Leakage causes of branch pipe of unit thermal networks were discussed based on macroscopic observation, chemical composition analysis, metallurgical microstructure inspection, mechanical property tests, SEM and EDS analysis. The experimental results showed that frequent contact of outer pipe wall with corrosion media and thermal fatigue load led to early crack of the pipe. During compression test, the crack propagated under increased compression stress and burst finally. Suggestions were provided to prevent similar events happening.
The cause of welding cracks in thermal sprayed water wall tubes was analyzed, the choice of nondestructive testing method was discussed, and a welding procedure for the water wall tube with thermal sprayed coatings was established successfully.
Failure causes on a condensate pump shaft were discussed by means of macroscopic observation, chemical composition analysis, metallurgical microstructure inspection, mechanical property tests and stress analysis. The experimental results showed that the improper material with disqualified chemical composition, improper microstructure and poor mechanical properties acted as inherent factor. In addition, structure design that led to stress concentration contributed to the failure as external factor. Finally, fatigue fracture happened at the reduce section of the pump shaft.
Fracture failure analysis on device clamp screws of one 110kV transmission line has been carried out based on results of macro-observation, pre-tightening test, mechanical property examination, chemical composition analysis, microstructure observation, SEM observation and EDAX analysis. It is concluded that the main reason of the screw fracture lies in misuse material and improper heat processing which led to material degradation. Suggestions are put forward finally.
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