Metallurgical failure analysis of a steam trap bypass tube

Abstract

A steam trap bypass tube (SA-335-P22 grade steel) in a coal fired power plant operating at 540°C had totally fractured. The aim of this study is to explore the evidence related to the steam trap bypass tube and to investigate the cause of failure. Using metallurgical failure analysis method, a detailed investigation was carried out by means of visual inspection, optical microscope examination and scanning electron microscopy examination. Based on all the evidences, the tube had fractured due to multi causes which consist of hydrogen embrittlement and high temperature creep. To avoid further failure recurrence, corrective actions have to be taken which includes replacement of the fractured tube with higher Cr-Mo tube material content for higher creep resistance and continuous steam trap operation monitoring to eliminate condensate.