The problems easily occurred on ferritic heat-resisting steel and austenitic stainless heat-resisting steel tubes used on boilers of ultra-supercritical units after putting them into operation

such as cracking on the weld joints

dropping of oxide skin from inner wall

etc.

as well as over-temperature tube-burst occurred in operation of T91 and T92 steel tubes

have been analysed from aspects of microstructure and performance.It shows that the metallographic structure at thick-expanding location is white and bright fine ferritic carbide and grey island structure;the tensile strength Rpo.2

RM

and hardness of bursted tube all have been considerably deacreased as compared with the blow-demaged tubes

the lowest value of diamond penetrator hardness at sharpened end of the burst hole has decreased to 162

while the said hardness value of the neighboaring thick-expanding tubes without burst is 175~187.