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　　The slag inclusion of welded steel pipe is the residual slag inside the weld. Theoretically, there are three main reasons for slag inclusion in automatic submerged arc welding welds:

　　1. There are many inclusions in raw materials;

　　2.The interlayer cleaning is not clean during multi-layer welding;

　　3. Improper welding process parameters are not conducive to the floating of slag.

　　According to the production characteristics of straight seam submerged arc welded steel pipe, the cause of slag inclusion in the weld caused by unclean interlayer cleaning during multi-layer welding can be eliminated.

　　In view of the slag inclusion in the weld caused by more inclusions in the raw materials, after taking measures such as pre welding inspection of the base metal, replacement of new welding wire and flux, the proportion of slag inclusion in the weld fusion line is only slightly reduced, indicating that the inclusions in the raw materials are not the main cause of slag inclusion.

　　Therefore, the main reason for slag inclusion in the fusion line of thick wall straight seam submerged arc welded steel pipe is the improper welding process parameters. The welding process parameters of thick wall straight seam submerged arc welded pipe mainly include: line energy, welding current, welding voltage, welding speed, welding wire spacing, groove size, etc.

　　From the further analysis of welding metallurgy, it can be seen that the main reason for slag inclusion in the weld fusion line is that the temperature of the fusion line is too low, making it too late for the liquid slag to precipitate; The reason for the low temperature of the fusion line is that the peak temperature of heating is too low or the cooling speed is too fast.

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