A Study on the Direction of Crack Propagation at Damaged Parts of Hot Dip Galvanizing Bath

At start-up operation of hot dip galvanizing baths to galvanize steel products, several leakage accidents of liquid zinc due to the damage at the vicinity of welded parts between side and bottom plates have been reported. Among these accidents, it is found that transferred liquid zinc solidified in the bath heated inadequately. In another paper, the authors investigate stress levels and directions at corners of the bath to clarify the cause of the damage applying unsteady heat conduction analysis, elastic and elastic-plastic analysis for solidified zinc inside of the bath as mechanical approaches. However, they have not studied the direction of the crack, that is, it starts from the vicinity of a welded part at the bottom plate and propagates downward vertically or 45 degrees toward outside of side plate, then changes its direction to be parallel to the bottom plate. This paper investigates the cause of the direction change of crack, which propagates downward then horizontally, at the corner of the bottom plate from mechanical and material aspects.