How to choose oil analysis tests for each industrial machine

Order viscosity, acid number, elements, water and particle count for most sumps; add ferrous debris for gearboxes and pumps, RPVOT and MPC for turbine oils. RPVOT is the rotating pressure vessel oxidation test; MPC is membrane patch colorimetry. The slate assumes mineral oils trended against a baseline and is adjusted to each machine's failure modes (ASTM D7874-13, 2022).

• ASTM D5185 determines 22 elements in used oils, but its results are particle size dependent, and low results are obtained for particles larger than a few micrometers (ASTM D5185-26, 2026).

• ASTM D7647 counts particles from 4 µm(c) to 200 µm(c) in oils with a viscosity up to 1000 mm2/s at 40 °C (ASTM D7647-24, 2024).

• ASTM D8184 assigns no general limits to PQ values; they are read against the machine's own history and service logs (ASTM D8184-18e1, 2019).

• ASTM D6224-23 covers gears, hydraulic systems, pumps and compressors in power plants on mineral oil and phosphate ester fluids, while ASTM D4378-24 covers mineral turbine oils (ASTM, 2023 and 2024).

This guide covers stationary industrial machines on mineral oil, sampled on a schedule and trended. It does not cover engine oils, which add base number and fuel dilution tests, greases or insulating oils. Where the machine maker specifies tests and limits, start from those and add to them.

Which conditions decide the oil analysis test slate?

Four conditions decide the oil analysis test slate for an industrial machine: its failure modes, the consequence of a failure, the oil type and the operating conditions of the sump. ASTM D7874 is a guide that applies failure mode and effect analysis (FMEA) to choose in-service lubricant tests, so each test is linked to a failure mode it can detect at an early stage (ASTM D7874-13, 2022). The same guide notes that failure modes may be similar from one application to the next, but the risk and consequences of failure may differ, so two identical gearboxes can justify different slates. Consequence sets the depth: tests and their frequency should be balanced between the associated risks and the expected program savings (ASTM D7874-13, 2022). Oil type limits which practices apply. ASTM D6224-23 is written for mineral oils and phosphate ester control fluids, not other synthetics, whose users should consult the manufacturer (ASTM D6224-23, 2023). Operating conditions add tests: heat speeds oxidation, so a sump at or above 70 °C (158 °F) is a strong candidate for rapid lubricant degradation (STLE TLT, 2009), and water exposure calls for a water screen confirmed by Karl Fischer testing (STLE TLT, 2009). Record these four per machine first.

What are the main types of oil analysis tests?

The main types of oil analysis tests fall into three groups: oil condition, contamination and wear. Oil condition tests include kinematic viscosity (ASTM D445), acid number by potentiometric titration (ASTM D664), RPVOT (ASTM D2272) and, for turbine oils, MPC (ASTM D7843) (ExxonMobil, 2016). Contamination tests include water by Karl Fischer titration, ASTM D6304, and particle count (ExxonMobil, 2016). Automatic particle counters are calibrated to ISO 11171 (ASTM D7647-24, 2024), and ISO 4406:2021 specifies the code used to define the quantity of solid particles in a hydraulic fluid (ISO 4406:2021). Wear tests include elemental analysis (ASTM D5185), ferrous density by a particle quantifier (ASTM D8184) or direct reading ferrography, and analytical ferrography. The groups overlap, because elements also reveal dirt, coolant leaks and the wrong oil: ASTM D5185 states that a marked increase in boron, sodium or potassium can indicate coolant leakage (ASTM D5185-26, 2026). STLE recommends building each slate in two layers, primary tests for every sample and secondary tests that run automatically once predefined alarm values for the primary tests are surpassed (STLE TLT, 2009). Elemental analysis gives low results for particles larger than a few micrometers (ASTM D5185-26, 2026), so on its own it misses the large debris of severe wear.

Decision table: oil analysis test slate by machine

The decision table below sets the minimum oil analysis tests to order for each machine type, with the failure mode each added test catches. The base slate in every row is viscosity (ASTM D445), acid number (ASTM D664), elements (ASTM D5185), water by Karl Fischer (ASTM D6304) and particle count coded to ISO 4406:2021. The Bureau of Reclamation lists the same five as periodic laboratory tests (USBR FIST 2-4, 2024).

The row that most often changes an order is the gearbox: STLE states that in industrial gearbox and pump applications, where gears and element bearings are the primary wearing parts, ferrous density analysis should also be part of a standard test slate (STLE TLT, 2009). Turbine rows follow ASTM D4378-24, which covers mineral turbine oils in steam, gas and combined cycle turbines (ASTM D4378-24, 2024). Auxiliary power plant equipment such as gears, hydraulic systems, pumps and compressors falls under ASTM D6224-23 instead (ASTM D6224-23, 2023). The failure mode column applies the FMEA logic of ASTM D7874 (ASTM D7874-13, 2022); the row assignments combine the STLE failure mode guidance (STLE TLT, 2009) with the ASTM practices and are a starting point, not a rule.

Which oil analysis tests does a hydraulic system need?

A hydraulic system needs the base oil analysis slate with particle count as the lead test, because hard particles drive wear of hydraulic pumps and valves. ASTM D7647 states that hard particles can have a serious impact on the life of pumps, pistons, gears, bearings and other moving parts by accelerating wear and erosion, and that high contaminant levels can cause filter blockages (ASTM D7647-24, 2024). The same method states that particle count results help assess the filtration system, decide whether off-line filtration is needed, or decide whether a fluid change is required. Two interferences matter in hydraulic oil. Free water is counted as particles unless masked, and soft particles such as silicone defoamant and oxidation by-products cause falsely high counts; ASTM D7647 uses dilution to remove both (ASTM D7647-24, 2024). Report the result as an ISO 4406:2021 code for targets, but for wear trending STLE advises monitoring the raw count above 14 µm rather than the code, since a rise in large particles quickly reveals the onset of aggressive wear (STLE TLT, 2009). Hydraulic vane and piston pumps are among the components that STLE lists as susceptible to severe wear (STLE TLT, 2009). Water by Karl Fischer and acid number complete the slate. Phosphate ester control fluids in power plants are covered by ASTM D6224-23 (ASTM D6224-23, 2023).

Which oil analysis tests does a turbine oil need?

A turbine oil needs the routine oil analysis slate plus tests for remaining oxidation life and varnish potential, mainly RPVOT and MPC. STLE lists viscosity, elemental spectroscopy, particle count, water content and FTIR as routine tests, and names water separability, foaming, rust prevention, RPVOT, linear sweep voltammetry, ultracentrifuge testing and MPC as tests commonly added for in-service turbine oils (STLE TLT, 2015). The same source states that basic testing may be conducted at monthly or quarterly intervals and additional testing annually or semiannually. RPVOT reports the minutes until a 175 kPa pressure drop, and the in-service result should be compared to the new oil value for that product, because starting values vary greatly between products (STLE TLT, 2015). ExxonMobil reported that ASTM D4378 identifies a decline to 25 percent of the new oil RPVOT value with an increase in acid number as a warning limit, and recommended annual RPVOT testing (ExxonMobil, 2016); that report cites an earlier D4378 edition, so confirm the limit in a licensed copy of D4378-24. MPC extracts insoluble contaminants onto a membrane patch and reports a ΔE color value, and its results are intended as a trending tool within a program such as ASTM D4378 (ASTM D7843-25e1, 2025). ASTM D4378-24 itself states that its test values are purely indicative (ASTM D4378-24, 2024).

Which oil analysis tests does an industrial gearbox need?

An industrial gearbox needs the base oil analysis slate plus a ferrous density test, because gear and bearing wear produces iron debris too large for elemental analysis. ASTM D5185 uses oil-soluble metals for calibration, and low results are obtained for particles larger than a few micrometers (ASTM D5185-26, 2026). STLE explains that a severe wear mode produces large debris that elemental analysis cannot detect, so a gearbox slate should include ferrous density by direct reading ferrography or a particle quantifier (STLE TLT, 2009). ASTM D8184 applies particle quantifier (PQ) magnetometry to trend the mass of ferrous debris in machinery such as engines and gearboxes, and reports a PQ Index that scales with the ferrous debris burden (ASTM D8184-18e1, 2019). The method also states that it is not possible to assign general limits for abnormal conditions, so PQ values should be read against historical data and service history, with ASTM D7720 for setting alarm limits. Particle counts on high-viscosity gear oils need care: ASTM D7647 uses dilution to counteract viscosity effects in highly viscous oils and applies up to 1000 mm2/s at 40 °C (ASTM D7647-24, 2024); the heaviest worm gear oils may exceed it, so ask the laboratory which count method it uses. Worm gears slide rather than roll, and their mating gears are usually made of dissimilar materials (USBR FIST 2-4, 2024), so a worm gear sump may show both gear metals; trend each against its baseline (ASTM D5185-26, 2026).

What are common mistakes in choosing oil analysis tests?

The most common mistake in choosing oil analysis tests is ordering one generic package for every machine. STLE calls for replacing generic oil analysis test slates with machine-specific test slates and alarm sets, and states that basic or comprehensive test groups are not appropriate for current maintenance needs (STLE TLT, 2009). A second mistake is relying on elemental analysis to catch severe wear in gearboxes and pumps, when its results fall for particles larger than a few micrometers (ASTM D5185-26, 2026). A third is judging a single result with no baseline. ASTM D5185 states that wear metal concentrations can indicate abnormal wear if there are baseline concentration data for comparison (ASTM D5185-26, 2026). A fourth is reading the ISO 4406 code alone when the raw count above 14 µm is the early sign of aggressive wear (STLE TLT, 2009). A fifth is applying a published limit to every machine: ASTM D4378-24 states its values are purely indicative and depend on equipment type, workload, circuit design and top-up level (ASTM D4378-24, 2024). A sixth is running MPC on dyed turbine oils, for which ASTM D7843 states the method is not appropriate (ASTM D7843-25e1, 2025). Finally, do not choose a new turbine oil by its RPVOT value alone (STLE TLT, 2015).

When should you call an oil analysis specialist?

Call an oil analysis specialist when the test slate, the alarm limits or a result needs judgment that the decision table cannot give. ASTM D7874 states that its FMEA method serves as an initial justification for selecting tests and sampling frequencies, and that plant operating experience along with the review and benchmarking of similar applications is required (ASTM D7874-13, 2022). Typical triggers are a machine whose failure could cause component disintegration, where ASTM D7874 says any fluid test that can predict the condition should be included; a turbine with a varnish caution result, which ExxonMobil recommends confirming by visual inspection of components (ExxonMobil, 2016); a synthetic fluid outside the scope of ASTM D6224-23; and a reservoir that has been topped up with more than one oil. STLE places responsibility on the machine owner to define test methods, secondary tests and alarm limits, and to give the laboratory the lubricant brand, type, grade and operating hours (STLE TLT, 2009). Before that call, Lubinpla can organize the machine conditions from your own documents and site history and return one cited document for the specialist to review, with your approval at each step. Bring the oil data sheets, the last reports and the maintenance history.

FAQ

How often should industrial oil be sampled for analysis?

Sampling frequency follows risk. ASTM D7874 can also be used to select the monitoring frequencies needed for each failure mode (ASTM D7874-13, 2022). For turbine oils, STLE reports basic testing at monthly or quarterly intervals and additional tests annually or semiannually (STLE TLT, 2015).

Can on-site test kits replace laboratory oil analysis?

No. On-site viscosity, water and particle count tests allow quick decisions, but the Bureau of Reclamation notes that field testing is not as complete or as accurate as laboratory analysis, and that laboratory tests should be performed as well (USBR FIST 2-4, 2024).

Should FTIR be part of a routine oil analysis slate?

Often, yes. STLE lists FTIR spectroscopy among the basic routine tests for rotating equipment (STLE TLT, 2015), and a rise in acid number together with FTIR oxidation is a strong indicator of fluid degradation (STLE TLT, 2009).

Working a case like this? Lubinpla works it from your own documents and site history, step by step with your approval. Free to start, no card.

Lubinpla does not sell chemical products and names no brands in recommendations. Our reviewer also leads a specialty chemicals distribution company.

Sources checked 2026-10-13.

Sources

1. ASTM International. D7874-13(2022) Standard Guide for Applying Failure Mode and Effect Analysis (FMEA) to In-Service Lubricant Testing. 2022. https://www.astm.org/standards/d7874

2. ASTM International. D4378-24 Standard Practice for In-Service Monitoring of Mineral Turbine Oils for Steam, Gas, and Combined Cycle Turbines. 2024. https://www.astm.org/standards/d4378

3. ASTM International. D6224-23 Standard Practice for In-Service Monitoring of Lubricating Oil for Auxiliary Power Plant Equipment. 2023. https://www.astm.org/standards/d6224

4. ASTM International. D5185-26 Standard Test Method for Multielement Determination of Used and Unused Lubricating Oils and Base Oils by ICP-AES. 2026. https://www.astm.org/standards/d5185

5. ASTM International. D7647-24 Standard Test Method for Automatic Particle Counting of Lubricating and Hydraulic Fluids Using Dilution Techniques. 2024. https://www.astm.org/standards/d7647

6. ASTM International. D7843-25e1 Standard Test Method for Measurement of Lubricant Generated Insoluble Color Bodies in In-Service Turbine Oils using Membrane Patch Colorimetry. 2025. https://www.astm.org/standards/d7843

7. ASTM International. D8184-18e1 Standard Test Method for Ferrous Wear Debris Monitoring in In-Service Fluids Using a Particle Quantifier Instrument. 2019. https://www.astm.org/standards/d8184

8. ISO. ISO 4406:2021 Hydraulic fluid power, Fluids, Method for coding the level of contamination by solid particles. Edition 4, confirmed 2026. https://www.iso.org/standard/79716.html

9. ExxonMobil. Technical topic: Laboratory tests for steam and gas turbine oils. 2016. https://www.global.mobil.com/-/media/project/wep/shared/lubricant-expertise/resources/pdf/marcom_techtopic_laboratory_tests_for_steam_and_gas_turbine_oils_us.pdf

10. Johnson, M. and Spurlock, M. Strategic oil analysis: Developing the test slates. STLE TLT Best Practices, July 2009. https://www.stle.org/files/TLTArchives/2009/07_July/Best_Practices.aspx

11. Malcolm, M. Turbine oil analysis report interpretation. STLE TLT, June 2015. https://www.stle.org/images/pdf/STLE_ORG/BOK/LS/Condition_Monitoring/Turbine%20Oil%20Analysis%20Report%20Interpretation_June15%20TLT.pdf

12. U.S. Bureau of Reclamation. FIST Volume 2-4, Lubrication of Equipment. Minor revisions approved 2024-05-29. https://www.usbr.gov/power/data/fist/FIST_2-4_(5-2024).pdf

Written by the Lubinpla team from the sources listed and checked against them before publication.