ASTM D4378 Standard Practice for In-Service Monitoring of Mineral Turbine Oils
ASTM D4378 Standard Practice for In-Service Monitoring of Mineral Turbine Oils for Steam and Gas Turbines
9. Monitoring Program
9.1 A sound monitoring program is based on four factors: (1) obtaining representative samples and testing at appropriate intervals; (2) logging, trending, and interpretation of test data; (3) action steps; and (4) insurance of maintenance follow-up.
9.2 Sampling and Testing of Oil Samples - Schedules for routine monitoring should be tailored to the individual facility depending on the criticality and severity of usage of the turbines. The schedules included in Table 1 (for steam turbines) and Table 2 (for gas turbines) are typical and should only be used as a guide. Refer to the OEM (original equipment manufacturer) instructions or other regulatory guidelines for lubricant testing requirements. In addition to the tests in Tables 1 and 2, any deposits found in the oil or removed from the system should be examined and identified (if possible).
9.3 Logging, Trending, and Interpretation of Test Data - It is important to keep accurate records of test results and make-up. Graphical representations are highly recommended for key parameters such as acid number, oxidation inhibitor, wear particle concentration, wear metals, and RPVOT. In this way, unusual trends become apparent and better estimates made of remaining service life. Interpretation of test data should take into account such factors as oil addition (make-up or replacement oil), possible intermixing of oils, newly installed parts, and recent system inspections. Guidelines for warning levels are provided for various lubricant types in Table 3. Oil supplier guidelines or original equipment manufacturer (OEM) guidelines, or both, supersede Table 3. These warning levels should also be considered with trending information.
9.4 Action Steps - The main purpose of a monitoring program is to ensure long trouble-free operation of the equipment. This can only be achieved by prompt and proper action steps when necessary. Such action steps must be based on a correct interpretation of test results (see Table 3), usually gathered over a period of time. Corrective action should generally never be taken on the basis of one test result since it may be incorrect due to poor sampling or faulty testing. Resampling and retesting is recommended before proceeding. Actions recommended by the oil supplier or the original equipment manufacturer, or both, supersede those in Table 3.
9.5 Maintenance Follow-Up - When maintenance is performed on equipment included in the oil monitoring program, the records of work performed and problems found should be documented and made available to those responsible for interpreting the oil test data. In this way, the test data interpreter can (1) ensure that recommended maintenance was performed, (2) make better recommendations, and (3) learn better how test data correlate with equipment problems.
10. Sludge and Deposits
10.1 The accumulation of sludge or deposits in any part of a turbine system is cause for concern. During outages, inspection should be made of all accessible parts of the system, in particular the reservoir, turning gear, and so forth. Varnishing is usually an indication that the oil has been in service too long. Samples of the deposits should be taken for analysis. During operation, any unusual amount of solids removed during centrifugation or filtration should be noted. An initial examination of any deposit can be made very simply. For this, a small amount of the deposit is washed free of oil with a petroleum solvent from a squeeze bottle. After drying, a small magnet can be used to separate iron-derived matter. Examination with a simple 10-power pocket magnifying glass will often help to decide the nature and source of the debris. If necessary, the deposit can be sent to a well-equipped laboratory for full identification. If significant amounts of sludge, arising from oil oxidation, are found in the system, action should be taken to clean out the system and replace the oil charge. If the deposit consists essentially of contaminant material such as fly ash or other debris, appropriate action is necessary to remedy the cause.
