Lubrication-Related Inspections in Turbomachinery

1. Introduction

Lubrication is one of the most critical support systems in turbomachinery. In turbines, compressors, expanders, pumps, gearboxes, and high-speed auxiliary drives, the lubricant is not only reducing friction. It is also removing heat, carrying away wear debris, protecting surfaces from corrosion, supporting hydrodynamic oil films, supplying control-oil circuits, and, in some machines, supporting oil-type shaft-sealing systems.

For large industrial turbomachinery, the lubrication system normally includes a reservoir, pumps, filters, coolers, piping, valves, controls, and instrumentation. A classic Turbomachinery Symposium paper describes a significant turbomachinery lube-oil system as generally consisting of “a reservoir, pump, filter, cooler, piping and controls,” and emphasizes that cleanliness, water separation, proper oil temperature, and contamination control are central to reliability. API 614 is the main industry standard normally referenced for lubrication, oil-type shaft-sealing, oil-control systems, and auxiliaries for equipment trains such as compressors, gears, pumps, and drivers. (standards.globalspec.com)

A complete lubrication-related inspection program should therefore cover the oil, the oil system, the lubricated components, and the instrumentation that protects the machine.

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2. Main Objectives of Lubrication Inspections

Lubrication inspections aim to confirm that:

1. The correct lubricant is being used.
2. Oil is clean, dry, chemically healthy, and compatible with the system.
3. Adequate oil pressure, flow, and temperature are maintained.
4. Filters, coolers, pumps, reservoirs, and valves are working correctly.
5. Bearings, gears, couplings, seals, and control-oil components show no signs of lubrication distress.
6. Protection systems will alarm or trip before lubrication failure causes major damage.
7. Trends are identified early enough to plan maintenance instead of reacting to failures.

ASTM D4378-24, the current ASTM practice for in-service monitoring of mineral turbine oils, states that oil monitoring is intended to help operators maintain effective turbine lubrication and guard against oil degradation and contamination. It also notes that results must be interpreted with the equipment type, workload, lube circuit design, and top-up history in mind. (ASTM International | ASTM)

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3. Documentation and Program Inspections

Before inspecting hardware, the lubrication program itself should be checked. This is often missed, but it is the foundation of good turbomachinery reliability.

Documents to inspect include:

Item	What to verify
OEM manual	Correct oil grade, viscosity, cleanliness target, sampling interval, change-out criteria, bearing clearances, flushing requirements
P&ID and lube-oil schematic	Correct valve lineup, bypasses, filter/cooler arrangement, standby pump logic, alarm and trip points
Lubricant specification	ISO VG grade, turbine oil type, synthetic/mineral compatibility, additive type, approved brands
Oil analysis history	Trends in viscosity, acid number, water, particle count, wear metals, varnish potential, antioxidant depletion
Maintenance history	Filter changes, cooler cleaning, pump repairs, bearing inspections, oil changes, flushing records
Calibration records	Pressure, temperature, level, flow, differential pressure, vibration, and bearing-temperature instruments
Alarm/trip records	Low oil pressure events, high bearing temperature, filter differential pressure, high tank level, low tank level
Top-up log	Quantity and frequency of make-up oil; sudden increase may indicate leaks or carryover
Contamination events	Water ingress, process gas ingress, seal failure, cooler leak, incorrect oil addition, failed flushing

A good inspection program should be trend-based, not only checklist-based. A single oil-analysis result may not be enough to condemn oil, but a consistent upward trend in water, acid number, particles, varnish potential, or wear metals should trigger investigation.

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4. Routine Running Inspections

These are inspections performed while the machine is operating. They are usually done by operators, reliability technicians, or rotating-equipment inspectors.

4.1 Reservoir and Oil Level

Inspect:

Inspection point	What to look for	Possible concern
Oil level gauge or transmitter	Level within normal band	Low level may indicate leakage; high level may indicate water ingress, overfilling, or process contamination
Sudden level change	Rapid increase or decrease	Cooler leak, seal leak, drain restriction, incorrect filling
Tank sight glass	Oil clarity, color, foam	Milky oil suggests water; dark oil suggests oxidation or overheating; foam suggests air entrainment
Reservoir vent or breather	Clean, dry, not blocked	Poor breathing can pull in moisture/dirt or cause pressure imbalance
Bottom drain	Water/sludge check	Water accumulation can cause rust, additive depletion, bearing distress
Tank heater	Proper operation	Oil too cold can cause poor flow and poor water separation; oil too hot accelerates oxidation
Tank temperature	Stable and within OEM range	High temperature accelerates degradation and may reduce viscosity

The reservoir is not just an oil storage tank. It allows air, water, and contaminants to separate from returning oil. The Turbomachinery Symposium paper notes that reservoirs should be designed to allow water and vapor separation and that filters should maintain low contamination levels.

4.2 Oil Pressure

Inspect:

Inspection point	What to check
Main oil header pressure	Stable and within OEM/API requirement
Pump discharge pressure	No abnormal fluctuation
Bearing supply pressure	Correct pressure at each branch or header
Control-oil pressure	Correct pressure for actuators, governors, trip valves, servo valves
Seal-oil pressure	Correct differential pressure over process gas pressure, where oil seals are used
Low-pressure alarm	Proper setpoint and no nuisance alarms
Low-low pressure trip	Proper trip setpoint and tested logic
Pressure-regulating valve	Stable control, no hunting
Relief valve	Not leaking or lifting unexpectedly
Accumulator pressure	Correct pre-charge and response, if installed

Low oil pressure is one of the most serious lubrication-related conditions. It can result from pump failure, suction blockage, low reservoir level, relief valve malfunction, filter blockage, air entrainment, excessive bearing clearance, or major leakage.

4.3 Oil Flow

Inspect:

Inspection point	What to check
Flow indicators	Correct flow to bearings, gears, couplings, control circuits
Bearing drain flow	Free flow, no restriction, no abnormal splashing
Flow switches	Functional and correctly set
Orifices/restrictors	Not plugged, eroded, or incorrectly installed
Spray nozzles	Correct pattern for gearboxes or accessory drives
Oil-return lines	No flooding, foaming, or poor slope
Sight glasses	Clear indication of oil movement

Adequate pressure alone does not guarantee adequate flow. A blocked bearing orifice can show good header pressure while starving one bearing.

4.4 Oil Temperature

Inspect:

Inspection point	Why it matters
Reservoir temperature	Affects viscosity, water separation, oxidation rate
Oil cooler inlet/outlet temperature	Confirms cooler performance
Supply header temperature	Confirms correct oil delivered to machine
Bearing drain temperature	Indicates bearing heat removal
Bearing metal temperature	Direct indication of bearing condition
Gearbox oil temperature	Indicates gear mesh and bearing health
Control-oil temperature	High temperature can promote varnish and servo-valve sticking

Temperature should be trended. A slowly rising bearing temperature at constant load may indicate varnish, loss of clearance, oil starvation, cooler fouling, oil viscosity change, misalignment, or bearing damage.

4.5 Leakage and Housekeeping

Inspect:

Area	What to look for
Pump seals	External leaks, seal weep, oil mist
Cooler flanges	Oil or water leakage
Filter housings	Gasket leaks, drain leaks
Bearing housings	Oil leakage, seal leakage, misting
Piping flanges	Drips, staining, loose bolts
Flexible hoses	Cracking, swelling, rubbing, expired service life
Instrument connections	Leaks at gauge roots, impulse lines
Reservoir manway	Gasket leakage
Floor and baseplate	Oil accumulation, slip hazard, fire hazard

Oil leaks are not only housekeeping issues. They may create low oil level, air ingress, fire risk, environmental issues, and hidden bearing starvation.

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5. Oil Sampling and Oil Condition Inspections

Oil analysis is one of the most important lubrication inspections. STLE describes common turbine-oil tests as including viscosity, elemental spectroscopy, particle count, water content, and FTIR, with additional tests such as demulsibility, foaming, rust prevention, RPVOT, RULER, ultracentrifuge testing, and membrane patch colorimetry. (stle.org)

5.1 Sampling Point Inspection

Before trusting an oil sample, inspect the sampling method.

Check:

Inspection item	Requirement
Sample location	Preferably live oil zone, not stagnant drain point
Sample port	Clean, capped, clearly labeled
Flushing before sample	Enough oil flushed to remove dead-leg contamination
Bottle cleanliness	Lab-supplied clean bottle
Sample timing	Consistent operating condition each time
Labeling	Machine ID, oil type, operating hours, oil hours, date, top-up quantity
Chain of custody	Proper submission to lab
Baseline sample	New oil reference sample retained

Poor sampling creates false alarms and missed failures. Sampling from a dead leg, dirty valve, or recently disturbed drain can make clean oil look contaminated.

5.2 Basic Oil Analysis Inspections

Test	What it detects	Lubrication issue indicated
Viscosity at 40°C	Oil thickening or thinning	Oxidation, wrong oil, contamination, fuel/process ingress, shear
Acid number / TAN / AN	Acidic degradation products	Oxidation, additive depletion, varnish risk, corrosion risk
Water by Karl Fischer	Dissolved/free water	Cooler leak, steam seal leak, condensation, poor breather
Particle count / ISO cleanliness	Solid contamination	Dirty oil, filter failure, wear debris, poor flushing
Elemental spectroscopy	Wear metals and additives	Bearing wear, gear wear, contamination, wrong oil
FTIR oxidation/nitration	Chemical degradation	Oxidation, thermal stress, contamination
Color/appearance	Visual condition	Darkening, oxidation, water, sludge
Insolubles	Degradation products and solids	Oxidation, contamination, poor filtration

5.3 Advanced Oil Analysis Inspections

Test	Purpose
RPVOT / RBOT	Estimates remaining oxidation stability compared with reference oil
RULER / linear sweep voltammetry	Measures remaining antioxidant additives
MPC / membrane patch colorimetry	Measures varnish potential
Ultracentrifuge	Detects fine insoluble degradation products
Demulsibility	Checks ability of oil to separate from water
Foam tendency/stability	Checks air-release and foam behavior
Air release	Checks how quickly entrained air leaves oil
Rust prevention	Checks corrosion protection
Ferrography	Examines wear-particle shape and severity
PQ index / ferrous density	Detects larger ferrous particles missed by spectroscopy
Patch microscopy	Visual inspection of particles, fibers, sludge, varnish, dirt
Dielectric constant	Online or offline indication of oil degradation/contamination
Varnish-solvency tests	Assesses soluble and insoluble varnish tendency

Varnish deserves special attention in gas turbines, compressors, and control-oil systems. A 2023 review notes that varnish contamination can cause filter plugging, hydraulic-valve sticking, flow obstruction, clearance reduction, poor heat transfer, and increased friction and wear. (PMC)

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6. Filter, Strainer, and Contamination-Control Inspections

6.1 Main Oil Filters

Inspect:

Inspection item	What to check
Differential pressure	Rising DP indicates loading; sudden drop may indicate rupture or bypass
Filter bypass	Should not be open unless design allows; bypass can send dirty oil to bearings
Transfer valve	Smooth transfer between duplex filters without pressure dip
Element rating	Correct micron/beta rating and collapse rating
Element compatibility	Compatible with oil chemistry and temperature
Filter housing	No leakage, corrosion, or incorrect assembly
Venting	Filter properly vented after change
Drains	No sludge/water accumulation
Used filter cut-open	Inspect for metal, sludge, varnish, fibers, gasket debris

Used filters are valuable evidence. Cutting open and inspecting the element can reveal bearing metal, gear debris, seal material, varnish, corrosion products, or dirt.

6.2 Suction Strainers

Inspect:

Inspection item	What to check
Pump suction strainer	Clean, not collapsed, correct mesh
DP across suction strainer	No abnormal restriction
Debris type	Rust, gasket, paint, weld slag, sludge, fibers
Suction piping	No air leaks, loose flanges, vortexing from low level

Blocked suction strainers can cause pump cavitation, unstable pressure, low flow, and bearing damage.

6.3 Offline Filtration and Purification

Inspect:

System	Inspection points
Kidney-loop filter	Flow rate, DP, element condition, correct connection
Vacuum dehydrator	Water removal rate, vacuum level, heater, seals, discharge cleanliness
Centrifuge	Bowl condition, water/sludge discharge, correct temperature and flow
Coalescer	Element condition, water drain, surfactant contamination
Electrostatic cleaner	Cleanliness trend, varnish trend, collector condition
Resin/varnish-removal unit	Media saturation, MPC trend, pressure drop
Magnetic separator	Ferrous debris amount and morphology

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7. Oil Cooler and Heat Exchanger Inspections

Oil coolers are essential because oil temperature affects viscosity, bearing temperature, oxidation rate, and varnish tendency.

Inspect:

Inspection item	What to check
Oil inlet/outlet temperature	Cooler duty and temperature drop
Cooling-water inlet/outlet temperature	Water-side performance
Oil pressure vs water pressure	Helps assess leak direction risk
Cooler fouling	Reduced heat transfer, rising oil temperature
Tube leaks	Water in oil or oil in cooling water
Cooler bypass valve	Proper position and operation
Temperature-control valve	Stable control, no hunting
Standby cooler	Clean, isolated correctly, ready for transfer
Cooler transfer valve	Transfer without pressure loss
Vents and drains	No trapped air, water, or sludge
Corrosion	Tube, shell, gasket, channel cover condition
Hydrotest/pressure test	During outage or suspected leak

Water contamination after a cooler should trigger immediate investigation. Check water content, reservoir bottom drain, cooler pressure balance, and oil appearance.

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8. Pump and Standby/Emergency Oil System Inspections

Most critical turbomachinery uses multiple oil pumps: main pump, auxiliary pump, standby pump, emergency DC pump, shaft-driven pump, or jacking-oil pump depending on design.

Inspect:

Pump/system	What to inspect
Main lube-oil pump	Discharge pressure, vibration, noise, seal leakage, motor current
Auxiliary/standby pump	Auto-start logic, manual start, pressure response
Emergency DC pump	Battery condition, charger, start test, flow/pressure response
Shaft-driven pump	Coupling, suction condition, output at speed
Pre-lube pump	Required pre-start oil pressure and timer
Post-lube pump	Coastdown and cooldown lubrication
Jacking/lift-oil pump	High-pressure lift, rotor lift confirmation, interlocks
Relief valve	Correct set pressure, no leakage
Check valves	No reverse flow, no chatter
Pump coupling	Alignment, guard, lubrication, wear
Pump suction	Adequate NPSH, no vortexing, no air ingress
Pump baseplate	Soft foot, looseness, vibration

A standby pump that has not been tested is not a reliable standby pump. Auto-start should be tested under controlled procedures approved by the site.

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9. Piping, Valves, and Distribution Inspections

The distribution system can create lubrication failures even when the oil and pumps are healthy.

Inspect:

Area	What to check
Supply piping	Leaks, vibration, support, corrosion, correct valve lineup
Return piping	Correct slope, no flooding, no backpressure, no foaming
Drain headers	Proper venting, no restrictions, no submerged returns causing aeration
Orifices/restrictors	Correct size, clean, installed in correct direction
Control valves	Stable pressure/temperature control
Relief valves	Correct setpoint and discharge routing
Check valves	Proper seating, no leakage or chatter
Flexible hoses	Age, cracks, swelling, rubbing, pressure rating
Dead legs	Possible contamination pockets
Flushing connections	Capped, clean, documented
Sight-flow indicators	Clear, not stained or blocked
Instrument impulse lines	Not plugged, leaking, or air-bound

After maintenance, always verify valve lineup. Many lube-oil incidents occur after a filter change, cooler transfer, flushing activity, or valve misposition.

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10. Bearing Inspections

Bearings are the most important lubricated components in turbomachinery. Most large turbomachines use hydrodynamic journal bearings and thrust bearings. Hydrodynamic bearings depend on a pressure field created in the lubricant film; inspection of babbitt or whitemetal surfaces can reveal problems in the machine, bearing, or lubrication system. (MDPI)

10.1 Online Bearing Inspections

Inspect during operation:

Parameter	What it may indicate
Bearing metal temperature	Oil starvation, overload, misalignment, varnish, clearance loss
Bearing drain temperature	Heat removal effectiveness
Shaft vibration	Oil whirl/whip, imbalance, rub, bearing instability
Shaft position/orbit	Bearing load, alignment, rubs, instability
Axial position	Thrust bearing condition, thrust load change
Oil supply pressure	General lube supply health
Oil flow	Local starvation or blockage
Bearing drain appearance	Metal flakes, discoloration, foam, water
Noise	Wiping, rubs, gear/bearing distress

API 670 covers machinery protection systems measuring radial shaft vibration, casing vibration, shaft axial position, shaft speed, surge detection, overspeed, and critical temperatures such as bearing metal temperature. (American Petroleum Institute)

10.2 Shutdown Bearing Inspections

When bearings are opened, inspect:

Bearing area	Inspection details
Babbitt surface	Wiping, scoring, polishing, fatigue cracks, pitting, corrosion
Oil grooves and feed holes	Blockage, varnish, sludge, machining burrs
Tilting pads	Free movement, pivot wear, pad thickness, offset, surface condition
Thrust pads	Load pattern, equalization, leveling plates, pivot marks
Journal surface	Scoring, heat discoloration, roughness, deposits
Thrust collar	Runout, surface finish, scoring, heat marks
Bearing clearance	Diametral clearance, side clearance, crush, preload
Bearing housing	Fretting, distortion, dirt, oil drain restriction
Thermocouples/RTDs	Location, damage, calibration, wire condition
Seals near bearing	Labyrinth rubs, oil leakage, carbonization
Electrical damage	Frosting, pitting, arc marks; check grounding/shaft brushes
Varnish deposits	Brown/orange/black films on pads, journals, housings
Embedded debris	Dirt, metal, fibers, rust particles in babbitt

10.3 Common Bearing Findings and Lubrication Causes

Finding	Possible lubrication-related cause
Wiped babbitt	Oil starvation, low viscosity, low pressure, high temperature, start/stop without lift oil
Circumferential scoring	Dirt or hard particles in oil
Local hot spot	Restricted oil flow, misalignment, overload, varnish
Fatigue cracking	High dynamic load, vibration, poor oil film support
Corrosion	Water, acidic oil, additive depletion
Cavitation erosion	Poor oil supply geometry or pressure fluctuations
Electrical pitting	Shaft current discharging through oil film
Varnish film	Oxidized oil, thermal stress, poor varnish control
Blue/brown heat marks	Excessive temperature or oil starvation
Uneven pad loading	Misalignment, thrust load issue, equalizer problem

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11. Gearbox and Gear-Coupling Inspections

Many turbomachinery trains include speed reducers, increasers, accessory gearboxes, turning gears, and oil-lubricated couplings.

Inspect:

Component	Inspection points
Gear teeth	Pitting, scoring, scuffing, polishing, abnormal contact pattern
Spray nozzles	Blockage, correct orientation, correct spray pattern
Gear mesh oil supply	Adequate flow and pressure
Magnetic plugs	Ferrous debris quantity and shape
Gearbox sump	Sludge, water, varnish, foam
Gearbox filters	DP, debris, collapse, bypass
Bearings	Temperature, vibration, end float, wear
Seals	Leakage, hardening, air ingress
Breather	Clean, dry, correctly sized
Coupling teeth	Wear, fretting, sludge, water separation
Coupling oil level	Correct fill and drain condition
Turning gear	Lubrication during start/stop, clutch condition

Gear couplings can act like centrifuges, collecting heavier solids and water in the tooth area. For this reason, coupling oil condition, cleanliness, and drain inspections are important.

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12. Seal-Oil System Inspections

Oil-type shaft seals are common in some compressors and process turbomachinery. API 614 includes oil-type shaft-sealing systems but excludes dry gas seal systems and fuel systems. (standards.globalspec.com)

Inspect:

Inspection item	What to check
Seal-oil supply pressure	Correct pressure above process gas pressure
Differential-pressure regulator	Stable operation
Seal-oil flow	Adequate flow to each seal
Seal-oil temperature	Within OEM range
Seal-oil filters	DP, element condition
Seal-oil cooler	Temperature control and leaks
Degassing tank	Proper level, venting, gas removal
Overhead tank / rundown tank	Correct level and emergency capacity
Traps and drains	No blockage, correct discharge
Process contamination	Gas, condensate, sour gas, chemicals in oil
Oil carryover	Excess oil entering process side
Seal leakage	High leakage, abnormal trend
Separation/purification	Vacuum degassing, centrifuge, coalescer performance

Process contamination of seal oil can degrade the lubricant, increase corrosion risk, and contaminate the main lube system if systems are connected.

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13. Control-Oil and Hydraulic System Inspections

Some turbines and compressors use oil for governors, trip systems, inlet guide vanes, variable stator vanes, steam valves, fuel valves, or compressor anti-surge systems.

Inspect:

Component	Inspection points
Control-oil pump	Pressure, flow, standby logic
Servo valves	Sticking, sluggish response, varnish sensitivity
Trip valves	Stroke test, response time, cleanliness
Actuators	Leakage, smooth movement, correct position feedback
Accumulators	Pre-charge, bladder condition, isolation valves
Fine filters	DP, correct micron rating
Solenoid valves	Energize/de-energize test, leakage
Hydraulic lines	Leaks, vibration, rubbing
Oil cleanliness	Often stricter than bearing oil cleanliness
Varnish potential	Important because servo valves have tight clearances

Control-oil systems are highly sensitive to varnish. A turbine may have acceptable bearing temperatures but still trip or fail to start because varnish causes servo-valve sticking.

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14. Jacking-Oil / Lift-Oil System Inspections

Large turbines and compressors may use high-pressure jacking oil to lift the rotor during turning gear operation, startup, and shutdown.

Inspect:

Inspection point	What to check
Jacking-oil pump	Pressure, flow, noise, vibration
Lift pressure	Correct pressure at each bearing
Rotor lift	Verified by displacement or OEM method
High-pressure hoses	Condition, rating, leakage
Filters	Cleanliness and DP
Check valves	No backflow
Interlocks	Machine cannot roll without required lift oil, where applicable
Bearing pads	No wiping from failed lift oil
Start/stop sequence	Pre-lube and lift-oil timing correct

Failure of lift oil during low-speed rotation can wipe bearings even if the main lube-oil system is healthy.

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15. Oil-Mist, Air-Oil, and Grease Lubrication Inspections

Some auxiliary bearings, small turbines, pumps, or gear units may use oil mist, air-oil, or grease instead of a full circulating oil system.

15.1 Oil-Mist Systems

Inspect:

Inspection item	What to check
Mist generator	Oil level, air pressure, temperature
Header pressure	Stable and within design range
Reclassifiers	Correct type, not plugged
Piping slope	No oil pooling
Drains	Condensed oil removed
Bearing vents	Not blocked
Mist density	Correct for system
Air quality	Dry, clean instrument air
Alarm system	Low oil, low air, low pressure

15.2 Air-Oil Systems

Inspect:

Inspection item	What to check
Metering units	Correct oil delivery rate
Air pressure	Correct atomizing/transport pressure
Lines	No blockage, leaks, oil pooling
Nozzles	Correct aim at bearing or gear contact
Timer/controller	Correct cycle
Reservoir	Correct oil, no contamination

15.3 Grease-Lubricated Auxiliary Bearings

Inspect:

Inspection item	What to check
Grease type	Correct thickener and base oil
Quantity	Avoid under-greasing and over-greasing
Regreasing interval	Based on speed, temperature, bearing size
Purge path	Old grease can exit
Bearing temperature	High temperature may indicate over-grease or starvation
Grease condition	Hardening, bleeding, contamination
Seals	Prevent dirt/water ingress

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16. Instrumentation and Protection-System Inspections

Lubrication failure can develop quickly, so protection devices must be reliable.

Inspect and test:

Instrument	Inspection
Oil pressure transmitters	Calibration, impulse line condition, alarm/trip setpoint
Pressure switches	Functional test, repeatability
Temperature RTDs/thermocouples	Calibration, wiring, location
Bearing metal temperature probes	Channel check, alarm/trip logic
Oil level transmitters	Calibration, high/low alarms
Flow switches/meters	Proof test, correct range
Filter DP transmitters	Calibration and alarm
Moisture sensors	Calibration and correlation with lab data
Particle counters	Trend validation and sample correlation
Vibration probes	Gap voltage, calibration, probe condition
Axial position probes	Setpoint, calibration, thrust reference
Speed probes	Signal quality, overspeed logic
Alarm/trip bypasses	Controlled, documented, removed after work
Event recorder	Time synchronization and data retrieval

API 670 is the key standard normally referenced for machinery protection systems, including vibration, shaft axial position, speed, surge detection, overspeed, and critical machine temperatures such as bearing metal temperature. (American Petroleum Institute)

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17. Commissioning and Pre-Startup Lubrication Inspections

Before a new or overhauled turbomachine is started, lubrication inspections should be more intensive.

Inspect:

Area	Pre-start inspection
Oil type	Correct oil charged; compatibility verified
Reservoir	Internally clean, dry, no rags, tools, weld slag, rust
Piping	Flushed, cleaned, no dead-leg debris
Filters	Correct elements installed, clean housings
Temporary strainers	Installed/removed according to flushing plan
Flushing records	Flow, temperature, duration, cleanliness result
Oil sample	Meets target cleanliness, water, viscosity, chemistry
Pumps	Main, auxiliary, standby, emergency tested
Coolers	Leak tested, vented, correct lineup
Bearings	Pre-lubed, correct clearances, thermocouples connected
Jacking oil	Rotor lift verified
Turning gear	Lubrication confirmed
Alarms/trips	Low pressure, high temperature, level, DP tested
Valve lineup	Independently verified
Oil heaters	Functional if required
Accumulators	Pre-charge verified
Documentation	Punch list closed before start

Commissioning cleanliness is critical. The Turbomachinery Symposium paper specifically warns that improper cleaning of a new system before operation can result in continuing problems for years.

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18. Shutdown and Overhaul Inspections

During planned outages, perform inspections that cannot be done while running.

18.1 Reservoir Internal Inspection

Check:

Inspection item	What to look for
Sludge	Bottom deposits, oxidation products
Water pockets	Rust, free water, microbial growth
Varnish	Sticky brown/orange films
Paint/coating	Peeling, blistering, incompatibility
Rust	Internal corrosion
Baffles	Damage, looseness, poor welds
Suction area	Debris near pump suction
Return area	Foaming marks, splash patterns
Heater	Deposits, overheating marks
Manway	Gasket condition
Drains	Clear and functional

18.2 Bearing Inspection

Inspect all journal and thrust bearings as described earlier. Record photographs, dimensions, clearances, and deposit locations.

18.3 Cooler Inspection

Open and inspect as required:

Inspection item	What to check
Tube bundle	Fouling, corrosion, leaks
Tube sheet	Cracking, erosion
Gaskets	Hardening, leakage paths
Oil side	Sludge, varnish
Water side	Scale, biological fouling, corrosion
Pressure test	Confirm integrity

18.4 Pump Inspection

Inspect:

Area	What to check
Impeller/gears/screws	Wear, scoring, cavitation
Clearances	Internal wear
Shaft seal	Leakage path
Coupling	Wear and alignment
Relief valve	Seat condition
Check valve	Seat and disc condition
Motor	Alignment, bearings, insulation condition

18.5 Piping Inspection

Inspect:

Area	What to check
Return lines	Sludge, poor slope, restrictions
Supply lines	Cleanliness, corrosion
Orifices	Plugging or erosion
Dead legs	Sediment accumulation
Hoses	Replace if aged or damaged
Supports	Looseness, cracked brackets

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19. Failure-Response Inspections

When a lubrication-related alarm or trip occurs, inspect systematically rather than replacing parts blindly.

19.1 High Bearing Temperature

Check:

1. Oil supply pressure and flow.
2. Oil inlet temperature.
3. Cooler performance.
4. Bearing drain temperature.
5. Recent oil-analysis trends.
6. Filter DP.
7. Bearing vibration and shaft position.
8. Oil viscosity and water content.
9. Varnish potential.
10. Bearing thermocouple accuracy.
11. Bearing clearance and pad condition during outage.

19.2 Low Oil Pressure Trip

Check:

1. Reservoir level.
2. Pump status.
3. Pump suction strainer.
4. Relief valve position.
5. Filter blockage or wrong valve lineup.
6. Header leak.
7. Pressure transmitter calibration.
8. Standby pump auto-start.
9. Accumulator condition.
10. Air entrainment or foaming.

19.3 High Filter Differential Pressure

Check:

1. Oil temperature and viscosity.
2. Filter element condition.
3. Water contamination.
4. Varnish/sludge loading.
5. Wear debris.
6. Incorrect element rating.
7. Collapsed or blocked element.
8. Bypass valve condition.
9. Recent maintenance contamination.

19.4 Water in Oil

Check:

1. Oil cooler tube leak.
2. Steam seal leak.
3. Condensation from reservoir breathing.
4. Open or failed breather.
5. Water washing/cleaning ingress.
6. Seal-oil contamination.
7. Rainwater ingress through tank fittings.
8. Reservoir bottom drain.
9. Demulsibility test.
10. Karl Fischer water result.

19.5 Rising Wear Metals

Check:

1. Which metal is increasing: Fe, Cu, Pb, Sn, Cr, Al.
2. Bearing metallurgy.
3. Gear metallurgy.
4. Filter debris.
5. Magnetic plug debris.
6. Ferrography.
7. Vibration trend.
8. Bearing temperature trend.
9. Oil cleanliness.
10. Recent maintenance or flushing activity.

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20. Typical Inspection Frequency Matrix

Actual frequency must follow the OEM manual, plant criticality, duty cycle, and oil-analysis trend. A typical structure is:

Frequency	Inspections
Each shift / daily	Oil level, pressure, temperature, bearing temperatures, leaks, filter DP, cooler performance, pump status, vibration alarms, reservoir appearance
Daily / weekly	Drain reservoir bottom water, visual bottle sample, standby pump check, breather check, oil mist check, cooler water check
Monthly	Routine oil sample, filter inspection, valve lineup audit, pump vibration, instrument cross-check
Quarterly	Full oil analysis: viscosity, water, TAN/AN, particle count, spectroscopy, FTIR; review trends
Semiannual	Demulsibility, foam, air release, MPC, RULER/RPVOT as applicable; cooler performance test; trip/alarm proof tests
Annual	Instrument calibration, reservoir inspection if possible, cooler cleaning if needed, standby/emergency system test
Major outage	Internal tank cleaning, bearing inspection, gear inspection, pump overhaul, cooler pressure test, piping inspection, flushing if contamination exists
After failure/contamination	Emergency oil sample, filter cut-open, reservoir drain, root-cause inspection, bearing/gear inspection as needed

STLE notes that basic turbine-oil testing may be monthly or quarterly, while additional tests may be performed at longer intervals such as semiannually or annually, depending on the application and recommendations. (stle.org)

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21. Summary Checklist of Lubrication-Related Inspections

A comprehensive turbomachinery lubrication inspection program should include:

1. Lubricant specification and compatibility inspection.
2. Oil storage and handling inspection.
3. Oil sampling system inspection.
4. Routine oil-analysis inspection.
5. Advanced varnish and oxidation testing.
6. Reservoir level, cleanliness, water, sludge, and breather inspection.
7. Lube-oil pump inspection.
8. Standby and emergency pump inspection.
9. Jacking-oil system inspection.
10. Filter and strainer inspection.
11. Cooler and temperature-control inspection.
12. Piping, valve, orifice, and drain inspection.
13. Bearing metal temperature and drain-temperature inspection.
14. Journal bearing internal inspection.
15. Thrust bearing internal inspection.
16. Gear and gear-spray inspection.
17. Coupling lubrication inspection.
18. Seal-oil system inspection.
19. Control-oil and servo-valve inspection.
20. Oil mist, air-oil, or grease system inspection where applicable.
21. Online sensor and machinery-protection inspection.
22. Alarm, trip, and interlock testing.
23. Commissioning flushing and cleanliness inspection.
24. Shutdown internal inspection.
25. Failure-response and root-cause inspection.

The strongest lubrication programs combine operator rounds, oil analysis, instrumented protection, component inspection, and trend review. No single inspection method is enough by itself. Clean, dry, cool, chemically stable oil delivered at the correct pressure and flow is the core requirement for reliable turbomachinery operation.