ASTM D4378-24

Standard Practice for In-Service Monitoring of Mineral Turbine Oils for Steam, Gas, and Combined Cycle Turbines

SIGNIFICANCE AND USE
4.1 This practice is intended to assist the user, in particular the power-plant operations and maintenance departments, to maintain effective lubrication of all parts of the turbine and guard against the onset of problems associated with oil degradation and contamination. The values of the various test parameters mentioned in this practice are purely indicative. In fact, for proper interpretation of the results, many factors, such as type of equipment, operation workload, design of the lubricating oil circuit, and top-up level, should be taken into account.
SCOPE
1.1 This practice covers the requirements for the effective monitoring of mineral turbine oils in service in steam and gas turbines, as individual or combined cycle turbines, used for power generation. This practice includes sampling and testing schedules to validate the condition of the lubricant through its life cycle and by ensuring required improvements to bring the present condition of the lubricant within the acceptable targets. This practice is not intended for condition monitoring of lubricants for auxiliary equipment; it is recommended that the appropriate practice be consulted (see Practice D6224).  
1.2 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.3 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 29-Feb-2024
• ICS: 27.040 - Gas and steam turbines. Steam engines
• ICS: 75.100 - Lubricants, industrial oils and related products
• Technical Committee: D02 - Petroleum Products, Liquid Fuels, and Lubricants
• Drafting Committee: D02.C0.01 - Turbine Oil Monitoring, Problems and Systems

Relations

• Replaces: ASTM D4378-22 - Standard Practice for In-Service Monitoring of Mineral Turbine Oils for Steam, Gas, and Combined Cycle Turbines
• Effective Date: 01-Mar-2024
• Refers: ASTM D445-24 - Standard Test Method for Kinematic Viscosity of Transparent and Opaque Liquids (and Calculation of Dynamic Viscosity)
• Effective Date: 01-Apr-2024
• Refers: ASTM D1500-24 - Standard Test Method for ASTM Color of Petroleum Products (ASTM Color Scale)
• Effective Date: 01-Mar-2024
• Refers: ASTM D445-23 - Standard Test Method for Kinematic Viscosity of Transparent and Opaque Liquids (and Calculation of Dynamic Viscosity)
• Effective Date: 01-Nov-2023
• Refers: ASTM D8112-22 - Standard Guide for Obtaining In-Service Samples of Turbine Operation Related Lubricating Fluid
• Effective Date: 01-May-2022
• Refers: ASTM D1500-12(2017) - Standard Test Method for ASTM Color of Petroleum Products (ASTM Color Scale)
• Effective Date: 01-Oct-2017
• Referred By: ASTM D6224-23 - Standard Practice for In-Service Monitoring of Lubricating Oil for Auxiliary Power Plant Equipment
• Effective Date: 01-Mar-2024
• Referred By: ASTM D6439-23 - Standard Guide for Cleaning, Flushing, and Purification of Steam, Gas, and Hydroelectric Turbine Lubrication Systems
• Effective Date: 01-Mar-2024
• Referred By: ASTM D7720-21 - Standard Guide for Statistically Evaluating Measurand Alarm Limits when Using Oil Analysis to Monitor Equipment and Oil for Fitness and Contamination
• Effective Date: 01-Mar-2024
• Referred By: ASTM D8506-23 - Standard Guide for Microbial Contamination and Biodeterioration in Turbine Oils and Turbine Oil Systems
• Effective Date: 01-Mar-2024
• Referred By: ASTM D8112-24 - Standard Guide for Obtaining In-Service Samples of Turbine Operation Related Lubricating Fluid
• Effective Date: 01-Mar-2024
• Referred By: ASTM D7843-21 - Standard Test Method for Measurement of Lubricant Generated Insoluble Color Bodies in In-Service Turbine Oils using Membrane Patch Colorimetry
• Effective Date: 01-Mar-2024
• Referred By: ASTM D8185-23 - Standard Guide for In-Service Lubricant Viscosity Measurement
• Effective Date: 01-Mar-2024
• Referred By: ASTM D6971-22 - Standard Test Method for Measurement of Hindered Phenolic and Aromatic Amine Antioxidant Content in Non-zinc Turbine Oils by Linear Sweep Voltammetry
• Effective Date: 01-Mar-2024
• Referred By: ASTM D6810-22 - Standard Test Method for Measurement of Hindered Phenolic Antioxidant Content in Non-Zinc Turbine Oils by Linear Sweep Voltammetry
• Effective Date: 01-Mar-2024

Overview

ASTM D4378-24 is the recognized standard practice for in-service monitoring of mineral turbine oils in steam, gas, and combined cycle turbines. Published by ASTM International, this standard guides power generation facilities in maintaining effective lubrication for critical turbine components. The aim is to safeguard turbine reliability, prevent lubrication failures, and mitigate problems caused by oil degradation and contamination. By following ASTM D4378-24, power plant operations and maintenance professionals can implement a structured program for sampling, analysis, and corrective action throughout the lubricant lifecycle.

Key Topics

• Scope of Application
  • Applies to mineral turbine oils used in steam, gas, and combined cycle turbines for power generation.
  • Provides guidance for sampling, testing, and monitoring in-service lubricants, excluding auxiliary equipment (see ASTM D6224 for auxiliaries).
• Purpose and Benefits
  • Assists users in validating oil condition, tracking trends, and identifying the onset of oil degradation or contamination.
  • Aids in maximizing equipment uptime, ensuring long service life, and reducing unscheduled maintenance.
• Sampling and Testing
  • Recommends proper sampling locations and methods to attain representative samples from oil storage, delivery, and in-service equipment.
  • Outlines testing schedules (e.g., visual inspection, viscosity, acid number, oxidation stability) for new oils upon delivery, post-circulation, and during routine operation.
  • Emphasizes the importance of baseline sampling to enable accurate trend analysis.
• Oil Properties Monitored
  • Key properties include viscosity, oxidation stability, resistance to sludge and varnish formation, cleanliness, anticorrosion protection, water separability, and foaming tendencies.
  • Monitoring these properties helps ensure continued oil performance and prevent lubrication-related failures.
• Operational and Environmental Considerations
  • Details how factors such as equipment design, startup condition, contamination sources, oil makeup rates, and storage practices impact oil life.
  • Encourages safe, health-conscious, and environmentally responsible handling as part of good maintenance practices.

Applications

ASTM D4378-24 is highly relevant in the power generation industry, particularly in:

• Steam and Gas Turbine Power Plants
  • Enables operations and maintenance teams to systematically assess lubricant health, prolong oil service life, and optimize turbine reliability.
• Combined Cycle Facilities
  • Addresses specific needs where both steam and gas turbines operate jointly, with either shared or separate lubrication circuits.
• Routine Oil Analysis Programs
  • Serves as the foundational framework for oil testing laboratories and in-house condition monitoring programs.
  • Supports proactive maintenance by trending test results, identifying abnormal conditions, and facilitating informed decision-making regarding oil replacement or corrective action.
• Supplier Quality Assurance
  • Provides objective criteria for acceptance of new oils and ensures compliance with manufacturers’ and end users’ quality standards.

Related Standards

Using ASTM D4378-24 in conjunction with other standards enhances the effectiveness of in-service oil monitoring. Key related ASTM and ISO standards include:

• ASTM D4057: Manual Sampling of Petroleum and Petroleum Products
• ASTM D6224: In-Service Monitoring of Lubricating Oil for Auxiliary Power Plant Equipment
• ASTM D943 / D2272: Oxidation Stability of Steam Turbine Oils
• ASTM D5185: Multielement Determination of Used and Unused Lubricating Oils by ICP-AES
• ASTM D8112: Obtaining In-Service Samples of Turbine Lubricating Fluid
• ASTM D6439: Cleaning and Purification of Turbine Lubrication Systems
• ISO 4406 / ISO 11500: Particulate Contamination Measurement and Coding

By following ASTM D4378-24 and the referenced test methods, power generation facilities can ensure superior turbine performance, reduce unexpected downtime, and maintain compliance with industry best practices in lubricant management.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: D4378 − 24
Standard Practice for
In-Service Monitoring of Mineral Turbine Oils for Steam,
Gas, and Combined Cycle Turbines
This standard is issued under the fixed designation D4378; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
INTRODUCTION
The in-service monitoring of turbine oils has long been recognized by the power-generation
industry as being necessary to ensure long, trouble-free operation of turbines.
The two main types of stationary turbines used for power generation are steam and gas turbines; the
turbines can be used as individual turbines, or can be configured as combine cycle turbines. Combined
cycle turbines are of two types; the first type connects a gas turbine with a steam turbine, with separate
lubricant circuits, and the second type mounts a steam and a gas turbine on the same shaft and has a
common lubricant circuit. The lubrication requirements are quite similar but there are important
differences in that gas turbine oils are subjected to significantly higher localized “hot spot”
temperatures and water contamination is less likely. Steam turbine oils are normally expected to last
for many years. In some turbines up to 20 years of service life has been obtained. Gas turbine oils, by
comparison, have a shorter service life from 2 to 5 years depending on severity of the operating
conditions. One of the benefits of the gas turbine is the ability to respond quickly to electrical power
generation dispatching requirements. Consequently, a growing percentage of modern gas turbines are
being used for peaking or cyclic duty (frequent unit stops and starts) subjects the lubricant to a wide
range of temperatures from ambient conditions to normal operating temperatures, which put additional
stresses on the lubricant.
This practice is designed to assist the user to validate the condition of the lubricant through its life
cycle by carrying out a meaningful program of sampling and testing of oils in service. This practice
is performed in order to collect data and monitor trends which suggest any signs of lubricant
deterioration and to ensure a safe, reliable, and cost-effective operation of the monitored plant
equipment.
1. Scope* 1.2 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
1.1 This practice covers the requirements for the effective
responsibility of the user of this standard to establish appro-
monitoring of mineral turbine oils in service in steam and gas
priate safety, health, and environmental practices and deter-
turbines, as individual or combined cycle turbines, used for
mine the applicability of regulatory limitations prior to use.
power generation. This practice includes sampling and testing
1.3 This international standard was developed in accor-
schedules to validate the condition of the lubricant through its
dance with internationally recognized principles on standard-
life cycle and by ensuring required improvements to bring the
ization established in the Decision on Principles for the
present condition of the lubricant within the acceptable targets.
Development of International Standards, Guides and Recom-
This practice is not intended for condition monitoring of
mendations issued by the World Trade Organization Technical
lubricants for auxiliary equipment; it is recommended that the
Barriers to Trade (TBT) Committee.
appropriate practice be consulted (see Practice D6224).
2. Referenced Documents
2.1 ASTM Standards:
This practice is under the jurisdiction of ASTM Committee D02 on Petroleum
Products, Liquid Fuels, and Lubricants and is the direct responsibility of Subcom-
mittee D02.C0.01 on Turbine Oil Monitoring, Problems and Systems. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved March 1, 2024. Published March 2024. Originally contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
approved in 1984. Last previous edition approved in 2022 as D4378 – 22. DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/D4378-24. the ASTM website.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D4378 − 24
D92 Test Method for Flash and Fire Points by Cleveland Antioxidant Content in Non-Zinc Turbine Oils by Linear
Open Cup Tester Sweep Voltammetry
D93 Test Methods for Flash Point by Pensky-Martens D6971 Test Method for Measurement of Hindered Phenolic
Closed Cup Tester and Aromatic Amine Antioxidant Content in Non-zinc
D130 Test Method for Corrosiveness to Copper from Petro- Turbine Oils by Linear Sweep Voltammetry
leum Products by Copper Strip Test D7042 Test Method for Dynamic Viscosity and Density of
D445 Test Method for Kinematic Viscosity of Transparent Liquids by Stabinger Viscometer (and the Calculation of
and Opaque Liquids (and Calculation of Dynamic Viscos- Kinematic Viscosity)
ity) D7094 Test Method for Flash Point by Modified Continu-
D664 Test Method for Acid Number of Petroleum Products ously Closed Cup (MCCCFP) Tester
by Potentiometric Titration D7155 Practice for Evaluating Compatibility of Mixtures of
D665 Test Method for Rust-Preventing Characteristics of Turbine Lubricating Oils
Inhibited Mineral Oil in the Presence of Water D7464 Practice for Manual Sampling of Liquid Fuels, As-
D892 Test Method for Foaming Characteristics of Lubricat- sociated Materials and Fuel System Components for
ing Oils Microbiological Testing
D943 Test Method for Oxidation Characteristics of Inhibited D7647 Test Method for Automatic Particle Counting of
Mineral Oils Lubricating and Hydraulic Fluids Using Dilution Tech-
D974 Test Method for Acid and Base Number by Color- niques to Eliminate the Contribution of Water and Inter-
Indicator Titration fering Soft Particles by Light Extinction
D1401 Test Method for Water Separability of Petroleum Oils D7669 Guide for Practical Lubricant Condition Data Trend
and Synthetic Fluids Analysis
D1500 Test Method for ASTM Color of Petroleum Products D7687 Test Method for Measurement of Cellular Adenosine
(ASTM Color Scale) Triphosphate in Fuel and Fuel-associated Water With
D2272 Test Method for Oxidation Stability of Steam Tur- Sample Concentration by Filtration
bine Oils by Rotating Pressure Vessel D7720 Guide for Statistically Evaluating Measurand Alarm
D2273 Test Method for Trace Sediment in Lubricating Oils Limits when Using Oil Analysis to Monitor Equipment
(Withdrawn 2022) and Oil for Fitness and Contamination
D2422 Classification of Industrial Fluid Lubricants by Vis- D7843 Test Method for Measurement of Lubricant Gener-
cosity System ated Insoluble Color Bodies in In-Service Turbine Oils
D2668 Test Method for 2,6-di-tert-Butyl- p-Cresol and 2,6- using Membrane Patch Colorimetry
di-tert-Butyl Phenol in Electrical Insulating Oil by Infra- D7978 Test Method for Determination of the Viable Aerobic
red Absorption Microbial Content of Fuels and Associated Water—
D3427 Test Method for Air Release Properties of Hydrocar- Thixotropic Gel Culture Method
bon Based Oils D8072 Classification for Reporting Solids and Insoluble
D4057 Practice for Manual Sampling of Petroleum and Water Contamination of Hydrocarbon-Based Petroleum
Petroleum Products Products When Analyzed by Imaging Instrumentation
D4175 Terminology Relating to Petroleum Products, Liquid D8112 Guide for Obtaining In-Service Samples of Turbine
Fuels, and Lubricants Operation Related Lubricating Fluid
D4898 Test Method for Insoluble Contamination of Hydrau- D8506 Guide for Microbial Contamination and Biodeterio-
lic Fluids by Gravimetric Analysis ration in Turbine Oils and Turbine Oil Systems
D5185 Test Method for Multielement Determination of F311 Practice for Processing Aerospace Liquid Samples for
Used and Unused Lubricating Oils and Base Oils by Particulate Contamination Analysis Using Membrane Fil-
Inductively Coupled Plasma Atomic Emission Spectrom- ters
etry (ICP-AES) F312 Test Methods for Microscopical Sizing and Counting
D6224 Practice for In-Service Monitoring of Lubricating Oil Particles from Aerospace Fluids on Membrane Filters
for Auxiliary Power Plant Equipment
2.2 International Organization for Standardization Stan-
D6304 Test Method for Determination of Water in Petro-
dards:
leum Products, Lubricating Oils, and Additives by Cou-
ISO 4406 Hydraulic fluid power—Fluids—Method for Cod-
lometric Karl Fischer Titration
ing the Level of Contamination by Solid Particles, Second
D6439 Guide for Cleaning, Flushing, and Purification of
Edition, 1999
Steam, Gas, and Hydroelectric Turbine Lubrication Sys-
ISO 4407 Hydraulic Fluid Power—Fluid Contamination—
tems
Determination of Particulate Contamination by Counting
D6450 Test Method for Flash Point by Continuously Closed
Method Using an Optical Microscope, Second Edition,
Cup (CCCFP) Tester
D6810 Test Method for Measurement of Hindered Phenolic
ISO 11500 Hydraulic Fluid Power—Determination of the
3 4
The last approved version of this historical standard is referenced on Available from American National Standards Institute (ANSI), 25 W. 43rd St.,
www.astm.org. 4th Floor, New York, NY 10036, http://www.ansi.org.
D4378 − 24
Particulate Contamination Level of a Liquid Sample by into the valve for the purpose of opening the valve and
Automatic Particle Counting Using the Light Extinction, allowing fluid to flow out.
Second Edition, 2008
3.2.12 sample valve sampling, v—to obtain a sample from
ISO 11171 Hydraulic Fluid Power—Calibration of Auto-
either pressurized or non pressurized lines or reservoirs.
matic Particle Counters for Liquids
3.2.12.1 Discussion—When sampling non-pressurized res-
ervoirs this sampling method usually applies a vacuum gener-
3. Terminology
ating device and sampling tubing to extract a sample into a
3.1 For definitions of terms used in this practice, refer to
sampling container from a strategically located sampling valve.
Terminology D4175.
When sampling pressurized reservoirs or lines, this sampling
3.2 Definitions of Terms Specific to This Standard:
method is completed by using system pressure to force
3.2.1 bulk oil tote, n—any container for lubrication or
lubricating fluid into a sampling container through a sampling
control fluid with working volume approximately 1000 L to
valve.
1300 L designed for fluid storage at atmospheric pressure.
3.2.13 vacuum generating device, n—a pump used to create
3.2.2 continuous sampling loop, n—a limited flow of fluid
a low pressure in a sample container to cause fluid to move
from a point in a pressurized system to a point of lower
from a non-pressurized reservoir to the container through
pressure used to decrease required purge fluid and sample time
disposable tubing.
during the sampling process.
3.2.14 weighted drop tube device, n—a mass attached to a
3.2.3 disposable sample tubing, n—any single-use flexible
piece of steel or stainless steel tubing with a method to attach
plastic tubing used to transfer fluid during the sampling
disposable sampling tubing to the steel or stainless steel tubing.
process.
3.2.14.1 Discussion—This device is used during drop tube
3.2.4 drain sampling, n—a method of sampling used fluid
sampling.
for non-pressurized reservoirs or lines occurring when the
lubricating fluid is being drained from the reservoir during a
4. Significance and Use
fluid change.
4.1 This practice is intended to assist the user, in particular
3.2.4.1 Discussion—As part of a fluid change, the drain plug
the power-plant operations and maintenance departments, to
is removed to allow the fluid to drain into an appropriate
maintain effective lubrication of all parts of the turbine and
container under gravity. Mid way through the draining, a
guard against the onset of problems associated with oil
sample bottle is filled by placing it in the fluid stream and once
degradation and contamination. The values of the various test
filled immediately capped.
parameters mentioned in this practice are purely indicative. In
3.2.5 drop tube sampling, n—a method of sampling used
fact, for proper interpretation of the results, many factors, such
fluid for non-pressurized reservoirs when sampling is com-
as type of equipment, operation workload, design of the
pleted by dropping an appropriate length of sampling tubing
lubricating oil circuit, and top-up level, should be taken into
into the reservoir and using a vacuum generating device to
account.
extract the sample.
3.2.6 permanent sample tube, n—any tubing installed in a
5. Properties of Turbine Oils
reservoir or pipe used to extract a sample from a specific
5.1 Most turbine oils consist of a highly refined paraffinic
location within the system.
mineral oil compounded with oxidation and rust inhibitors with
3.2.7 purge, v—to remove the existing non-representative
a lesser number of turbines using a synthetic type of fluid.
fluid and contaminants from the sample valve and tubing
Depending upon the performance level desired, small amounts
during the sampling process.
of other additives such as metal deactivators, pour depressants,
3.2.8 remote access hose, n—any permanently installed
extreme pressure additives, and foam suppressants can also be
metallic or elastomeric tube or hose used to transfer fluid from
present. The turbine oil’s primary function is to provide
the system to a point outside the system to facilitate sampling.
lubrication and cooling of bearings and gears. In some equip-
3.2.9 reservoir, n—any equipment-based container that
ment designs, they also can function as a governor hydraulic
holds a volume of fluid, usually under atmospheric condition, fluid.
for use in the lubrication, sealing or control process.
5.2 New turbine oils should exhibit good resistance to
3.2.10 sample container, n—a clean, fresh plastic bottle
oxidation, inhibit sludge and varnish deposit formation, and
used for system fluid analysis (see Section 7).
provide adequate antirust, water separability, and non-foaming
3.2.11 sample valve, n—a system consisting of a male and properties. However, these oils cannot be expected to remain
female component used specifically for the extraction of a fluid unchanged during their use in the lubrication systems of
sample either by internal system pressure or by an externally turbines, as lubricating oils experience thermal and oxidative
generated vacuum. stresses which degrade the chemical composition of the oil’s
3.2.11.1 Discussion—The male component, referred to as a basestock and gradually deplete the oil’s additive package.
probe, may be for one time use or permanently attached to the Some deterioration can be tolerated without harming the safety
female component, referred to as a sample valve, is used by or efficiency of the system. Good monitoring procedures are
either threading the probe onto the valve or pushing the probe necessary to determine when the oil properties have changed
D4378 − 24
sufficiently to justify scheduling corrective actions which can quality standards. A sample of the oil should be taken after
be performed with little or no detriment to production sched- charging the new oil and circulating (24 h) to confirm the
ules. typical test data and to use as a baseline. This baseline should
act as a starting point for the physical and chemical properties
of the lubricant, and for future comparisons with used oil
6. Operational Factors Affecting Service Life
information. This is most important! Recommended tests for
6.1 The factors that affect the service life of turbine lubri-
new oil are given in the schedules of this practice (see Tables
cating oils are as follows: (1) type and design of system, (2)
1 and 2).
condition of system on startup, (3) original oil quality, (4)
6.1.3.3 When new turbine oil is to be mixed with a charge
system operating conditions, (5) contamination, (6) oil makeup
of a different composition prior checks should be made to
rate, and (7) handling and storage.
ensure no loss of expected properties due to incompatibility
6.1.1 Type and Design of System—Most modern turbine
(see lubricant suppliers’ specifications). These should include
lubricating systems are similar in design, especially for the
functional tests and checks for formation of insoluble materi-
larger units. For lubrication, the usual practice is to pressure-
als. Guidance for such compatibility testing can be referenced
feed oil directly from the main oil pump. The rest of the system
in Practice D7155 for evaluating compatibility of mixtures of
consists of a reservoir, oil cooler, strainer, piping and additional
turbine lubricating oils.
purification or filtration equipment, or a combination thereof.
6.1.4 System Operating Conditions:
Miscellaneous control and indicating equipment completes the
6.1.4.1 The most important factors affecting the anticipated
system.
service life of a given lubricating oil in a given turbine system
6.1.2 Condition of System on Start-up:
are the operating conditions within the system. Air (oxygen),
6.1.2.1 The individual components of a lubrication system
elevated operating temperatures, metals, and water (moisture)
are usually delivered on-site before the system is installed. The
are always present to some extent in these oil systems. These
length of on-site storage and means taken to preserve the
elements promote oil degradation and must consequently be
integrity of the intended oil wetted surfaces will determine the
recorded.
total amount of contamination introduced during this period,
6.1.4.2 Most turbine oil systems are provided with oil
the magnitude of the task of cleaning and flushing prior to use,
coolers to control temperature. In many cases, bulk oil tem-
and the detrimental effects of the contaminants. Guidance on
peratures are maintained so low, below 60 °C (140 °F), that
cleaning, flushing, and purification of steam, gas, and hydro-
moisture condensation can occur. Even with low bulk oil
electric turbine lubrication systems is provided in Guide D6439
temperatures, however, there can be localized hot spots such as
or may be sought from the equipment/lubricant supplier or
in bearings, at gas seals, and in throttle control mechanisms
other industry experts.
that can cause oil degradation and eventually cause system oil
6.1.2.2 Turbine oil system contamination prior to startup
to show signs of deterioration.
usually consists of preservatives, paint, rust particles, and the
6.1.4.3 Under the higher temperature conditions which are
various solids encountered during construction, which can
present in gas and steam turbines, oxidation of the oil can be
range from dust and dirt to rags, bottles, and cans. Their effect
accelerated by thermal-oxidative cracking leading to the pro-
on turbine oil systems is obvious. Incompatible fluid is also
duction of viscous resins and deposits particularly at the point
considered a contaminant and can include system flushing lube
of initiation.
oil from improper drain and clean-out.
6.1.5 Contamination:
6.1.2.3 Ongoing purification may be required to maintain
the in-service oils at an acceptable particle cleanliness level
6.1.5.1 Contamination of turbine oils is often the most
and water content level in the case of steam turbines for significant factor affecting oil service life. Contamination
reliable lubrication and control systems operation. In opera-
occurs both from outside the system and from within due to oil
tional systems, the emphasis is on the removal of contaminants degradation and moisture condensation or leaks. Development
that may be generated due to normal oil degradation or
of a clean turbine oil system on start-up or following mainte-
ingressed during operation and by malfunctions that occur nance is essential (following the steps in Guide D6439) prior to
during operation or contaminants that are introduced during
filling with the new oil. Once attained, the danger of external
overhaul, or both. contamination is less but should be guarded against. The oil
6.1.3 Original Oil Quality: can be contaminated by the introduction of different type oils,
which are of the wrong type or are incompatible with the
6.1.3.1 Use of a high-quality oil is the best assurance of
potentially long service life. Oils meeting recognized standards system oil. The oil supplier or the turbine manufacturer, or
both, should be consulted before additions are made (see
are generally available, and one that at least meets the
requirements of the turbine manufacturer shall be used. Careful Practice D7155).
oil storage, including labeling and rotation of lubricant 6.1.5.2 External contamination can enter the system through
containers, is vital to ensure proper use and prevent degrada-
bearing seals and vents. Internal contaminants are always being
tion of the physical, chemical, and cleanliness requirements of generated. These include water, dirt, fly ash, wear particles,
the lubricant throughout storage and dispensing.
insoluble particulate oil degradation products and microbial
6.1.3.2 It is advisable to obtain typical test data from the oil growth. From whatever source, contamination must be dealt
supplier. Upon receipt of the first oil charge, take a baseline with by monitoring oil condition and the use of purification
sample from the barrel, tote or tanker to ensure the oil meets devices such as filters, centrifuges, coalescers, and vacuum
D4378 − 24
TABLE 1 Minimum Sampling and Inspection Testing Schedule for New Oils
Schedule 1 New Oil-All Turbine Types
Samples:
(a) From transport or drums
(b) From storage tank
Tests Method Recommended Minimum Requirements for Acceptance of
New Oil as Received
Viscosity D445, D7042 Should meet Classification D2422 consistent with user
purchase specifications or manufacturer’s requirements.
Acid Number D974 or D664 Acceptance limits should be consistent with user purchase
specifications, new oil reference or manufacturer’s require-
ments or a combination thereof.
Appearance visual clear and bright
Water Content visual no free water
Color D1500 Acceptance limits should be consistent with user purchase
specifications, new oil reference or manufacturer’s require-
ments or a combination thereof.
Rust Test D665 Required for Steam and Single Shaft combined cycle tur-
bines. Should pass D665A for land-based turbines and
D665B for marine turbines.
Oxidation Stability or Inhibition D2272, D6810, Most suitable methods and acceptance limits should be
(RPVOT/Voltammetry/FTIR) D6971 consistent with user purchase specifications, new oil refer-
ence or manufacturer’s requirements or a combination
thereof.
Elemental Analysis (Suggested) D5185 Comparison with new oil reference on delivery may indi-
cate the presence of contaminants or mislabeled oil ship-
ment. (Other spectrochemical method may be substituted
for the ICP method.)
Air Release (Suggested) D3427 Comparison with new oil reference on delivery may indi-
cate the presence of contaminants or mislabeled oil ship-
ment.
Water Separation (Suggested) D1401 Steam Turbine and Combined Cycle Systems only.
Foam (Suggested) D892 Comparison with new oil reference on delivery may indi-
cate the presence of contaminants or mislabeled oil
shipment.
dehydrators on a regular basis. Contamination of the system oil 6.2 The combination of all of the preceding operational
is a valid reason to change oil or flush a unit, or both, to restore factors for a given turbine determines its severity level. Each
system cleanliness. unit is different and the equilibrium operating conditions for
6.1.6 Oil Makeup Rate—The amount and frequency of
each system must be determined in order to fix its severity
makeup oil added to the system plays a very significant part in
level; OEM operating and maintenance specifications can also
determining the life of a system oil charge. Makeup varies from
be used in setting the severity levels. The more severe a turbine
below 5 % per year to as much as 30 % in extreme cases. In
system, the shorter the service life for a given oil. A useful
turbines where makeup is relatively high compared to the oil
approach to determine the severity of a turbine is given in
degradation rate, the degree of degradation is compensated for
Appendix X1.
and long oil life can be expected. In turbines where the makeup
is very low (below 5 %), a truer picture of oil degradation is
7. Sampling
obtained. However, such a system should be carefully watched
7.1 General—When taking oil samples from storage tanks
since the oil life is dependent almost exclusively on its original
or equipment in service, it is important that the extracted
quality. In the United States, the average makeup is typically
sample is representative and is taken from a specified loca-
around 7 % to 10 % per year.
tion(s) to monitor the properties of the lubricant. Correct and
6.1.7 Handling and Oil Storage—Handling and dispensing
consistent sampling techniques are vital to achieve this. The
methods must ensure that the quality and the cleanliness of the
recommended guidelines for proper sampling technique and
lubricant meet the specifications required by the equipment.
sample handling techniques are part of Guide D8112. The user
Oils must be properly labeled to ensure proper selection and
should have written standard operating procedures to ensure
use. Proper stock rotation and storage methods must be
considered to prevent the possible degradation of the physical that samples are taken consistently according to good mainte-
nance practices. In addition to the Guide D8112 method the
and chemical properties of the lubricant during storage and
dispensing. following recommendations are to be considered:
D4378 − 24
A
TABLE 2 Minimum Sampling and Inspection Testing Schedule for New Oil Charge
Schedule 2 Installation of a New Oil Charge
Samples:
After 24 h circulation in Turbine
Retain approximately 4 L (1 gal)
Tests Method Recommended minimum requirements for assessment of
new oil charge
Viscosity D445, D7042 Should meet Classification D2422 consistent with user pur-
chase specifications or manufacturer’s requirements.
Acid Number D974 or D664 Should be consistent with user purchase specifications
and new oil reference.
Appearance visual clear and bright
Water Content visual no free water
Color D1500 Should be consistent with user purchase specifications
and new oil reference.
Particle Count--Cleanliness (after fil- F311 or F312 or user Definition of suitable cleanliness levels determined by par-
tration into equipment) defined ticle count distribution depends on turbine builder and user
requirements Filtration or centrifugation, or both of oil into
turbine and during in-service is recommended.
Oxidation Stability or Inhibition D2272, D6810, D6971 Should be consistent with user purchase specifications
B
(RPVOT/Voltammetry/FTIR) and new oil reference.
Elemental Analysis (Suggested) D5185 Comparison with new oil reference on delivery may indi-
cate the presence of contaminants or mislabeled oil ship-
ment. (Other spectrochemical method may be substituted
for the ICP method.)
Air Release (Suggested) D3427 Comparison with new oil reference on delivery may indi-
cate the presence of contaminants or mislabeled oil ship-
ment.
Water Separation (Suggested) D1401 Steam Turbine and Combined Cycle Systems only.
Foam (Suggested) D892 Comparison with new oil reference on delivery may indi-
cate the presence of contaminants or mislabeled oil
shipment.
A
Follow recommended flushing procedures prior to installing initial fill or replacement oil charge. For general guidance, see Guide D6439.
B
Important as a baseline to determine turbine system severity. It is recommended that all tests which are performed on in-service oils for trending purposes should also
be performed on a new oil charge for baseline information.
7.1.1 Microbiological Testing—When sampling in order to 7.3 Sampling of New Oil Deliveries:
perform microbiological testing, refer to Practice D7464 and 7.3.1 A sample of the new lubricant is required to provide a
Guide D8506 for guidance on sample collection and handling.
baseline for the physical and chemical properties of the
lubricant. Also samples taken should be representative of the
NOTE 1—For samples intended for microbiological testing, see Practice
oil being examined but obtained from the point(s) most
D7464. Although the guidance provided in Practice D7464 is nominally
indicative of gross contamination by debris and water, that is,
for fuel sample collection, the procedures provided are equally applicable
to turbine oils.
just above the bottom of the drum or tanker compartment
bottom.
7.2 Sample Labeling—A sample bottle should be properly
7.3.2 When consignments of oil are in drums, sample them
labeled in order to track the history of a particular piece of
in accordance with Practice D4057.
equipment. The equipment must be identified uniquely. Labels
7.3.3 For bulk consignments, sample each tanker compart-
should include the following information as appropriate:
7.2.1 Customer name (if appropriate), ment. If these are clear of debris and water, then the samples
can be combined for subsequent laboratory analysis of the
7.2.2 Site (or plant name),
7.2.3 Location (unit number, tank number, compartment consignment.
7.3.4 In cases where the product is suspected of being
number, and so forth),
7.2.4 Turbine serial number (or other ID), nonuniform, sample a larger number of drums. Where contami-
nation is suspected there is no alternative to sampling every
7.2.5 Turbine service hours,
7.2.6 Oil service hours, drum.
7.2.7 Date sample taken, 7.3.5 From tanker deliveries, in addition to sampling indi-
7.2.8 System operating temperature and temperature of oil vidual tanker compartments, further sample(s) should be taken
at sampling point, preferably from the outlet of the flexible pipework or at least
7.2.9 Type of oil sampled (lubricant ID), from the tanker bottom valve manifold. This further sampling
7.2.10 Sampling point/port ID, is necessary because the tanker contents can become contami-
7.2.11 Type of purification system (filters/centrifuge, and so nated by residual material left in the bottom valve manifold.
forth), and This can occur particularly when different products are being
7.2.12 Makeup (volume) since last sample was taken. carried in separate compartments or previous deliveries of a
D4378 − 24
different product have been made to other locations without 8.7 Handling and dispensing methods contribute to the
subsequent adequate cleaning and flushing. required health and cleanliness specifications of the lubricant.
All sources and opportunities of contamination must be
7.3.6 Bottom samples must be collected by either a tube or
thief sampler (for example, Bacon bomb). These samplers avoided.
permit collection of settlings on the bottom of the container
without introducing false contamination by scraping the con- 9. Deterioration of Turbine Oils in Service
tainer lining or wall.
9.1 How Turbine Oils Degrade—Irrespective of initial
7.3.7 Take the sample(s) from the outlet of the flexible
quality, during their use in lubrication systems of turbines,
pipework or the tanker bottom valve manifold while maintain-
lubricating oils will experience thermal and oxidative stresses,
ing a good flow after flushing the line.
loss of foam control, poor oil demulsibility and loss of wear
7.4 Preservation of Sample and Analysis of Oil Samples—It protection, which degrade the chemical composition of the oil.
In order to avoid these degradation problems, lubricating oils
is generally advised to ship the oil samples immediately to the
oil analysis laboratory, as ideally, oil should be analyzed as are developed with a strong ability to control oxidation
soon as reasonably achievable after being sampled. If oil processes, degradation by wear, and other degradation
samples are stored for an extended period of time, this may mechanisms, by using a combination of good quality base oil
result in a non-representative sample. together with a mixture of additives. For turbine oils, it is very
common for high quality products to have long periods of
7.4.1 If the samples are to be retained for extended periods
successful field operation, so that for many years the oil may
of time, special arrangements should be made in agreement
perform like new. Lubricant deterioration occurs by one or
with the oil analysis laboratory to ensure that the integrity of
more of the following processes:
the sample is not compromised. The special arrangement may
9.1.1 Oxidative Degradation—This occurs as the result of
include storing in dark amber glass bottles in an ambient
chemical changes brought about by oxygen in the atmosphere
temperature area as the longer an oil sample is stored in the
and proceeds by a chain reaction.
container/bottle, the more oxidation products will be generated.
9.1.1.1 Thermal/Oxidative Degradation—This degradation
7.4.2 Store the sample(s) away from strong light and as
can occur when the oil encounters hot spots or experiences
close to room temperature as possible.
electrostatic discharges, or microdieseling in turbines. During
thermal degradation at elevated temperatures, hydrocarbons
8. Examination of New Oil on Delivery
may form unstable and insoluble compounds. These unstable
8.1 Experience has shown the need for standardizing pro-
compounds are easily oxidized and also tend to polymerize to
cedures to be undertaken for the sampling, examination, and
form resins and sludge. For example, adiabatic compression of
acceptance of incoming supplies of turbine oil. It is essential
bubbles can cause small localized hot-spots of 3000° or the arc
that personnel responsible for sampling and testing shall have
quenching high temperatures.
the necessary experience and skills, and that scrupulous atten-
9.1.2 Water Accumulation in the System—Accumulated wa-
tion to detail be applied at all times to avoid erroneous results.
ter promotes oil degradation as well as additive depletion,
8.2 It is equally essential that all incoming supplies of oil be
corrosion, reduced lubricating film thickness and microbial
adequately monitored to guard against incorrect or contami-
growth. It is advised to operate without the presence of free or
nated material being delivered. Cleanliness of the delivery
emulsified water.
container should be noted; if the container is dirty on the
9.1.3 Loss of Additives—This can result in more rapid
outside, there may be particulate contamination on the inside.
oxidation and premature rusting.
Particulate contamination can also be a problem when the
9.1.4 Influx of Contaminants—Contaminants arising within
lubricant comes in contact with dirty or poorly maintained
the system (corrosion and wear products) or from without (fly
equipment.
ash, dirt, and fluids) cause lubrication and wear problems.
8.3 Sampling of incoming supplies should be in accordance
9.2 Properties of Oils That Must Be Retained—In determin-
with proper sampling procedures (see Section 7).
ing the condition of the system oil for continued service, the
most important properties of the in-service oil are: viscosity,
8.4 All samples should be immediately examined for ap-
oxidation stability reserve, freedom from sludge/varnish, free-
pearance.
dom from abrasive contaminants, anticorrosion protection,
8.5 A testing schedule for new oil is included in this practice
demulsibility, air release, and freedom from water contamina-
(see Table 1 and Table 2). With drums, tests should be
tion. (See Table 3.)
completed on the bulk sample before the oil is used in service.
9.2.1 Viscosity—Viscosity is the most important character-
Individual samples should be retained until the bulk sample is
istic of a turbine oil, as the oil film thickness under hydrody-
passed as satisfactory.
namic lubrication conditions is critically dependent on the oil’s
8.6 With tanker deliveries the additional tests to be com- viscosity characteristics. The viscosity of most commercial
pleted before the tanker is discharged can only be judged from turbine oils are classified according to ISO (International
the risk involved by the acceptance of nonspecification Standards Organization) viscosity classification system. Oils
product, that is, can the charge be readily recovered and fall into ISOVG32, VG46, VG68, and VG100 viscosity grades
2 2 2
corrected before passing into service if the subsequent tests corresponding to 32 mm /s (cSt), 46 mm /s (cSt), 68 mm /s
indicate this to be necessary. (cSt), and 100 mm /s (cSt) at 40 °C and to approximately
D4378 − 24
A
TABLE 3 Visual Inspection of In-service Oil Samples
NOTE 1—For consistency, the following are suggested: (1) visual inspections be performed after a 5 min settling time, (2) use of clear sample
containers, and (3) use of focused lighting to enhance visual observations.
Appearance of Oil Appearance of Oil Possible Cause Action Steps
B
just after Sampling after 1 h Settling
Clear Clear . .
Foam collapsed Air entry likely of mechanical origin or Investigate cause
from sampling process
Foam at the Surface
Stable persistent foam High foaming tendency- Possibly con- Investigate cause and conduct labora-
tamination or antifoam depletion. tory control test for foam
Clear Aeration if bubbles persist for more Investigate cause
Sample contains small air bubbles at than 5 min.
sampling then becomes clear from the
bottom Persistent entrained small air bubbles High air entrainment- Possibly Investigate cause and conduct labora-
contamination, oil degradation tory control test for air release
Clear or slightly opaque, decanted Unstable water emulsion Determine source of water ingress
free water
Sample cloudy and becoming clear Hazy Presence of soft contaminants and Determine possible presence of var-
from the top insolubles nish contaminants
Milky Stable water emulsion Investigate cause and conduct labora-
tory control test for water separation
Dirty Presence of decanted solid particles Contamination, possible filtration prob- Investigate cause and re-filter
lem
Strange color, rapid and unusual dark- . Contamination or excessive degrada- Investigate cause and conduct labora-
ening tion tory control test for oxidation
Acrid Oil cracking due to overheating Investigate cause. Check Viscosity,
Acid No, Flash point
Putrid or rancid Growth of bacteria or fungi Check for presence of water. With-
Unusual odor
Rotten eggs Growth of anaerobic Sulfate draw the separated water. Test for mi-
Reducing Bacteria crobial contamination and consult with
oil supplier regarding biocide treat
A
These visual screening tests can be performed on site by the turbine unit operator.
B
A complete reference to visual inspection definitions can be found in D7155.
165 SUS, 240 SUS, 350 SUS, and 515 SUS at 100 °F (Classi- lubricant contains no antioxidant other than 2,6-di-t-butyl-p-
fication D2422). The main purpose for checking the viscosity cresol or 2,6-di-t-butylphenol.)
of used turbine oil is to determine if the correct oil is being 9.2.2.2 Voltammetry—Voltammetry is an electrochemical
used and to detect contamination. Used turbine oils rarely show test technique, which can be used for measuring primary
significant viscosity changes due to degradation. Occasionally, antioxidant additives. The technique applies a voltage ramp
viscosity increases due to an emulsion with water contamina- through a three electrode sensing system and measures the
tion. The method normally used for viscosity determinations is current flow that occurs when the applied voltage equals the
Test Method D445 or D7042. oxidation potential of the antioxidant. The potential of the
9.2.2 Oxidation Inhibitor—The monitoring of antioxidant produced voltammetric peak aids in the identification of the
concentration is important for controlling the oxidation of antioxidant and the height of the produced peak is proportional
industrial lubricants and their remaining useful life. Some to the concentration of the antioxidant. Antioxidants such as
practices for measuring the concentration of phenolic (or phenols (in accordance with Test Method D6810 and D6971),
amine) antioxidants include infrared spectrometry (including amines, and ZDDP can be measured. A product type baseline
Fourier Transform Infrared) and voltammetry. When setting up must be available to a baseline test from a new oil sample of
one of these techniques, it is advisable to consult with the that fluid product name.
lubricant supplier who has a working knowledge of the 9.2.3 Oxidation Stability Reserve:
antioxidants used in the turbine oil formulation. 9.2.3.1 One of the important properties of new turbine oil is
9.2.2.1 FTIR—The Fourier Transform Infrared (FTIR) prac- its oxidation stability. Traditionally, this has been measured by
tice is a refined infrared spectroscopy method, which can be Test Method D943 with Test Method D2272 being used as an
used to monitor change in the availability of the original ancillary (rapid) method for following changes of oil condition
antioxidants blended into the oil. It can also be used to monitor in service. Oxidation stability will gradually decrease in
the change in oxidation products as the oil degrades. Each oil service, deterioration being promoted by the catalytic effects of
will produce a unique spectrum and a baseline must be metals in the system (iron and copper) as well as by the
established to obtain benefit from this technique. Each antioxi- depletion of the antioxidant. The latter occurs as a result of the
dant is a specific chemical substance and will absorb infrared normal function of the additive (chemically it acts as a
light at a particular wavelengths and absorptivities; some chain-stopper in controlling oxidation), or by volatilization. As
antioxidants may not be detectable by infrared spectroscopy. the oxidation stability reserve decreases, acidic compounds are
(Test Method D2668 may be used for antioxidants if the produced which in turn undergo further reactions to form more
wavelengths and absorptivities are known and in the case the complex compounds. The end products of these processes are
D4378 − 24
insoluble sludge and lacquering. Although only a minute be removed by the use of filters or centrifuge, or both. When
fraction of the oil is converted in this way, sufficient sludge and the amount of makeup is low and the various filters and
lacquering can form to settle in critical areas of the system, purifiers are operating satisfactorily, abrasive solids are gener-
leading to filter blockage, interference with proper lubrication ally removed before any damage is done. In a properly
and cooling of bearings and moving parts. maintained system the particulate level presents no problem.
Cleanliness of the system oil can be determined by gravimetric
9.2.3.2 The test method to detect severe oxidative degrada-
means (Practice F311 or Methods F312) or by particle counting
tion is the acid number (Test Methods D664 and D974). Most
(Test Method D7647), the latter normally by means of elec-
rust inhibitors used in turbine oils are acidic and contribute to
tronic particle counters. Cleanliness levels can be represented
the acid number of the new oil. An increase in acid number
by classification systems such as ISO 4406:1999. ISO
above the value for new oil indicates the presence of acidic
4406:1999 uses a numeric code to reference the number of
oxidation products, microbial growth in the system or, less
particles larger than 4 μm, 6 μm, and 14 μm/mL of oil. ISO
likely, contamination with acidic substances. An accurate
4406:1999 assigns integer values to denote a range of particles
determination of the acid number is very important. However,
whose upper limit doubles with each successive number.
this test does not measure oxidation stability reserve, which is
Desired cleanliness levels are sometimes designated by the
better determined by Test Method D2272. This latter test is
equipment manufacturer or user. If a cleanliness level is not
included in the recommended testing schedules (see Table 1
specified by the manufa
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: D4378 − 22 D4378 − 24
Standard Practice for
In-Service Monitoring of Mineral Turbine Oils for Steam,
Gas, and Combined Cycle Turbines
This standard is issued under the fixed designation D4378; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
INTRODUCTION
The in-service monitoring of turbine oils has long been recognized by the power-generation
industry as being necessary to ensure long, trouble-free operation of turbines.
The two main types of stationary turbines used for power generation are steam and gas turbines; the
turbines can be used as individual turbines, or can be configured as combine cycle turbines. Combined
cycle turbines are of two types; the first type connects a gas turbine with a steam turbine, with separate
lubricant circuits, and the second type mounts a steam and a gas turbine on the same shaft and has a
common lubricant circuit. The lubrication requirements are quite similar but there are important
differences in that gas turbine oils are subjected to significantly higher localized “hot spot”
temperatures and water contamination is less likely. Steam turbine oils are normally expected to last
for many years. In some turbines up to 20 years of service life has been obtained. Gas turbine oils, by
comparison, have a shorter service life from 2 to 5 years depending on severity of the operating
conditions. One of the benefits of the gas turbine is the ability to respond quickly to electrical power
generation dispatching requirements. Consequently, a growing percentage of modern gas turbines are
being used for peaking or cyclic duty (frequent unit stops and starts) subjects the lubricant to a wide
range of temperatures from ambient conditions to normal operating temperatures, which put additional
stresses on the lubricant.
This practice is designed to assist the user to validate the condition of the lubricant through its life
cycle by carrying out a meaningful program of sampling and testing of oils in service. This practice
is performed in order to collect data and monitor trends which suggest any signs of lubricant
deterioration and to ensure a safe, reliable, and cost-effective operation of the monitored plant
equipment.
1. Scope*
1.1 This practice covers the requirements for the effective monitoring of mineral turbine oils in service in steam and gas turbines,
as individual or combined cycle turbines, used for power generation. This practice includes sampling and testing schedules to
validate the condition of the lubricant through its life cycle and by ensuring required improvements to bring the present condition
of the lubricant within the acceptable targets. This practice is not intended for condition monitoring of lubricants for auxiliary
equipment; it is recommended that the appropriate practice be consulted (see Practice D6224).
1.2 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of
regulatory limitations prior to use.
This practice is under the jurisdiction of ASTM Committee D02 on Petroleum Products, Liquid Fuels, and Lubricants and is the direct responsibility of Subcommittee
D02.C0.01 on Turbine Oil Monitoring, Problems and Systems.
Current edition approved July 1, 2022March 1, 2024. Published August 2022March 2024. Originally approved in 1984. Last previous edition approved in 20202022 as
D4378 – 20.D4378 – 22. DOI: 10.1520/D4378-22.10.1520/D4378-24.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D4378 − 24
1.3 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
D92 Test Method for Flash and Fire Points by Cleveland Open Cup Tester
D93 Test Methods for Flash Point by Pensky-Martens Closed Cup Tester
D130 Test Method for Corrosiveness to Copper from Petroleum Products by Copper Strip Test
D445 Test Method for Kinematic Viscosity of Transparent and Opaque Liquids (and Calculation of Dynamic Viscosity)
D664 Test Method for Acid Number of Petroleum Products by Potentiometric Titration
D665 Test Method for Rust-Preventing Characteristics of Inhibited Mineral Oil in the Presence of Water
D892 Test Method for Foaming Characteristics of Lubricating Oils
D943 Test Method for Oxidation Characteristics of Inhibited Mineral Oils
D974 Test Method for Acid and Base Number by Color-Indicator Titration
D1401 Test Method for Water Separability of Petroleum Oils and Synthetic Fluids
D1500 Test Method for ASTM Color of Petroleum Products (ASTM Color Scale)
D2272 Test Method for Oxidation Stability of Steam Turbine Oils by Rotating Pressure Vessel
D2273 Test Method for Trace Sediment in Lubricating Oils (Withdrawn 2022)
D2422 Classification of Industrial Fluid Lubricants by Viscosity System
D2668 Test Method for 2,6-di-tert-Butyl- p-Cresol and 2,6-di-tert-Butyl Phenol in Electrical Insulating Oil by Infrared
Absorption
D3427 Test Method for Air Release Properties of Hydrocarbon Based Oils
D4057 Practice for Manual Sampling of Petroleum and Petroleum Products
D4175 Terminology Relating to Petroleum Products, Liquid Fuels, and Lubricants
D4898 Test Method for Insoluble Contamination of Hydraulic Fluids by Gravimetric Analysis
D5185 Test Method for Multielement Determination of Used and Unused Lubricating Oils and Base Oils by Inductively
Coupled Plasma Atomic Emission Spectrometry (ICP-AES)
D6224 Practice for In-Service Monitoring of Lubricating Oil for Auxiliary Power Plant Equipment
D6304 Test Method for Determination of Water in Petroleum Products, Lubricating Oils, and Additives by Coulometric Karl
Fischer Titration
D6439 Guide for Cleaning, Flushing, and Purification of Steam, Gas, and Hydroelectric Turbine Lubrication Systems
D6450 Test Method for Flash Point by Continuously Closed Cup (CCCFP) Tester
D6810 Test Method for Measurement of Hindered Phenolic Antioxidant Content in Non-Zinc Turbine Oils by Linear Sweep
Voltammetry
D6971 Test Method for Measurement of Hindered Phenolic and Aromatic Amine Antioxidant Content in Non-zinc Turbine Oils
by Linear Sweep Voltammetry
D7042 Test Method for Dynamic Viscosity and Density of Liquids by Stabinger Viscometer (and the Calculation of Kinematic
Viscosity)
D7094 Test Method for Flash Point by Modified Continuously Closed Cup (MCCCFP) Tester
D7155 Practice for Evaluating Compatibility of Mixtures of Turbine Lubricating Oils
D7464 Practice for Manual Sampling of Liquid Fuels, Associated Materials and Fuel System Components for Microbiological
Testing
D7647 Test Method for Automatic Particle Counting of Lubricating and Hydraulic Fluids Using Dilution Techniques to
Eliminate the Contribution of Water and Interfering Soft Particles by Light Extinction
D7669 Guide for Practical Lubricant Condition Data Trend Analysis
D7687 Test Method for Measurement of Cellular Adenosine Triphosphate in Fuel and Fuel-associated Water With Sample
Concentration by Filtration
D7720 Guide for Statistically Evaluating Measurand Alarm Limits when Using Oil Analysis to Monitor Equipment and Oil for
Fitness and Contamination
D7843 Test Method for Measurement of Lubricant Generated Insoluble Color Bodies in In-Service Turbine Oils using
Membrane Patch Colorimetry
D7978 Test Method for Determination of the Viable Aerobic Microbial Content of Fuels and Associated Water—Thixotropic Gel
Culture Method
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
The last approved version of this historical standard is referenced on www.astm.org.
D4378 − 24
D8072 Classification for Reporting Solids and Insoluble Water Contamination of Hydrocarbon-Based Petroleum Products When
Analyzed by Imaging Instrumentation
D8112 Guide for Obtaining In-Service Samples of Turbine Operation Related Lubricating Fluid
D8506 Guide for Microbial Contamination and Biodeterioration in Turbine Oils and Turbine Oil Systems
F311 Practice for Processing Aerospace Liquid Samples for Particulate Contamination Analysis Using Membrane Filters
F312 Test Methods for Microscopical Sizing and Counting Particles from Aerospace Fluids on Membrane Filters
2.2 International Organization for Standardization Standards:
ISO 4406 Hydraulic fluid power—Fluids—Method for Coding the Level of Contamination by Solid Particles, Second Edition,
ISO 4407 Hydraulic Fluid Power—Fluid Contamination—Determination of Particulate Contamination by Counting Method
Using an Optical Microscope, Second Edition, 2002
ISO 11500 Hydraulic Fluid Power—Determination of the Particulate Contamination Level of a Liquid Sample by Automatic
Particle Counting Using the Light Extinction, Second Edition, 2008
ISO 11171 Hydraulic Fluid Power—Calibration of Automatic Particle Counters for Liquids
3. Terminology
3.1 For definitions of terms used in this practice, refer to Terminology D4175.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 bulk oil tote, n—any container for lubrication or control fluid with working volume approximately 1000 L to 1300 L designed
for fluid storage at atmospheric pressure.
3.2.2 continuous sampling loop, n—a limited flow of fluid from a point in a pressurized system to a point of lower pressure used
to decrease required purge fluid and sample time during the sampling process.
3.2.3 disposable sample tubing, n—any single-use flexible plastic tubing used to transfer fluid during the sampling process.
3.2.4 drain sampling, n—a method of sampling used fluid for non-pressurized reservoirs or lines occurring when the lubricating
fluid is being drained from the reservoir during a fluid change.
3.2.4.1 Discussion—
As part of a fluid change, the drain plug is removed to allow the fluid to drain into an appropriate container under gravity. Mid
way through the draining, a sample bottle is filled by placing it in the fluid stream and once filled immediately capped.
3.2.5 drop tube sampling, n—a method of sampling used fluid for non-pressurized reservoirs when sampling is completed by
dropping an appropriate length of sampling tubing into the reservoir and using a vacuum generating device to extract the sample.
3.2.6 permanent sample tube, n—any tubing installed in a reservoir or pipe used to extract a sample from a specific location within
the system.
3.2.7 purge, v—to remove the existing non-representative fluid and contaminants from the sample valve and tubing during the
sampling process.
3.2.8 remote access hose, n—any permanently installed metallic or elastomeric tube or hose used to transfer fluid from the system
to a point outside the system to facilitate sampling.
3.2.9 reservoir, n—any equipment-based container that holds a volume of fluid, usually under atmospheric condition, for use in
the lubrication, sealing or control process.
3.2.10 sample container, n—a clean, fresh plastic bottle used for system fluid analysis (see Section 7).
3.2.11 sample valve, n—a system consisting of a male and female component used specifically for the extraction of a fluid sample
either by internal system pressure or by an externally generated vacuum.
Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036, http://www.ansi.org.
D4378 − 24
3.2.11.1 Discussion—
The male component, referred to as a probe, may be for one time use or permanently attached to the female component, referred
to as a sample valve, is used by either threading the probe onto the valve or pushing the probe into the valve for the purpose of
opening the valve and allowing fluid to flow out.
3.2.12 sample valve sampling, v—to obtain a sample from either pressurized or non pressurized lines or reservoirs.
3.2.12.1 Discussion—
When sampling non-pressurized reservoirs this sampling method usually applies a vacuum generating device and sampling tubing
to extract a sample into a sampling container from a strategically located sampling valve. When sampling pressurized reservoirs
or lines, this sampling method is completed by using system pressure to force lubricating fluid into a sampling container through
a sampling valve.
3.2.13 vacuum generating device, n—a pump used to create a low pressure in a sample container to cause fluid to move from a
non-pressurized reservoir to the container through disposable tubing.
3.2.14 weighted drop tube device, n—a mass attached to a piece of steel or stainless steel tubing with a method to attach disposable
sampling tubing to the steel or stainless steel tubing.
3.2.14.1 Discussion—
This device is used during drop tube sampling.
4. Significance and Use
4.1 This practice is intended to assist the user, in particular the power-plant operations and maintenance departments, to maintain
effective lubrication of all parts of the turbine and guard against the onset of problems associated with oil degradation and
contamination. The values of the various test parameters mentioned in this practice are purely indicative. In fact, for proper
interpretation of the results, many factors, such as type of equipment, operation workload, design of the lubricating oil circuit, and
top-up level, should be taken into account.
5. Properties of Turbine Oils
5.1 Most turbine oils consist of a highly refined paraffinic mineral oil compounded with oxidation and rust inhibitors with a lesser
number of turbines using a synthetic type of fluid. Depending upon the performance level desired, small amounts of other additives
such as metal deactivators, pour depressants, extreme pressure additives, and foam suppressants can also be present. The turbine
oil’s primary function is to provide lubrication and cooling of bearings and gears. In some equipment designs, they also can
function as a governor hydraulic fluid.
5.2 New turbine oils should exhibit good resistance to oxidation, inhibit sludge and varnish deposit formation, and provide
adequate antirust, water separability, and non-foaming properties. However, these oils cannot be expected to remain unchanged
during their use in the lubrication systems of turbines, as lubricating oils experience thermal and oxidative stresses which degrade
the chemical composition of the oil’s basestock and gradually deplete the oil’s additive package. Some deterioration can be
tolerated without harming the safety or efficiency of the system. Good monitoring procedures are necessary to determine when the
oil properties have changed sufficiently to justify scheduling corrective actions which can be performed with little or no detriment
to production schedules.
6. Operational Factors Affecting Service Life
6.1 The factors that affect the service life of turbine lubricating oils are as follows: (1) type and design of system, (2) condition
of system on startup, (3) original oil quality, (4) system operating conditions, (5) contamination, (6) oil makeup rate, and (7)
handling and storage.
6.1.1 Type and Design of System—Most modern turbine lubricating systems are similar in design, especially for the larger units.
For lubrication, the usual practice is to pressure-feed oil directly from the main oil pump. The rest of the system consists of a
reservoir, oil cooler, strainer, piping and additional purification or filtration equipment, or a combination thereof. Miscellaneous
control and indicating equipment completes the system.
6.1.2 Condition of System on Start-up:
6.1.2.1 The individual components of a lubrication system are usually delivered on-site before the system is installed. The length
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of on-site storage and means taken to preserve the integrity of the intended oil wetted surfaces will determine the total amount of
contamination introduced during this period, the magnitude of the task of cleaning and flushing prior to use, and the detrimental
effects of the contaminants. Guidance on cleaning, flushing, and purification of steam, gas, and hydroelectric turbine lubrication
systems is provided in Guide D6439 or may be sought from the equipment/lubricant supplier or other industry experts.
6.1.2.2 Turbine oil system contamination prior to startup usually consists of preservatives, paint, rust particles, and the various
solids encountered during construction, which can range from dust and dirt to rags, bottles, and cans. Their effect on turbine oil
systems is obvious. Incompatible fluid is also considered a contaminant and can include system flushing lube oil from improper
drain and clean-out.
6.1.2.3 Ongoing purification may be required to maintain the in-service oils at an acceptable particle cleanliness level and water
content level in the case of steam turbines for reliable lubrication and control systems operation. In operational systems, the
emphasis is on the removal of contaminants that may be generated due to normal oil degradation or ingressed during operation
and by malfunctions that occur during operation or contaminants that are introduced during overhaul, or both.
6.1.3 Original Oil Quality:
6.1.3.1 Use of a high-quality oil is the best assurance of potentially long service life. Oils meeting recognized standards are
generally available, and one that at least meets the requirements of the turbine manufacturer shall be used. Careful oil storage,
including labeling and rotation of lubricant containers, is vital to ensure proper use and prevent degradation of the physical,
chemical, and cleanliness requirements of the lubricant throughout storage and dispensing.
6.1.3.2 It is advisable to obtain typical test data from the oil supplier. Upon receipt of the first oil charge, take a baseline sample
from the barrel, tote or tanker to ensure the oil meets quality standards. A sample of the oil should be taken after charging the new
oil and circulating (24 h) to confirm the typical test data and to use as a baseline. This baseline should act as a starting point for
the physical and chemical properties of the lubricant, and for future comparisons with used oil information. This is most important!
Recommended tests for new oil are given in the schedules of this practice (see Tables 1 and 2).
6.1.3.3 When new turbine oil is to be mixed with a charge of a different composition prior checks should be made to ensure no
loss of expected properties due to incompatibility (see lubricant suppliers’ specifications). These should include functional tests
and checks for formation of insoluble materials. Guidance for such compatibility testing can be referenced in Practice D7155 for
evaluating compatibility of mixtures of turbine lubricating oils.
6.1.4 System Operating Conditions:
6.1.4.1 The most important factors affecting the anticipated service life of a given lubricating oil in a given turbine system are the
operating conditions within the system. Air (oxygen), elevated operating temperatures, metals, and water (moisture) are always
present to some extent in these oil systems. These elements promote oil degradation and must consequently be recorded.
6.1.4.2 Most turbine oil systems are provided with oil coolers to control temperature. In many cases, bulk oil temperatures are
maintained so low, below 60 °C (140 °F), that moisture condensation can occur. Even with low bulk oil temperatures, however,
there can be localized hot spots such as in bearings, at gas seals, and in throttle control mechanisms that can cause oil degradation
and eventually cause system oil to show signs of deterioration.
6.1.4.3 Under the higher temperature conditions which are present in gas and steam turbines, oxidation of the oil can be
accelerated by thermal-oxidative cracking leading to the production of viscous resins and deposits particularly at the point of
initiation.
6.1.5 Contamination:
6.1.5.1 Contamination of turbine oils is often the most significant factor affecting oil service life. Contamination occurs both from
outside the system and from within due to oil degradation and moisture condensation or leaks. Development of a clean turbine oil
system on start-up or following maintenance is essential (following the steps in Guide D6439) prior to filling with the new oil.
Once attained, the danger of external contamination is less but should be guarded against. The oil can be contaminated by the
introduction of different type oils, which are of the wrong type or are incompatible with the system oil. The oil supplier or the
turbine manufacturer, or both, should be consulted before additions are made (see Practice D7155).
6.1.5.2 External contamination can enter the system through bearing seals and vents. Internal contaminants are always being
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TABLE 1 Minimum Sampling and Inspection Testing Schedule for New Oils
Schedule 1 New Oil-All Turbine Types
Samples:
(a) From transport or drums
(b) From storage tank
Tests Method Recommended Minimum Requirements for Acceptance of
New Oil as Received
Viscosity D445, D7042 Should meet Classification D2422 consistent with user
purchase specifications or manufacturer’s requirements.
Acid Number D974 or D664 Acceptance limits should be consistent with user purchase
specifications, new oil reference or manufacturer’s require-
ments or a combination thereof.
Appearance visual clear and bright
Water Content visual no free water
Color D1500 Acceptance limits should be consistent with user purchase
specifications, new oil reference or manufacturer’s require-
ments or a combination thereof.
Rust Test D665 Required for Steam and Single Shaft combined cycle tur-
bines. Should pass D665A for land-based turbines and
D665B for marine turbines.
Oxidation Stability or Inhibition D2272, D6810, Most suitable methods and acceptance limits should be
(RPVOT/Voltammetry/FTIR) D6971 consistent with user purchase specifications, new oil refer-
ence or manufacturer’s requirements or a combination
thereof.
Elemental Analysis (Suggested) D5185 Comparison with new oil reference on delivery may indi-
cate the presence of contaminants or mislabeled oil ship-
ment. (Other spectrochemical method may be substituted
for the ICP method.)
Air Release (Suggested) D3427 Comparison with new oil reference on delivery may indi-
cate the presence of contaminants or mislabeled oil ship-
ment.
Water Separation (Suggested) D1401 Steam Turbine and Combined Cycle Systems only.
Foam (Suggested) D892 Comparison with new oil reference on delivery may indi-
cate the presence of contaminants or mislabeled oil
shipment.
generated. These include water, dirt, fly ash, wear particles, insoluble particulate oil degradation products and microbial growth.
From whatever source, contamination must be dealt with by monitoring oil condition and the use of purification devices such as
filters, centrifuges, coalescers, and vacuum dehydrators on a regular basis. Contamination of the system oil is a valid reason to
change oil or flush a unit, or both, to restore system cleanliness.
6.1.6 Oil Makeup Rate—The amount and frequency of makeup oil added to the system plays a very significant part in determining
the life of a system oil charge. Makeup varies from below 5 % per year to as much as 30 % in extreme cases. In turbines where
makeup is relatively high compared to the oil degradation rate, the degree of degradation is compensated for and long oil life can
be expected. In turbines where the makeup is very low (below 5 %), a truer picture of oil degradation is obtained. However, such
a system should be carefully watched since the oil life is dependent almost exclusively on its original quality. In the United States,
the average makeup is typically around 7 % to 10 % per year.
6.1.7 Handling and Oil Storage—Handling and dispensing methods must ensure that the quality and the cleanliness of the
lubricant meet the specifications required by the equipment. Oils must be properly labeled to ensure proper selection and use.
Proper stock rotation and storage methods must be considered to prevent the possible degradation of the physical and chemical
properties of the lubricant during storage and dispensing.
6.2 The combination of all of the preceding operational factors for a given turbine determines its severity level. Each unit is
different and the equilibrium operating conditions for each system must be determined in order to fix its severity level; OEM
operating and maintenance specifications can also be used in setting the severity levels. The more severe a turbine system, the
shorter the service life for a given oil. A useful approach to determine the severity of a turbine is given in Appendix X1.
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A
TABLE 2 Minimum Sampling and Inspection Testing Schedule for New Oil Charge
Schedule 2 Installation of a New Oil Charge
Samples:
After 24 h circulation in Turbine
Retain approximately 4 L (1 gal)
Tests Method Recommended minimum requirements for assessment of
new oil charge
Viscosity D445, D7042 Should meet Classification D2422 consistent with user pur-
chase specifications or manufacturer’s requirements.
Acid Number D974 or D664 Should be consistent with user purchase specifications
and new oil reference.
Appearance visual clear and bright
Water Content visual no free water
Color D1500 Should be consistent with user purchase specifications
and new oil reference.
Particle Count--Cleanliness (after fil- F311 or F312 or user Definition of suitable cleanliness levels determined by par-
tration into equipment) defined ticle count distribution depends on turbine builder and user
requirements Filtration or centrifugation, or both of oil into
turbine and during in-service is recommended.
Oxidation Stability or Inhibition D2272, D6810, D6971 Should be consistent with user purchase specifications
B
(RPVOT/Voltammetry/FTIR) and new oil reference.
Elemental Analysis (Suggested) D5185 Comparison with new oil reference on delivery may indi-
cate the presence of contaminants or mislabeled oil ship-
ment. (Other spectrochemical method may be substituted
for the ICP method.)
Air Release (Suggested) D3427 Comparison with new oil reference on delivery may indi-
cate the presence of contaminants or mislabeled oil ship-
ment.
Water Separation (Suggested) D1401 Steam Turbine and Combined Cycle Systems only.
Foam (Suggested) D892 Comparison with new oil reference on delivery may indi-
cate the presence of contaminants or mislabeled oil
shipment.
A
Follow recommended flushing procedures prior to installing initial fill or replacement oil charge. For general guidance, see Guide D6439.
B
Important as a baseline to determine turbine system severity. It is recommended that all tests which are performed on in-service oils for trending purposes should also
be performed on a new oil charge for baseline information.
7. Sampling
7.1 General—When taking oil samples from storage tanks or equipment in service, it is important that the extracted sample is
representative and is taken from a specified location(s) to monitor the properties of the lubricant. Correct and consistent sampling
techniques are vital to achieve this. The recommended guidelines for proper sampling technique and sample handling techniques
are part of Guide D8112. The user should have written standard operating procedures to ensure that samples are taken consistently
according to good maintenance practices. In addition to the Guide D8112 method the following recommendations are to be
considered:
7.1.1 Microbiological Testing—When sampling in order to perform microbiological testing, refer to Practice D7464 and Guide
D8506 for guidance on sample collection and handling.
NOTE 1—For samples intended for microbiological testing, see Practice D7464. Although the guidance provided in Practice D7464 is nominally for fuel
sample collection, the procedures provided are equally applicable to turbine oils.
7.2 Sample Labeling—A sample bottle should be properly labeled in order to track the history of a particular piece of equipment.
The equipment must be identified uniquely. Labels should include the following information as appropriate:
7.2.1 Customer name (if appropriate),
7.2.2 Site (or plant name),
7.2.3 Location (unit number, tank number, compartment number, and so forth),
7.2.4 Turbine serial number (or other ID),
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7.2.5 Turbine service hours,
7.2.6 Oil service hours,
7.2.7 Date sample taken,
7.2.8 System operating temperature and temperature of oil at sampling point,
7.2.9 Type of oil sampled (lubricant ID),
7.2.10 Sampling point/port ID,
7.2.11 Type of purification system (filters/centrifuge, and so forth), and
7.2.12 Makeup (volume) since last sample was taken.
7.3 Sampling of New Oil Deliveries:
7.3.1 A sample of the new lubricant is required to provide a baseline for the physical and chemical properties of the lubricant. Also
samples taken should be representative of the oil being examined but obtained from the point(s) most indicative of gross
contamination by debris and water, that is, just above the bottom of the drum or tanker compartment bottom.
7.3.2 When consignments of oil are in drums, sample them in accordance with Practice D4057.
7.3.3 For bulk consignments, sample each tanker compartment. If these are clear of debris and water, then the samples can be
combined for subsequent laboratory analysis of the consignment.
7.3.4 In cases where the product is suspected of being nonuniform, sample a larger number of drums. Where contamination is
suspected there is no alternative to sampling every drum.
7.3.5 From tanker deliveries, in addition to sampling individual tanker compartments, further sample(s) should be taken preferably
from the outlet of the flexible pipework or at least from the tanker bottom valve manifold. This further sampling is necessary
because the tanker contents can become contaminated by residual material left in the bottom valve manifold. This can occur
particularly when different products are being carried in separate compartments or previous deliveries of a different product have
been made to other locations without subsequent adequate cleaning and flushing.
7.3.6 Bottom samples must be collected by either a tube or thief sampler (for example, Bacon bomb). These samplers permit
collection of settlings on the bottom of the container without introducing false contamination by scraping the container lining or
wall.
7.3.7 Take the sample(s) from the outlet of the flexible pipework or the tanker bottom valve manifold while maintaining a good
flow after flushing the line.
7.4 Preservation of Sample and Analysis of Oil Samples—It is generally advised to ship the oil samples immediately to the oil
analysis laboratory, as ideally, oil should be analyzed as soon as reasonably achievable after being sampled. If oil samples are
stored for an extended period of time, this may result in a non-representative sample.
7.4.1 If the samples are to be retained for extended periods of time, special arrangements should be made in agreement with the
oil analysis laboratory to ensure that the integrity of the sample is not compromised. The special arrangement may include storing
in dark amber glass bottles in an ambient temperature area as the longer an oil sample is stored in the container/bottle, the more
oxidation products will be generated.
7.4.2 Store the sample(s) away from strong light and as close to room temperature as possible.
8. Examination of New Oil on Delivery
8.1 Experience has shown the need for standardizing procedures to be undertaken for the sampling, examination, and acceptance
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of incoming supplies of turbine oil. It is essential that personnel responsible for sampling and testing shall have the necessary
experience and skills, and that scrupulous attention to detail be applied at all times to avoid erroneous results.
8.2 It is equally essential that all incoming supplies of oil be adequately monitored to guard against incorrect or contaminated
material being delivered. Cleanliness of the delivery container should be noted; if the container is dirty on the outside, there may
be particulate contamination on the inside. Particulate contamination can also be a problem when the lubricant comes in contact
with dirty or poorly maintained equipment.
8.3 Sampling of incoming supplies should be in accordance with proper sampling procedures (see Section 7).
8.4 All samples should be immediately examined for appearance.
8.5 A testing schedule for new oil is included in this practice (see Table 1 and Table 2). With drums, tests should be completed
on the bulk sample before the oil is used in service. Individual samples should be retained until the bulk sample is passed as
satisfactory.
8.6 With tanker deliveries the additional tests to be completed before the tanker is discharged can only be judged from the risk
involved by the acceptance of nonspecification product, that is, can the charge be readily recovered and corrected before passing
into service if the subsequent tests indicate this to be necessary.
8.7 Handling and dispensing methods contribute to the required health and cleanliness specifications of the lubricant. All sources
and opportunities of contamination must be avoided.
9. Deterioration of Turbine Oils in Service
9.1 How Turbine Oils Degrade—Irrespective of initial quality, during their use in lubrication systems of turbines, lubricating oils
will experience thermal and oxidative stresses, loss of foam control, poor oil demulsibility and loss of wear protection, which
degrade the chemical composition of the oil. In order to avoid these degradation problems, lubricating oils are developed with a
strong ability to control oxidation processes, degradation by wear, and other degradation mechanisms, by using a combination of
good quality base oil together with a mixture of additives. For turbine oils, it is very common for high quality products to have
long periods of successful field operation, so that for many years the oil may perform like new. Lubricant deterioration occurs by
one or more of the following processes:
9.1.1 Oxidative Degradation—This occurs as the result of chemical changes brought about by oxygen in the atmosphere and
proceeds by a chain reaction.
9.1.1.1 Thermal/Oxidative Degradation—This degradation can occur when the oil encounters hot spots or experiences
electrostatic discharges, or microdieseling in turbines. During thermal degradation at elevated temperatures, hydrocarbons may
form unstable and insoluble compounds. These unstable compounds are easily oxidized and also tend to polymerize to form resins
and sludge. For example, adiabatic compression of bubbles can cause small localized hot-spots of 3000° or the arc quenching high
temperatures.
9.1.2 Water Accumulation in the System—Accumulated water promotes oil degradation as well as additive depletion, corrosion,
reduced lubricating film thickness and microbial growth. It is advised to operate without the presence of free or emulsified water.
9.1.3 Loss of Additives—This can result in more rapid oxidation and premature rusting.
9.1.4 Influx of Contaminants—Contaminants arising within the system (corrosion and wear products) or from without (fly ash, dirt,
and fluids) cause lubrication and wear problems.
9.2 Properties of Oils That Must Be Retained—In determining the condition of the system oil for continued service, the most
important properties of the in-service oil are: viscosity, oxidation stability reserve, freedom from sludge/varnish, freedom from
abrasive contaminants, anticorrosion protection, demulsibility, air release, and freedom from water contamination. (See Table 3.)
9.2.1 Viscosity—Viscosity is the most important characteristic of a turbine oil, as the oil film thickness under hydrodynamic
lubrication conditions is critically dependent on the oil’s viscosity characteristics. The viscosity of most commercial turbine oils
D4378 − 24
A
TABLE 3 Visual Inspection of In-service Oil Samples
NOTE 1—For consistency, the following are suggested: (1) visual inspections be performed after a 5 min settling time, (2) use of clear sample
containers, and (3) use of focused lighting to enhance visual observations.
Appearance of Oil Appearance of Oil Possible Cause Action Steps
B
just after Sampling after 1 h Settling
Clear Clear . .
Foam collapsed Air entry likely of mechanical origin or Investigate cause
from sampling process
Foam at the Surface
Stable persistent foam High foaming tendency- Possibly con- Investigate cause and conduct labora-
tamination or antifoam depletion. tory control test for foam
Clear Aeration if bubbles persist for more Investigate cause
Sample contains small air bubbles at than 5 min.
sampling then becomes clear from the
bottom Persistent entrained small air bubbles High air entrainment- Possibly Investigate cause and conduct labora-
contamination, oil degradation tory control test for air release
Clear or slightly opaque, decanted Unstable water emulsion Determine source of water ingress
free water
Sample cloudy and becoming clear Hazy Presence of soft contaminants and Determine possible presence of var-
from the top insolubles nish contaminants
Milky Stable water emulsion Investigate cause and conduct labora-
tory control test for water separation
Dirty Presence of decanted solid particles Contamination, possible filtration prob- Investigate cause and re-filter
lem
Strange color, rapid and unusual dark- . Contamination or excessive degrada- Investigate cause and conduct labora-
ening tion tory control test for oxidation
Acrid Oil cracking due to overheating Investigate cause. Check Viscosity,
Acid No, Flash point
Putrid or rancid Growth of bacteria or fungi Check for presence of water. With-
Unusual odor
Rotten eggs Growth of anaerobic Sulfate draw the separated water. Test for mi-
crobial contamination and consult with
Reducing Bacteria
oil supplier regarding biocide treat
A
These visual screening tests can be performed on site by the turbine unit operator.
B
A complete reference to visual inspection definitions can be found in D7155.
are classified according to ISO (International Standards Organization) viscosity classification system. Oils fall into ISOVG32,
2 2 2 2
VG46, VG68, and VG100 viscosity grades corresponding to 32 mm /s (cSt), 46 mm /s (cSt), 68 mm /s (cSt), and 100 mm /s (cSt)
at 40 °C and to approximately 165 SUS, 240 SUS, 350 SUS, and 515 SUS at 100 °F (Classification D2422). The main purpose for
checking the viscosity of used turbine oil is to determine if the correct oil is being used and to detect contamination. Used turbine
oils rarely show significant viscosity changes due to degradation. Occasionally, viscosity increases due to an emulsion with water
contamination. The method normally used for viscosity determinations is Test Method D445 or D7042.
9.2.2 Oxidation Inhibitor—The monitoring of antioxidant concentration is important for controlling the oxidation of industrial
lubricants and their remaining useful life. Some practices for measuring the concentration of phenolic (or amine) antioxidants
include infrared spectrometry (including Fourier Transform Infrared) and voltammetry. When setting up one of these techniques,
it is advisable to consult with the lubricant supplier who has a working knowledge of the antioxidants used in the turbine oil
formulation.
9.2.2.1 FTIR—The Fourier Transform Infrared (FTIR) practice is a refined infrared spectroscopy method, which can be used to
monitor change in the availability of the original antioxidants blended into the oil. It can also be used to monitor the change in
oxidation products as the oil degrades. Each oil will produce a unique spectrum and a baseline must be established to obtain benefit
from this technique. Each antioxidant is a specific chemical substance and will absorb infrared light at a particular wavelengths
and absorptivities; some antioxidants may not be detectable by infrared spectroscopy. (Test Method D2668 may be used for
antioxidants if the wavelengths and absorptivities are known and in the case the lubricant contains no antioxidant other than
2,6-di-t-butyl-p-cresol or 2,6-di-t-butylphenol.)
9.2.2.2 Voltammetry—Voltammetry is an electrochemical test technique, which can be used for measuring primary antioxidant
additives. The technique applies a voltage ramp through a three electrode sensing system and measures the current flow that occurs
when the applied voltage equals the oxidation potential of the antioxidant. The potential of the produced voltammetric peak aids
in the identification of the antioxidant and the height of the produced peak is proportional to the concentration of the antioxidant.
Antioxidants such as phenols (in accordance with Test Method D6810 and D6971), amines, and ZDDP can be measured. A product
type baseline must be available to a baseline test from a new oil sample of that fluid product name.
9.2.3 Oxidation Stability Reserve:
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9.2.3.1 One of the important properties of new turbine oil is its oxidation stability. Traditionally, this has been measured by Test
Method D943 with Test Method D2272 being used as an ancillary (rapid) method for following changes of oil condition in service.
Oxidation stability will gradually decrease in service, deterioration being promoted by the catalytic effects of metals in the system
(iron and copper) as well as by the depletion of the antioxidant. The latter occurs as a result of the normal function of the additive
(chemically it acts as a chain-stopper in controlling oxidation), or by volatilization. As the oxidation stability reserve decreases,
acidic compounds are produced which in turn undergo further reactions to form more complex compounds. The end products of
these processes are insoluble sludge and lacquering. Although only a minute fraction of the oil is converted in this way, sufficient
sludge and lacquering can form to settle in critical areas of the system, leading to filter blockage, interference with proper
lubrication and cooling of bearings and moving parts.
9.2.3.2 The test method to detect severe oxidative degradation is the acid number (Test Methods D664 and D974). Most rust
inhibitors used in turbine oils are acidic and contribute to the acid number of the new oil. An increase in acid number above the
value for new oil indicates the presence of acidic oxidation products, microbial growth in the system or, less likely, contamination
with acidic substances. An accurate determination of the acid number is very important. However, this test does not measure
oxidation stability reserve, which is better determined by Test Method D2272. This latter test is included in the recommended
testing schedules (see Table 1 and Table 2).
9.2.4 Freedom from Sludge/Varnish:
9.2.4.1 Due to the nature of the highly refined lubricant basestocks used in the manufacture of turbine oils, they are very poor
solvents for sludge/varnish. This is the main reason why the oxidation stability reserve of the oil must be carefully monitored. Only
a relatively small degree of oxidation can be permitted, otherwise there is considerable risk of sludge/varnish deposition in bearing
housings, seals, gears, and pistons.
9.2.4.2 Measurement of the amounts of sludge/varnish as insoluble, soft contaminants (coloured bodies) in turbine oils (Test
Method D7843) is possible. Sludge/varnish already laid down within the system would not be included in such a determination.
Other tests, however, can signal deteriorat
...