Fast identification of O2 corrosion in economiser tubes

Failure investigation was conducted on three tube samples via visual/metallographic examination and analysis of operational history. The investigation employed a fast-identification approach, which allowed a shorter down time and faster production recovery after tube failure. Visual and metallographic evidence showed that the tube samples had suffered from abnormally high wastage at the external and internal surfaces; the latter surface, in addition had suffered from deep pitting. Analysis of operational history confirmed the presence of dissolved O2 in the feedwater. It was concluded that leakage was primarily caused by tube thinning from internal wastage/pitting, aggravated by external wastage.