A manufacturer of industrial products had 32 hydraulic systems, all filled with mineral oil-based fluid. Six of the systems were near potential ignition sources, so they decided to fill them with one of our synthetic ester-based fluids for safety reasons.

Robert Johnson

They informed their contract laboratory that these six systems now contained synthetic ester instead of mineral oil. When the monthly report came back, their lab said that three of the six systems showed “low viscosity readings,” and low phosphorus levels. They claimed to have experience in testing our product, and concluded that the fluid had been improperly blended, resulting in low viscosity and low phosphorus levels. They also concluded that there had been “no cross contamination” between the systems.

Seeing the peak clearly

Our technical representative visited the plant, and he and the chief engineer personally collected samples from all six systems. When I received them, we immediately prepared infrared spectra of all six. Fourier Transform Infrared Spectroscopy, or FTIR, is a tool that helps us identify chemical compounds, based on the fact that every molecule has a unique spectrum. Mineral oils have a very simple spectrum with only four major peaks, but esters have a more complex spectrum that is easily identifiable. Pure ester has a major peak near the center of the spectrum, while mineral oil has no peak there. Not only is it possible to easily distinguish between mineral oil and ester, but by blending known amounts of the two, it becomes possible to compare a spectrum of an ester-based system sample and calculate the actual amount of mineral oil contamination.

Testing ensures safety

Mineral oil and Ester-based hydraulic fluid spectra
Select for full image

The FTIR analysis showed that three of the six systems contained pure mineral oil — in other words, our customer’s maintenance department never changed over to ester-based fluid as they claimed. Elemental analysis by X-Ray spectroscopy showed that all three contained zinc dithiophosphate additive, which is used in mineral oils but not in esters. The other three systems did contain ester fluid, but contaminated with mineral oil ranging from 9 to 18%, probably from inadequate draining during change-over. Because 5% mineral oil contamination is considered the maximum level for safe use, all six of the systems were out of specification.

I informed our customer that three of his systems still contained mineral oil in spite of the incorrect conclusions from his contract laboratory, and that the other three were considered too contaminated for safe use. If the contract lab had used FTIR, or had analyzed for zinc and sulfur in addition to phosphorus, or had simply checked specific gravity, they should have recognized that these samples were not ester-based fluid. Unfortunately, they did not have the capability of recognizing that completely wrong fluid was in the systems, rather than “improperly blended” material, a potentially deadly conclusion.

Because we offer free testing, we suggested they send system samples to us for periodic analysis.

Robert Johnston is group leader, Analytical Services for Houghton International. Contact Johnston at (610) 666-4114 or via email RJohnston@houghtonintl.com