Verification of the fatigue life extension and practicality of the LTT elongated bead welding method for boxing fillet joints.

Abstract

　To extend the fatigue life of the boxing fillet joint widely existing in ship structures, the newly developed 16Cr-8Ni low transformation temperature (LTT) flux cored welding wire available to all welding positions and LTT elongated bead method were applied to this joint. The repair procedures of LTT elongated bead method using semi-automatic CO₂ welding practically suitable at ship yard were explored for weld defect prevention. Based on the results of fatigue test on 38 pieces of large size specimens welded in all welding positions, the welding operation guideline was derived. The experimental results showed that, the fatigue life of both the flat and horizontally welded specimens was extended more than 6 times compared with those of conventional boxing fillet joint; The fatigue life of vertically welded specimens reached about 4 times; that of overhead welded specimens was between 2.5 with welding defects and more than 6 times without welding defects.