Elements of porosity in spiral steel pipe welds

The factors that cause porosity in the welding seam of the spiral steel pipe include: dirt, moisture, oxide scale and iron filings in the flux, welding components and covering thickness, the surface quality of the steel plate and the treatment of the edge plate of the steel plate, the welding process and the forming process of the spiral steel pipe, etc. The related prevention methods of spiral steel pipe are: flux composition. When welding contains an appropriate amount of CaF2 and SiO2, it will react and absorb a lot of H2, generate HF with high stability and insoluble in liquid metal, and then avoid the formation of hydrogen pores.

The accumulation thickness of the flux is generally 25-45mm. The maximum thickness of the flux is large and the density is small. Otherwise, the minimum value is taken; the maximum current and low welding speed are used. When the humidity is high, the recovered flux should be dried before use.

Steel plate edge treatment. The edge of the steel plate should be equipped with rust and burr eradication equipment to reduce the possibility of pores. The position of the eradication equipment is best installed after the edge milling machine and the disc shear. The structure of the equipment is an automatic wire wheel with two upper and lower positions on one side, which can adjust the gap, and press the edge of the plate up and down. Surface treatment of steel plate. In order to prevent sundries such as iron oxide scale falling from uncoiling and leveling from entering the forming process, board surface cleaning equipment should be installed.

Weld drawing. The forming coefficient of the spiral steel pipe 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. Generally, the welding seam forming coefficient is controlled at 1.3-1.5, the maximum value for the thick-walled spiral steel pipe, and the minimum value for the thin-walled spiral steel pipe. Reduce the secondary magnetic field. In order to reduce the influence of magnetic bias blowing, the connection position of the welding cable on the workpiece should be kept away from the welding terminal only, so as to avoid the secondary magnetic field generated by some welding cables on the workpiece.