Gear and Hydraulic Oil Analysis Consulting
A gear or hydraulic oil analysis measures wear metals, particles, water, viscosity and additives in the oil that lubricates a gearbox or transmits power in a hydraulic system. It shows whether components wear, whether the oil is clean and dry, and whether it still protects. We turn the results into an equipment assessment and a recommendation: monitor, filter or change the oil.
TriboTech is a consulting engineering company, not a laboratory. Ask us for an analysis programme for your gearboxes and hydraulic systems.
Consultants, not a laboratory
We plan the analysis programme, supply the sampling kit and instructions, take the sample ourselves by agreement, and interpret the results. The analyses are carried out by our partner laboratories.
The laboratory measures. The interpretation and the recommendation are what you buy from us.
What does oil analysis tell you about a gearbox or hydraulic system?
We ask four questions of every sample:
- Are the components wearing? Wear metals and ferrous wear debris.
- Is the oil clean? The ISO 4406 cleanliness code.
- Is the oil dry? Water content.
- Does the oil still protect? Viscosity, additives, oxidation and acid number.
The questions cover the three categories that ASTM D8112, the sampling guide for in-service industrial oils and hydraulic fluids, sorts oil analysis into: equipment wear, system contamination and lubricant chemical condition. The guide recommends an alarm limit for at least one key measurement in each category.
The analysis programme
We agree the programme per component. ✓ means the test is a standing part of the programme.
| Parameter | Method | Gear oil | Hydraulic oil (pitch) |
|---|---|---|---|
| Cleanliness, ISO 4406 code | Microscope count on a membrane filter; for hydraulic oil also an automatic particle counter | ✓ | ✓, the primary parameter |
| Ferrous wear debris | Magnetometry, ASTM D8120 | ✓ | ✓ |
| Elements: wear, additives, contaminants | ICP, ASTM D5185 | ✓ | ✓ |
| Water content | Karl Fischer, ASTM D6304 | ✓ | ✓ |
| Acid number | ASTM D664 | ✓ | ✓ |
| Viscosity at 40 °C | ASTM D445 | ✓ | ✓ |
| Viscosity index | Calculated, ASTM D2270 | When viscosity at 100 °C is measured | When viscosity at 100 °C is measured |
| Oxidation, qualitative | FTIR | ✓ | Usually not |
| Antioxidant and ZDDP reserve | Voltammetry | Not routine | ✓ on zinc (ZDDP) oils |
Add-ons
- MPC test for varnish.
- Extended elemental analysis, for example extra elements when grease or coolant ingress is suspected.
How we interpret
Wear: two iron measurements and images of the debris
ICP is calibrated on oil-soluble metals, and ASTM D5185 states that it gives low results for particles larger than a few micrometres. Magnetometry to ASTM D8120 measures ferrous debris across the full range of particle sizes. When the two iron measurements agree, the wear signal is corroborated.
For units with a finding, the report shows microscope images of the membrane, so you see whether the particles are wear debris or outside dirt.
Cleanliness: the ISO 4406 code
ISO 4406 defines the code only and sets no target. We assess the code against the cleanliness limit we recommend for the component in your programme, and against the trend. Where the component manufacturer sets a cleanliness requirement, for example as a warranty condition, it is taken into account once you give it to us.
A microscope and an automatic particle counter size particles differently, and ISO 4406 notes that the two methods give a different size for the same particle in most cases. A change of laboratory or counting method can shift the code without any change in the oil.
Gear oil is always counted by microscope on a membrane filter. The oil is dark and viscous, and what has to be judged is the debris itself. For hydraulic oil, the counting method is agreed per programme, and an elevated automatic count is confirmed by microscope before it is reported.
Additives and oxidation
Additives are read against the specific oil product. The same element can be an additive in one oil and a contaminant in another: zinc is part of the anti-wear package in a ZDDP hydraulic oil, but a contamination indicator in some zinc-free gear and hydraulic oils.
- Gear oil: the routine programme rests on elemental, functional and wear analysis. Voltammetric antioxidant monitoring is not routine on gear oil. See Gear Oil Additives.
- Zinc (ZDDP) hydraulic oil: every sample gets a voltammetric reading, trended against the oil's own reference. According to ASTM D7590, there is no ASTM method for ZDDP-type antioxidants in industrial lubricants, so the ZDDP reading is a trend, not a standard limit. In our pitch-system experience, additive depletion and particle count end the oil's life, and oxidation lags. See Hydraulic Oil Condition Monitoring.
- Zinc-free hydraulic oil: here our routine programme has a real gap where the anti-wear additive is concerned (see the question on zinc-free oil below).
Acid number is trended on both oils. On gear oil it is supplemented by a qualitative FTIR assessment of oxidation.
Viscosity and viscosity index
The viscosity index is calculated to ASTM D2270 from the viscosity at 40 °C and 100 °C. In our practice, a change in viscosity index on a PAO gear oil points to a top-up with the wrong oil. On a high-VI hydraulic oil, a drop points to mechanical shear of the viscosity-index improver.
Wind turbine gearboxes, pitch hydraulics and industrial plant
Main gearbox
The programme can be used for routine fleet campaigns, end-of-warranty campaigns and follow-up after a gearbox replacement.
Pitch hydraulics
Cleanliness leads the assessment. Offshore, an oil change typically means a vessel mobilisation, which makes changing oil on suspicion rather than data expensive.
Industrial plant
ASTM D8112 is written for industrial applications, so the method basis is the same. We also interpret fire-resistant and less flammable hydraulic fluids (HFC and HFDU) and aviation hydraulic fluids.
From result to action
Depending on what drives the result, the recommendation can be:
- continued trending
- a control sample or a shorter interval
- a filter change
- offline filtration or dewatering
- a partial or full oil change
- for gear oil: readditivation, only where the oil supplier supports it
We also advise on filtration and filtration equipment, and follow the effect with condition monitoring.
How it works
- The agreement. Before we deliver the first analysis or interpretation, you and we sign a framework agreement, and each task is agreed separately.
- The programme. We set the programme per component and campaign: routine, end of warranty or follow-up after a repair.
- Sampling kit and instructions. We send the sampling kit and instructions. By agreement, we take the sample or train your staff on site.
- Sampling. ASTM D8112 names the choice of sampling port location as the most critical factor.
- Shipping. The sample is sent to the laboratory as soon as possible after sampling. ASTM D8112 recommends that samples for an external laboratory be transported within 48 h.
- Analysis, interpretation and report. Our partner laboratories analyse the sample. We interpret each sample against the oil product, the component and its history, and issue TriboTech's report.
The delivery time is agreed in the task agreement.
What you get
For each unit: status, findings, recommended action and the next sampling date, set against earlier results, ours or ones you send us.
For a campaign across a fleet, also:
- a fleet overview with every unit and parameter in one matrix
- membrane images for the units with a finding
- numbered recommendations per unit
Who we work for
We work for clients in offshore and onshore wind in Northern Europe, and in industry and production.
Independent advice
We sell neither lubricants, filters nor filtration equipment. Our recommendation rests on your data, the standards and our professional judgement – not on equipment we have to sell. If your data do not show a need for filtration or an oil change, we do not recommend one.
Your advisors
Jesper Vinther is Managing Director and Partner at TriboTech, holds a PhD and is a Certified Lubrication Specialist (STLE). Hans Møller is Market Director and Partner and holds an M.Sc. in Physics and Chemistry; his professional foundation is the Theory of Sampling (TOS). They are your advisors on gear and hydraulic oil programmes.
Frequently asked questions
What does a gear oil analysis show about the gearbox?
It shows whether the gearbox wears, whether the oil is clean and dry, and whether it still protects. Wear is read from iron measured two ways: magnetometry captures ferrous debris regardless of particle size, including the coarse particles that ICP under-reads. Cleanliness is read from the ISO 4406 code, water by Karl Fischer titration, and protection from viscosity, additive elements and acid number.
What does an ISO 4406 code such as 18/16/13 mean?
Measured with an automatic particle counter, the three numbers are scale numbers for particles of at least 4, 6 and 14 µm(c) per mL. One step up in a number generally represents a doubling of the contamination. The code in the question is only an example, not a target. ISO 4406 sets no target. The target comes from the component manufacturer or from the limit we recommend in your programme. Try the ISO 4406 tool.
How often should gear and hydraulic oil be analysed?
ASTM D8112 ties the interval to how fast a failure develops. Typically it is half the time from when a fault becomes detectable until it becomes a functional failure. For critical equipment, or where repair times matter, it should be a third. The interval is then adjusted for operating severity, criticality, machine age and oil condition. We set the interval per component in your programme.
How do you take a representative sample from a gearbox or hydraulic system?
Take it from a fixed sampling port downstream of the components, after the equipment has run at normal load and temperature for at least 20 minutes. If the equipment must be shut down, take the sample within 10 minutes of the stop, to minimise particle settling. Use the same procedure every time. Those are the instructions in ASTM D8112. We send sampling instructions and, by agreement, take the sample on site.
Should the oil be changed, or can it be filtered?
It depends on what drives the result. Particles can be removed with a filter change or offline filtration. Filtration does not help with depleted additives, because it does not restore them. Then the choice is a partial or full oil change. We sell neither oil, filters nor filtration equipment, so the recommendation rests on your data – not on equipment or oil we have to sell.
Can the additives in zinc-free hydraulic oil be measured?
Only partly. On zinc-containing oils, a voltammetric reading follows the anti-wear and antioxidant additives against the oil's own reference. On zinc-free oils there is no ZDDP signal to follow, and for the anti-wear additive, total phosphorus by ICP is all our routine programme has left. It does not show the additive's condition, and we say so openly in the report.
Can oil analysis miss damage?
Yes. ICP gives low results for particles larger than a few micrometres, and in our experience some damage releases little debris into the circulating oil. Oil analysis complements vibration monitoring and inspection. It does not replace them.
Contact us
Tell us about your gearboxes and hydraulic systems, and we will propose an analysis programme. If you have a gear or hydraulic oil report from another laboratory, send it to us and we will come back with a proposal for interpreting it, as far as the measured data allow.