Failure investigation of an economiser tube of coal-fired power plant

This investigation was conducted to determine the probable cause of failure of an economiser tube from a 140 MW thermal power plant. Preliminary macroscopic examinations along with visual examination, dimensional measurement, chemical analysis, magnetic particle examination, hardness measurement, and fractography study were carried out to predict the probable cause/causes of failure in the form of weld cracking. In addition, optical microscopy and field emission scanning electron microscopy were the necessary supplements to understand the reason for the failure. The cracks were observed on the surface of the fillet weld. The hydrogen content in the weld may exceed the standard and result in discontinuous cracks between base metal and weld metal and between weld metal and heat affected zone (HAZ) leading to failure of the economiser tube.