Causes of porosity at the weld seam of spiral welded steel pipe

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2021-04-14

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Many workers involved in processing steel pipes have reported the occurrence of porosity at the butt welds of spiral welded pipes. Spiral welded pipes are manufactured by rolling strip steel on a forming machine to create a helical shape, followed by double-sided submerged arc welding. During the production process, common defects such as incomplete penetration and edge misalignment often arise. However, among these issues, porosity at the butt welds is particularly difficult to control. Porosity refers to the presence, either on the weld surface or within the weld metal, of partially fused particles or gas bubbles, as well as sand‑like pits on the weld surface.

　　Many workers involved in processing steel pipes have reported that… Spiral steel pipe Porosity appears at the butt welds. Spiral welded steel pipes are manufactured by rolling strip steel into a spiral shape using a forming machine, followed by double-sided submerged arc welding. During the production process, defects such as incomplete penetration and edge misalignment are common; however, among these issues, porosity at the butt welds is particularly difficult to control. Porosity refers to the presence of partially unfused particles or gas bubbles on or within the weld surface, as well as sand‑grain‑shaped pits on the weld surface.

　　The spiral steel pipe plant’s analysis indicates that the causes of pitting are as follows:

　　1. During welding, if the current supplied to the welding torch is too low and the capacitor‑charging time is too short, the weld surface hardens before the weld has fully penetrated. As a result, porosity or voids may remain inside, indicating incomplete penetration.

　　2. When the steel strip enters the knife‑shaped forming arc, the joints are not properly aligned; the seams do not fit tightly, resulting in excessive gaps between the joined strips.

　　3. When butt-welding the steel strip, failure to promptly remove rust or scale from both edges of the strip.

　　4. Production equipment was not maintained and cleaned in a timely manner, and dust or contaminants on the workbench may have inadvertently fallen into the weld gaps of the butt‑joined steel strips.

　　5. The temperature in the operating workshop may be too low or excessively humid, thereby affecting the temperature and dryness of the solder joints.

　　Guangxi Nanning Canghai Steel Co., Ltd. specializes in producing straight-seam welded pipes, steel plate‑rolled pipes, large‑diameter steel pipes, spiral pipes, spiral‑welded pipes, straight‑seam pipes, spiral steel pipes, and steel casing pipes. As a professional manufacturer of spiral pipes, our products are widely used in pipeline systems for natural gas, petroleum, chemical processing, power generation, heating, water supply and drainage, sugar production, papermaking, as well as in pile‑driving applications and steel support structures for subway projects.

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