Through some methods

such as macroscopic inspection

chemical composition analysis

metallographic examination

and mechanical performance examination etc.

the causes leading to welded seam cracking occurred on tubes of T91/TH347H high-temperature reheater in one power plant have been analysed.Results show that the inner wall in section 12.5 mm at two sides of the welded seam with different steels in the high-temperature reheater has been thinly peeled

the chemical composition conforms with the requirements specified in ASME SA-213M 2008a

the microstructure being aged

the tensile strength conforming with the requirements.Therefore

the cracking in annular direction at the side of P91 steel is due to local overtemperature resulted from the working medium flow variation caused by the thinly peeling of inner wall structure at tube ends of two sides concerning the welded joint under specific condition

making the area of thinly weakened structure to bear larger thermal expansion stress.