Failure cause analysis for the suspension element of boiler superheater

Abstract

This paper presents the results of tests that resulted in determination of the reasons for a failure to the suspension of a steam superheater coil. The analysed element of the suspension was made of heat-resistant ferritic steel H25T. The scope of performed research included: the structural tests using optical microscopy and scanning electron microscopy, the fractographic tests, as well as the tests of mechanical properties which involved the hardness measurement, the static test of tension, and the impact strength test. The examined steel in the after-service condition was characterized by high strength of TS = 680 MPa and hardness of 313 HV30 with virtually zero ductility of KV300/7.5 = 2 J. The metalography investigation demonstrated that the main reason for destruction to the suspension was brittle rupture which was caused by the presence of continuous grid of sigma phase precipitates at the ferrite grain boundaries.