As an important part of oil and gas pipelines, the quality and safety of bend pipes affect the safe operation of pipelines. In this paper, a case of a bending pipe leakage accident was tested and analyzed. Through non-destructive testing, physical and chemical property inspection, and defect anatomy analysis, it was found that the bending section of the bending pipe did not meet the standard requirements and the material was hard and brittle. It is concluded that the leakage of the bend pipe belongs to low-stress brittle failure. The main reasons for the failure of the bend pipe are improper material selection and unreasonable heating process, a hard and brittle martensitic structure formed in the bending section, deformation, and reduced bearing capacity.
KEYWORDS: Material fatigue, Teeth, Failure analysis, Scanning electron microscopy, Plastics, Deformation, Chemical analysis, Wind turbine technology, Chemical composition, Analytical research
The bolts of wind farm are prone to fatigue failure during service. Generally, the fatigue stress does not require too much external force. Sometimes the stress generated by bolts is much lower than the yield strength of bolts. In view of the failure problem of connecting bolts used in wind farms, the failure causes of the double-head bolt were studied by macroscopic inspection, chemical composition analysis, metallographic analysis, and scanning electron microscopy. The results showed that the fracture was a fatigue fracture, and the fatigue source area was located at the bottom of the thread tooth. Under the action of long-term alternating stress, the single source crack evolved into multi-source fatigue cracks, where the fracture was related to the larger stress in the process of installation and service. This paper analyzed the causes of bolt failure and put forward effective suggestions for the service environment of wind turbine bolts.
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