The method of reducing the porosity of the ssaw steel pipe

The porosity of the large-diameter ssaw steel pipe not only affects the fineness of the welding seam of the pipeline, causing leakage of the pipeline, but also becomes the induction point of corrosion, which seriously reduces the strength and resistance of the welding seam.The bubbles in the spiral steel pipe mostly occur in the center of the weld bead, the main reason is that the hydrogen is still hidden inside the weld metal in the form of bubbles.At the same time, the moisture, dirt, oxide scale and iron filings in the flux, the welding composition and covering thickness, the surface quality of the steel plate and the treatment of the steel plate side plate, the welding technology and the steel pipe forming technology may induce the generation of pores on the spiral steel pipe.

Therefore, in order to eliminate this defect, it is necessary to clean the rust, oil, moisture and moisture of the welding wire and welding seam, and dry the flux to remove the moisture. In addition, it is also effective to increase the current, reduce the welding speed, and slow down the solidification rate of the molten metal.

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 kept away from the welding terminal as far as possible to prevent some welding cables from generating secondary magnetic fields on the workpiece.

2. Technical aspects. The welding speed should be appropriately reduced or the current should be increased, so as to reduce the crystallization speed of the metal in the weld pool, so that the gas can escape. At the same time, if the delivery position of the strip is unstable, it should be adjusted in time to avoid frequent fine-tuning of the front axle or the rear axle stays in shape, making it hard for the gas to escape.

3. Flux composition. When welding is rich in appropriate amount of CaF2 and SiO2, it will absorb a large amount of H2, and the generated HF is highly stable and insoluble in liquid metal. This method can prevent the formation of hydrogen holes.

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

5. Steel plate treatment. In order to prevent sundries such as iron oxide scale falling from uncoiling and leveling from entering the forming process, a cleaning program should be set up. Rust and burr removal equipment should be installed on the edge of the steel plate to reduce the probability of blowholes. The removal equipment is best installed after the edger and disc shear.

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

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