Welding treatment of thick-walled SSAW steel pipe

Thick-walled SSAW steel pipe is welded using arc welding under the flux layer. The process generates heat from the arc burning between the flux and the welding wire, as well as the base metal and the melted welding wire flux, which forms the weld.

During use, the principal stress direction of thick-walled SSAW steel pipes, or the equivalent defect length in the axis direction of the steel pipe, is smaller than that of straight seam pipes. If the pipe length is l, the weld length is l/cos(θ). The debate between SSAW steel pipes and straight seam steel pipes has been ongoing for some time. Firstly, because the defects are parallel to the welds, for SSAW pipes, the defects in the welds are considered "oblique defects." Secondly, pipeline steels are all rolled steel plates, and the impact toughness exhibits significant anisotropy. The CVN (Charpy V-notch) value along the rolling direction can be up to three times higher than the CVN value perpendicular to the rolling direction. Additionally, the weld seam of an SSAW steel pipe is longer than that of a straight seam pipe, especially when compared to UOE steel pipes, which presents a more superior advantage. With the advancement of SSAW pipe manufacturing technology, it is important to evaluate and compare these factors comprehensively and rethink the issue of longer weld seams in SSAW steel pipes.

The main stress on thick-walled SSAW steel pipes is oriented exactly perpendicular to the direction of the pipe's impact resistance. SSAW steel pipes are formed by bending hot-rolled strip steel into a spiral shape, and the inner and outer seams are welded by automatic submerged arc welding. The resulting spiral seam steel pipe has the advantage of staggering the direction of the pipe's impact resistance, turning the typically disadvantageous long weld seam into an advantage. This design allows SSAW steel pipes to be widely used in the production of large-diameter steel pipes for the following reasons:

1.The pipe is continuously bent and formed, so the fixed length of the steel pipe is not limited.

2.By adjusting the forming angle, steel pipes of various diameters can be produced from strip steel of the same width.

3.The process allows for easy size changes, making it suitable for small-batch and multi-variety production of steel pipes.

4.The welds are evenly spirally distributed around the entire circumference of the steel pipe, providing high dimensional accuracy and strength.

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