Why do SSAW steel pipes have pores?

Why do SSAW steel pipes have pores?

The pores in large-diameter spiral welded pipes not only affect the precision of the pipe welds and cause pipeline leakage, but also become corrosion induction points, seriously reducing the strength and resistance of the welds. Most of the bubbles in spiral steel pipes appear in the center of the weld bead. The main reason is that hydrogen is still hidden in the form of bubbles inside the weld metal. At the same time, moisture, dirt, oxide scale and iron filings in the flux, welding components and covering layer thickness, surface quality of the steel plate and treatment of the steel plate side plates, welding processes and steel pipe forming technology may all induce the occurrence of pores in spiral steel pipes.

Therefore, in order to eliminate this defect, it is necessary to remove rust, oil, moisture, and moisture from the welding wire and welding seam, and dry the flux to remove moisture. In addition, increasing the current, reducing the welding speed, and slowing down the solidification rate of the molten metal are also effective.

The specific method is as follows:


1. Reduce the secondary magnetic field. In order to reduce the influence of magnetic deflection, the connection position of the welding cable on the workpiece should be as far away from the welding terminal as possible to prevent some welding cables from generating a secondary magnetic field on the workpiece.

2. Technical aspects. The welding speed should be appropriately reduced or the current should be increased to reduce the crystallization speed of the molten pool metal and allow gas to escape. At the same time, if the strip conveying position is unstable, it should be adjusted in time to avoid frequent fine-tuning of the front axle or the rear axle to maintain its shape, making it difficult for gas to escape.

3. Flux composition. It is rich in appropriate amounts of CaF2 and SiO2 during welding, which will absorb a large amount of H2. The generated HF is highly stable and insoluble in liquid metal. This method prevents the formation of hydrogen holes.

4. The flux accumulation thickness is generally 25-45mm. The maximum value of the accumulation thickness of flux with large particle size and small density, otherwise the minimum value is taken; the maximum value of the cumulative thickness when welding with high current and low speed, otherwise the minimum value is taken. In summer or when the air humidity is high, the recycled flux should be dried first to prevent moisture and other impurities in the flux from affecting welding.

5. Steel plate processing. In order to prevent iron oxide scale and other debris dropped during unwinding and leveling from entering the molding process, a cleaning procedure should be set up. Rust removal and deburring equipment should be installed on the edge of the steel plate to reduce the probability of pores. Removal equipment is best installed after the edger and disc shears.

6. Weld seam tracking. The weld forming coefficient is too small, the weld shape is narrow and deep, gas and inclusions are not easy to float, and pores and slag inclusions are easily formed. Usually, the weld forming coefficient is controlled at 1.3-1.5, with the maximum value for thick-walled welded pipes and the minimum value for thin-walled pipes.