Local-dry underwater welding preheating technology and development of special drain cover

A kind of special fixed drain cover used for local-dry underwater welding has been developed. The drain cover can be used for semi-automatic local-dry underwater welding process with flux-cored wire and had the function of underwater preheating before welding, by which preheating temperature can range from 60 to 80 ℃. Preheating welding was performed before groove welding by heat conduction from preheating plate covered on the groove in the drainage cover. The welding experiment results carried out in a pool using the drain cover indicated that the welding joint quality reached class A according to AWS D3.6M standard. The maximum hardness of welding joint decreased significantly, while toughness improved dramatically by using fixed drainage cover with preheating function compared with other underwater welding methods.