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
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.
Figure 1 high-pressure hydraulic system
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
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
Figure 3. A sample of hydraulic oil from a pre-feeder
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