On a same pipe of the platen superheater in boiler of ultra-supercritical 1 000 MW unit in one power plant

two times of tube-burst have successively occurred.Through macroscopic inspection

chemical composition analysis

tensile test

metallographic examination

scanning electronic microscopic and energy spectrum analysis etc.

it shows that the main cause leading to tube-burst is the blockage of foreign maters in the said tube

resulting in reduction of flow passage area in the tube

making the cooling effect of steam onto the tubes to be reduced

and a part of them was in an overtemperature condition

thereby

the high-temperature creep strength being reduced.