What are the measures to prevent pores in welded pipes?
Welded steel pipe weld porosity not only affects the sealing of pipeline welds, causing pipeline leakage, but also becomes the inducing point of corrosion, seriously reducing the strength and toughness of welds.
The factors that cause weld porosity are: moisture in flux, dirt, scale and iron filings, welding composition and thickness of covering layer, surface quality of steel plate, edge treatment of steel plate, welding process and steel pipe forming process.
Measures to prevent pores in welded steel pipes:
1) Flux composition: When the welded steel pipe contains an appropriate amount of CaF2 and SiO2, it will react, absorb a large amount of H2, and generate HF, which has high stability and is insoluble in liquid metal, which can prevent the formation of hydrogen pores.
2) Flux accumulation thickness is generally 25-45mm. The maximum value of the accumulation thickness of the flux with large particle size and low density, otherwise it is the minimum value; the maximum value of the accumulation thickness when the flux is high current and low welding speed, otherwise it is the minimum value. In addition, in summer or when the air humidity is high, the recycled flux should be dried before use.
3) Steel plate surface treatment: In order to avoid uncoiling, leveling and peeling scale and other debris from entering the forming process, a plate surface cleaning device should be installed.
4) Steel plate edge treatment: The edge of the steel plate should be equipped with derusting and deburring devices to reduce the possibility of air holes. The location of the removal device is best installed after the edge milling machine and disc shears. The structure of the device is two movable wire wheels with adjustable clearance up and down on one side, pressing the edge of the plate up and down.
5) Weld seam section: The weld seam forming coefficient is too small, the weld seam shape is narrow and deep, the gas and inclusions are not easy to emerge, and it is easy to form pores and slag inclusions. Generally, the weld formation coefficient is controlled at 1.3-1.5, the maximum value is taken for thick-walled welded pipes, and the minimum value is taken for thin-walled pipes.
6) Reduce the secondary magnetic field: In order to reduce the influence of bias magnetic blowing, the connection position of the welding cable on the workpiece should be close to the welding terminal, so as to avoid the secondary magnetic field generated by some welding cables on the workpiece.
7) In terms of technology: the welding speed should be appropriately reduced or the current should be increased to delay the crystallization speed of the metal in the molten pool to facilitate the escape of gas; at the same time, if the strip conveying position is unstable, it should be adjusted in time to prevent frequent passage. Fine-tuning the front or rear axle maintains shape and makes it difficult for gases to escape.
Welded steel pipe refers to a steel pipe welded by steel plate or strip steel by crimping, generally with a fixed length of 6 meters. The production process is simple, the production efficiency is high, the cost is low, and the development is fast, but the strength is generally lower than that of seamless steel pipes.
