Because the multi-wire submerged arc welding of longitudinally welded pipes
has the characteristics of large undercooling and fast welding speed, the equilibrium state is basically eliminated. If the same chemical composition as the base metal is used as the welding material, the weld metal will have low plasticity, Low toughness, high strength mechanical properties.
When operating the oil and gas transportation longitudinally welded pipes(lsaw steel pipe
) with high technical requirements, if the safe operation of the pipeline is to be fully ensured, it is necessary to have good impact toughness and plastic welds, in order to avoid the crack resistance, plasticity and toughness of the welded joints. The high strength of the weld metal is reduced. When welding high-strength, low-carbon and low-alloy straight seam welded pipes, it is necessary to control the mass fraction of alloy elements and carbon elements in the weld. Therefore, when choosing welding materials, you need to consider the weld The crack resistance, plasticity and toughness of metals in all directions.
At the same time, when welding large-diameter straight seam steel pipes and other medium-thick plates with greater rigidity, in order to prevent cracks from being caused by greater joint restraint, within the allowable design range, choose a slightly lower strength Welding materials based on the base metal, that is, the use of low-matching joints. This method can prevent the actual strength of the weld from being reduced due to the decrease in the strength of the welding material, thereby greatly increasing the toughness of the weld and reducing the tendency of the joint to crack , Increase the comprehensive mechanical properties of the joint weld.
Welding wires of different diameters have different current adaptation ranges in submerged arc welding. The melting amount of the welding wire will increase with the increase of the current within this range, which will affect the welding seam forming effect, and the adjustment effect of the arc itself will be due to the inability to reach The current in this range is affected and the arc is unstable. Therefore, in the multi-wire submerged arc welding of the longitudinally welded pipe, the diameter of the welding wire needs to be selected according to the welding current.
If you can ensure the welding current of the multi-wire submerged arc welding wire within the uniform wire diameter range, you can use the same diameter welding wire for welding. If you can’t ensure it, you can’t choose different welding wire combinations when welding. Longitudinal welded pipes with multi-wire submerged arc The welding quality of welding is also affected by many factors, such as the dry elongation of the welding wire, the inclination of the welding wire, the spacing of the welding wire and the arrangement of the welding wire. There are three types of welding wire arrangement, namely in-line, horizontal and vertical. Comparing the three arrangement methods with the forming angle, it can be found that the inline weld is relatively small, the horizontal weld is wider, and the longitudinal weld is deeper and narrower.
In the process of multi-wire submerged arc welding of longitudinally welded pipes, the following issues need to be paid attention to. Generally, a mixed configuration of DC-AC is used as the power source for multi-wire submerged arc welding, while reverse connection is used as DC, which requires good arc stability and moderate viscosity. The high-alkali flux with high melting point and fine particles is used in the multi-wire submerged arc welding of longitudinally welded pipes. Through the above research, it is hoped that it will be beneficial to the further development of the multi-wire submerged arc welding process in different materials and different diameters.
Tips: ERW welded pipe is formed by rolling strip and welding the seam, with tighter dimensional tolerances and less weight. The weld seam is heat treated after welding that no untempered martensite remains, and the weld flash can be removed from both inner and outer surfaces.