Weld leveling of straight seam steel pipe

Weld leveling of straight seam steel pipe (lsaw/erw):

Due to the impact of the welding current and the influence of gravity, the internal weld of the pipe will protrude, and the external weld will also sag. If these problems are used in an ordinary low-pressure fluid environment, they will not be affected.

If it is used in high temperature, high pressure and high speed fluid environment, it will cause problems in use. This defect must be eliminated using dedicated weld leveling equipment.

The working principle of the welding seam leveling equipment is: a mandrel with a diameter of 0.20mm smaller than the inner diameter of the pipe is set in the welded pipe, and the mandrel is connected to the cylinder through a wire rope. Through the action of the air cylinder, the mandrel can be moved within the fixed area. Within the length of the mandrel, a set of upper and lower rolls are used to roll the weld in a reciprocating motion perpendicular to the position of the weld. Under the rolling pressure of the mandrel and the roll, the protrusions and depressions are eliminated, and the contour of the weld and the pipe contour are smoothly transitioned. At the same time as the welding leveling treatment, the coarse grain structure inside the weld will be compressed, and it will also play a role in enhancing the density of the weld structure and improving the strength.

Weld leveling introduction:

During the roll-bending process of the steel strip, work hardening will occur, which is not conducive to the post-processing of the pipe, especially the bending of the pipe.
During the welding process, a coarse grain structure will be generated at the weld, and there will be welding stress at the weld, especially at the connection between the weld and the base metal. . Heat treatment equipment is required to eliminate work hardening and refine the grain structure.
At present, the commonly used heat treatment process is bright solution treatment in a hydrogen protective atmosphere, and the stainless steel pipe is heated to above 1050°.
After a period of heat preservation, the internal structure changes to form a uniform austenite structure, which does not oxidize under the protection of hydrogen atmosphere.
The equipment used is an online bright solution (annealing) equipment. The equipment is connected with the roll-bending forming unit, and the welded pipe is subjected to bright solution treatment online at the same time. The heating equipment adopts the medium frequency or high frequency power supply for rapid heating.
Introduce pure hydrogen or hydrogen-nitrogen atmosphere for protection. The hardness of the annealed pipe is controlled at 180±20HV, which can meet the requirements of post-processing and use.