This chapter provides guidelines for conducting metallographic evaluations and offers suggestions on how to effectively report the results. It explains how the approach depends on the objective of the evaluation, which is usually to measure a structural feature, test a hypothesis, or investigate structure-related effects. The chapter addresses each case, tailoring its guidelines and suggestions accordingly.

This report describes the failure of a gas turbine in a combined-cycle power plant and the examination and tests that were conducted to determine the cause. Based on microstructural analysis, hardness measurements, and tensile tests, the failure was attributed to inadequate clearances in the seal land region between two stages in the compressor section of the rotor. The report also recommends changes to remediate the problem.

Irradiation-assisted stress-corrosion cracking (IASCC) has been a topic of engineering interest since it was first reported in the 1960s, having been observed in stainless steel cladding on light water reactor fuel elements. This chapter summarizes the results of decades of investigation, showing that IASCC can essentially be defined as the intergranular cracking of austenitic alloys in high-temperature water, where both the material and its environment have been altered by radiation. Of the many interactions that can occur when metals and water are exposed to radiation, the international consensus is that the three with the greatest impact on crack growth rates are the formation of material defects, radiation-induced segregation, and chemical reactions that increase the corrosion potential of water. The chapter discusses each of these in great detail, and includes information on predictive modeling as well.

Stress-corrosion cracking (SCC) in magnesium alloys was first reported in the 1930s and, within ten years, became the focus of intense study. This chapter provides a summary of all known work published since then on the nature of SCC in magnesium alloys and how it is related to composition, microstructure, and heat treatment. It describes the types of environments where magnesium alloys are most susceptible to SCC and the effect of contributing factors such as temperature, strain rate, and applied and residual stresses. The chapter also discusses crack morphology and what it reveals, provides information on proposed cracking mechanisms, and presents a practical approach for preventing SCC.

This chapter discusses the techniques applicable to the diagnosis of corrosion failures, including visual and microscopic examination of corroded surfaces and microstructure; chemical analysis of the metal, corrosion products, and bulk environment; nondestructive evaluation methods; corrosion testing techniques; and mechanical testing techniques. A guide to investigative techniques used in corrosion failure analysis is provided in a table, describing the advantages and limitations of each technique. The principal stages of the investigation and analysis of corrosion failures discussed in the chapter are: collection of background information and sampling; preliminary laboratory examination; detailed metallographic and fractographic examinations; chemical analysis of corrosion products and bulk materials; corrosion testing for quality control; mechanical testing for quality control; and analysis of results and report writing.

This appendix focuses on procedures, techniques, and precautions associated with the investigation and analysis of metallurgical failures that occur in service. It describes the steps of an orderly failure analysis from collecting and examining samples to performing mechanical and nondestructive tests, preparing and examining fractographs and micrographs, determining failure mode, writing the report, and developing follow-up recommendations. It also examines the fundamental mechanisms of failure, why they occur, and how to identify them by their characteristic features.

This chapter provides an overview of the possible mechanisms of failure for heat treated steel components and discusses the techniques for examining fractures, ductile and brittle failures, intergranular failure mechanisms, and fatigue. It begins with a description of the general sources of component failure. This is followed by a section on the stages of a failure analysis, which can proceed one after the other or occur at the same time. These stages of analysis are collection of background data, preliminary visual examination, nondestructive testing, selection and preservation of specimens, mechanical testing, macroexamination, microexamination, metallographic examination, determination of the fracture mechanism, chemical analysis, exemplar testing, and analysis and writing the report. The chapter ends with a discussion on various processes involved in the determination of the fracture mechanism.

This chapter discusses some of the promising developments in the use of titanium, including titanium aluminides, titanium matrix composites, superplastic forming, spray forming, nanotechnology, and rapid solidification rate processing. It also reports on efforts to increase the operating temperature range of conventional titanium alloys and reduce costs.

This chapter discusses the basic steps of a failure investigation. It explains that the first step is to gather and document information about the failed component and its operating history. It advises investigators to visit the failure site as soon as possible to record damages and collect test specimens for subsequent examination and chemical analysis. It also discusses the role of mechanical property testing, the use of nondestructive evaluation, and the final step of generating a report.

A driven gear in the gear box of an aircraft engine fractured after a 40 h test run. The driving gear and gear shaft were also damaged. Based on the results of fractography, chemical analysis, metallography, and hardness testing, the fracture was caused by a fatigue crack initiating at the corner of the inner rim near an inclusion. The report recommends the use of a cleaner material and more carefully controlling case hardening process.

The nose landing gear on an aircraft malfunctioned during landing roll. After the incident, two fractured studs were found in the retraction jack support beam. Based on visual examination and the results of SEM fractography, investigators concluded that the studs failed by fatigue, a vulnerability because of the way they were mounted. A sketch showing the correct mounting configuration is included in the report.

A pair of bolts on a connecting rod failed during a test run for a prototype engine. They were replaced by bolts made from a stronger material that also failed, one due to fatigue, the other by tensile overload. The fracture surfaces on all four bolts were examined using optical and electron microscopes, indicating that the operating loads on the bolts far exceeded the design loads. Based on their observations, which are summarized in the report, failure analysts concluded that the design of the connecting rod system needs to be reassessed.

A generating system in a hydroelectric power plant was shut down to investigate an abnormal sound coming from one of the turbines. A piece of metal that had broken off one of the vanes on the runner was found in the tail race and was subsequently examined along with the runner. Based on the fracture characteristics, as described in the report, the vane failed in fatigue due to a crack that initiated in an area of stress concentration.

Fastening screws used in fuel-injection pumps failed during assembly and were examined to determine the cause. Based on observations and the result SEM fractography and hardness measurements, the screws failed by brittle intergranular fracture due to hydrogen embrittlement associated with plating procedures. The report includes recommendations for improving the quality of the screws.

One of the rotor bearings in an electric motor failed, producing excessive vibrate. The bearing was removed and disassembled, revealing craters and bruises on the inner ring raceway and balls along with evidence of melting and burning of metal. Scanning electron microscopy revealed metal particles near the craters, and energy-dispersive x-ray analysis showed that slivers recovered from the grease had the same composition as the bearing raceway and balls. Based on these observations, it was concluded that the bearing failed due to electrostatic discharge, which would have led to seizure if it continued. The report recommends the use of electrically conductive grease and proper grounding practices.

Beryllium-related lung diseases were first reported in the 1930s, several years after the emergence of beryllium metals in manufactured products. Since then, there have been numerous studies around the world and continued refinement of recommendations and safety standards. This chapter provides a summary of the studies that have been conducted along with the findings. It discusses the effects of acute and chronic exposure, toxicity levels, potential sources and risks, treatment, and protective and preventive measures.

This chapter focuses on the effects of microscopic organisms and the by-products they produce on the electrochemical corrosion of metals. It begins by considering the characteristics of organisms that allow them to interact with the corrosion processes, the mechanisms by which organisms can influence the occurrence or rate of corrosion, and the types of corrosion most often influenced by microbes. The chapter then discusses the formation of biofilms on the surface of metals. This is followed by a list of industries most often reported as being affected by microbiological corrosion, along with the organisms usually implicated in the attack. The types of attack that have most commonly been documented are illustrated through generalized case histories for different classes of alloys. The chapter also describes the general approaches to be taken to prevent microbiologically influenced corrosion. It ends with some information on the inhibition of corrosion by the action of bacteria.

This chapter concentrates almost exclusively on inspection techniques related to pressure vessels and pipework. The discussion covers the general aspects associated with inspection and the key factors relevant to it. In addition, the chapter addresses processes involved in data collection and management, namely data acquisition, reporting, trending, reviewing, and auditing. Capabilities and limitations of in-service inspection techniques are discussed in the Appendix to this chapter.

This chapter describes the corrosion behavior of beryllium in gaseous atmospheres, including oxygen, nitrogen, carbon dioxide, and carbon monoxide. It also discusses the development of high-temperature corrosion-resistant beryllium alloys.