Failure analysis of blowholes in welded boiler water walls

Abstract

Water walls are subjected to thermo-mechanical loading, which potentially leads to fatigue crack initiation and growth from the weld defects. This study comprehensively analyzes the blowout failure (blowholes) occurring in boiler water walls. An experimental-simulation mixed approach has been adopted to establish the effect of weld defects on fatigue crack initiation, crack growth, and ultimate failure by blowhole. The effect of the defect position on the propagation and failure has also been modeled by extended Finite Element Method (XFEM) based on the criteria of energy release rate. A combination of XFEM and Direct Cyclic Analysis (DCA) is used to calculate low-cycle fatigue life. The cracks are shown to have originated from lack-of-fusion defects, causing the membrane to disconnect and reducing heat transfer efficiency, which may lead to localized thermal hotspots and membrane rupture, leaving molten slag residues on the airside of water walls.