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Crack Propagation in a Compressor

Background: A client had a compressor distance piece fail in a catastrophic manner, leading to an internal root cause failure analysis. To successfully perform the internal analysis, the client needed to know the origin of the crack, and the manner in which the crack propagated through the distance piece. KML was contracted to provide this information as part of the client’s internal root cause investigation.

Figure 1: Optical Micrograph (Left) and SEM Micrograph (Right) of Signs of RCF on the Bearing Balls

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Summary: The failure of the compressor distance piece was the result of fatigue. Rubbing damage on various fracture surfaces of the compressor revealed that certain cracks had formed while the compressor was still operational. By studying the extent and severity of the rubbing damage, KML was able to determine that the compressor distance piece failed as a result of crack initiation at a stress riser caused by looseness in the compressor. The crack then propagated as shown in Figure 1, and the increased looseness of the compressor caused by this crack led to initiation of secondary and tertiary cracks, which in turn began to propagate. Finally, sufficient crack propagation led to the final overload failure.

Take Away: By observing the fracture surface features, it is possible to track crack propagation, even through very large failures and multiple initiation locations. KML is capable of performing this work, either as part of an internal investigation or as part of a root cause failure analysis performed by KHE.

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