A section from a stop-block guide fell to the floor on a crane runway after it failed. A brittle crystalline-type break was disclosed by examination of the fracture surface. The point of initiation was in a hardened heat-affected layer that had developed during flame cutting and welding. The metal was identified to be 1020 steel. It was indicated by the coarse as-rolled structure (grain size of ASTM 00 to 4) of the base metal that the weldment (stop block and guide) had not been normalized. The brittle failure was evaluated to have been initiated at a metallurgical and mechanical notch produced by flame cutting and welding. As corrective measures, fully silicon-killed 1020 steel with a maximum grain size of ASTM 5 were used to make new stop-block weldments. The weldments were normalized at 900 deg C after flame cutting and welding to improve microstructure and impact strength. All flame-cut surfaces were ground to remove notches.

The crane hook (rated for 13000 kg) failed in the threaded shank while lifting a load of 9072 kg. The metal in the hook was revealed by chemical analysis to be killed 1020 steel. It was disclosed by visual examination that the fracture had at the last thread on the shank and rough machining and chatter marks were evident on the threads. Beach marks that emanated from the thread-root locations on opposite sides of the fracture surface identified these locations to be the origins of the fracture. A medium-coarse slightly acicular structure was revealed by metallographic examination which indicated that the material was in the as-forged condition (which meant lower fatigue strength). The fracture was concluded to have occurred due to stress concentration in the root of the last thread. Normalizing of the crane hook after forging was suggested as a corrective measure. A stress-relief groove with a diam slightly smaller than the root diam was placed at the end of the thread and a large-radius fillet was machined at the change in diameter of the shank.

An 1100 aluminum alloy connector of a high-tension aluminum conductor steel-reinforced (ACSR) transmission cable failed after more than 20 years in service, in a region of consider able industrial pollution. The steel core was spliced with a galvanized 1020 carbon steel sheath. Visual examination showed that the connector had undergone considerable plastic deformation and necking before fracture. The steel sheath was severely corroded, and the steel splice was pressed off-center in the axial direction inside the connector. Examination of the fracture surface and micro-structural analysis indicated that the failure was caused by mechanical overload, which occurred because of weakening of the steel support cable by corrosion inside the fitting. The corrosion was ascribed to defective assembly of the connector which allowed moisture penetration.

Replacement sprockets installed on chain drive shafts for winding fibers exhibited excessive wear. Metallographic and chemical analyses conducted on the original and replacement sprockets showed that the material of the replacement sprocket was 1020 low-carbon steel, whereas the original (and specified) material was medium-carbon 1045 steel. The low-carbon steel also had lower hardness because of a lower pearlite fraction in the microstructure. It was recommended that replacement sprockets be made of normalized 1045 steel. It was further suggested that wear resistance could be improved by through hardening or induction surface hardening of the teeth.

A high-pressure steam pipe specified to be P22 low-alloy steel failed after 25 years of service. Located at the end of the steam line, the pipe reportedly received no steam flow during normal service. Visual examination of the failed pipe section revealed a window fracture that appeared brittle in nature. Specimens from the fracture area and from an area well away from the fracture were examined metallographically and chemically analyzed. Results indicated that the pipe had failed by hydrogen damage that resulted in brittle fracture. Chemical analysis indicated that the pipe material was 1020 carbon steel, not P22. The misapplication of pipe material was considered to be a contributing factor. Position of the pipe within the system caused the localized damage.

AM350 stainless steel bellows used in the control rod drive mechanism of a fast breeder reactor failed after 1000 h of service in sodium at 550 deg C (1020 deg F). Helium leak testing indicated that leaks had occurred at various regions of the welded joints between the convolutes in the bellows. The weld failure was attributed to poor quality assurance during fabrication, which resulted in cracklike openings at the fusion zone. The openings extended during tensile loading. Use of proper welding procedures and quality control measures were recommended to prevent future failures.

Two AISI type 316 stainless steel dished ends failed through the formation of intergranular stress-corrosion cracks (IGSCC) within a few months of service. The dished ends failed in the straight portions near the circumferential welds that joined the ends to the cylindrical portions of the vessel. Both dished ends were manufactured from the same batch and were supplied by the same manufacturer One of the dished ends had been exposed to sodium at 550 deg C (1020 deg F) for 500 h before failure due to sodium leakage was detected. The other dished end was used to fabricate a second vessel that was kept in storage for 1 year Clear evidence of sensitization was found in areas where IGSCC occurred. Sensitization was extensive in the dished end that had been exposed to sodium at high temperature, and it occurred in a narrow band similar to that typical of weld decay in the dished end that had been kept in storage. Solution annealing was recommended to relieve residual stress, thereby reducing the probability of failure. It was also recommended that the carbon content of the steel be lowered, i.e., that a 316L grade be used.

A hook on a two-leg chain (each 13 mm diam, included angle 60 deg) failed at the junction of the eye and shank while lifting a 4990 kg load. The diam of the hook at this junction was approximately 22 mm. Light intergranular oxidation at the surface on the side of the hook where cracking started was revealed by visual examination of the fracture region. Almost 50% of the fracture surface was found to contain beach marks (indicative of fatigue failure) while the remainder contained cleavage facets. A medium-coarse acicular as-forged structure was revealed by metallographic examination and the metal was showed by chemical analysis to be semikilled 1015 steel. The fatigue fracture was concluded to have initiated in the intergranular oxidation region and the failure of the hook was contributed by the poor fatigue and impact properties of the forged structure. As a corrective measure, the chain-sling hook was replaced with one made of normalized, fully killed, finegrain 1020 steel.

A hook on a two-leg chain (each 13 mm diam, included angle 60 deg) failed at the junction of the eye and shank while lifting a 4990 kg load. The diam of the hook at this junction was approximately 22 mm. Light intergranular oxidation at the surface on the side of the hook where cracking started was revealed by visual examination of the fracture region. Almost 50% of the fracture surface was found to contain beach marks (indicative of fatigue failure) while the remainder contained cleavage facets. A medium-coarse acicular as-forged structure was revealed by metallographic examination and the metal was showed by chemical analysis to be semikilled 1015 steel. The fatigue fracture was concluded to have initiated in the intergranular oxidation region and the failure of the hook was contributed by the poor fatigue and impact properties of the forged structure. As a corrective measure, the chain-sling hook was replaced with one made of normalized, fully killed, finegrain 1020 steel.

A large pressure vessel that had been in service as a hydrogen sulfide (H2S) absorber developed cracks and began leaking at a nozzle. The vessel contained a 20% aqueous solution of potassium hydroxide (KOH), potassium carbonate (K2CO3), and arsenic. The vessel wall was manufactured of ASTM A516, grade 70, low-carbon steel plate. A steel angle had been formed into a ring was continuously welded to the inside wall of the vessel. The groove formed by the junction of the lower tray-support weld and the top part of the weld around the nozzle was found to have a crack. Pits and scale near the crack origin were revealed by microscopic examination and cracking was found to be transgranular. Periods of corrosion alternated with sudden instances of cleavage, under a tensile load, along preferred slip planes were interpreted during examination with a microscope. It was concluded that the combination of the residual plus operating stresses and the amount of KOH present would have caused stress corrosion as a result of caustic embrittlement. It was recommended that the tray support should be installed higher on the vessel wall to prevent coincidence of the lower tray-support weld with the nozzle weld.

A large pressure vessel designed for use in an ammonia plant failed during hydrostatic testing. It was fabricated from ten Mn-Cr-Ni-Mo-V steel plates which were rolled and welded to form ten cylindrical shell sections and three forgings of similar composition. The fracture surfaces were metallographically examined to be typical for brittle steel fracture and associated with the circumferential weld that joined the flange forging to the first shell section. Featureless facets in the HAZ were observed and were revealed to be the fracture-initiation sites. Pronounced banding in the structure of the flange forging was revealed by examination. A greater susceptibility to cracking was interpreted from the higher hardenability found within the bands. Stress relief was concluded to have not been performed at the specified temperature level (by hardness and impact tests) which caused the formation of hard spots. The mode of crack propagation was established by microstructural examination to be transgranular cleavage. It was concluded that failure of the pressure vessel stemmed from the formation of transverse fabrication cracks in the HAZ fostered by the presence of hard spots. It was recommended that normalizing and tempering temperatures be modified and a revised forging practice explored.

Erosion is the progressive loss of original material from a solid surface due to mechanical interaction between that surface and a fluid, a multicomponent fluid, an impinging liquid, or impinging solid particles. The detrimental effects of erosion have caused problems in a number of industries. This article describes the processes involved in erosion of ductile materials, brittle materials, and elastomers. Some examples of erosive wear failures are given on abrasive erosion, liquid impingement erosion, cavitation, and erosion-corrosion. In addition, the article provides information on the selection of materials for applications in which erosive wear failures can occur.

High-temperature corrosion can occur in numerous environments and is affected by various parameters such as temperature, alloy and protective coating compositions, stress, time, and gas composition. This article discusses the primary mechanisms of high-temperature corrosion, namely oxidation, carburization, metal dusting, nitridation, carbonitridation, sulfidation, and chloridation. Several other potential degradation processes, namely hot corrosion, hydrogen interactions, molten salts, aging, molten sand, erosion-corrosion, and environmental cracking, are discussed under boiler tube failures, molten salts for energy storage, and degradation and failures in gas turbines. The article describes the effects of environment on aero gas turbine engines and provides an overview of aging, diffusion, and interdiffusion phenomena. It also discusses the processes involved in high-temperature coatings that improve performance of superalloy.

Thermomechanical fatigue (TMF) is the general term given to the material damage accumulation process that occurs with simultaneous changes in temperature and mechanical loading. TMF may couple cyclic inelastic deformation accumulation, temperature-assisted diffusion within the material, temperature-assisted grain-boundary evolution, and temperature-driven surface oxidation, among other things. This article discusses some of the major aspects and challenges of dealing with TMF life prediction. It describes the damage mechanisms of TMF and covers various experimental techniques to promote TMF damage mechanisms and elucidate mechanism coupling interactions. In addition, life modeling in TMF conditions and a practical application of TMF life prediction are presented.

Distortion often is observed in the analysis of other types of failures, and consideration of the distortion can be an important part of the analysis. This article first considers that true distortion occurs when it was unexpected and in which the distortion is associated with a functional failure. Then, a more general consideration of distortion in failure analysis is introduced. Several common aspects of failure by distortion are discussed and suitable examples of distortion failures are presented for illustration. The article provides information on methods to compute load limits, errors in the specification of the material, and faulty process and their corrective measures to meet specifications. It discusses the general process of material failure analysis and special types of distortion and deformation failure.

This article focuses on characterizing the fracture-surface appearance at the microscale and contains some discussion on both crack nucleation and propagation mechanisms that cause the fracture appearance. It begins with a discussion on microscale models and mechanisms for deformation and fracture. Next, the mechanisms of void nucleation and void coalescence are briefly described. Macroscale and microscale appearances of ductile and brittle fracture are then discussed for various specimen geometries (smooth cylindrical and prismatic) and loading conditions (e.g., tension compression, bending, torsion). Finally, the factors influencing the appearance of a fracture surface and various imperfections or stress raisers are described, followed by a root-cause failure analysis case history to illustrate some of these fractography concepts.

This article discusses the organization required at the outset of a failure investigation and provides a methodology with some organizational tools. It focuses on the use of problem-solving tools such as a fault tree analysis combined with critical thinking. The discussion covers nine steps to organize a good failure investigation. They are as follows: understand and negotiate goals of the investigation, obtain a clear understanding of the failure, identify all possible root causes, objectively evaluate the likelihood of each root cause, converge on the most likely root cause(s), objectively and clearly identify all possible corrective actions, objectively evaluate each corrective action, select optimal corrective action(s), and evaluate effectiveness of selected corrective action(s). Common problems detrimental to a failure investigation are also covered.

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 aims to identify and illustrate the types of overload failures, which are categorized as failures due to insufficient material strength and underdesign, failures due to stress concentration and material defects, and failures due to material alteration. It describes the general aspects of fracture modes and mechanisms. The article briefly reviews some mechanistic aspects of ductile and brittle crack propagation, including discussion on mixed-mode cracking. Factors associated with overload failures are discussed, and, where appropriate, preventive steps for reducing the likelihood of overload fractures are included. The article focuses primarily on the contribution of embrittlement to overload failure. The embrittling phenomena are described and differentiated by their causes, effects, and remedial methods, so that failure characteristics can be directly compared during practical failure investigation. The article describes the effects of mechanical loading on a part in service and provides information on laboratory fracture examination.

Stress-corrosion cracking (SCC) is a form of corrosion and produces wastage in that the stress-corrosion cracks penetrate the cross-sectional thickness of a component over time and deteriorate its mechanical strength. Although there are factors common among the different forms of environmentally induced cracking, this article deals only with SCC of metallic components. It begins by presenting terminology and background of SCC. Then, the general characteristics of SCC and the development of conditions for SCC as well as the stages of SCC are covered. The article provides a brief overview of proposed SCC propagation mechanisms. It discusses the processes involved in diagnosing SCC and the prevention and mitigation of SCC. Several engineering alloys are discussed with respect to their susceptibility to SCC. This includes a description of some of the environmental and metallurgical conditions commonly associated with the development of SCC, although not all, and numerous case studies.