Contamination Guide

Type: / Effect: / Type: / Effect:
Mainly rust; white particles: additives / Rapid oil ageing
Breakdowns in pumps & valves
Wear and tear. / Oil ageing products / Blocking of filters
Silting-up of system
Metal swarf / Breakdowns in pumps & valves
Wearing of seals
Leakage
Oil ageing / Particles and swarf in bronze, brass and copper / Breakdowns in pumps & valves
Oil ageing
Leakage
Wearing of seals
Gel-type residue from
filter element / Blocking of filter
Silting-up / Silicates due to lack of, or inadequate, air breather filter / Heavy wear on components
Breakdowns in pumps, valves
Wearing of seals
Coloured particles
(red/brown) Synthetic particles (blue) / Breakdowns in pumps & valves
Wearing of seals / Fibres due to initial contamination, open tank, cleaning cloths etc. / Blocking of nozzles
Leaking from seat valves
The patch shows debris deposited onto a 3 µm patch. The sample was a 320 cSt gear oil from a reduction gearbox. The bronze particles shown are typical of this type of application. The particle size, shape, morphology and number are indicative of the severity of wear
Typical SEM image of the severe visible contamination

US Navy Codes

Severe / Severe

Advantages of the Patch Test

Figure 1 high-pressure hydraulic system / In a high-pressure hydraulic system, the operator suspected that the axial flow piston pump had suffered damage and was operating with reduced efficiency. The laboratory analysis suggested that the system was satisfactory with no evidence of iron, copper, zinc or tin, and its 16/13 ISO code was within the target cleanliness level for that system. A routine patch test (1 µm) showed the presence of numerous brass/bronze cutting wear particles (Figure 1). Subsequent examination of the piston pump revealed serious wear at the slipper pad/swash plate surfaces.
The spectrographic analysis failed to detect any abnormal wear or contamination. However, in this case, the PQ index and particle counts showed an abnormal contamination level. Spectrometry failed to detect iron due to the analysis limitation of particle size (less than 5 µm).
The patch test, however, showed a high concentration of spherical particles ranging in size from 20 µm to 75 µm - typical of welding debris / Figure 2. A sample of hydraulic oil from a pre-feeder
Figure 3. A sample of hydraulic oil from a pre-feeder / The sample of hydraulic oil from a pre-feeder similar to the unit detailed in Example No. 2. The spectrographic analysis, particle counting and PQ index failed to detect any abnormal wear or contamination. Although the viscosity of the hydraulic fluid was lower than the specification, there was no obvious problem. The patch test, however, revealed possible filter element deterioration
Fibers were prevalent over the whole patch surface. A faulty element that had collapsed was subsequently changed
The large bronze-type particles greater than 100 µm (Figure 4) were not detected by the emission spectrometer or the PQ instrument which measures the ferromagnetic debris in the sample.
It is important to note that the bronze forces a negative PQ measurement in relation to the positive ferrous reading.

Reference: Mervin H. Jones, Swansea Tribology Services Ltd. U.K., "Effective Use of the Patch Test for Simple On-site Analysis". Practicing Oil Analysis Magazine. September 2004