The purpose of this investigation was to determine the cause of the ultrasonic signal attenuation noted during an inspection of a composite aircraft component. Although ultrasonics was able to identify the location of the defective areas, destructive analysis had to be utilized to determine the exact nature of the defect. The investigation describes how cross-sectioning, fractography, and chemical analysis were utilized to determine the type of defect responsible for the signal attenuation.

Cracking occurred in type 304L stainless steel sheaths on nichrome wire heaters that had been in storage for about 5 years in a coastal atmosphere. The cracks were discovered when the heater coils were removed from storage in their original polyethylene packing materials and straightened for use. Fractography established that fracture occurred by stress-corrosion cracking. The cracks originated at rusted areas on the cladding that occurred under iron particles left on the surface during manufacture. High hardness values indicated that solution annealing following cold working had not been carried out as specified. It was recommended that the sheathing material be fully annealed and that the outer surface be pickled and passivated.

A section of type 304 stainless steel pipe from a stand by system used for emergency injection of cooling water to a nuclear reactor failed during precommissioning. Leaking occurred in only one spot. Liquid penetrant testing revealed a narrow circumferential crack. Metallographic examination of the cracked area indicated stress-corrosion cracking, which had originated at rusted areas that had formed on longitudinal scratch marks on the outer surface of the pipe. The material was free from sensitization, and there was no significant amount of cold work. It was recommended that the stainless steel be kept rust free.

A failure analysis was conducted on a flow-sensing device that had cracked while in service. The polysulfone sensor body cracked radially, adjacent to a molded-in steel insert. This article describes the investigative methods used to conduct the failure analysis. The techniques utilized included scanning electron microscopy, Fourier transform infrared spectroscopy, differential scanning calorimetry, thermomechanical analysis, and melt flow rate determination. It was the conclusion of the investigation that the part failed via brittle fracture, with evidence also indicating low cycle fatigue associated with cyclic temperature changes from normal service. The design of the part and the material selection were significant contributing factors because of stresses induced during molding, physical aging of the amorphous polysulfone resin, and the substantial differential in coefficients of thermal expansion between the polysulfone and the mating steel insert.

Corrosion failure occurred in a titanium clad tubesheet because of a corrosive tube-side gas-liquid mixture leaking through fatigue cracks in the seal welds at tube-to-tubesheet joints. The tubesheet was a carbon steel plate clad with titanium on the tube side face. The seal weld cracks were initiated by cyclic stress imposed by exchanger tubes. The gas-liquid mixture passed through cracks under tube-side pressure, resulting in severe corrosion of the steel backing plate. The failure started with the loosening of the expanded tube-to-tubesheet joints. Loose joints allowed the exchanger tubes to impose load on seal welds and the shell side cooling water entered the crevice between the tubesheet and the tubes. The cooling water in the crevice caused galvanic reaction and embrittlement of seal welds. Brittle crack opening and crack propagation in seal welds occurred due to the cyclic stress imposed by the tubes. The cyclic stress arised from the thermal cycling of the heat exchanger. The possible effects of material properties on the failure of the tubesheet are discussed.

The article commences with an overview of short-term and long-term mechanical properties of polymeric materials. It discusses plasticization, solvation, and swelling in rubber products. The article further describes environmental stress cracking and degradation of polymers. It illustrates how surface degradation of a plain strain tension specimen alters the ductile brittle transition in polyethylene creep rupture. The article concludes with information on the effects of temperature on polymer performance.

This article provides an overview of the classification of hydrogen damage. Some specific types of the damage are hydrogen embrittlement, hydrogen-induced blistering, cracking from precipitation of internal hydrogen, hydrogen attack, and cracking from hydride formation. The article focuses on the types of hydrogen embrittlement that occur in all the major commercial metal and alloy systems, including stainless steels, nickel-base alloys, aluminum and aluminum alloys, titanium and titanium alloys, copper and copper alloys, and transition and refractory metals. The specific types of hydrogen embrittlement discussed include internal reversible hydrogen embrittlement, hydrogen environment embrittlement, and hydrogen reaction embrittlement. The article describes preservice and early-service fractures of commodity-grade steel components suspected of hydrogen embrittlement. Some prevention strategies for design and manufacturing problem-induced hydrogen embrittlement are also reviewed.

Plastics or polymers are used in a variety of engineering and nonengineering applications where they are subjected to surface damage and wear. This article discusses the classification of polymer wear mechanisms based on the methodologies of defining the types of wear. The first classification is based on the two-term model that divides wear mechanisms into interfacial and bulk or cohesive. The second is based on the perceived wear mechanism. The third classification is specific to polymers and draws the distinction based on mechanical properties of polymers. In this classification, wear study is separated as elastomers, thermosets, glassy thermoplastics, and semicrystalline thermoplastics. The article describes the effects of environment and lubricant on the wear failures of polymers. It presents a case study on nylon as a tribological material. The article explains the wear failure of an antifriction bearing, a nylon driving gear, and a polyoxymethylene gear wheel.

Hydrogen damage is a term used to designate a number of processes in metals by which the load-carrying capacity of the metal is reduced due to the presence of hydrogen. This article introduces the general forms of hydrogen damage and provides an overview of the different types of hydrogen damage in all the major commercial alloy systems. It covers the broader topic of hydrogen damage, which can be quite complex and technical in nature. The article focuses on failure analysis where hydrogen embrittlement of a steel component is suspected. It provides practical advice for the failure analysis practitioner or for someone who is contemplating procurement of a cost-effective failure analysis of commodity-grade components suspected of hydrogen embrittlement. Some prevention strategies for design and manufacturing problem-induced hydrogen embrittlement are also provided.

This article provides an overview of the electrochemical nature of corrosion and analyzes corrosion-related failures. It describes corrosion failure analysis and discusses corrective and preventive approaches to mitigate corrosion-related failures of metals. These include: change in the environment; change in the alloy or heat treatment; change in design; use of galvanic protection; use of inhibitors; use of nonmetallic coatings and liners; application of metallic coatings; use of surface treatments, thermal spray, or other surface modifications; corrosion monitoring; and preventive maintenance.

Corrosion is the deterioration of a material by a reaction of that material with its environment. The realization that corrosion control can be profitable has been acknowledged repeatedly by industry, typically following costly business interruptions. This article describes the electrochemical nature of corrosion and provides the typical analysis of environmental- and corrosion-related failures. It presents common methods of testing of laboratory corrosion and discusses the processes involved in the prevention of environmental- and corrosion-related failures of metals and nonmetals.

Failures in boilers and other equipment taking place in power plants that use steam as the working fluid are discussed in this article. The discussion is mainly concerned with failures in Rankine cycle systems that use fossil fuels as the primary heat source. The general procedure and techniques followed in failure investigation of boilers and related equipment are discussed. The article is framed with an objective to provide systematic information on various damage mechanisms leading to the failure of boiler tubes, headers, and drums, supplemented by representative case studies for a greater understanding of the respective damage mechanism.

This article briefly reviews the various metallurgical or environmental factors that cause a weakening of the grain boundaries and, in turn, influence the occurrence of intergranular (IG) fractures. It discusses the mechanisms of IG fractures, including the dimpled IG fracture, the IG brittle fracture, and the IG fatigue fracture. The article describes some typical embrittlement mechanisms that cause the IG fracture of steels.

Examination of a damaged component involves a chain of activities that, first and foremost, requires good observation and documentation. Following receipt and documentation, the features of damage can be recorded and their cause(s) investigated, as this article briefly describes, for typical types of damage experienced for metallic components. This article discusses the processes involved in visual or macroscopic examination of damaged material; the interpretation of fracture features, corrosion, and wear damage features; and the analysis of base material composition. It covers the processes involved in the selection of metallurgical samples, the preparation and examination of metallographic specimens in failure analysis, and the analysis and interpretation of microstructures. Examination and evaluation of polymers and ceramic materials in failure analysis are also briefly discussed.

This article focuses on the visual or macroscopic examination of damaged materials and interpretation of damage and fracture features. Analytical tools available for evaluations of corrosion and wear damage features include energy dispersive spectroscopy, electron probe microanalysis, Auger electron spectroscopy, secondary ion mass spectroscopy, and X-ray powder diffraction. The article discusses the analysis and interpretation of base material composition and microstructures. Preparation and examination of metallographic specimens in failure analysis are also discussed. The article concludes with a review of the evaluation of polymers and ceramic materials in failure analysis.

This article briefly reviews the factors that influence the occurrence of intergranular (IG) fractures. Because the appearance of IG fractures is often very similar, the principal focus is placed on the various metallurgical or environmental factors that cause grain boundaries to become the preferred path of crack growth. The article describes in more detail some typical mechanisms that cause IG fracture. It discusses the causes and effects of IG brittle cracking, dimpled IG fracture, IG fatigue, hydrogen embrittlement, and IG stress-corrosion cracking. The article presents a case history on IG fracture of steam generator tubes, where a lowering of the operating temperature was proposed to reduce failures.

This article briefly reviews the general causes of weldment failures, which may arise from rejection after inspection or failure to pass mechanical testing as well as loss of function in service. It focuses on the general discontinuities observed in welds, and shows how some imperfections may be tolerable and how the other may be root-cause defects in service failures. The article explains the effects of joint design on weldment integrity. It outlines the origins of failure associated with the inherent discontinuity of welds and the imperfections that might be introduced from arc welding processes. The article also describes failure origins in other welding processes, such as electroslag welds, electrogas welds, flash welds, upset butt welds, flash welds, electron and laser beam weld, and high-frequency induction welds.

This article describes the characteristics of tubing of heat exchangers with respect to general corrosion, stress-corrosion cracking, selective leaching, and oxygen-cell attack, with examples. It illustrates the examination of failed parts of heat exchangers by using sample selection, visual examination, microscopic examination, chemical analysis, and mechanical tests. The article explains corrosion fatigue of tubing of heat exchangers caused by aggressive environment and cyclic stress. It also discusses the effects of design, welding practices, and elevated temperatures on the failures of heat exchangers.

A 22 m (72 ft) diameter filled grain storage bin made from a 0.2% carbon steel collapsed at a temperature of −1 to 4 deg C (30 to 40 deg F). Failure analysis indicated that fracture occurred in a two-step process: first downward, by ductile failure of small ligament from a bolt hole near the bottom of the tank to create a crack 25 mm (1 in.) long, and then upward, by brittle fracture through successive 1.2 m (4ft) wide sheets of ASTM A446 material. Site investigation showed that the concrete base pad was not level. Chemical analysis indicated that the material had a high nitrogen content (0.020%). The allowable stress based on yield was estimated using four different design criteria. Correlation among those results was poor. The different criteria indicated that the material was loaded from the maximum allowable to approximately 30% less than allowable. Nevertheless, at this stress level, fracture mechanics indicated that the 25 mm (1 in.) starter crack exceeded or was very near the critical crack length for the material. Additional factors not taken into account in the design equations included cold work from a hole punching operation, thread imprinting in bolt holes, and an additional hoop stress created by forcing an incorrectly formed panel to fit the pad base radius. These factors increased the nominal design stress to a sufficiently large value to cause the critical crack length to be exceeded.

This article briefly introduces the concepts of failure analysis and root cause analysis (RCA), and the role of failure analysis as a general engineering tool for enhancing product quality and failure prevention. It reviews four fundamental categories of physical root causes, namely, design deficiencies, material defects, manufacturing/installation defects, and service life anomalies, with examples. The article describes several common charting methods that may be useful in performing an RCA. It also discusses other failure analysis tools, including review of all sources of input and information, people interviews, laboratory investigations, stress analysis, and fracture mechanics analysis. The article concludes with information on the categories of failure and failure prevention.