4 2 0 0 2 4 6 8 10

Anti-foamzero

0.2 ppm 2.0 ppm

12

Time (minutes)


Effect of oil reservoir design on deaeration

d

d

y

Oil volume = constant Residence time = constant Bubble rise time (DEAERATION) @ depth d, dx


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Dangers of Excessive Aeration and Foam Loss of oil pressure Reduced oil flow Increased oil compressibility Failure to reach minimum pressure Poor response in high pressure servos Local oxidation of oil Adiabatic compression of air bubbles Highly loaded areas e.g. thrust bearings Possible blackening of white metal bearings Filter blocking Excessive pressure drop associated with no apparent contamination


Visible Foam in Oil Reservoir

Breaks in foam layer

Excessive Foaming

Acceptable Foaming Shell Global Solutions International B.V., 2008. All rights rights reserved. Shell Global Solutions International B.V., 2010. All reserved.

21

Principle Causes of Excessive Aeration Inadequately specified new oil Presence of silicone anti-foam agents System design and/or operation Excessive oil circulation rate Vertical section in oil return line Oil cascading down from excessive height Highly aerated oil fed too close to suction strainer Air leaks in pump suction system Oil pressure too high Vacuum entrainment on high speed plain bearings

Excessive build up of oxidation products Basic metal salts and/or greases


Aeration and foaming: equipment and operation Excessive oil circulation rate Vertical section in oil return line Oil cascading down from excessive height Highly aerated oil fed too close to suction strainer Air leaks in pump suction system Oil pressure too high Vacuum entrainment on high speed plain bearings


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Dangers of excessive aerationLoss of oil pressure Reduced oil flow Increased oil compressibility Failure to reach minimum pressure Poor response in high pressure servos

Local oxidation of oil Adiabatic compression of air bubbles Highly loaded areas e.g. thrust bearings Possible blackening of white metal bearings

Filter blocking Excessive pressure drop associated with no apparent contamination


Diagnosis of aeration / foaming problems

ARV

Foam

Probable cause of fault condition Excessive air entrainment Possible mechanical fault Contamination with silicones Contamination with basic metal salts e.g. engine oil, pipe lagging

Low High

Low Low

High

High


23

Measuring Air Release and Foam Tendency, Air release ASTM D 3427, Foaming ASTM D 892This test evaluates the oils capacity to release air, blown through the sample in a cylinder. The time required is reported The shorter the time the better the result, indicating good performance in the field Test conditions for air release: Temperature 50C reported as time for 0.2 % V/V of air to remain In this particular test the volume of foam, after air has been blown through the sample is measured. Lesser the foam, the better the oil. Test conditions for foam test: Temperature at 24C for 1st & 3rd test Temperature at 94C for 2nd test Shell Global Solutions International B.V., 2008. All rights rights reserved. Shell Global Solutions International B.V., 2010. All reserved.

Key property #3: Minimizing the Effect of Water a) Water Separation (Demulsibility) b) Rust and Corrosion inhibition


24

Sources of Water Contamination

Steam leaking from shaft gland Water contamination of top-up oil Oil cooler leaks Condensation of ambient moisture Poor handling practises


When Water is Present in a Turbine System

It should be removed as soon as possible It must remain as free water, rather than emulsified water Its source of ingression should be located and eliminated as soon as possible The amount of water in a turbine system should remain below 500 ppm If correctly applied, centrifugation or vacuum dehydration are affective ways to remove water


25

Excesses Amount of Water can Cause:

Increased system wear break down of oil film Promote corrosion of metal parts Enhance oxidation of the lubricant Degrade filter performance Remove additives Fatigue life of ball bearings used in steam governors Microbial growth in static areas


Causes of Reduced DemulsibilityTurbine oils are formulated with excellent water separation properties. However the following can degrade performance: Solids: Carbon residue, rust, fly ash and fine particulates, these can be removed by filtration Liquids: Engine Oils (1 part in 1000 is sufficient) Oil soluble materials cannot be removed by filtration, i.e other lubricant, greases, etc. Surface active additives can be removed by excessive water contamination Other: Oxidation by-products Contamination with other fluids containing emulsifiers, metal protective oils, etc. Formation of soaps with rust inhibitors and acidic oxidation products


26

Measuring Water Separation ASTM D 1401, Demulsibility Characteristics

ASTM D 1401 40 ml oil, 40 ml water at 54C reported as time to 3 ml emulsion (nearest 5 min) e.g. 40 - 40 - 0 (5 min)

Clear Oil Layer

No Clear Separation

Clear Water Layer


Measuring Water Separation Steam Demulsibility (IP 19)This method gives a measure of the oils ability to separate from an emulsion with steam. As the oil gets contaminated with fine dispersed water droplets at high temperature this test method is regarded to be much more severe than ASTM D1401 Demulsibility Test (where a 50/50 water/oil mixture is placed at 54 C (130 F) The time for 20 ml of oil to separate is recorded (in seconds) The shorter the time, the better the oil performance Test conditions: 20 ml of oil is violently emulsified with steam at about 90 C (194F) The emulsified test oil is placed in a bath at about 94 C (201F) The time to separate condensed steam (water) is measured

AP/Wide World Photo, www.state.gov


27

Measuring Corrosion Protection Rust test ASTM D 665 / IP 135To evaluate the ability of oils to prevent the rusting of ferrous parts should water become mixed with the oil. Procedure A= distilled water Procedure B= synthetic sea water The specimens are inspected after the test and are classified as follows: A) B) C) D) E) F) Pass Fail- Dark grey staining noted Fail Light Fail Moderate Fail Severe Fail Severe


Key property #4: Filterability


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Filterability

Oil filterability is quantified by the measuring the ease with which a volume of oil passes through a filter of known size, or the time taken to block the filter.

Finer filtration is increasingly common in turbines New oil vs. oil in service Good quality new oil should never cause filter blockage >80% problems in service caused by contamination An oil with excellent filterability will allow the use of finer filtration which will help to improve contamination control


Causes of Poor Turbine Oil Filterability Contamination A mixture with engine oils Solid, liquid or gaseous (eg process gases like ammonia) contaminant reacts with the additives Water

Oxidation products from oil Insoluble oxidation products (sludge) Organic acids form soaps with metal salt contaminants

Particulate contamination Filter debris Rust and dirt


29

Measuring FilterabilityFilterability of Turbine Oils Contaminated with Water & Calcium, TMS 511 Hydraulic oil tests ISO, AFNOR, etc Shell uses own method (TMS 511), done wet, with calcium. Calcium additive is similar to the additive used in many motor oils

Blank Filter Membrane (0.8m)

Oil with Acidic Components

High quality turbine oil

SEM Images of filter Elements


Filterability and cleanliness of turbine oils

Protection of control system servo valves Hydraulic component clearance: up to 5 m high pressure up to 20 m low pressure

Servo valves protected by 5- 10 m filters to achieve target cleanliness of 13/11 to 12/9 within the closed circuit

Service life of filters

Oil must not block the servo final filters throughout service life

In service filterability of the oil determines the lifetime of the servo valve protection filters


30

Filterability of fluids important

The same type MOOG servo final filters after 24000 running hours on SHELL TURBO GT 32

MOOG Servo valve final filter 10 m. Heavy sludge formation after 17000hr


Key property #5: Extra load carrying capacity


31

Extra Load Carrying Capacity

Relevant for turbines with reducing gear sets Some gearboxes require lubricant with enhanced anti-wear performance Poor load carrying capacity leads to accelerated wear


Measuring Load Carrying Capacity FZG Spur Gear Test Rig DIN ISO 14635-11750 Load Clutch r/min Load Arm Test Gears

Lubricant

load is raised in stages, inspecting gears at end of each load stage

Failure load stage is when total scouring /scuffing exceeds limits


32

Some examples of high and low quality oils


Field cases

Some examples of high and low quality oils


33

Low quality oils

General Electric Frame 9E A low quality mineral oil resulted in deposit formation on alternator bearing in this turbine


Low quality oilsPower turbine thrust bearing pads: General varnish deposition

Shell Global Solutions International B.V., 2010. All reserved. Shell Global Solutions International B.V., 2008. All rights rights reserved.

34

Low quality oilsGenerally bearing in good condition, however black carbonaceous deposits formed after relatively low hours of operation


Low quality oilsBearing housing cover: Heavy varnish/ carbon deposits, labyrinth seal wear


35

Low quality oilsVery heavy deposition, overlay loss, less than 1 year operation


The right oil makes all the difference

MAAG GEAR BOX, ABB GASTURBINE TYPE 9DAFTER 24000 HOURS ON A NORMAL TYPE STEAM TURBINEOIL ISO VG 46 SAME GEAR BOX AFTER 35000 HOURS ON SHELL TURBO GT 32


36

High quality oils

35,000 Hrs Turbo GT32 oil service life

Number 9 bearing - right hand of pinion


High quality oils

General Electric Frame 9E Flevo 32 Centre bearing # 2 after 40,000 hours on Shell Turbo GT 32

No deposit formation Absolutely clean labyrinths


37

High quality oils

The same gear box thrust bearing, after 30,000 running hours on SHELL TURBO GT 32 JUNE 1993

Gear box thrust bearing after running on a mineral turbine oil before the swap to SHELL TURBO GT 32 JUNE 1988


Flushing and Filling


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Why Flush? Critically important to minimise the harmful effects of material debris and chemical contamination on the turbine operation Material Debris from assembly, transport, maintenance, wear, environment Chemical contaminants improper oils, chemical cleaners, corrosion preventives, water

Proper flushing and filling at the turbine commissioning step will maximise the turbine oils lifetime minimise turbine outages reduce costs

Shortcuts here can cause problems later Flushing should be seen as an integral part of fluid and equipment life cycle.


Principles of FlushingFlushing normally requires: fast turbulent flow (often three times normal system velocity) to dislodge contaminants the fast flow rate is one reason sensitive components must be blanked off turbulent flow rate

hot fluid, thermo shock to expand components of the system and further dislodge contaminants heat also increases the solvency power of the fluid

vibration/agitation to dislodge contamination by mechanical vibration

efficient filtration to remove the contamination


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Requirements of a flushing fluid A flushing fluid must: be unaffected by the thermal stress of operating at the flushing temperature for a period of hours solvate sludge and oil deposits not remove anti-rust coating from tanks be compatible with all system components and coatings possess good filterability possess anti-rust properties be compatible with the current or previous fill, particularly is a flying flush is being performed Consider the use of a lower viscosity to reach turbulent flow With Shell products it is normally recommended to flush with a charge of the fresh product


Turbine oil flushing and fillingOEM requirement

GE Lubricating oil recommendations (GEK..) refers to ASTM D6439 flushing & filling, & ASTM D4378 monitoring,

Alstom HTGD 90117 supply --/18/15 or NAS 9, if EHC --/16/13 Service --/16/13 or NAS 7, limit --/17/14 or NAS 8

Siemens TLV 9013 04 supply

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20 Lubrication