Hi Jeff
With large compression ignition engines oil filter inspection is often the only way you can be sure of contamination ingression.
We are very fortunate in so much that we are able to view engine oil samples from large spark ignition, nat gas, and compression ignition engines Sized 1000-2500 kw with the microscope.
We have noted 5 substancial failures where the ICP only gave an increase of 5-10 ppm of SI, 5-15 Fe, 1-3 Chrome and 5-10 ppm Pb,
certainly not enough info to pull a 1200 KW engine off line.
Approx two weeks after the slight increase in the ICP results one engine put two legs out of bed with the repair bill > $500,000.
Our experience indicates the best way to monitor engines appears to be the ICP including PQ and as soon as there is an flutter in the figures remove and section the oil filter to confirm,
cut a 50X50 mm, 2" X 2" peice of element out and ultrasonic in filtered solvent and refilter @ 11 µm and again @ 3 µm if required,
Slide mount and take images with the microscope
usually there is a huge amount of wear debris present and rather than forcing the operator to service the application he usually runs out the door and commences to service the machine immediately.
Remember as per grease exams by microscope this is qualative and not quantative,
Rob S