Analysis of mechanical properties and application effect of over-matching lap angle weld joint

The experimental analysis of repairing high-grade steel pipeline with high-grade B-type sleeves is completed by using matching and over-matching welding materials. The results show that the fillet weld joints of matching welding and over-matching welding have good tensile strength and impact toughness. The impact toughness of cladding metal of over-matching welded joint is slightly lower than that of matching, and the ductility of welded joint is slightly poor. No welding defects were found in the matching lap fillet weld after welding. The maximum Vickers hardness of the welded joint was 293 HV10, which appeared at the lap weld between the outer surface of the fillet weld and the sleeve. The transverse crack originated from the outer surface layer of the fillet weld appeared in the high match lap fillet weld, and the hardness of the welded joint is generally high. The maximum value appears at the weld at the center of the outer surface, with a value of 403 HV10, which corresponds to the crack initiation position. The reason is related to the cooling rate of molten pool metal in different parts during the welding process, especially the cooling rate at the welding place of the outer surface cover is fast, the hardness value of the outer wall layer is abnormally high, and cracks are initiated. Therefore, it is suggested that when selecting welding materials for lap fillet weld, try to reduce the matching strength grade of the weld without affecting the sealing and bearing.