In the production of spiral-welded pipes, since the primary processing is carried out in a heated state, the heating operation is a crucial process that determines the quality of the finished product. The heat used in the thermal wind furnace, and the welding area of spiral steel pipes, are prone to defects such as gas pores, thermal cracks, and undercutting. Gas pores in the weld seam of spiral steel pipes not only affect the density of the pipeline weld but also cause leakage and act as initiation points for corrosion, significantly reducing the strength and toughness of the weld. Factors contributing to the formation of gas pores in the weld include moisture, impurities, oxide scale, and iron filings in the flux, the composition and covering thickness of the welding, the surface quality of the steel plate, the treatment of the steel plate edges, the welding process, and the pipe forming process. Flux composition. When welding with an appropriate amount of CaF2 and SiO2, it reacts to absorb a significant amount of H2, forming a highly stable HF that is insoluble in liquid metal, thereby preventing the formation of hydrogen pores. Bubbles. Bubbles often occur at the center of the weld bead, primarily due to hydrogen still being hidden in the weld metal in the form of bubbles.

The manufacturing process of spiral steel pipes results in higher residual stresses, some even approaching the yield limit, according to foreign data. Straight seam submerged arc welded pipes, due to the use of expansion techniques, have residual stresses close to zero. Improper heating can lead to cracks, folds, and other defects on the inner or outer surfaces of the billet. (2) Monitoring the welding of spiral seams and online ultrasonic detection is challenging, thus the probability of exceeding weld defects is higher than in straight seam submerged arc pipes. The key to this heating operation is to uniformly heat the billet to a temperature suitable for processing. Since穿孔 significantly affects quality, meaning the temperature during bending pipe processing is a critical factor, it is generally necessary to control the billet temperature during piercing. (3) The misalignment of spiral pipe welds is typically between 1.1 to 1.2 mm, and according to international standards, the misalignment should be less than 10% of the thickness. If the pipe wall thickness is small, the misalignment is difficult to meet the requirements, whereas straight seam submerged arc pipes do not have this issue.

To eliminate this drawback, it is first necessary to remove rust, oil, moisture, and humidity from the welding wire and seam. Secondly, it is essential to properly dry the flux to remove moisture. Additionally, increasing the current, reducing the welding speed, and slowing the solidification rate of the molten metal are also effective methods. The stacking thickness of the flux is generally 25-45mm; for larger particle size and lower density, a thicker stack is used, while a thinner stack is used for smaller particle size. A thicker stack is also preferred with higher current and lower welding speed. Moreover, during summer or high humidity, the recovered flux should be dried before use. Sulfur cracking (cracking caused by sulfur). When welding plates with a strong sulfur segregation band (especially soft boil steel), sulfur compounds in the segregation band enter the weld metal and cause cracking. The reason is the presence of low-melting-point iron sulfide in the sulfur segregation band and hydrogen in the steel. Therefore, using semi-steel or steel with less sulfur segregation is effective in preventing this condition. Secondly, the cleanliness and dryness of the weld seam surface and the flux are also very important. Surface treatment of steel plates. To prevent iron oxide scales and other debris from falling off during uncoiling and leveling from entering the forming process, a plate surface cleaning device should be installed.