By Robert Johnston
Houghton International
Valley Forge, Pa.

Most producers of hydraulic fluids have laboratories responsible for routine testing of customer systems. Some also have an analytical services laboratory for troubleshooting customer problems, such as fluid contamination, pump wear, seal damage, and other nonroutine situations. As the manager of such a laboratory, it is my job to assign relevant tests to my chemists, and then use the data to try to solve the customer’s problem — sort of a detective agency for hydraulic system problems.

This is the first of what I plan to be many columns in Hydraulics & Pneumatics summarizing interesting stories about systems gone wrong, in the hope you will pick up tips to keep your systems working properly.

Case background

In December 1997, a steel mill sent us a filter from one of its hydraulic systems. Our technical service lab had been reporting high particle counts in this user’s routine fluid samples for several months, and now they were experiencing rapid clogging of filters.

We opened the filter and scraped off some of the solid debris. After rinsing it with solvent to remove the residual ester-based hydraulic fluid, we began analysis of the solids. Microscopic examination showed a large amount of what appeared to be irregularly shaped white pebbles. Fourier Transform Infrared Spectroscopy indicated that carbonates and silicates were present, and Energy Dispersive X-Ray Spectroscopy showed high levels of calcium, silicon, and iron.

Over the years, I had examined dozens of filters from steel mills that were experiencing pump failures, and most were found to be contaminated with slag dust. Chemically, slag dust contains most of the compounds our analysis had identified, but it looks different through a microscope. Slag dust normally contains small nodules of metal, grains of sand, limestone dust, and other recognizable debris, but the filter from this user contained some odd-looking pebbles, wear metal debris, and not much else.

It didn’t seem to be slag dust, more likely some type of clay mixture. We contacted them and asked if they ever used kitty litter or something similar to treat oil spills. They replied that they kept drums of “floor dry” on hand, and they sent a sample. We analyzed it as soon as it arrived, and it turned out to be identical to what we had found in their filter. Apparently someone had spread it on top of the hydraulic tank to pick up an oil spill, and it had gotten into the system.

The neverending problem

During the following Easter shutdown, the mill contracted a company to clean out their hydraulic system. One week later we received a sample of varnish that they found on hose fittings. Analysis of this dry white material identified it as a combination of citrate and phosphate salts. A check of the material safety data sheets showed that the solution for cleaning out the system contained sodium citrate and sodium phosphate. The solution had never been properly rinsed out, leaving this dry residue on surfaces. The contractor was called back to perform a second cleaning to prevent further contamination of the hydraulic oil.

Seven years later, in 2005, this user began experiencing massive pump failures. We obtained a filter and a fluid sample from their system, and once again, kitty litter was identified as the culprit. A new generation of workers had replaced the old timers — a reminder that those who do not remember the past are condemned to repeat it.

Robert Johnston is group leader, Analytical Services for Houghton International, Valley Forge, Pa. Contact him at (610) 666-4114 or email