How to avoid the formation of large bubbles during welding of large diameter spiral tubes
When welding spiral tubes, among the many common welding problems, it is common to have air bubbles at the welds. In particular, the large-diameter spiral tube weld holes not only affect the tightness of the pipe welds, but also cause the pipeline to leak and become corroded. Induced points, severely reduce weld strength and toughness. The factors causing the pores in the weld are: moisture, dirt, scale and iron filings in the flux, welding composition and thickness, steel surface quality and steel edge treatment, welding process and steel tube forming process. Flux composition. When the solder contains an appropriate amount of CaF2 and SiO2, it absorbs a large amount of H2 and generates HF which is highly stable and insoluble in the liquid metal, thereby preventing the formation of hydrogen pores.
Bubbles occur mostly in the center of the 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 the rust, oil, moisture and moisture of the wire and weld. The substance is followed by a good drying of the flux to remove moisture. In addition, it is also effective to increase the current, reduce the welding speed, and slow down the solidification speed of the molten metal.
The deposition thickness of the flux is generally 25-45mm, the flux particle size is large, the density is small, and the stacking thickness takes a larger value, and vice versa. The large current and low welding speed stacking thickness take the maximum value, and vice versa. Or when the air humidity is high, the recovered flux should be dried before use. Sulfur cracking (sulphur-induced cracking). A crack generated by the sulfide in the sulfur segregation zone entering the weld metal when the sulfur is segregated with a strong plate (especially soft boiling steel). The reason for this is that hydrogen sulfide is present in the sulfur segregation zone containing iron sulfide having a low melting point and steel. Therefore, in order to prevent this, it is also effective to use semi-killed steel or killed steel with less sulfur segregation belt.
http://www.xysteelpipe.com/info/How-to-avoid-the-formation-of-large-bubbles-during-welding-of-large-diameter-spiral-tubes-1456-1.htm
Bubbles occur mostly in the center of the 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 the rust, oil, moisture and moisture of the wire and weld. The substance is followed by a good drying of the flux to remove moisture. In addition, it is also effective to increase the current, reduce the welding speed, and slow down the solidification speed of the molten metal.
The deposition thickness of the flux is generally 25-45mm, the flux particle size is large, the density is small, and the stacking thickness takes a larger value, and vice versa. The large current and low welding speed stacking thickness take the maximum value, and vice versa. Or when the air humidity is high, the recovered flux should be dried before use. Sulfur cracking (sulphur-induced cracking). A crack generated by the sulfide in the sulfur segregation zone entering the weld metal when the sulfur is segregated with a strong plate (especially soft boiling steel). The reason for this is that hydrogen sulfide is present in the sulfur segregation zone containing iron sulfide having a low melting point and steel. Therefore, in order to prevent this, it is also effective to use semi-killed steel or killed steel with less sulfur segregation belt.
http://www.xysteelpipe.com/info/How-to-avoid-the-formation-of-large-bubbles-during-welding-of-large-diameter-spiral-tubes-1456-1.htm
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