Playing a part in wear metal analysis

The analysis of lubricating oils has been used in predictive maintenance and monitoring of machinery for more than 50 years, and has wide application in areas that include transportation, construction and power generation. Within this context, effective wear metal analysis can save substantial time and money, enabling users to monitor the condition of equipment and to act in advance to address any developing problems.

During regular machine use, traces of metal are generated, as a result of friction between moving parts, abrasion by contaminants and corrosion. These ‘wear metals’ are typically detected as particles suspended in lubricating oil, usually in concentration ranges of 1 – 500 parts per million. By analysing these traces, laboratories can get an indication of whether there is a problem with the equipment and, by recognising and understanding the metallurgy, define which components are in need of maintenance.

This involves specialist service laboratories and major plant operators analysing hundreds of oil samples for a wide range of elements, (demonstrated in table 1), every day.

Since there are cost implications to undertaking multiple tests at this scale, there is always pressure to find convenient, cost-effective methods. Various techniques have been adopted for the analysis of metal traces in oils, including XRF spectrometry and ICP-OES.

XRF’s simple sample preparation, high accuracy and good detection limits support its use in wear metal analysis. A key advantage is the technique's ability to analyse samples of many different types. For example, when working with solid or powder samples, it is possible to filter these from the oil. This eliminates the complex oil matrix which can cause intense scattering of primary X-rays, along with distorting matrix effects resulting from the difference in X-ray absorption with the oil.

XRF’s ability to analyse large particles (diameter  >10 microns) is also an advantage, as this can be vital in diagnosing wear debris. When used with a simple particle count, XRF reveals valuable and reliable information about the rate of wear and  sources of contamination.

However, XRF may miss smaller particles that emit radiation below the detection limit of the spectrometer. These are found in cases where damage is less severe, and a different approach is needed for successful analysis. Due to its ability to detect and analyse these smaller particles, ICP-OES can be used for the analysis of fuels and lubricating oils in several national and standard methods, including ASTM D 4951-09, ASTM D 5708-11 and ASTM 7111-11.

Although the matrix of a used oil sample was originally considered unsuitable for direct presentation to an ICP-OES instrument, recent technology developments mean plasma systems are much less susceptible to problems. Instruments such as the Spectro Genesis ICP-OES allow direct measurement for simultaneous ICP-OES, eliminating the need for complex sample preparation and aiding lab efficiency and throughput by measuring all programmed elements at one time. In addition, samples only require a simple kerosene dilution to overcome the physical variations between samples, avoiding complex and time-consuming digestions and multiple dilutions.

The differences between the XRF and ICP-OES techniques, especially considering the potential size variety of wear metal particles, suggests that applying both XRF and ICP-OES spectrometry offers benefits. This combination enables comprehensive analysis of the wide range of differently sized particles produced throughout a machine’s life. However, using multiple techniques and instruments comes with its own financial implications.

Cost-efficient analysis has a particular focus in the current financial climate. Instrument manufacturers can assist through technological advancements that make XRF and ICP-OES instruments more economical, from implementing automated systems for sample preparation to reduced energy consumption. Such systems can deliver lower overall running costs, making a big impact on laboratories’ budgets

By purchasing high-quality analytical instruments, ensuring they are well maintained and that good practice guidelines are followed, users can ensure their wear metal testing is efficient and effective. Suppliers of analytical equipment can help customers achieve maximum return on their investments with comprehensive, tailored support and training. The Spectro Genesis ICP-OES instrument line, for example, offers factory-installed applications packages to provide a comprehensive introduction to simultaneous ICP-OES. All of these lead to additional cost savings, on top of the financial impact that preventative maintenance itself provides.

With a range of techniques and instruments available to monitor the condition of equipment, there is always a method which will allow efficient, economical wear metal analysis. With wear metal tests triggering preventative maintenance early and optimising maintenance programmes, issues can be dealt with long before component wear leads to expensive, potentially catastrophic equipment failure.