Failure of a Pendent Reheater Tube in a 110 MW Thermal Power Plant

摘要

This investigation was conducted to examine the probable cause of failure of one pendent reheater tube of a 110 MW thermal power plant. Preliminary macroscopic examinations along with visual examination, dimensional measurement, chemical analysis, evaluation of mechanical properties, oxide scale thickness measurement were carried out to predict the probable cause/ causes of failure. In addition, optical microscopy was a necessary supplement to understand the reason for the failure. It was concluded that due to progressive erosion caused by the high velocity flue gas streams on the fire side wall, the tube had thinned down and could not cope the prevailing working stress. As a result, the affected areas of the tube suffered plastic deformation. Apart from that, formation of micro creep cavities due to rise in tube metal temperature (on the steam side) at localized places led to initiation of minor cracks before culminating to final rupture. The final failure is due to both these mechanisms occurring simultaneously.