A water tube boiler is a type of boiler in which water circulates in tubes heated externally by fire. It was found that the water tube economizers are often subject to the serious damage mainly because of the overheating and corrosion. Thus, the metallurgical investigation procedures starts with the visual inspection, stereomicroscopy, metallography and chemical analysis methods. It was identified that the failure of the u-bend tube was due to the cracking caused by bending forces during the procedures. This cracking causes a leak for the tube. The appearance of corrosion on the shell side is due to the presence of small content of sulphur under the boiler environment. Several welding imperfections were also detected, however, both corrosion and welding imperfections were not the primary caused of the tube failure. From the analysis, the use of SUS304 grade stainless steel was discovered to be the appropriate material selection for the tube boiler.
