Through macroscopic observation

chemical compostion analysis

low-magnification inspection

metallographic examination

hardness test

and tensle and impact tests under room temperature

the causes leading to tube burst occurred on final-stage superheater of boilers for 2×362 MW units in first-phase project of one power plant have been analysed.Results shows that the breakage of tube 1(T22) on final-stage superheater was related to improper design of the welding seam

the metallographic structure and mechanical property of tube materials being unqualified;the rupture of tube 2(T91) on final-stage superheater was caused by improper execution of welding technology

making slag to be existed on fusion line and high hardness in welded seam.For this

it is recommented that the angle-welding seam of roof-entrance tube and the sealing plate have to keep away from the butt-welding seams on sealing plate as possible

improving the weld structure of sealing plate and tubes

decreasing the thickness of locating block.