ASTM D7873-22a

Standard Test Method for Determination of Oxidation Stability and Insolubles Formation of Inhibited Turbine Oils at 120 °C Without the Inclusion of Water (Dry TOST Method)

SIGNIFICANCE AND USE
5.1 Insoluble material may form in oils that are subjected to oxidizing conditions.  
5.2 Significant formation of oil insolubles or metal corrosion products, or both, during this test may indicate that the oil will form insolubles or corrode metals, or both, resulting in varnish formation during field service. The level of varnish formation in service will be dependent on many factors (turbine design, reservoir temperature, duty-cycle, for example. peaking, cycling, or base-load duty, maintenance, and so forth) and a direct correlation between results in this test and field varnish formation are yet to be established.  
5.3 Oxidation condition at 120 °C under accelerated oxidation environment of Test Method D4310 and measurement of sludge and RPVOT value could reflect a practical oil quality in actual turbine operations. Results from this test should be used together with other key lubricant performance indicators (including other established oxidation and corrosion tests) to indicate suitability for service.
SCOPE
1.1 This test method is used to evaluate the sludging tendencies of steam and gas turbine lubricants during the oxidation process in the presence of oxygen and metal catalyst (copper and iron) at an elevated temperature. This test method may be used to evaluate industrial oils (for example, circulating oils and so forth).  
1.2 This test method is a modification of Test Method D4310 where the sludging and corrosion tendencies of the same kinds of oils are determined after 1000 h at 95 °C in the presence of water. Water is omitted in this modification.  
1.3 The values stated in SI units are to be regarded as standard.  
1.3.1 Exception—The values in parentheses in some of the figures are provided for information only for those using old equipment based on non-SI units.  
1.4 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.  
1.5 WARNING—Mercury has been designated by many regulatory agencies as a hazardous substance that can cause serious medical issues. Mercury, or its vapor, has been demonstrated to be hazardous to health and corrosive to materials. Use Caution when handling mercury and mercury-containing products. See the applicable product Safety Data Sheet (SDS) for additional information. The potential exists that selling mercury or mercury-containing products, or both, is prohibited by local or national law. Users must determine legality of sales in their location.  
1.6 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: 31-Oct-2022
• ICS: 75.080 - Petroleum products in general
• ICS: 75.100 - Lubricants, industrial oils and related products
• Technical Committee: D02 - Petroleum Products, Liquid Fuels, and Lubricants
• Drafting Committee: D02.09.0C - Oxidation of Turbine Oils

Relations

• Refers: ASTM D4175-23a - Standard Terminology Relating to Petroleum Products, Liquid Fuels, and Lubricants
• Effective Date: 15-Dec-2023
• Refers: ASTM E230/E230M-23a - Standard Specification for Temperature-Electromotive Force (emf) Tables for Standardized Thermocouples
• Effective Date: 01-Nov-2023
• Refers: ASTM D4175-23e1 - Standard Terminology Relating to Petroleum Products, Liquid Fuels, and Lubricants
• Effective Date: 01-Jul-2023
• Refers: ASTM E230/E230M-23 - Standard Specification for Temperature-Electromotive Force (emf) Tables for Standardized Thermocouples
• Effective Date: 01-May-2023
• Refers: ASTM D4310-20 - Standard Test Method for Determination of Sludging and Corrosion Tendencies of Inhibited Mineral Oils
• Effective Date: 01-Jan-2020
• Refers: ASTM B1-13(2018) - Standard Specification for Hard-Drawn Copper Wire
• Effective Date: 01-Oct-2018
• Refers: ASTM D943-17 - Standard Test Method for Oxidation Characteristics of Inhibited Mineral Oils
• Effective Date: 15-Jun-2017
• Refers: ASTM D2272-14 - Standard Test Method for Oxidation Stability of Steam Turbine Oils by Rotating Pressure Vessel
• Effective Date: 01-Jul-2014
• Refers: ASTM B1-13 - Standard Specification for Hard-Drawn Copper Wire
• Effective Date: 01-Oct-2013
• Refers: ASTM E1-13 - Standard Specification for ASTM Liquid-in-Glass Thermometers
• Effective Date: 01-May-2013
• Refers: ASTM B1-12 - Standard Specification for Hard-Drawn Copper Wire
• Effective Date: 15-Nov-2012
• Refers: ASTM D4057-06(2011) - Standard Practice for Manual Sampling of Petroleum and Petroleum Products
• Effective Date: 01-Jun-2011
• Refers: ASTM E230/E230M-11 - Standard Specification and Temperature-Electromotive Force (emf) Tables for Standardized Thermocouples
• Effective Date: 15-May-2011
• Refers: ASTM E230/E230M-11e1 - Standard Specification and Temperature-Electromotive Force (emf) Tables for Standardized Thermocouples
• Effective Date: 15-May-2011
• Refers: ASTM D4310-09 - Standard Test Method for Determination of Sludging and Corrosion Tendencies of Inhibited Mineral Oils
• Effective Date: 01-Oct-2009

Overview

ASTM D7873-22a is the internationally recognized standard test method for determining the oxidation stability and insoluble formation of inhibited turbine oils at 120 °C, without the inclusion of water-commonly referred to as the "Dry TOST Method." Developed by ASTM International, this method evaluates the tendency of steam and gas turbine lubricants, as well as other industrial oils, to form sludge and insoluble materials under elevated temperatures in the presence of oxygen and metal catalysts such as copper and iron. The results are key indicators of oil performance and suitability for use in demanding turbine applications.

Key Topics

• Oxidation Stability: The method measures the oil’s resistance to oxidation, a primary cause of lubricant degradation, oil thickening, and varnish formation in turbines.
• Insolubles Formation: Quantifies the formation of sludge-an insoluble material that results from oil oxidation and is a critical contaminant leading to operational issues such as blocked filters or deposits on mechanical parts.
• Accelerated Aging Conditions: Simulates harsh operating environments by maintaining oil samples at 120 °C in the presence of oxygen and metal catalysts but without water, offering a rapid assessment of oil stability compared to field conditions.
• Measurement Techniques: Utilizes a membrane filtration process to determine the mass of insoluble materials (mg/kg) generated. Results are correlated with the Rotating Pressure Vessel Oxidation Test (RPVOT) residual ratio, another key measurement for lubricant life.
• Safety Considerations: Includes cautionary notes about the handling of hazardous materials such as mercury, and recommends best practices to ensure health and regulatory compliance.

Applications

This test method is a critical tool in:

• Turbine Oil Formulation and Qualification: Used by oil manufacturers to develop and approve lubricants for steam and gas turbine systems, ensuring products can withstand severe oxidation without forming excessive sludge.
• Quality Control in Industrial Oils: Serves as a benchmark for circulating oils and other industrial lubricants, facilitating routine monitoring and quality assurance.
• Predicting Field Performance: While direct correlation to in-service varnish formation may depend on turbine design, operation, and maintenance practices, the dry TOST results offer valuable insights when combined with other oil performance indicators.
• Corrosion Assessment: Identifies the potential for corrosion by measuring insoluble metal-containing byproducts, supporting preventative maintenance programs in power plants and industrial facilities.
• Regulatory Compliance and Safety: Assists organizations in meeting international standards, supporting safer handling and legal use of lubricants in regulated environments.

Related Standards

ASTM D7873-22a is frequently referenced alongside related standards in the assessment of turbine oil performance, oxidation, and corrosion:

• ASTM D4310: Test Method for Determination of Sludging and Corrosion Tendencies of Inhibited Mineral Oils (with water included).
• ASTM D2272: Test Method for Oxidation Stability of Steam Turbine Oils by Rotating Pressure Vessel.
• ASTM D943: Test Method for Oxidation Characteristics of Inhibited Mineral Oils.
• ASTM D4057: Practice for Manual Sampling of Petroleum and Petroleum Products.
• ISO 3696: Specification for Water for Analytical Laboratory Use.

Practical Value

Implementing ASTM D7873-22a helps organizations:

• Extend equipment life by selecting and maintaining turbine oils with proven oxidation stability.
• Reduce downtime and maintenance costs related to oil degradation, filter blockage, or varnish build-up.
• Enhance reliability and safety in steam and gas turbine operations through informed lubricant selection and monitoring.
• Maintain compliance with international standards and best practices for lubrication management.

Keywords: ASTM D7873-22a, turbine oil oxidation, dry TOST method, turbine oil testing, lubricant oxidation stability, sludge formation, industrial oil quality, ASTM turbine oil standard.

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: D7873 − 22a
Standard Test Method for
Determination of Oxidation Stability and Insolubles
Formation of Inhibited Turbine Oils at 120 °C Without the
Inclusion of Water (Dry TOST Method)
This standard is issued under the fixed designation D7873; 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.
1. Scope* ization established in the Decision on Principles for the
Development of International Standards, Guides and Recom-
1.1 This test method is used to evaluate the sludging
mendations issued by the World Trade Organization Technical
tendencies of steam and gas turbine lubricants during the
Barriers to Trade (TBT) Committee.
oxidation process in the presence of oxygen and metal catalyst
(copper and iron) at an elevated temperature. This test method
2. Referenced Documents
may be used to evaluate industrial oils (for example, circulat-
2.1 ASTM Standards:
ing oils and so forth).
A510M Specification for General Requirements for Wire
1.2 This test method is a modification of Test Method
Rods and Coarse Round Wire, Carbon Steel (Metric)
D4310 where the sludging and corrosion tendencies of the 3
(Withdrawn 2011)
same kinds of oils are determined after 1000 h at 95 °C in the
B1 Specification for Hard-Drawn Copper Wire
presence of water. Water is omitted in this modification.
D943 Test Method for Oxidation Characteristics of Inhibited
1.3 The values stated in SI units are to be regarded as Mineral Oils
standard. D1193 Specification for Reagent Water
1.3.1 Exception—The values in parentheses in some of the D2272 Test Method for Oxidation Stability of Steam Tur-
figures are provided for information only for those using old bine Oils by Rotating Pressure Vessel
equipment based on non-SI units. D4057 Practice for Manual Sampling of Petroleum and
Petroleum Products
1.4 This standard does not purport to address all of the
D4175 Terminology Relating to Petroleum Products, Liquid
safety concerns, if any, associated with its use. It is the
Fuels, and Lubricants
responsibility of the user of this standard to establish appro-
D4310 Test Method for Determination of Sludging and
priate safety, health, and environmental practices and deter-
Corrosion Tendencies of Inhibited Mineral Oils
mine the applicability of regulatory limitations prior to use.
E1 Specification for ASTM Liquid-in-Glass Thermometers
1.5 WARNING—Mercury has been designated by many
E230/E230M Specification for Temperature-Electromotive
regulatory agencies as a hazardous substance that can cause
Force (emf) Tables for Standardized Thermocouples
serious medical issues. Mercury, or its vapor, has been dem-
2.2 Other Standards:
onstrated to be hazardous to health and corrosive to materials.
Specification for IP Standard Thermometers
Use Caution when handling mercury and mercury-containing
ISO 3696 Water for Analytical Laboratory Use—
products. See the applicable product Safety Data Sheet (SDS)
Specification and Test Methods
for additional information. The potential exists that selling
mercury or mercury-containing products, or both, is prohibited
3. Terminology
by local or national law. Users must determine legality of sales
3.1 Definitions:
in their location.
1.6 This international standard was developed in accor-
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
dance with internationally recognized principles on standard-
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.
1 3
This test method is under the jurisdiction of ASTM Committee D02 on The last approved version of this historical standard is referenced on
Petroleum Products, Liquid Fuels, and Lubricants and is the direct responsibility of www.astm.org.
Subcommittee D02.09.0C on Oxidation of Turbine Oils. Available from Energy Institute, 61 New Cavendish St., London, WIG 7AR,
Current edition approved Nov. 1, 2022. Published November 2022. Originally U.K., http://www.energyinst.org.
approved in 2013. Last previous edition approved in 2022 as D7873 – 22. DOI: Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
10.1520/D7873-22A. 4th Floor, New York, NY 10036, http://www.ansi.org.
*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
D7873 − 22a
3.1.1 See Terminology D4175 for a list of terms relating to minimize effects of light exposure on the lubricant being
petroleum products, liquid fuels, and lubricants. tested, light shall be excluded from the lubricant by one or
3.2 Definitions of Terms Specific to This Standard: more of the following ways:
3.2.1 sludge, n—a precipitate or sediment from oxidized 6.2.1.1 Use of heated liquid baths that are designed and
mineral oil that is insoluble in n-heptane.
constructed of metal, or combinations of metals and other
suitable opaque materials, that prevent light from entering the
4. Summary of Test Method
test cell from the sides is preferred. If a viewing window is
4.1 Atotalofsixtoeighttubescontaining360mLofsample
includedinthedesign,thisviewingwindowshallbefittedwith
each are heated at 120 °C with oxygen in the presence of an
a suitable opaque cover and be kept closed when no observa-
iron-copper catalyst. Each tube is removed over time and the
tion is being made.
sample is analyzed by Test Method D2272 and the insolubles
6.2.1.2 If glass heating baths are used, the bath shall be
are measured until the RPVOT residual ratio reaches below
wrapped with aluminum foil or other opaque material.
25 % or an agreed-upon percentage or specified time. Test run
6.2.1.3 Bright light entering the test cell from directly
for a specified time(s) may be run using a single tube or as
overhead can be eliminated by use of an opaque shield.
many as specified by the requestor. The mass of insoluble
6.3 Flowmeter, with a flow capacity of at least 3 L of
material of each oil sample is determined gravimetrically by
oxygen/hour, and an accuracy of 60.1 L⁄h.
filtration of a 100 g oil sample through a membrane filter with
pore size 1 µm. The insoluble mass (mg/kg oil) is plotted 6.4 Heating Bath Thermometer,ASTMSolventsDistillation
against RPVOT residual ratio. The insoluble mass in milli- Thermometer having a range from 98 °C to 152 °C and
grams per kilogram oil at 25 % or an agreed-upon RPVOT conforming to the requirements for Thermometer 41C as
residual ratio or specified time is reported. prescribed in Specification E1, or for Thermometer 81C as
prescribed in Specifications for IP Standard Thermometers.
5. Significance and Use
Alternatively,temperature-measuringdevicesofequalorbetter
5.1 Insoluble material may form in oils that are subjected to
accuracy and precision may be used.
oxidizing conditions.
6.5 Oxidation Cell Thermometer, A 76 mm immersion LIG
5.2 Significant formation of oil insolubles or metal corro-
having a range of 110 °C to 130 °C, graduated in 0.1 °C, total
sion products, or both, during this test may indicate that the oil
length of 300 mm 6 5 mm, and stem diameter of 6.0 mm to
will form insolubles or corrode metals, or both, resulting in
7.0 mm.Alternatively, temperature-measuring devices or DCT,
varnish formation during field service. The level of varnish
of equal or better accuracy and precision may be used.
formation in service will be dependent on many factors
Temperature of the sample shall be measured at 76 mm from
(turbinedesign,reservoirtemperature,duty-cycle,forexample.
the top of the sample. See Fig. 2 and Fig. 3.
peaking, cycling, or base-load duty, maintenance, and so forth)
NOTE 1—Temperature gradient within the sample may exist from the
heating system and temperature control design.
and a direct correlation between results in this test and field
varnish formation are yet to be established.
6.6 Wire Coiling Mandrel, as shown in Fig. 4.
5.3 Oxidation condition at 120 °C under accelerated oxida-
6.7 Thermometer Bracket, for holding the oxidation cell
tion environment of Test Method D4310 and measurement of
thermometer, of 18-8 stainless steel, having the dimensions
sludge and RPVOTvalue could reflect a practical oil quality in
shown in Fig. 5.The thermometer is held in the bracket by two
actual turbine operations. Results from this test should be used
fluoro-elastomer O-rings of approximately 5 mm inside diam-
together with other key lubricant performance indicators (in-
eter. Alternatively, thin stainless steel wire may be used.
cluding other established oxidation and corrosion tests) to
6.8 Abrasive Cloth, silicon carbide, 100 grit with cloth
indicate suitability for service.
backing.
6. Apparatus
6.9 Flexible Tubing, poly vinyl chloride approximately
1 3
6.1 Oxidation Cell, of borosilicate glass, as shown in Fig. 1,
6.4 mm( ⁄4 in.)insidediameterwitha2.4 mm( ⁄32 in.)wallfor
consisting of a test tube, condenser, and oxygen delivery tube.
delivery of oxygen to the oxidation cell.
It is recommended to have a test tube with a calibration line at
6.10 Membrane Filters, white, plain, 47 mm in diameter,
360 mL(maximum error 1 mL). This calibration applies to the
pore size 1 µm. The recommended membrane filters are PTFE
test tube without inserts at 20 °C.
and cellulose acetate plus nitrocellulose material.
6.2 Heating Bath, thermostatically controlled, capable of
6.11 Filter Holder, 47 mm, consisting of a borosilicate glass
maintaining the oil sample in the oxidation cell at a tempera-
funnel and a funnel base with a coarse grade fritted-glass filter
ture of 120 °C 6 0.5 °C, fitted with a suitable stirring device to
support with a length of 40 µm to 60 µm, or stainless steel
provide a uniform temperature throughout the bath, and large
screen support such that the filter can be clamped between the
enoughtoholdthedesirednumberofoxidationcellsimmersed
ground-glass sealing surfaces of the funnel and its base by
in the heating bath to a depth of 355 mm 6 10 mm. Heated
means of a metal clamp.
metal block baths meeting the test method requirements may
also be used. 6.12 Weighing Bottle, cylindrical body with ground-glass
6.2.1 Studies have suggested that direct sunlight or artificial stopper; approximate inside diameter 65 mm, height of body
light may adversely influence the results of this test. To 45 mm, capacity 60 mL.
D7873 − 22a
NOTE 1—All dimensions are in millimetres (inches).
NOTE 2—The oxidation test tube has a calibration line at 360 mL. This calibration applies to the test tube alone at 20 °C.
NOTE 3—Open tube ends to be ground and fire-polished.
FIG. 1 Oxidation Cell
D7873 − 22a
6.18 Pipette Bulb.
7. Reagents and Materials
7.1 Purity of Reagents—Reagent grade chemicals shall be
used in all tests. Unless otherwise indicated, it is intended that
all reagents shall conform to the specifications of the commit-
tee onAnalytical Reagents of theAmerican Chemical Society,
where such specifications are available.
7.2 Reagent Water, Unless otherwise indicated, reference to
water shall be understood to mean distilled, deionized water as
defined by Type I or Type II in Specification D1193 or Grade
3 in ISO 3696.
7.3 Acetone, Reagent grade. (Warning—Health hazard,
flammable.)
7.4 Cleaning Reagent, cleaning by a 24 h soak at room
temperature in a free rinsing liquid acid cleaner with a pH of 2
to 4.5.
7.5 n-heptane, Reagent grade. (Warning—Flammable.
Harmful if inhaled.)
7.6 Isopropyl Alcohol, Reagent grade. (Warning—
Flammable.)
7.7 Catalyst Wires,
7.7.1 Low-Metalloid Steel Wire—1.59 mm (0.0625 in.) in
diameter (No. 16 Washburn and Moen Gage).
NOTE 2—Carbon steel wire, soft bright annealed and free from rust of
Grade 1008 as described in Specification A510M is satisfactory. Similar
wire conforming to Specification E230/E230M is also satisfactory
7.8 Electrolytic Copper Wire, 1.63 mm (0.064 in.) in diam-
eter (No. 16 Imperial Standard Wire Gage or No. 14American
Wire Gage), 99.9 % purity, conforming to Specification B1.
NOTE 3—Alternatively, suitably prepared steel and copper catalyst coils
FIG. 2 Oxidation Cell with Thermometer
may be purchased from a supplier.
7.9 Detergent, free rinsing, water-soluble, anionic detergent
with a pH of 9.5 to 11.
7.10 Oxygen—(Warning—Oxygen vigorously accelerates
combustion.) 99.5 % minimum purity, with pressure regulation
adequate to maintain a constant flow of gas through the
apparatus. The use of a two-stage pressure regulator on tank
oxygen is recommended.
8. Sampling
8.1 Samples for this test can come from tanks, drums, small
containers, or even operating equipment. Therefore, use the
FIG. 3 76 mm Immersion LIG Thermometer applicable apparatus and techniques described in Practice
D4057.
8.2 For one single determination at a specified time the
6.13 Vacuum Source, to provide pressure reduction to
minimum required sample size is 360 mL. However, 6 to 8
13.3 kPa 6 0.7 kPa (100 mm 6 5 mm Hg) absolute pressure.
tubes will be required to develop the data points to obtain the
6.14 Cooling Vessel, A desiccator or other type of tightly
sludge mass at 25 % or agreed-upon residual RPVOT ratio by
covered vessel for cooling the weighing vessels before weigh-
ing. The use of a drying agent is not recommended.
ACS Reagent Chemicals, Specifications and Procedures for Reagents and
6.15 Drying Oven, capable of maintaining a temperature of
Standard-Grade Reference Materials, American Chemical Society, Washington,
70 °C 6 5 °C.
DC. For suggestions on the testing of reagents not listed by theAmerican Chemical
Society, see Analar Standards for Laboratory Chemicals, BDH Ltd., Poole, Dorset,
6.16 Forceps, having unserrated tips.
U.K., and the United States Pharmacopeia and National Formulary, U.S. Pharma-
6.17 Rubber Policeman. copeial Convention, Inc. (USPC), Rockville, MD.
D7873 − 22a
FIG. 4 Mandrel for Winding Catalyst Coils
logarithmic interpolation. Therefore, approximately 2200 mL overall length of the finished coil should be 225 mm 65mm
to 2900 mL will be required for this test. (8.9 in. 6 0.2 in.). If necessary, the coil may be stretched to
give the required length (Note 4).
9. Preparation of Apparatus
NOTE 4—The finished catalyst coil is a double spiral of copper and iron
wire, 225 mm 6 5 mm (8.9 in. 6 0.2 in.) overall length and 15.9 mm to
9.1 Cleaning Catalyst—Immediately prior to winding a
16.5 mm (0.625 in. to 0.650 in.) inside diameter. The turns of wire are
catalyst coil, clean a 3.00 m 6 0.01 m length of iron wire and
evenly spaced, and two consecutive turns of the same wire are 3.96 mm to
an equal length of copper wire with wads of absorbent cotton
4.22 mm (0.156 in. to 0.166 in.) apart, center to center. The mandrel
wet with n-heptane and follow by abrasion with abrasive cloth
showninFig.4isdesignedtoproducesuchacoil.Usingthismandrel,the
ironwireiswoundonathreadof14.98 mm(0.590 in.)diameter,whilethe
until a fresh metal surface is exposed. Then wipe with dry
copper wire is wound on a thread of 15.9 mm (0.625 in.) diameter. The
absorbent cotton until all loose particles of metal and abrasive
smaller diameter is to allow for “springback” of the steel wire after
have been removed. In subsequent operations, handle the
winding, so as to give 15.9 mm consistent inside diameter. Use of a very
catalyst wires with clean gloves (cotton, rubber, or plastic) to
softannealedsteelwiremayallowuseofidenticalthreaddiametersforthe
prevent contact with the skin.
two wires.Any arrangement that leads to the coil configuration described
above is satisfactory.
9.2 Preparation of Catalyst Coil—Twist the iron and copper
wires tightly together at one end for three turns and then wind 9.3 Catalyst Storage—The catalyst coil may be stored in a
them simultaneously alongside each other on a threaded dry, inert atmosphere prior to use. A suitable procedure for
mandrel (see Fig. 4), inserting the iron wire in the deeper catalyst storage is given in Appendix X1. Before use, it should
thread. Remove the coil from the mandrel, twist the free ends be inspected to ensure that no corrosion products or contami-
of the iron and copper wires together for three turns, and bend nating materials are present. For overnight storage (less than
the twisted ends to conform to the shape of the spiral coil. The 24 h) the coil may be stored in n-heptane.
D7873 − 22a
NOTE 1—All dimensions are in millimetres (inches).
NOTE 2—Material—18-8 stainless steel, 22 gage (0.792 mm).
FIG. 5 Thermometer Bracket
9.3.1 n-heptane used for catalyst storage must
...

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: D7873 − 22 D7873 − 22a
Standard Test Method for
Determination of Oxidation Stability and Insolubles
Formation of Inhibited Turbine Oils at 120 °C Without the
Inclusion of Water (Dry TOST Method)
This standard is issued under the fixed designation D7873; 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.
1. Scope*
1.1 This test method is used to evaluate the sludging tendencies of steam and gas turbine lubricants during the oxidation process
in the presence of oxygen and metal catalyst (copper and iron) at an elevated temperature. This test method may be used to evaluate
industrial oils (for example, circulating oils and so forth).
1.2 This test method is a modification of Test Method D4310 where the sludging and corrosion tendencies of the same kinds of
oils are determined after 1000 h at 95 °C in the presence of water. Water is omitted in this modification.
1.3 The values stated in SI units are to be regarded as standard.
1.3.1 Exception—The values in parentheses in some of the figures are provided for information only for those using old equipment
based on non-SI units.
1.4 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.
1.5 WARNING—Mercury has been designated by many regulatory agencies as a hazardous substance that can cause serious
medical issues. Mercury, or its vapor, has been demonstrated to be hazardous to health and corrosive to materials. Use Caution
when handling mercury and mercury-containing products. See the applicable product Safety Data Sheet (SDS) for additional
information. The potential exists that selling mercury or mercury-containing products, or both, is prohibited by local or national
law. Users must determine legality of sales in their location.
1.6 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:
This test method is under the jurisdiction of ASTM Committee D02 on Petroleum Products, Liquid Fuels, and Lubricants and is the direct responsibility of Subcommittee
D02.09.0C on Oxidation of Turbine Oils.
Current edition approved July 1, 2022Nov. 1, 2022. Published July 2022November 2022. Originally approved in 2013. Last previous edition approved in 20202022 as
D7873 – 20.D7873 – 22. DOI: 10.1520/D7873-22.10.1520/D7873-22A.
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.
*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
D7873 − 22a
A510M Specification for General Requirements for Wire Rods and Coarse Round Wire, Carbon Steel (Metric) (Withdrawn
2011)
B1 Specification for Hard-Drawn Copper Wire
D943 Test Method for Oxidation Characteristics of Inhibited Mineral Oils
D1193 Specification for Reagent Water
D2272 Test Method for Oxidation Stability of Steam Turbine Oils by Rotating Pressure Vessel
D4057 Practice for Manual Sampling of Petroleum and Petroleum Products
D4175 Terminology Relating to Petroleum Products, Liquid Fuels, and Lubricants
D4310 Test Method for Determination of Sludging and Corrosion Tendencies of Inhibited Mineral Oils
E1 Specification for ASTM Liquid-in-Glass Thermometers
E230/E230M Specification for Temperature-Electromotive Force (emf) Tables for Standardized Thermocouples
2.2 Other Standards:
Specification for IP Standard Thermometers
ISO 3696 Water for Analytical Laboratory Use—Specification and Test Methods
3. Terminology
3.1 Definitions:
3.1.1 See Terminology D4175 for a list of terms relating to petroleum products, liquid fuels, and lubricants.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 sludge, n—a precipitate or sediment from oxidized mineral oil that is insoluble in n-heptane.
4. Summary of Test Method
4.1 A total of six to eight tubes containing 360 mL of sample each are heated at 120 °C with oxygen in the presence of an
iron-copper catalyst. Each tube is removed over time and the sample is analyzed by Test Method D2272 and the insolubles are
measured until the RPVOT residual ratio reaches below 25 % or an agreed-upon percentage or specified time. Test run for a
specified time(s) may be run using a single tube or as many as specified by the requestor. The mass of insoluble material of each
oil sample is determined gravimetrically by filtration of a 100 g oil sample through a membrane filter with pore size 1 μm. The
insoluble mass (mg/kg oil) is plotted against RPVOT residual ratio. The insoluble mass in milligrams per kilogram oil at 25 % or
an agreed-upon RPVOT residual ratio or specified time is reported.
5. Significance and Use
5.1 Insoluble material may form in oils that are subjected to oxidizing conditions.
5.2 Significant formation of oil insolubles or metal corrosion products, or both, during this test may indicate that the oil will form
insolubles or corrode metals, or both, resulting in varnish formation during field service. The level of varnish formation in service
will be dependent on many factors (turbine design, reservoir temperature, duty-cycle, for example. peaking, cycling, or base-load
duty, maintenance, and so forth) and a direct correlation between results in this test and field varnish formation are yet to be
established.
5.3 Oxidation condition at 120 °C under accelerated oxidation environment of Test Method D4310 and measurement of sludge and
RPVOT value could reflect a practical oil quality in actual turbine operations. Results from this test should be used together with
other key lubricant performance indicators (including other established oxidation and corrosion tests) to indicate suitability for
service.
6. Apparatus
6.1 Oxidation Cell, of borosilicate glass, as shown in Fig. 1, consisting of a test tube, condenser, and oxygen delivery tube. It is
recommended to have a test tube with a calibration line at 360 mL (maximum error 1 mL). This calibration applies to the test tube
without inserts at 20 °C.
The last approved version of this historical standard is referenced on www.astm.org.
Available from Energy Institute, 61 New Cavendish St., London, WIG 7AR, U.K., http://www.energyinst.org.
Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036, http://www.ansi.org.
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NOTE 1—All dimensions are in millimetres (inches).
NOTE 2—The oxidation test tube has a calibration line at 360 mL. This calibration applies to the test tube alone at 20 °C.
NOTE 3—Open tube ends to be ground and fire-polished.
FIG. 1 Oxidation Cell
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6.2 Heating Bath, thermostatically controlled, capable of maintaining the oil sample in the oxidation cell at a temperature of
120 °C 6 0.5 °C, fitted with a suitable stirring device to provide a uniform temperature throughout the bath, and large enough to
hold the desired number of oxidation cells immersed in the heating bath to a depth of 355 mm 6 10 mm. Heated metal block baths
meeting the test method requirements may also be used.
6.2.1 Studies have suggested that direct sunlight or artificial light may adversely influence the results of this test. To minimize
effects of light exposure on the lubricant being tested, light shall be excluded from the lubricant by one or more of the following
ways:
6.2.1.1 Use of heated liquid baths that are designed and constructed of metal, or combinations of metals and other suitable opaque
materials, that prevent light from entering the test cell from the sides is preferred. If a viewing window is included in the design,
this viewing window shall be fitted with a suitable opaque cover and be kept closed when no observation is being made.
6.2.1.2 If glass heating baths are used, the bath shall be wrapped with aluminum foil or other opaque material.
6.2.1.3 Bright light entering the test cell from directly overhead can be eliminated by use of an opaque shield.
6.3 Flowmeter, with a flow capacity of at least 3 L of oxygen/hour, and an accuracy of 60.1 L ⁄h.
6.4 Heating Bath Thermometer, ASTM Solvents Distillation Thermometer having a range from 98 °C to 152 °C and conforming
to the requirements for Thermometer 41C as prescribed in Specification E1, or for Thermometer 81C as prescribed in
Specifications for IP Standard Thermometers. Alternatively, temperature-measuring devices of equal or better accuracy and
precision may be used.
6.5 Oxidation Cell Thermometer, A 76 mm immersion LIG having a range of 110 °C to 130 °C, graduated in 0.1 °C, total length
of 300 mm 6 5 mm, and stem diameter of 6.0 mm to 7.0 mm. Alternatively, temperature-measuring devices or DCT, of equal or
better accuracy and precision may be used. Temperature of the sample shall be measured at 76 mm from the top of the sample.
See Fig. 2 and Fig. 3.
NOTE 1—Temperature gradient within the sample may exist from the heating system and temperature control design.
6.6 Wire Coiling Mandrel, as shown in Fig. 4.
6.7 Thermometer Bracket, for holding the oxidation cell thermometer, of 18-8 stainless steel, having the dimensions shown in Fig.
5. The thermometer is held in the bracket by two fluoro-elastomer O-rings of approximately 5 mm inside diameter. Alternatively,
thin stainless steel wire may be used.
6.8 Abrasive Cloth, silicon carbide, 100 grit with cloth backing.
1 3
6.9 Flexible Tubing, poly vinyl chloride approximately 6.4 mm ( ⁄4 in.) inside diameter with a 2.4 mm ( ⁄32 in.) wall for delivery
of oxygen to the oxidation cell.
6.10 Membrane Filters, white, plain, 47 mm in diameter, pore size 1 μm. The recommended membrane filters are PTFE and
cellulose acetate plus nitrocellulose material.
6.11 Filter Holder, 47 mm, consisting of a borosilicate glass funnel and a funnel base with a coarse grade fritted-glass filter support
with a length of 40 μm to 60 μm, or stainless steel screen support such that the filter can be clamped between the ground-glass
sealing surfaces of the funnel and its base by means of a metal clamp.
6.12 Weighing Bottle, cylindrical body with ground-glass stopper; approximate inside diameter 65 mm, height of body 45 mm,
capacity 60 mL.
6.13 Vacuum Source, to provide pressure reduction to 13.3 kPa 6 0.7 kPa (100 mm 6 5 mm Hg) absolute pressure.
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FIG. 2 Oxidation Cell with Thermometer
FIG. 3 76 mm Immersion LIG Thermometer
6.14 Cooling Vessel, A desiccator or other type of tightly covered vessel for cooling the weighing vessels before weighing. The
use of a drying agent is not recommended.
6.15 Drying Oven, capable of maintaining a temperature of 70 °C 6 5 °C.
6.16 Forceps, having unserrated tips.
6.17 Rubber Policeman.
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FIG. 4 Mandrel for Winding Catalyst Coils
6.18 Pipette Bulb.
7. Reagents and Materials
7.1 Purity of Reagents—Reagent grade chemicals shall be used in all tests. Unless otherwise indicated, it is intended that all
reagents shall conform to the specifications of the committee on Analytical Reagents of the American Chemical Society, where
such specifications are available.
7.2 Reagent Water, Unless otherwise indicated, reference to water shall be understood to mean distilled, deionized water as defined
by Type I or Type II in Specification D1193 or Grade 3 in ISO 3696.
7.3 Acetone, Reagent grade. (Warning—Health hazard, flammable.)
7.4 Cleaning Reagent, cleaning by a 24 h soak at room temperature in a free rinsing liquid acid cleaner with a pH of 2 to 4.5.
ACS Reagent Chemicals, Specifications and Procedures for Reagents and Standard-Grade Reference Materials, American Chemical Society, Washington, DC. For
suggestions on the testing of reagents not listed by the American Chemical Society, see Analar Standards for Laboratory Chemicals, BDH Ltd., Poole, Dorset, U.K., and
the United States Pharmacopeia and National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville, MD.
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NOTE 1—All dimensions are in millimetres (inches).
NOTE 2—Material—18-8 stainless steel, 22 gage (0.792 mm).
FIG. 5 Thermometer Bracket
7.5 n-heptane, Reagent grade. (Warning—Flammable. Harmful if inhaled.)
7.6 Isopropyl Alcohol, Reagent grade. (Warning—Flammable.)
7.7 Catalyst Wires,
7.7.1 Low-Metalloid Steel Wire—1.59 mm (0.0625 in.) in diameter (No. 16 Washburn and Moen Gage).
NOTE 2—Carbon steel wire, soft bright annealed and free from rust of Grade 1008 as described in Specification A510M is satisfactory. Similar wire
conforming to Specification E230/E230M is also satisfactory
7.8 Electrolytic Copper Wire, 1.63 mm (0.064 in.) in diameter (No. 16 Imperial Standard Wire Gage or No. 14 American Wire
Gage), 99.9 % purity, conforming to Specification B1.
NOTE 3—Alternatively, suitably prepared steel and copper catalyst coils may be purchased from a supplier.
7.9 Detergent, free rinsing, water-soluble, anionic detergent with a pH of 9.5 to 11.
7.10 Oxygen—(Warning—Oxygen vigorously accelerates combustion.) 99.5 % minimum purity, with pressure regulation
adequate to maintain a constant flow of gas through the apparatus. The use of a two-stage pressure regulator on tank oxygen is
recommended.
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8. Sampling
8.1 Samples for this test can come from tanks, drums, small containers, or even operating equipment. Therefore, use the applicable
apparatus and techniques described in Practice D4057.
8.2 For one single determination at a specified time the minimum required sample size is 360 mL. However, 6 to 8 tubes will be
required to develop the data points to obtain the sludge mass at 25 % or agreed-upon residual RPVOT ratio by logarithmic
interpolation. Therefore, approximately 2200 mL to 2900 mL will be required for this test.
9. Preparation of Apparatus
9.1 Cleaning Catalyst—Immediately prior to winding a catalyst coil, clean a 3.00 m 6 0.01 m length of iron wire and an equal
length of copper wire with wads of absorbent cotton wet with n-heptane and follow by abrasion with abrasive cloth until a fresh
metal surface is exposed. Then wipe with dry absorbent cotton until all loose particles of metal and abrasive have been removed.
In subsequent operations, handle the catalyst wires with clean gloves (cotton, rubber, or plastic) to prevent contact with the skin.
9.2 Preparation of Catalyst Coil—Twist the iron and copper wires tightly together at one end for three turns and then wind them
simultaneously alongside each other on a threaded mandrel (see Fig. 4), inserting the iron wire in the deeper thread. Remove the
coil from the mandrel, twist the free ends of the iron and copper wires together for three turns, and bend the twisted ends to conform
to the shape of the spiral coil. The overall length of the finished coil should be 225 mm 6 5 mm (8.9 in. 6 0.2 in.). If necessary,
the coil may be stretched to give the required length (Note 4).
NOTE 4—The finished catalyst coil is a double spiral of copper and iron wire, 225 mm 6 5 mm (8.9 in. 6 0.2 in.) overall length and 15.9 mm to 16.5 mm
(0.625 in. to 0.650 in.) inside diameter. The turns of wire are evenly spaced, and two consecutive turns of the same wire are 3.96 mm to 4.22 mm (0.156 in.
to 0.166 in.) apart, center to center. The mandrel shown in Fig. 4 is designed to produce such a coil. Using this mandrel, the iron wire is wound on a thread
of 14.98 mm (0.590 in.) diameter, while the copper wire is wound on a thread of 15.9 mm (0.625 in.) diameter. The smaller diameter is to allow for
“springback” of the steel wire after winding, so as to give 15.9 mm consistent inside diameter. Use of a very soft annealed steel wire may allow use of
identical thread diameters for the two wires. Any arrangement that leads to the coil configuration described above is satisfactory.
9.3 Catalyst Storage—The catalyst coil may be stored in a dry, inert atmosphere prior to use. A suitable procedure for catalyst
storage is given in Appendix X1. Before use, it should be inspected to ensure that no corrosion products or contaminating materials
are present. For overnight storage (less than 24 h) the coil may be stored in n-heptane.
9.3.1 n-heptane used for catalyst storage must
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