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The butt joint of the high temperature superheater inlet tee of 330MW Unit Boiler in a thermal power plant cracked. The causes of the weld cracking were analyzed by means of macroscopic morphology observation, fracture SEM inspection, microstructure inspection, mechanical property inspection and chemical composition inspection. The results show that a large number of small thermal cracks are formed in the weld due to improper welding process or operation during boiler installation. At the same time, the improper post weld heat treatment of the joint results in the high hardness of the weld, the insufficient toughness reserve and the decrease of the crack growth resistance. During the long-term operation of the boiler, under the combined action of the primary stress caused by the medium pressure in the pipe and the secondary stress caused by the expansion and contraction of the pipe system, the small crystal cracks in the weld continue to expand, which eventually leads to the macro cracks.

Analysis of the causes of the cracking of the tee joint of the header of the utility boiler