What this product reference covers.
Circulating oil is a continuously recirculated lubricant selected for reliable film formation, cooling, demulsibility and long oxidation life.
Products within the family.
Names used in commerce can overlap. Use the nominated standard and exact grade rather than relying on a generic product label.
R&O circulating oil
R&O circulating oil is a recognised circulating oil category whose exact composition, grade limits and suitability must be confirmed from the governing specification and equipment requirement.
Paper-machine oil
Paper-machine oil is a recognised circulating oil category whose exact composition, grade limits and suitability must be confirmed from the governing specification and equipment requirement rather than inferred from the generic label.
Bearing circulation oil
Bearing circulation oil is a recognised circulating oil category whose exact composition, grade limits and suitability must be confirmed from the governing specification and equipment requirement rather than inferred from the generic label.
Synthetic circulating fluid
Synthetic circulating fluid is a recognised circulating oil category whose exact composition, grade limits and suitability must be confirmed from the governing specification and equipment requirement rather than inferred from the generic label.
What the product is built from.
| Component | Technical role |
|---|---|
| Mineral, synthetic or renewable base fluid | Provides the principal lubricating film and viscosity-temperature foundation. |
| Anti-wear / extreme-pressure system | Protects loaded contacts where the application requires it. |
| Antioxidant and corrosion inhibitors | Control ageing, deposits and surface corrosion. |
| Application-specific additives | Tune detergency, friction, demulsibility, air release, tackiness or seal compatibility. |
Define the decision before selecting the panel.
- 01
Confirm new circulating oil identity, grade and fitness for the intended application.
- 02
Detect contamination, degradation, mixing or storage-related change.
- 03
Investigate abnormal equipment, combustion, filtration or handling behaviour.
- 04
Establish a representative baseline for later comparison.
- 05
Support specification, maintenance and root-cause decisions with corroborated evidence.
What each result contributes.
“High” and “low” are directional investigation prompts, not pass/fail decisions. Corroborate them using the correct specification, baseline and companion evidence.
Open ASTM, ISO, IS/BIS, DIN and companion methods →| Test / parameter | Typical methods | Why it matters | Possible causes when high | Possible causes when low |
|---|---|---|---|---|
| Kinematic viscosity | ASTM D445 / ISO 3104 | Confirms grade and detects dilution, shear, oxidation or mixing. | Oxidation, wrong oil, soot, evaporation or heavy contamination. | Shear, fuel/solvent dilution, wrong grade or lighter make-up oil. |
| Acid number | ASTM D664 | Trends acidic constituents, oxidation and contamination against a new-oil baseline. | Oxidation, overheating, acidic contamination or wrong fluid. | Fresh oil, make-up dilution or formulation difference. |
| Water | ASTM D6304 | Quantifies moisture relevant to corrosion, additive loss and film strength. | Condensation, cooler/seal leak, washdown, storage or sampling contamination. | Dry operation or dehydration; hot sampling can reduce free-water representation. |
| Elemental analysis | ASTM D5185 with PQ / ferrography where needed | Screens wear, contaminants and additive chemistry within method limitations. | Wear, corrosion, dirt, additive source, wrong oil or maintenance debris. | Stable wear, dilution, filtration or particles too large for ICP response. |
| FTIR condition | ASTM E2412 trending | Tracks oxidation and selected molecular contaminants against a comparable reference. | Heat, extended service, contamination or depleted antioxidant reserve. | Fresh oil, make-up dilution or a non-comparable baseline. |
| Particle count / cleanliness | ISO 11500; reporting to ISO 4406 | Quantifies solid-particle cleanliness where component clearances and servo reliability are sensitive. | Dirt ingress, active wear, ineffective filtration, maintenance debris or wrong sampling point. | Effective filtration or clean new oil; settling, dilution or non-representative sampling can under-report. |
| Water separability / demulsibility | ASTM D1401; ISO 6614 | Assesses the oil's ability to release water in circulating, turbine, gear and hydraulic systems. | Report as persistent emulsion or longer separation time: oxidation products, incompatible mixing, detergency or contamination. | Faster separation is usually favourable but does not prove absence of dissolved or free water. |
| Air-release properties | ASTM D3427; ISO 9120 | Measures how rapidly entrained air separates from oil in turbines, hydraulics and high-circulation systems. | Report as longer release time: oxidation, contamination, wrong viscosity, silicone contamination or formulation mismatch. | Shorter time is usually favourable; compare at the specified temperature and viscosity grade. |
| Foaming tendency and stability | ASTM D892; ASTM D6082 where high-temperature sequence is relevant | Screens air-handling behaviour associated with reservoir foaming, compressibility, oxidation and pump or clutch performance. | Air leaks, contamination, additive depletion, overfilling, wrong oil or poor reservoir return design. | Low foam is generally favourable; antifoam overdose can impair air release even when surface foam is low. |
| Remaining oxidation stability / RPVOT | ASTM D2272 | Estimates remaining oxidation resistance for comparable turbine or circulating oils; best interpreted as retention against a new-oil baseline. | Higher minutes or retention usually indicate more remaining reserve; unusually high values can reflect a non-comparable formulation. | Antioxidant depletion, heat, air entrainment, catalytic metals, water or extended service. |
| Varnish potential / membrane patch colorimetry | ASTM D7843 | Measures lubricant-generated insoluble colour bodies associated with soft-contaminant and varnish risk in turbine and circulating systems. | Oxidation products, thermal stress, electrostatic discharge, additive reactions or poor solubility balance. | Lower insoluble loading; recent filtration or varnish removal can reduce the result without restoring antioxidant reserve. |
Five-step evidence analysis.
Move from a trustworthy sample to a tested failure hypothesis, proportionate maintenance response and documented confirmation. Each step increases or reduces diagnostic confidence.
Choose a representative sampling procedure →- 01Validate the evidence: confirm asset identity, a repeatable live-zone sampling point, operating state, oil hours, make-up volume and recent maintenance for paper machines. Repeat the sample when identity, container, flushing or handling is doubtful.
- 02Establish the correct baseline: confirm the declared circulating oil grade, base chemistry and additive profile. Compare method-consistent results with new oil, the previous stable sample and rate of change rather than a universal limit.
- 03Build the contamination pattern: Combine water, particles and process ingress with separator, breather, seal and filtration performance. Require an independent companion signal, inspection finding or filter observation before assigning a source.
- 04Test and localise the failure hypothesis: Correlate oxidation, varnish tendency and wear metals with bearing temperatures, flow and deposit inspection. Check whether the proposed mechanism explains the full pattern, including contradictory or absent evidence.
- 05Select and verify proportionate action: Correct ingress or circulation weakness, manage deposits, inspect the indicated bearing zone and confirm at comparable load. Record the intervention, resample at a risk-based interval from the same point and confirm that the trend responded as expected.