The slag in the welded steel pipe is the residual slag in the welded junctions. Theoretically speaking, the main reasons for slag in welded junctions are: for the raw materials (base metal, welding wire, flux), the finishing between layers during multi-layer welding is not clean and the welding process parameters Inappropriate.

According to the production characteristics of LSAW steel pipes, it is possible to eliminate the slag inclusion in the welded junctions due to the irregular arrangement of layers during multilayer welding. In view of the problem of slag inclusion in the welded junctions due to inclusions in the raw materials, checking material before welding, replacement of new welding wire and flux, etc., the slag inclusion in the welded junctions reduced. So it is not the main reason for slag inclusions.

Therefore, the main reason for slag inclusion in the welded junctions of thick-walled LSAW steel pipe is improper welding process parameters. The welding process parameters of thick-wall LSAW pipes are: heat input, welding current, welding voltage, welding speed, welding wire distance, groove size, etc. Through analysis of welding metallurgy, it can be seen that the main cause of slag inclusion in the welded junctions is that the temperature of the weld line is too low to separate the liquid slag, which leads to slag left at the welded junctions.