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Premature failure of headspan suspensions was mainly attributed to the fracture failure of the droppers. Various experiments were conducted to explore the fracture failure mechanism of the droppers used in headspan suspensions. Four notches along the axial direction of the dropper, corrosion pits and corrosion products were observed by visual examination. Although the axial cracks have little effect on the structural strength, they make it easier to form corrosion environment in the notches than on the exposed outer surfaces. Furthermore, energy spectrum analysis indicated the presence of chlorine and sulfur both in the corrosion products inside of axial cracks and corrosion pits. Meanwhile, typical microstructural features of intergranular cracking and corrosion products were observed by the scanning electron microscopy. Finally, finite element analysis was conducted to characterize the stress distribution near the corrosion pits. The simulation results showed that obvious stress concentration was formed near the corrosion area. All the results indicated that the droppers failed due to the combination of pitting corrosion and stress corrosion cracking. [ABSTRACT FROM AUTHOR]

This research was focused on the failure analysis of a cracked SS304 stainless steel elbow from a chemical plant. The service life of the elbow was 2 years and 8 months. The elbow was welded with two straight pipes at two ends. Cracks were located mainly at positions close to the weld joint and the arc where very strong tensile residual stress existed. Corrosion pits were distributed on the inner surface of the elbow. Cracks were initiated from the corrosion pit bottoms. Branching was observed from the cracks. Cl and S elements were detected in corrosion products from the corrosion pits and the cracks by EDS. SEM results reviewed the intergranular and transgranular brittle nature of the fracture. It is concluded that stress corrosion cracking was the main reason for the cracking of the elbow. [ABSTRACT FROM AUTHOR]

Cracking of an oil inlet pipe in an electrohydraulic governing system was detected and analyzed to determine its failure mechanism. Microscopic analysis methods, such as the scanning electron microscopy and energy-dispersive X-ray spectrum, were applied to obtain the effective information. Visual and micro-examination showed that the pipe suffered a brittle cracking at the elbow part. Corrosion pits and branched cracks had formed in the outer surface of the pipe. The element of chlorine was detected both in the corrosion pits and the corrosion products inside the cracks. In addition, the cracks were found initiating from the bottom of the corrosion pit. Transgranular cracking feature was identified for the cracks. All the collected evidences suggested that the EH oil pipe fractured due to the combination of a chloride pitting corrosion and a stress corrosion cracking failure. [ABSTRACT FROM AUTHOR]

Failure analysis was carried out on the stainless steel hooks in a brick kiln to confirm its failure mechanism. The collected evidence indicated that chemical composition of the stainless steel hook was consistent with the standard requirements for 304 stainless steel. The metallographic test showed that the microstructure of the stainless steel hook in the non-damaged areas was normal. However, serious chromium segregation which might be caused by secondary phase formation at the high temperature was found in the damaged material. This dramatically reduced the corrosion resistance of the material. The corrosion elements such as oxygen and sulfur were found playing a major role in the corrosion process. Thus, the failure of the stainless steel hook was induced by corrosion due to the chromium segregation and the existence of corrosive elements including oxygen and sulfur. [ABSTRACT FROM AUTHOR]

The failure mechanism of the connectors assembled on the isolating switches was analyzed. Under SEM examination, the fracture surface showed obvious crack propagation traces. Beach marks with a reverse bending pattern were found on the fracture surface. Fatigue striations, which were the micro-evidence of fatigue, were observed clearly on the propagation zone. Both the metallurgical examinations and XRD analysis showed that the material of the connector only contained the austenite phase. The collected evidence suggests that that failure of the connectors was induced by fatigue. The vibration of the specimen during transport was the most probable source of the alternating stress. The stretching assembly stress of the connector could increase the fatigue stress ratios of the specimen. Defects existing in the material might destroy the continuity of the material substrate and reduce the fatigue performance of the material. [ABSTRACT FROM AUTHOR]