It is very common for bubbles to exist in the welds of welded carbon steel pipes. Especially for large-diameter seamless steel pipes, the pores in the welds not only affect the sealing of the pipe welds and cause pipeline leakage, but also become the induction point of corrosion, seriously reducing the quality of the welds. strength and toughness. Factors causing weld porosity include: moisture, dirt, oxide scale and iron filings in the flux, welding composition and covering layer thickness, steel plate surface quality and steel plate side plate treatment, welding process and steel pipe. Molding process, etc. Flux ingredients. When the welding contains an appropriate amount of CaF2 and SiO2, a reaction will occur, absorbing a large amount of H2, and generating HF with high stability and insoluble in liquid metal, which can prevent the formation of hydrogen holes.
Bubbles mostly appear in the center of the weld bead. The main reason is that hydrogen is still hidden inside the weld metal in the form of bubbles. Therefore, the measure to eliminate this defect is to first remove rust, oil, water and moisture from the welding wire and weld. and other substances, subsequent flux must be sufficiently dried 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 flux accumulation thickness is generally 25-45mm. The maximum particle size and low density of the flux are taken as the maximum value, otherwise the minimum value is taken; the cumulative thickness is taken as the maximum current and low welding speed, otherwise the minimum value is taken. When the humidity is high, the recycled flux should be dried before use. Sulfur cracking (cracking caused by sulfur). When welding plates with strong sulfur segregation zones (especially soft boiling steel), cracks are caused by the sulfide in the sulfur segregation zone entering the weld metal. The reason is the presence of hydrogen in iron sulfide and low melting point steel in the sulfur segregation zone. Therefore, in order to prevent this from happening, it is also effective to use semi-killed steel or killed steel with less sulfur-containing segregation zones.
