Visual examination, using the unaided eye or a low-power optical magnifier, is typically one of the first steps in a failure investigation. This article presents the guidelines for selecting samples for scanning electron microscope examination and optical metallography and for cleaning fracture surfaces. It discusses damage characterization of metals, covering various factors that influence the damage, namely stress, aggressive environment, temperature, and discontinuities.

When a steam turbine was put out of service, cracks were noticed on many of the blades in the low pressure section round the stabilization bolts and perpendicular to the blade axis. The blades were made from chrome alloy steel X20-Cr13 (Material No. 1.402). When the bolts were brazed into the blades inadmissible localized overheating of the steel must have occurred, which resulted in transformation stresses and hence reduced deformability. The cracks arose as a consequence of careless brazing. Whether the cracks should be considered as stress cracks over their entire extent or partially as fatigue cracks produced by vibration in the operation of the turbine as a result of steplike growing of microcracks could not be deduced from the fracture surfaces. Microfractography showed that the cracks developed in stages.

This article outlines the basic steps to be followed and the range of techniques available for failure analysis, namely, background data assembling, visual examination, microfractography, chemical analysis, metallographic examination, electron microscopy, electron microprobe analysis, X-ray techniques, and simulations. It also describes the steps for analyzing the data, preparing the report, preservation of evidence, and follow-up on recommendations.