Cracking reason of flange weld of heat exchanger cylinder

Cracking occurred in the welded joint of heat exchanger cylinder and flange in a equipment manufacturer. The crack and fracture of the weld cracking area were analyzed by means of chemical composition analysis, hardness test, metallographic examination and scanning electron microscope analysis. The results show that the chemical composition of the cylinder and flange met the standard requirements, and the selection of welding materials was reasonable. The weld formed a hardened structure, and the overheated zone of the joint was a high hardness zone with a maximum hardness of 436 HV1. Under the action of circumferential tensile stress, an intergranular crack extending from the inner surface to the outer surface was generated in the welded joint. The crack ended at 70 mm from the surface of the backing weld, and the cracking property was hydrogen-induced delayed cracking. The high strength of the heat exchanger cylinder and the large hardening tendency were the root causes of hydrogen embrittlement cracking in the weld.