With the rapid development of high-quality strip continuous rolling production and advances in welding and inspection technology, the quality of welded joints has been continuously improved, and the number of welded pipes has also increased, and seamless steel pipes have been replaced in more and more fields. In the production process of welded pipes, the weld height is a very important detail. There are many hazards in the weld seam of the welded pipe. as follows:
Stress corrosion cracks are easily formed at the weld toe of the welded pipe
The stress concentration of the butt joint is mainly caused by the weld height, and the weld of the butt joint has the greatest stress at the weld toe.
The magnitude of the stress concentration factor depends on the weld height h, the angle θ at the weld toe, and the radius r of the corner. When the weld height h increases, the θ angle increases and the r value decreases, which increases the stress concentration factor.
The greater the residual height of the weld, the more severe the stress concentration and the lower the strength of the welded joint. After the welding, the remaining height is reduced, as long as it is not lower than the base metal, the stress concentration is reduced, and sometimes the strength of the welded joint can be increased.
The outer weld seam is high, which affects the shape of the pipe after water pressure expansion
When the lsaw steel pipe is expanded by water pressure, the steel pipe is wrapped by the left and right outer parts of the inner cavity and the steel pipe with the same diameter expansion diameter. Therefore, the residual height of the weld is too large, and the shear stress of the weld is large when the diameter is expanded, and the phenomenon of “small straight edge” is likely to occur on both sides of the weld.
However, experience has shown that when the residual height of the outer weld is controlled at about 2 mm, there will be no “small straight edge” phenomenon when the water pressure is expanded, and the shape of the pipe will not be affected. This is because the residual height of the outer weld is small and the shear stress on the welded joint is also small. As long as the shear stress is within the elastic deformation range, the rebound will occur after unloading and the tube will return to its original state.
The inner weld seam is high, increasing the energy loss of the conveying medium
If the inner surface of the submerged arc welded pipe for transportation is not treated with anti-corrosion treatment, the residual weld height of the inner surface of the submerged arc welded pipe is large, and the frictional resistance to the transport medium is also large, thereby increasing the energy consumption of the transfer line.
The outer weld seam is high, which is not conducive to corrosion protection.
If the epoxy resin glass cloth is used for anti-corrosion during operation, the outer weld seam is high, which will make it difficult to press the weld toe. At the same time, the higher the weld, the thicker the anti-corrosion layer should be. The thickness of the anti-corrosion layer is calculated based on the apex of the outer weld, which increases the anti-corrosion cost.