Understanding Machine Metallurgy Helps Identify Problem

David Doyle, ALS Staveley Services  David Doyle, Noria Corporation
Tags: oil analysis

Elemental analysis is a fundamental tool in used oil analysis. Used appropriately, trends in different wear metals can indicate a problem, allowing corrective action to be taken before catastrophic failures occur. However, the effectiveness of elemental analysis in pinpointing a problem and isolating it to one specific component or group of components can be greatly enhanced by taking some time in advance of the lab reporting “active machine wear” to identify the specific metallurgical composition of all oil-wetted components.

For example, high copper in an oil sample could indicate a host of potential problems. Seen in isolation, the copper is likely due to wear of a purely copper containing component such as a cooler core - baring any copper-containing additives in the oil. However, observed in conjunction with elements such as tin, zinc or aluminum, the copper is more likely to originate from a copper-containing alloy such as brass or bronze.

In order to make the most of elemental spectroscopic data, it is a good practice to spend some time gathering information about the metallurgy of each and every component, and compiling a reference, such as that shown in Table 1 in advance of the lab reporting a problem.

Metallurgy of Common Components

In particular, identifying not just major elements such as iron from steel, but also minor elements such as chromium and nickel, and trace elements such as vanadium and manganese, can help differentiate between different alloys of steel or other components.

It may also be appropriate to record the relative ratios of different elements in the various alloys present, so that these ratios can also be used as a characteristic fingerprint. However, care should be taken not to take the exact ratios too literally, because the ability of both inductively coupled plasma (ICP) and rotating disc electrode (RDE) spectrometers to accurately measure the absolute concentrations of certain elements such as copper and lead is significantly lower than other elements such as iron and chromium, due to difficulties in fully vaporizing and atomizing these elements.

David Doyle of CTC Analytical shares an example of how the identification of major and minor elements allowed a construction company to effectively isolate a specific problem on its cone crusher.

Case Study - Cone Crusher Wear Debris Analysis

Trend analysis of oil samples that were taken routinely on the cone crusher showed a steady increase in the amount of iron wear over successive samples, indicating an active wear problem. Each sample report was carefully reviewed by the original equipment manufacturer (OEM), who agreed with the lab’s assessment that iron levels were excessively high. Because the OEM was involved in the evaluation of the sample data, each wear metal present was carefully considered, as were the metals that did not show up in the analysis.

the worn part in time could have cost from $2,000 to $12,000 in additional damage, and an estimated minimum two-day downtime.

In this instance, understanding metallurgy of the key components and the typical failure modes of this system, along with using oil analysis as a predictive maintenance tool, allowed the construction company to prevent a larger problem. Knowing what to look for and having the right parts on hand kept a relatively minor problem from becoming a major one.