Welding process of multi-wire submerged arc welding for straight seam welded pipe

Because of the characteristics of super cooling and fast welding speed, the equilibrium state is basically removed. If the same chemical composition as the base metal is used as the welding material, the weld metal will have low plasticity, low toughness and high strength mechanical properties.

In order to fully ensure the safe operation of oil and gas pipeline, it is necessary to have good impact toughness and plastic weld. In order to avoid the reduction of crack resistance, plasticity and toughness of welded joint due to the high strength of weld metal, it is necessary to control the welding seam in the welding of high strength, low carbon and low alloy straight welded pipe Therefore, the crack resistance, plasticity and toughness of weld metal in all directions should be considered when selecting welding materials.

At the same time, in order to prevent cracks caused by large joint restraint, the welding material with strength slightly lower than the base metal should be selected within the allowable design range, that is, the low matching joint form should be adopted. This method can prevent cracks caused by the decrease of welding material strength As a result, the toughness of the weld is greatly increased, the crack tendency of the joint is reduced, and the comprehensive mechanical properties of the joint are increased.

Different diameters of welding wire have different current adaptation range in submerged arc welding. The melting amount of welding wire will increase with the increase of current in this range, which will affect the weld forming effect. However, the arc self-regulation effect will be affected because of the current not reaching this range, which will lead to the arc instability. Therefore, in the multi wire submerged arc welding of straight welded pipe, the diameter of welding wire will increase It needs to be selected according to the welding current.

If the welding current of multi wire submerged arc welding wire within the range of uniform wire diameter can be ensured, the same diameter wire can be used for welding. If it cannot be ensured, different wire combinations cannot be selected during welding. The welding quality of multi wire submerged arc welding of straight welded pipe is also affected by many factors, such as wire dry elongation, wire inclination, wire spacing and wire arrangement, etc There are three types of wire arrangement, i.e. in-line, horizontal and vertical. If the three types of wire arrangement are compared from the perspective of weld forming, it can be found that the fusion of in-line weld is smaller, the width of horizontal weld is larger, and the width of vertical weld is deeper and narrower.

In the process of longitudinal welded pipe multi wire submerged arc welding, we need to pay attention to the following problems. Generally, DC-AC hybrid configuration is used as the power source of multi wire submerged arc welding, while reverse connection is used as DC. High alkali type flux with good arc stability, moderate viscosity, high melting point and fine particles is needed to be used in longitudinal welded pipe multi wire submerged arc welding. Through the above research, we hope it can be conducive to multi wire submerged arc welding Further development of arc welding technology in different materials and different diameters.