Life assessment and operation strategy formulation of low-hardness P91 pipe in service
There was low local hardness of P91 main steam pipe in one thermal power unit.The non-destructive testing,thickness measurement,Brinell hardness testing and metallographic examination were conducted on site.The reasons for the low hardness were analyzed by combining with the unit maintenance and operation data.Moreover,the non-destructive life assessment and operation strategy formulation were performed.The results showed that the metallographic structure of the low hardness region was coarse,and the characteristic of martensite was nonobvious.One of the main causes was the improper preparation or execution of heat treatment procedures for welding line.According to the safety factor of 1.5,the residual life of the low hardness region was short.If the safety factor was further reduced,the corresponding residual life would increase,but the safety risk of continuous operation was also increased.It was necessary to reduce the operation pa-rameters to ensure the safety of subsequent operation.
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