Temperature requirements for submerged arc welded straight seam steel pipes

The welding process used for submerged arc welded straight seam steel pipe is submerged arc welding technology, which adopts filler welding and particle protection flux submerged arc. The diameter of production can reach 1500mm. LSAW is the English abbreviation of submerged arc welded straight seam steel pipe. The production process of submerged arc welded straight seam steel pipe includes JCOE forming technology and coil forming submerged arc welding technology. When the diameter is large, two steel plates may be used for rolling, which will form the phenomenon of double welds.

Requirements for welding temperature of straight seam steel pipe:

The material is low carbon steel, and the welding temperature is controlled at 1250~1460℃, which can meet the penetration requirements of 3~5mm tube wall thickness. The welding temperature is mainly controlled by adjusting the high-frequency eddy current thermal power and welding speed.

When the input heat is insufficient, the edge of the heated weld cannot reach the welding temperature, and the metal structure remains solid, resulting in incomplete fusion or incomplete penetration. When the input heat is too large, the edge of the heated weld exceeds the welding temperature, resulting in overburning or molten droplets, causing the weld to form a hole. 

The production characteristics of submerged arc welded straight seam steel pipe can eliminate the cause of weld slag inclusion due to unclean interlayer during multi-layer welding.

In view of the fact that there are many inclusions in the raw materials and the slag inclusion in the weld, after taking measures such as inspection of the base metal before welding, replacement of welding wire and flux, etc., the proportion of slag inclusion in the fusion line of the weld is only slightly reduced, indicating that inclusions in the raw materials. It is not the main cause of slag inclusions. 

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