Harm of excessive weld seam height of welded pipe

With the rapid development of high-quality strip continuous rolling production and the advancement of welding and inspection technology, the quality of welds continues to improve, and there are more and more types of welded pipes, which have replaced seamless steel pipes in more and more fields. In the production process of welded pipe, the weld reinforcement is a relatively important detail. Excessive weld reinforcement of welded pipe has many hazards, as follows:

Stress corrosion cracks are easy to form at the weld toe. The stress concentration of butt joints is mainly caused by the weld reinforcement. For the weld of butt joints, the stress at the weld toe is relatively large. The stress concentration factor depends on the weld reinforcement h , The weld toe included angle θ and the corner radius r, the increase of the weld reinforcement h, the increase of the θ angle, and the decrease of the value of r, which will increase the stress concentration factor.

The higher the excess height of the weld, the more serious the stress concentration, and the strength of the welded joint will be reduced. After welding, the excess height will be flattened. As long as the excess height is not lower than the base material, the stress concentration can be reduced, and the strength of the welded joint can sometimes be improved.

The extra height of the external weld is large, which affects the shape of the pipe after hydraulic expansion. When the longitudinal submerged arc welded pipe is expanded by water pressure, the steel pipe is covered by the outer mold with the same inner cavity and the expansion size of the steel pipe. Therefore, if If the reinforcement of the weld is too large, the shear stress during the expansion of the weld will be very large, and “small straight edges” are prone to appear on both sides of the weld. Experience shows that when the reinforcement of the outer weld is controlled at about 2mm, the water There will be no "small straight edge" phenomenon when the diameter is expanded, and the tube shape will not be affected. This is because the reinforcement of the outer weld is small, and the shear stress of the welded joint is also small, as long as the shear stress is within the elastic deformation range After unloading, springback occurs, and the pipe will return to its original state. The internal weld seam will have a large residual height, which will increase the energy loss of the conveying medium. If the inner surface of the submerged arc welded pipe for conveying is not treated with anti-corrosion treatment, and the internal weld seam has a large residual height, The frictional resistance of the conveying medium is also larger, which will increase the energy consumption of the conveying pipeline.

The extra height of the outer weld seam is not conducive to anti-corrosion. If the epoxy glass cloth is used for anti-corrosion during operation, the extra height of the outer weld seam will make the weld toe difficult to be pressed firmly. At the same time, the higher the weld seam, the thicker the anti-corrosion layer, because The standard stipulates that the thickness of the anti-corrosion layer is measured based on the vertex of the outer welding seam, which increases the cost of anti-corrosion. During spiral submerged arc welding, "fish-back-shaped" outer welding seams are often prone to appear, which makes it more difficult to guarantee the quality of anti-corrosion. Therefore, adjust it well The spatial position of the welding head and welding specifications are also very important to reduce or eliminate the "fish-back shape" of the outer welding seam.

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