Ferrous Debris Monitoring by PQ Index
by David Doyle, CLS, OMA I & II
General Manager, Tribology

PQ Index (Particle Quantification) is available as a quick and cost effective monitoring tool for ferrous particles in your routine oil analysis reports. By monitoring the level of ferrous (iron) particles over a period of time we can predict accelerated wear that may not be detected as early using standard spectrochemical analysis tools. This is because most standard spectrochemical analysis method for wear metals can be limited by particle size (8 to 10 micron maximum). PQI can detect larger ferrous (iron) wear particles that may not be detected or are partially detected in early stages of accelerated wear before they are small enough to be suspended in the oil.

PQI is similar to Direct Reading Ferrography in application. The advantage PQI has over Direct Reading Ferrography is that test results can be provided quicker to the customer at a reduced cost.

Reported test results are not an absolute quantity calculation. Instead results reported are a relative concentration index. A higher rate of ferrous wear will report an upswing in the trended index. Also equipment with a high concentration of iron, such as gear sets, will report higher trended historical data.

PQI data can also determine overall size concentration of iron particles. Low iron test results and a high PQI would indicate overall particles are large (<20 micron). High iron test results and a low PQI would indicate overall particles are small (<10 micron). If iron and PQI results are at relatively the same concentration then it usually indicates overall size range of particles is small. Seeing a test report with low iron test results and a high PQI, indicating overall large particles, can also predict accelerated wear or impending catastrophic wear, especially if there is a sudden upswing in the trend analysis.

PQI is especially suited for drive train components and gear sets in industrial settings and is an excellent trending tool. All ALS Tribology laboratories globally are equipped with PQ instrumentation. As well as being a quick and inexpensive trending tool it can also provide a trigger for more advanced testing such as Analytical Ferrography or microscopic debris analysis. PQI analysis trending can help maximize your wear debris monitoring for most heavy duty and industrial machinery.