Copper leaching is a chemical reaction that occurs when freshly machined copper surfaces interact with engine oils. Zinc additives in oil plate out on copper surfaces, while copper begins to “leach” into the oil. This copper leaching is in a dissolved state, as opposed to being a solid particle. As such, copper leaching does not result in additional secondary wear through abrasion. Based on this, most users tend to consider this to be a ‘normal’ aspect of break-in wear.
Most mobile equipment oil analysis end users have experienced high copper in their engines due to cooler core leaching. With 12% of all engine oil samples exhibiting copper >20ppm, it happens with enough frequency that many simply ignore the condition. However, the question you should ask is, “What real machine conditions can these high copper results be hiding?”
So, where’s the problem?
Sometimes, high copper is NOT due to leaching. In a recent study by Fluid Life based on advanced SEM-EDS Wear Debris Analysis results, we found that over 1/3 of engine samples reporting high copper in the ICP results are actually masking the presence of abnormal bearing wear. This means 1/3 of the time, if no advanced testing was done, users could be misidentifying the issue and not taking the appropriate maintenance actions needed.
Limitations of ICP Spectrometry
ICP Spectrometry is often included as a part of routine oil analysis test packages. This test can monitor for copper, however, there are limitations if this test is used as a stand-alone indicator of an issue.
The ICP cannot differentiate the specific source of most elements such as copper. Copper could come a variety of sources including material from bearings, brass, bronze, cooler core pacification, paints, anti-seize, mine dust and more. This ambiguity leaves many analysts in the dark as to the true nature of the problem.
Wear Debris Analysis
To get a more definitive answer on the source of high copper, you can turn to SEM-EDS Wear Debris Analysis. This methodology can determine the size, shape, and composition of thousands of particles per sample and can also differentiate between wear, contamination, and additives. From this analysis, size and severity can be determined quantitively and enables informed decision making.
As it relates to high copper, you can differentiate between leached copper, normal brass bushing wear and abnormal bearing wear.
- Copper Leaching – Copper generated due to leaching is aqueous, dissolved in solution and will be detected by the ICP. When a sample is prepped for SEM analysis it is filtered through a patch and the patch is analyzed. Any aqueous copper in the sample from the leaching process will pass through the patch and not be detected by the SEM.
- Normal Wear – The use of copper on some surfaces such as brass bushings will wear by design. Wear of these sacrificial surfaces is typically considered ‘normal’
- Abnormal Bearing Wear – Large particles detected by the SEM that can be traced back to various bearing layers and compositions.
Example 1: New Diesel Engine in a Komatsu 830E Haul Truck
This unit had a new QSK60 engine installed, and early oil samples were normal until approx. 1,000 hours of service when routine analysis showed increasing levels of copper. This seemed like a typical case of copper leaching, but the routine analysis was simply not able to definitively determine the source of the metal.
Fluid Life Specialists recommended an SEM be performed, just to be sure. The customer submitted a sample of the spinner filter cake for SEM-EDS analysis to see what might be masked by the high copper and/or what was hiding in the filter.
The SEM analysis revealed that high copper was due to wear of the top and intermediate layer of the main bearings and unrelated to cooler core leaching. The multi layer bearings in this engine had a 20-30µm thick Lead/indium (Pb/In) top layer, followed by a thin Indium/Tin (In/Sn) barrier layer and a ~270-280µm copper/lead intermediate layer with a steel (Fe) backing.
The SEM analysis of the spinner filter debris (~1000hours) showed significant quantities of copper/lead/tin as well as lead/indium consistent with the composition of the top layer and intermediate layer of the bearing.
What’s the Risk?
Engine Replacement Cost = $700,000
Engine Budgeted Life = 16,000 hrs
Engine Life in Jeopardy = 13,000 hrs
Approx. Component Exposure = $568,750
% of Samples with Cu > 50ppm = 5.44%*
% of High Cu Samples w/ Abnormal Bearing Wear = 36%
Approx. Risk per Sample with Cu >50ppm = $11,138
Cost of Triggered SEM Analysis = $450
Estimate ROI = 25:1 (2475%)
NOTES:
Figures are for demonstration purpose only.
* Based on review of all engine oil sample results in myLab from the last year
Example 2: In-Warranty Diesel Engine in D11T Dozer
Below is a snapshot of the routine oil analysis report for a CAT C32diesel engine with less than 1,200 hrs of service with one previous oil change. Initial review would likely suggest copper leeching with insignificant levels of “break-in” wear.
However, SEM-EDS analysis of this sample tells a much different story showing large particles of abnormal wear originating from the babbitt overlay of the bearings.
Identifying this condition before the unit was off warranty enables maintenance to request a warranty inspection/repair instead of a potentially massive off warranty failure a few thousand hours later.
What‘s the Risk?
Engine Replacement Cost = $250,000
Engine Budgeted Life = 16,000 hrs
Engine Life in Jeopardy = 12,000 hrs
Approx. Component Exposure = $187,500
% of Samples with Cu > 50ppm = 5.44%*
% of High Cu Samples w/ Abnormal Bearing Wear = 36%
Approx. Risk per Sample with Cu >50ppm = $3,672
Cost of Triggered SEM Analysis = $450
Estimate ROI = 816% (8:1)
NOTES:
Figures are for demonstration purpose only.
*Based on review of all engine oil sample results in myLab from the last year
How much can your maintenance program save with SEM?
If your organization does not want to operate with a high level of risk on critical, high value assets, then inspections must be performed. If an inspection is triggered by copper values more than 50ppm then approx. 5 inspections will need to be performed for every 100 engine oil samples tested (based on review of all engine oil samples results in myLab over the last year, % of Samples with Cu > 50ppm = 5.44%).
A conservative estimate of the cost to perform a Main Bearing Inspection is $1,200 (2 technicians for approx. 12 hrs @ $50/hr) labour only, not factoring in any cost associated with the unit’s downtime. Performing the inspection on 3 engines would be $3,600 but statistically only one of those engines may have abnormal bearing wear. Performing the SEM-EDS analysis on all 3 engines instead to identify which engine needs to be inspected would be $1,350 (3 x $450) plus the inspection cost for only one engine ($1,200) for a total of $2,550.
Using technology to answer this question instead of technician time can save ~30% and as much as 24 hrs of downtime time (a huge additional savings).
Summary
Copper is a tricky element to properly diagnose based on routine oil analysis alone. High copper is often interpreted as copper leaching – while values of more than 600ppm can be normal signs of copper leaching, the ICP result could be hiding something much more insidious. Conversely, a low ICP result of 50ppm may get ignored, but in fact, there’s a serious wear issue within your engine.
If you’re uncertain where high copper is coming from or suspect there’s another issue at play, give SEM-EDS wear debris analysis a try. Contact a Fluid Life specialist today!