The lining stainless steel composite steel pipe (304+Q235B) is a new type of composite pipe, which has the characteristics of corrosion resistance, high-temperature resistance, high extensibility, and high strength. It is widely used in the process of pipelines of new and expanded petrochemical plants. The biggest use problem of this kind of pipe is the complete fusion welding of the base layer and the composite layer. To achieve a good welding effect, the correct welding method is:


1. Preparation before welding
Before welding, clean the paint, dirt, and oxide layer of the contact layer to prevent impurities from decomposing into H2O and CO2 when heated during the welding process. The base layer and composite layer should be preheated before welding. Preheating adopts electric heating method, based on the centerline of the counterpart, the two sides are not less than 3 times the wall thickness, and not less than 50mm, and to prevent overheating.


2. The welding process
Weld the composite layer first, and then the base layer, the process: sealing layer-bottom welding-transition layer-filling layer-cover layer.


3. After welding
After welding, the weld slag, weld spatter and other dirt on the surface of the weldment should be carefully cleaned, and the weld should be partially trimmed if necessary. After welding, post-heat treatment should be carried out to eliminate residual stress. Post-welding treatment should be carried out by the design requirements. For local heat treatment, electric heating should be used. The post-weld treatment of the base layer should select the heat treatment temperature according to the material requirements of the base layer, and other parameters are calculated according to the total thickness of the stainless steel lining pipe (7±1.5) mm.