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ASTM Committee D-2.C Turbine Oils has been recently working on a pair of standards that provide guidance on monitoring and analysis of lubricating oils. While these standards were written for power plant applications, much of the content is broadly applicable to oil-lubricated machinery in process and manufacturing industries as well.
The Standard Practice for In-Service Monitoring of Mineral Turbine Oils for Steam and Gas Turbines (ASTM D4378) was first published in 1984 and was reviewed and revised in 1997. This Practice is intended to assist a turbine operator in maintaining effective lubrication of all parts of the turbine and guard against the onset of problems associated with oil degradation and contamination.
The Standard Practice for In-Service Monitoring of Lubricating Oil for Auxiliary Power Plant Equipment (ASTM D6224) was approved and published earlier this year. This Standard Practice complements ASTM D4378 in that it has a similar format and addresses important equipment other than the major turbines.
Lubricating oils in equipment such as gears, diesel engines, pumps, compressors, hydraulic systems, and electrohydraulic control systems are included. Like all ASTM standards, this is a consensus document and represents the expertise of oil producers, oil users, and those with a general interest (such as commercial testing laboratories).
This new Practice seeks to educate the user by describing the general properties of the various types of lubricating oils and by describing the various tests which can be used to monitor the lubricating oil or equipment in which it is used.
It also describes the factors affecting the service life of oils and defines proper sampling techniques. Users of this Practice should reduce operating costs by changing oil only when needed as determined by oil testing.
Users should also reduce maintenance costs by relying more on oil analysis results to determine when to make equipment repairs instead of doing so on a scheduled basis.
The five tables in this Practice provide guidance on sampling and testing. Table 1 provides guidelines on the types of testing that would be appropriate for characterizing or determining the acceptability of new oils.
Table 2 contains guidelines for sampling and testing in-service oils. In both tables, each type of test is described as being recommended, optional, as-needed, or not normally relevant for individual oil types. A recommended test is one which provides the most information about the oil quality or equipment condition and which should be included in a good oil-monitoring program. An optional test is one that may provide additional information but could be omitted with less impact if the sample amount or analysis time is limited.
A test that is deemed as-needed may be beneficial if there is an operational problem (e.g., foaming) or if another test result indicates the need. If a test is not generally informative for a given type of oil, then there will be no entry in Tables 1 and 2. Each user is able to customize their oil-monitoring program by using these guidelines and considering their own operation and resources. While this Practice references mostly ASTM methods, it does not preclude the use of alternative instrumentation or test methods.
Table 3 includes warning levels of in-service oil test results. These warning levels are either an absolute value, a percent of the new oil, or a statistical deviation from trend data. Table 4 provides an interpretation of the oil test results and gives recommended action steps. Table 5 lists possible sources of inorganic elements (wear metals and additive elements) in oil in order to help interpret elemental analysis results.
The 1997 version of ASTM D4378 is available in Volume 5.03 of the 1998 Annual Book of ASTM Standards. A copy of ASTM D6224 (or D4378) can be obtained by calling ASTM Customer Service at 610/832-9585 or from ASTM's website, www.astm.org.
Also, D-2.C Turbine Oils is planning a symposium on “New Generation Turbine Oils”. For more information contact Bill Herguth, Secretary D-2.C Turbine Oils at 800-645-5227.