Key factors that determine the quality of spiral welded pipes

Spiral welded pipes (SSAW), also called spiral steel pipes, are widely used in fluid transportation, gas transportation pipe networks, chemical pipeline insulation projects, petroleum, chemical industry, centralized supply and distribution, central air conditioning and ventilation, water supply and drainage, and tap water projects. Power Engineering. Urban gas transmission pipeline network, underground water transmission and drainage projects such as highways, marine oil transportation, petrochemical chemical industry, etc. Spiral welded pipes are produced by extrusion welding of strip steel coils. For example, high-frequency welding technology is used to produce smaller diameter pipes; double-sided submerged arc welding technology is used to produce larger diameter steel pipes; high-frequency welding Technology can improve efficiency and product quality in the production process of high-frequency welded pipes (ERW).

What is the key to determining the quality of spiral welded pipes?

1. The production process is strictly in accordance with the standard requirements, and 100% X-ray review of the welds is carried out to ensure that the mechanical properties and chemical composition of the welds meet the standard requirements.

The welding process of spiral welded pipe is divided into high frequency welding and low frequency welding. High-frequency welding mainly uses high-frequency current to heat the workpiece to the temperature required for welding, and uses high-frequency current to heat the workpiece to the temperature required for welding. When high-frequency current passes through the steel strip and high-frequency resistance welding wire for resistance welding, heat will be generated between the welding wire and the flux. Heat will change the chemical composition of the welding wire and flux and interact with the molten state, turning the welding product into a uniform metal molten pool, thereby obtaining a stable weld form. The low-frequency welding method can be used not only in large-diameter pipes but also in small-diameter pipes. High-frequency welding can increase the heating temperature by 1~2°C, allowing more welds in the weld to be evenly heated to obtain a uniform and dense weld form.

2. The welded pipe unit adopts automatic double-wire double-sided submerged arc welding process for welding. This process can save the number of welding passes and has high efficiency.

During the production process, only one operator and an automatic pipe welding unit are needed to complete the welding task, which has also been widely used in actual production. The automatic double-wire double-sided submerged arc welding process is a multi-functional welding process that can well solve various defects that may exist in manual welding. Therefore, it is widely used in the building decoration industry and has become widely popular in the construction industry.

3. Before forming, the tube blank must be chamfered and the steel pipe must be heated to a high temperature and a large number of spiral welds and misaligned edges are evenly distributed inside the tube blank.

In order to ensure the heating temperature, the surface of the heating tube must have a certain angle. During the heating process of the tube blanks, manual feeding is used, and the number of tube blanks is subject to not affecting the processing length, and is controlled between 5 and 6 mm. The tube blank is directly sent into the heating furnace for heating without heating, which can improve the utilization rate of the material.

4. After welding, annular brackets are welded at both ends of the pipe section. Their function is to disperse the stress in the weld area into the support belt and reduce the thermal stress generated by the weld.

The bending test of spiral welded pipes shows that the residual stress and plastic deformation of the welds are larger than those of straight seam welded pipes. The bending test is carried out under the conditions of use. The bending radius of the steel pipe is generally 50-200 mm. In order to obtain better bending performance, first of all, the bending direction of the steel pipe should be as opposite as possible to that of the straight seam welded pipe. When bending the pipe, pay attention to the bending radius not being too large to ensure that no bending stress is generated during the bending process and affecting the bending strength; the bending radius should not be too small to ensure that no bending stress is generated during the bending process and affecting the bending shape; ring brackets are welded at both ends of the bent pipe. Its function is to disperse the stress in the weld area into the support belt, reduce the stress in the weld area, and thereby reduce the bending performance;

As the spiral angle gradually decreases during the production process of spiral welded pipe manufacturers, some residual stress in the weld will affect the bending performance; if the diameter of the welding rod is too small, defects such as cracks will appear. If you do not pay attention to the bending angle during the bending process, bending stress will be generated during bending, which will affect the bending shrinkage and deformation; if the bending is excessive, it will cause fracture stress and affect the bending shrinkage temperature change and deformation amount.

5. Due to the large diameter of the tube blank, in order to ensure that the heat affected zone can be fully penetrated, manual arc welding or electric arc welding is generally used.

Near the arc, the direction of the welding current should be consistent with the axis of the tube blank. The metal melted by the arc flows in from the side of the weld and is evenly distributed along the weld. The direction of the current should be perpendicular to the axis of the tube blank, and the current should be evenly distributed. The weld metal should be flowing on both sides of the weld. If the molten pool of arc welding is in the weld zone, the molten metal will flow out along the weld zone, and during welding the molten pool will flow along both sides of the weld. If the molten pool on both sides of the weld is evenly distributed, the weld penetration on both sides of the weld will be very good; if the two weld areas are unevenly distributed, the welded joint will be prone to cracking.