Case studies in engineering failure analysis最新文献

In recent years, there has been a rise in the number of product liability cases involving the failure of toilet water supply line acetal plastic nuts. These nuts can fail in service, causing water leaks that result in significant property and financial losses. This study examines three possible failure modes of acetal plastic toilet water supply nuts. The three failure modes tested were all due to over load failure of the acetal nut and are as follows: (1) Overtightening of the supply line acetal nut, (2) Supply line lateral pull and, (3) Embrittled supply line lateral pull. Additionally, a “hand-tight” torque survey was conducted. The fracture surfaces and characteristics of these failure tests were examined with Stereo Microscopy and Scanning Electron Microscopy (SEM). The failure modes were compared and contrasted to provide guidance in determination of cause in these investigations.

In this study, the structural susceptibility of a 400 kV power transmission tower subjected to progressive collapse and methods of determining the critical areas of above mentioned structure are investigated. OpenSees program is used for numerical modeling and nonlinear dynamic analysis of the tower which considers the buckling possibility of compression members and the plasticity in the cross sections as well. First, the progressive collapse analysis is performed and the results are reported as time history diagrams. Then, the impact factor of members’ removal and the capacity-to-demand ratio are calculated for different failure scenarios of structural members due to the results of preliminary analysis of progressive collapse. The critical areas of the transmission tower through impact factor and capacity-to-demand ratio are determined so that it will be more feasible to propose retrofitting methods for the damaged structure in order to reduce the future risks. For the studied sample transmission tower, impact factors and capacity-to-demand ratios of 41% of APM cases can predict same critical areas.

Cause of failure of two adjacent super heater tubes made of Cr-Mo steel of a coal based 60 MW thermal power plant has been portrayed in present investigation. Oxide deposits were found on internal surface of tubes. Deposits created significant resistance to heat transfer and resulted in undesirable rise in component temperature. This situation, in turn, aggravated the condition of gas side that was exposed to high temperature. Localized heating coarsened carbides as well as propelled precipitation of new brittle phases along grain boundary resulting in embrittlement of tube material. Continuous exposure to high temperature softened the tube material and tube wall was thinned down with bulging toward outside. Creep void formation along grain boundary was observed and steered intergranular cracking. All these effects contributed synergistically and tubes were failed ultimately due to overload under high Hoop stress.

Amine exchangers are widely used in gas sweetening plants for amine solution regeneration process. This study is investigates cracking and leakage of a 304 type stainless steel plate in an amine exchanger unit, used between absorption and stripper towers. In this regard, micro and macro examinations were performed on the plate, and solution was analyzed. Micro cracks were observed on both sides of the plate, especially under the gasket region of the plate. Results showed that the main reason of cracking was intergranular corrosion accompanied by stress. High concentration of Formate in amine solution, and also high level of stress under gasket region, had initiated the intergranular corrosion and cracking.

Inspection is one of the important activities to detect and fix failures in repairable system. Optimization of inspection intervals has critical role in maintenance cost and operating system. When a component fails, it is renewed or repaired. A great deal of periodic inspection research is for hidden failure and considered one of the perfect (renew) and minimal repair policies. In literature, the lack of simultaneous consideration of both perfect and minimal repair in reliability model has been observed. This study presents new reliability model by synchronous consideration of both minimal and perfect repair. As well as, the expected total maintenance cost is presented and modeled to figure out the optimal inspection interval. The proposed model is more comprehensive model in reliability evaluation and can be applied in different pertinent problems. The model is applied to steam turbine system which the rotor considered as soft component and filter as hard component. The result revealed that the system should be inspected every 12 month.

This paper relates to an upgraded Industrial tracked vehicle which was found with a failed Balance arm during disassembly. The failure analysis of an actual Balance Arms surface was carried out using Fractography and Non Destructive testing techniques to dig out the root cause. The analysis revealed microscopic signatures categorically pointing towards post failure surface mechanical damage. The factor causing to promote failure was improper manufacturing i.e. casting which was further attributed to MnS inclusions.

Failure of a pipe elbow used in geothermal production facility was reported to occur after 2 months in service. A leak was found to form at the bottom of elbow of horizontal pipe. The main cause of failure was investigated through conducting standard failure analysis including visual examination, chemical analysis, mechanical characterization, metallurgical examinations using optical microscopy in combination with scanning electron microscopy (SEM) equipped with energy dispersive X-ray (EDX) analysis and corrosion test using a three-electrode potential technique. Results of this investigation indicated that the failure of elbow was caused by an erosion-corrosion with the presence of wall thinning in leak area. The failure mechanism was discussed in this paper.

The reasons for the failure of a buried pipeline perforated during construction were investigated by a chemical composition analysis; a metallographic test; macromorphology observation; characterization of the corrosion products by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction; field medium characterization; and an analysis of the working conditions. The results revealed that the material composition and organization of the steel pipe conformed to API Specification 5CT. However, the reason for the perforation of the L415 steel pipe was an ultrahigh growth rate of pitting corrosion, as high as 14 mm per year. We confirmed that the synergistic effect of a high partial pressure of oxygen introduced by an improper packing process and concentrated Cl⁻ in the corrosion product layer, which originated from groundwater with a high salt concentration that was used for the water pressure test, were responsible for the failure process.

In the present work, a failed connecting rod from a motorcycle engine was investigated for the root cause of and possible mechanisms leading to its premature failure. In addition to finding the root cause, the expectation from this study was to possibly improve the existing designs or practices to avoid similar failures in future. These results were validated using a finite element analysis (FEA) simulation. A Scanning Electron Microscope was used for investigating the mechanisms of fracture modes, optical microscopy for studying the microstructures and visual inspection were primarily utilised to determine the root cause of the failure. In conclusion, it was determined that the root cause for the premature failure of the connecting rod was the presence of scale build-up inclusions, which led to micro cracking during fatigue loading of the component.

In this study failure of AISI 347 stabilized stainless steel pipe after 60,000 of working in a petrochemical plant was investigated. Result showed that the main cause of failure was thermal stress fatigue. Fatigue cracks were formed at the outer surface of the investigated pipe, and were grown towards the inner surface at the fusion line of welded area. The formation of chromium-rich phases together with thermal fatigue stresses were found to be main causes of failure.