Oxidation Stability by RULER / RPVOT

RPVOT and RULER oil analysis tests are performed on industrial lubricants to determine the life left in the oil so as to identify when the oil needs changing. This is done by measuring anti-oxidants directly in RULER or through resistance to oxidation testing (RPVOT).

RPVOT (75ml)/ RULER (10ml)These tests measure the oxidation stability or concentration of antioxidants in a lubricant and hence it’s remaining life. RPVOT (Rotating Pressure Vessel Oxidation Test) submits a sample of the lubricant to high pressure, high temperature (150OC), pure oxygen and water with a copper catalyst to promote oxidation and measures the time in minutes for the oil to absorb 25% of the available oxygen (i.e. when the anti-oxidants in the oil are spent). The way this is achieved is during the process the oil absorbs oxygen once the anti-oxidants are spent and the pressure in the vessel drops. Oils in relatively good condition can take several days of running time to process if they have high RPVOT values. An advantage of the RULer (Remaining Useful Life) is that rather than oxidising the oil to indirectly measure how much anti-oxidant is remaining, the RULER directly measures how much is remaining making the test quicker. However, the disadvantage is that a reference oil is always required for comparison. Therefore:

  • RULER is ideal when a fast turnaround is required and a reference oil of the unused oil can be provided for comparison.
  • RPVOT is ideal when a reference oil of the unused oil cannot be obtained, or the oil in the system is unknown.

Tested On: Large circulating oil systems such as steam and gas turbines, Paper machines etc where the oil is likely to be in use for several years and a single oil change is a very large cost.

Diagnostic significance: The significance of the test is to allow a business to plan for oil changes, which can sometimes take several days to perform and require sometimes months of notice before implementing.

Typical Diagnostic limit: 75% drop in value from reference oil or 75% drop from first sample if no ref oil available. Serious limits are typical 90% drop from ref oil / first sample or on RPVOT <100 minutes remaining. This is a guide only, as customers may start planning for oil changes / consulting their oil supplier for advice much earlier than these limits so a plan can be made for corrective action.