The production process of spiral welded pipes for drainage pipelines is relatively simple, with high production efficiency and low production costs. Therefore, spiral steel pipes have developed in many industries. So, how should we proceed with the welding operation when using spiral steel pipes?
Before using spiral steel pipes, a deoxidizer must be used for deoxidation to reduce the quantity and size of impurities during operation. It is important to note that spiral steel pipes are directly welded into steel pipes from long steel strips of a certain specification through high-frequency welding.
The shape of steel pipes can be either round or square. The high-frequency welding of spiral steel pipes is based on the principles of electromagnetic induction and the eddy current heating effect of alternating charges in conductors, which heats the edges of the weld seam to a molten state. During welding, since the output current is subject to disruption, it is advisable for the design service life of magnesium alloy sacrificial anodes to match the service life of the pipeline.
In the production of spiral welded pipes, the stability of forming is closely related to welding quality. Only by improving the quality of forming can the welding quality be fully guaranteed. To ensure a good appearance and adequate penetration depth of the weld seam in spiral steel pipes, the gap between the steel plates for butt welding must be uniform. Meanwhile, different welding specifications must be adopted based on different butt welding gaps.
In spiral welded pipes, the unevenness of the forming seam gap caused by the crescent bend and "S" bend of the steel strip poses difficulties for welding, resulting in unstable weld penetration depth and variations in weld reinforcement height. When the forming seam is loose, the weld penetration depth is large and the reinforcement height decreases; when the forming seam is tight, the weld penetration depth is small and the reinforcement height increases. Therefore, during welding, the solution to this problem is to reduce the welding specifications when the forming seam is loose and increase them when the forming seam is tight.
The corrosion prevention methods for spiral welded pipes used in drainage pipelines also start by inhibiting one of the processes. The use of sacrificial anode protection, which connects a metallic material with a more negative potential than the spiral pipe to the spiral steel pipe, will not cause such issues. Therefore, the gas transmission trunk pipes in urban areas should adopt a combined method of anticorrosive coating and sacrificial anode protection. For other non-trunk pipelines with lower pressure, the anticorrosive coating method is generally used directly.
Currently, the commonly used external anticorrosive coatings for buried gas pipelines mainly include five types: three-layer PE composite structure, epoxy resin powder (FBE), coal tar enamel, epoxy coal tar pitch, and PE tape. These methods neither cause waste nor increase maintenance costs. However, it should be noted that when the soil resistivity is too high or the protected pipeline crosses water areas, sacrificial anode protection is not suitable. Different anticorrosion methods have varying degrees of anticorrosion quality and costs. Comprehensive consideration should be given to the anticorrosion methods and costs based on the different pressures, uses, environments, and transported gases of the protected spiral steel pipes.
