Although field corrosion tests had indicated that type 316L stainless steel would be a suitable material for neutralization tanks, the vessels suffered severe corrosion when placed in service. Welded coupons of type 316L had been tested along with similar Alloy 20Cb® (UNS NO8020) specimens in a lead-lined tank equipped with copper coils that had served in this function prior to construction of the new tanks. Both materials exhibited virtually no corrosion and no preferential weld attack. Type 316L was selected for the project. The subsequent corrosion was the result of the borderline passivity of type 316L in hot dilute sulfuric acid (about 0.1%). Inaccuracy of the testing was attributed to the presence of cupric ions in the lead-lined vessel fluids, which had been released by corrosion of the copper coils. Careful control of both temperature and pH was recommended to reduce the corrosion to an acceptable limit.

A two-section extension ladder, made from 6061-T6 aluminum alloy extrusions and stampings that were riveted together at each rung location and at the ends of side rails, broke in service after having been used at the sites of several fires by the fire department of a large city. The fracture surfaces were examined visually and by optical (light) stereomicroscopy. Material testing showed a sample to be within the specified material limits for aluminum alloy 6061. Microscopic examination showed no significant differences in microstructure or grain size among the four T-sections, and thickness measurements at various locations indicated that thicknesses were well within standard industry tolerances for aluminum extrusions in this size range. However, hardness testing of the four T-sections showed that in two, hardness was considerably lower than the acceptable hardness for the T6 temper and were within the range for 6061-T4 (acceptable hardness, 19 to 45 HRB). This indicated they had been naturally aged at room temperature after solution heat treatment instead of artificially aged as per specs. Edge cracking in two of the T-sections was the result of improper conditions during extrusion of the T-sections; however, this condition was not a primary cause of failure.

An investigation was conducted to determine what caused a bearing sleeve in a locomotive turbocharger to fail. The sleeve, which is made of nitrided 38CrMoAl steel, fractured at the transition fillet between the cylinder and plate. Visual examination revealed significant wear on the external surface of the cylinder, with multiple origin fatigue fracture appearing to be the dominant fracture mechanism. Metallurgical examination indicated that the nitrided layer was not as deep as it was supposed to be and had worn away on the outer surface of the sleeve, exposing the soft matrix underneath. This led to further wear and an increase in friction between the sleeve and bearing bush. Fatigue crack initiation occurred at the root fillet because of stress concentration and large frictional forces. Insufficient nitriding depth facilitated the propagation of fatigue cracks.

Following a fracture mechanics “fitness-for-purpose” analysis of petroleum industry cold service pressure vessels, using the British Standard PD 6493, it was realized that an analogous approach could be used for the failure analysis of a similar pressure vessel dome which had failed in service some years previously. The failed pressure vessel, with a diam of 2.5 m and several meters tall, had been made of 12 mm thick IZETT steel plate of the same type and heat treatment as used in the earlier fitness-for-purpose already measured. Examination of the fracture surfaces suggested, from fatigue striations manifested by SEM, that the vessel was subject to significant fatigue cracking, which was probably corrosion assisted. From COD measurements at the operating temperature of -130 deg C (-202 deg F), and a finite stress analysis, a fracture mechanics evaluation using BS PD6493 yielded realistic critical flaw sizes (in the range 51 to 150 mm). These sizes were consistent with the limited fracture surface observations and such flaws could well have been present in the vessel dome prior to catastrophic failure. For similar pressure vessels, an inspection program based on a leak-before-break philosophy was consequently regarded as acceptable.

During testing of compressors under start/stop conditions, several helical suspension springs failed. The ensuing failure investigation showed that the springs failed due to fatigue. The analysis showed that during start/stop testing the springs would undergo both a lateral and axial deflection, greatly increasing the torsional stresses on the spring. To understand the fatigue limits under these test conditions, a bench test was used to establish the fatigue strength of the springs. The bench tests showed that the failed springs had an unacceptable surface texture that reduced the fatigue life. Based on an understanding of the compressor motion, a Monte Carlo model was developed based on a linear damage theory to predict the fatigue life of the springs during start/stop conditions. The results of this model were compared to actual test data. The model showed that the design was marginal even for springs with acceptable surface texture. The model was then used to predict the fatigue life requirements on the bench test such that the reliability goals for the start/stop testing would be met, thus reducing the risk in qualifying the compressor.

Stator vanes (cast from a Cu-Mn-Al alloy) in a hydraulic dynamometer used in a steam-turbine test facility were severely eroded. The dynamometer was designed to absorb up to 51 MW (69,000 hp) at 3670 rpm, and constituted an extrapolation of previous design practices and experience. Its stator was subject to severe erosion after relatively short operating times and initially required replacement after each test program. Although up to 60 cu cm (3.7 cu in.) of material was being lost from each vane, it only reduced the power-absorption capacity by a small amount. Analysis supported the conclusion that the damage was due to liquid erosion, but it could not be firmly established whether it was caused by cavitation or by liquid impact. Recommendations included making a material substitution (to Mo-13Cr-4Ni stainless steel) and doing a redesign to reduce susceptibility to erosion as well as erosion-producing conditions.

A forged aluminum alloy 2014-T6 catapult-hook attachment fitting (anodized by the chromic acid process to protect it from corrosion) from a naval aircraft broke in service. Spectrographic analysis, visual examination, microscopic examination, and tensile analysis showed minute cracks on the inside surface of a bearing hole, and small areas of pitting corrosion were visible on the exterior surface of the fitting. The analysis also revealed a small number of rosettes, suggestive of eutectic melting, in an otherwise normal structure. These examinations and analyses support the conclusion that the presence of chromic acid stain on the fracture surface proved that the forging had cracked before anodizing. This suggest that the crack initiated during straightening, either after machining or after heat treatment. The structure and composition of the alloy appear to have been acceptable. Ductility was acceptable so rosettes found in the microstructure are believed to have been nondamaging. Had they contributed to the failure, the ductility would have been very low. The recommendations included inspection for cracks and revising the manufacturing process to include a fluorescent liquid-penetrant inspection before anodizing, because chromic acid destroys the penetrant. This inspection would reduce the possibility of cracked parts being used in service.

A sleeve-shaped fire shield that operates inside one of two burner trains in an oil and gas processing unit ruptured after 15 y of service. A detailed analysis was conducted to determine how and why the sleeve failed. The investigation included visual inspection, chemical and gas analysis, mechanical property testing, stereomicroscopy, and metallographic examination. The fire sleeves are fabricated from 3-mm thick plate made of Incoloy 800 rolled into 540-mm diam sections welded along the seam. Three such sections are joined together by circumferential welds to form a single 2.8 m sleeve. The findings from the investigation indicated that internal oxidation corrosion, driven by high temperatures, was the primary cause of failure. Prolonged exposure to temperatures up to 760 °C resulted in sensitization of the material, making it vulnerable to grain boundary attack. This led to significant deterioration of the grain boundaries, causing extensive grain loss (grain dropping) and the subsequent thinning of sleeve walls. Prior to failure, some portions of the sleeve were only 1.6 mm thick, nearly half their original thickness.

This article is a compilation of terms related to analysis and prevention of engineering failures.

This article is a compilation of terms and definitions related to failure analysis and prevention. This glossary is intended to help promote clear thinking and useful failure analysis. The definitions presented are those used in this volume and reflect common and modern understanding of these terms as used in the literature and in reports by practicing failure analysts.

This glossary is a compilation of terms related to the analysis and prevention of component and equipment failures. It is intended to help promote clear thinking and useful failure analysis. The definitions presented are those used in this Volume and reflect a common and modern understanding of these terms as used in the literature and in reports by practicing failure analysts.

An evaluation of indications in the main turbine building column horizontal plate welds was conducted by the joint efforts of field metallography and nondestructive examinations. The turbine building main column horizontal plate welds were selected at random and were inspected to find discontinuities, metallurgical evaluation of the discontinuities, analysis of any failure modes, and determination of the best repair techniques. The welds were made with prequalified joints in accordance with AWS D1.1-77 and required only visual inspection. More sensitive inspection methods were applied to the welds in order to better define the indications found with the visual inspections. Cracks were found in 17 field welds and in two test plate welds. The causes of the cracking are related to the weld design and installation procedure. Three field welds were rejected because of the depth of the cracks. The NDT inspections, evaluations, method of field metallography, analysis and conclusions are discussed with recommendations for corrective actions in the following report.

During the installation of power transmission lines across a major interstate highway, a temporary anchor stabilizing one of the poles failed, resulting in the loss of the pole and the associated power lines. It also contributed to a single vehicle incident on the adjacent roadway. Post-failure analysis revealed that the fracture was precipitated by a preexisting weld-related crack. Closed form and numerical stress analyses were also conducted, with the results indicating that the anchor was installed properly within the parameters intended by the manufacturer.

This article discusses the three legal theories on which a products liability lawsuit is based and the issues of hazard, risk, and danger in the context of liability. It describes manufacturing and design defects of various products. The article explains a design that is analyzed from the human factors viewpoint and details the preventive measures of the defects, with examples. It presents four paramount questions relating to the probability of injury which are asked even when one executes all possible preventive measures carefully and thoroughly.

This article provides information on life assessment strategies and conceptually illustrates the interplay of nondestructive evaluation (NDE) and fracture mechanics in the damage tolerant approach. It presents information on probability of detection (POD) and probability of false alarm (PFA). The article describes the damage tolerance approach to life management of cyclic-limited engine components and lists the commonly used nondestructive evaluation methods. It concludes with an illustration on the role of NDE, as quantified by POD, in fully probabilistic life management.

The intent of this article is to assist the failure analyst in understanding the underlying engineering design process embodied in a failed component or system. It begins with a description of the mode of failure. This is followed by a section providing information on the root cause of failure. Next, the article discusses the steps involved in the engineering design process and explains the importance of considering the engineering design process. Information on failure modes and effects analysis is also provided. The article ends with a discussion on the consequence of management actions on failures.

An investigation of a damaged crankshaft from a horizontal, six-cylinder, in-line diesel engine of a public bus was conducted after several failure cases were reported by the bus company. All crankshafts were made from forged and nitrided steel. Each crankshaft was sent for grinding, after a life of approximately 300,000 km of service, as requested by the engine manufacturer. After grinding and assembling in the engine, some crankshafts lasted barely 15,000 km before serious fractures took place. Few other crankshafts demonstrated higher lives. Several vital components were damaged as a result of crankshaft failures. It was then decided to send the crankshafts for laboratory investigation to determine the cause of failure. The depth of the nitrided layer near fracture locations in the crankshaft, particularly at the fillet region where cracks were initiated, was determined by scanning electron microscope (SEM) equipped with electron-dispersive X-ray analysis (EDAX). Microhardness gradient through the nitrided layer close to fracture, surface hardness, and macrohardness at the journals were all measured. Fractographic analysis indicated that fatigue was the dominant mechanism of failure of the crankshaft. The partial absence of the nitrided layer in the fillet region, due to over-grinding, caused a decrease in the fatigue strength which, in turn, led to crack initiation and propagation, and eventually premature fracture. Signs of crankshaft misalignment during installation were also suspected as a possible cause of failure. In order to prevent fillet fatigue failure, final grinding should be done carefully and the grinding amount must be controlled to avoid substantial removal of the nitrided layer. Crankshaft alignment during assembly and proper bearing selection should be done carefully.

A felt guide roll fractured in-service on a paper manufacturing machine, damaging the belt as well as multiple dryer rolls, nearby felt guide rolls, and the frame of the machine. The investigation included visual and stereoscopic examination, chemical and microstructural analysis, microhardness and tensile testing, stress calculations, and vibration measurements. Based on the results, the roll fracture was attributed to high-cycle fatigue associated with a plug weld over one of the five threaded fasteners added to secure a balance weight inside the roll. The balance weight was installed to compensate for variations in wall thickness (i.e., weight distribution) of the pipe product used to make the roll. According to the investigation, resonance and vibration, which were initially considered, did not cause the failure.

High-horsepower electric motors were utilized to drive large compressors (made of 4340 steel shafts and gear-type couplings) required in a manufacturing process. The load was transmitted by two keys 180 deg apart. Six of the eight compressor shafts were found cracked in a keyway and one of them fractured after a few months of operation. Visual examination of fractured shaft revealed that the cracks originated from one of the keyways and propagated circumferentially around the shaft. The shaft and coupling slippage was indicated by the upset keys and this type of fracture. The shaft surface both near and in the keyways indicated fretting which greatly reduced the fatigue limit of the shaft metal and initiated fatigue cracks. Fatigue marks were observed on the fractured key. Repetitive impact loading was responsible for propagation of the cracks. The high cyclic bending stresses were caused by misalignment between the electric motor and compressor and were transmitted to the shaft through the geared coupling. Flexible-disk couplings capable of transmitting the required horsepower were installed on the shafts as a corrective measure.

Statistical techniques provide the design engineer with a powerful tool for the analysis of failure data. By means of an actual case study, steps required to design a test yielding statistically meaningful data and procedures used in graphical analysis of results are presented. The Weibull distribution is the statistical model used as a basis for these techniques. This method of failure analysis provides the engineer with clear, positive design direction.