By Craig Winterfield & Jeff Walkup
Copper is a soft metal and the principal component of Brass (Copper + Zinc) and Bronze (Copper + Tin). Copper can be found in many bearings, bushings, gears, transmission components, cooler cores, oil pumps and drive gears.
Sources and Causes of Copper in Oil Analysis
Copper levels can increase significantly if a coolant leak is present in the crankcase oil. These leaks can be identified through routine oil analysis using Gas Chromatography to confirm he presence of coolant components in the oil including Ethylene and Propylene glycol.
A common source of copper is from chemical leaching of cooler cores caused by the interaction of ZDDP with the copper cooler tubes. This chemical process can lead to high concentrations of copper in the oil well above 500ppm. This type of leaching is generally considered normal and is not usually associated with increased cooler core failure or mechanical wear, but the source of the copper must be identified to take appropriate actions.
Other sources of copper include outside contamination (dirt/dust/process materials), anti-seize compounds, paint, gaskets, environmental welding/grinding/cutting of copper materials and other additives.
A best practice is to perform microscopic and elemental analysis on the individual particles in the oil and debris from the oil filter using SEM-EDS (Scanning Electron microscopy – Energy Dispersive X-ray Spectroscopy). This technique can help pinpoint the source of copper and ensure that the correct action is taken to minimize costly and unnecessary repairs.
Leaching Vs. Wear
Copper from wear processes typically appear in low concentrations (5-25ppm) on routine spectrometry-based oil analysis. A large oil sump will ‘dilute’ down the concertation of copper wear debris, the filter will remove some of the wear particles and a typical ICP is not sensitive to wear particles >10microns.
Copper leaching is a chemical process whereby the additives present in the oil react with the copper tubes in the cooler and shed high concentrations of copper into the oil. Although this can result in very high levels of copper in the oil, often >500ppm, this is not associated with increased wear or cooler core failure. In most cases if the cause of copper can be identified as leaching, it does not warrant further action.
While traditional methods such as ICP or XRF cannot distinguish leached copper from abnormal bearing wear, SEM-EDS analyses each particle individually and can distinguish between small particles produced by leaching (<1um) and larger particles (>10um) produced by mechanical wear.
Copper Bearing Wear
SEM-EDS can also be used to monitor the progression of bearing wear. Common bearing alloys including lead/Tin/Copper/Indium/Antimony can be detected, sized and imaged. This data can be documented and trended over time which allows us to monitor the progression of wear through multi-layer bearings and monitor bearing overlay, nickel barriers, intermediate layers and abnormal wear into the support shell.
What you can do if Copper is Detected in Routine ICP Spectrometry
- Confirm the source using SEM-EDS analysis of the Oil and Filter Debris
- Ensure the lab can perform both SEM and EDS analysis and can analyse a representative subset of the sample (>100 particles)
- If the sample is suspect, consider re-sampling
- Action may not be required if the copper is derived from routine cooler core leaching
Summary
SEM-EDS can identify the metallurgical composition of hundreds of individual particles in a sample, allowing the specific sources of copper to be differentiated and identified. Multiple modes of copper wear/leaching can be present in a single sample simultaneously. Cooler core leaching, bearing wear and environmental contamination can be present at the same time. These can be separated by analyzing each particle individually using SEM-EDS.
To learn more about SEM-EDS analysis, contact a Fluid Life representative.