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Welding defects in SSAW (Spiral Submerged Arc Welded) steel pipes can affect the strength, integrity, and performance of the final product. Understanding the types of welding defects and their causes is essential for ensuring the quality of welded pipes. Below are some of the most common welding defects encountered in SSAW steel pipe production.
1. Gas Bubbles
Gas bubbles typically occur in the center of the weld seam. This defect is caused by hydrogen that remains trapped as bubbles inside the weld metal. To prevent gas bubbles, it is essential to thoroughly remove contaminants like rust, oil, water, and moisture from the welding wire and workpiece before welding. Additionally, drying the flux properly to eliminate moisture is critical. Increasing the current and reducing the welding speed to slow down the solidification of the molten metal can also help mitigate this issue.
2. Sulfur Cracking (Sulfur-Induced Cracking)
Sulfur cracking occurs when sulfur in the steel, especially in high-sulfur regions (such as in soft-boiling steels), forms iron sulfide with a low melting point, which leads to cracks in the weld metal. The presence of hydrogen in the steel exacerbates this issue. To prevent sulfur-induced cracking, using semi-killed or killed steel with lower sulfur content can be effective. Additionally, cleaning and drying the weld surface and flux are essential measures to avoid this defect.
3. Thermal Cracking
Thermal cracks can form in the weld seam, particularly during the arc-starting and arc-quenching phases. These cracks are most likely to appear in the arc pits, where the heat stress is concentrated. To prevent thermal cracking, pads should be added at the arc and arc-quenching points, and spiral welding can be used in reverse to minimize stress. Thermal cracks are also more likely when there is high silicon content in the weld metal, which increases stress during solidification.
4. Involvement of Weld Slag
Involvement of weld slag refers to the inclusion of weld slag particles in the weld metal. This occurs when slag from the welding process is trapped within the molten weld pool, leading to weaknesses in the welded joint. Ensuring proper slag removal and consistent welding practices can help reduce this defect.
5. Poor Weld Penetration
Poor weld penetration happens when the weld metal does not adequately overlap both the internal and external surfaces of the pipe, resulting in an incomplete bond. This defect may also occur if the weld does not fully penetrate through the pipe wall. Ensuring proper weld settings and techniques is crucial for achieving sufficient penetration.
6. Edge Biting
Edge biting is a V-shaped groove along the centerline of the weld at the edge of the joint. It is caused by improper welding parameters, such as welding speed, current, and voltage. High welding speeds are particularly likely to cause edge biting, especially when the current is unsuitable. This defect is more common in SSAW pipes compared to submerged arc straight seam welded pipes, where the pipe distribution in the same area and higher speeds can exacerbate the problem.
By addressing these common welding defects, manufacturers can improve the quality and durability of SSAW steel pipes, ensuring their performance in various industrial applications.
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