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How to prevent Blowhole in spiral steel pipe weld

2020-05-14 11:11:37   COMMENT:0 HITS:
  In the production process of thick wall spiral steel pipe, because the key processing is carried out in the hot form, the heating operation is a very important process to determine the quality of the finished product. The disadvantages of the hot blast furnace for heating and the welding area of spiral steel pipe are porosity, hot crack, undercut, etc. The weld porosity of spiral steel pipe not only affects the weld compactness and forms the pipe leakage, but also becomes the initiation point of erosion, so it is important to reduce the weld strength and toughness.

  The factors of weld porosity are: moisture, dirt, oxide skin and iron scraps in the flux, welding elements and covering thickness, surface quality of steel plate and treatment of steel plate edge plate, welding process and API 5L Pls2 X65 Spiral Steel Pipe forming process, etc. Flux composition. When the welding contains appropriate amount of CaF2 and SiO2, a large amount of H2 will be absorbed by reaction to form HF which is highly stable and insoluble in the liquid metal, so as to prevent the formation of hydrogen pores. Bubble. Most of the bubbles occur in the center of the weld bead. The key reason is that hydrogen is buried in the weld metal in the bubble mode as usual.

  The residual stress of spiral steel pipe is large, some of which are close to the limit of compliance. The residual stress of spiral steel pipe is close to zero because of the expansion process. Improper heating will be the reason for exposing cracks, folds and eccentricities on the inner or outer surface of the tube blank.

  Spiral weld seam tracking and ultrasonic online detection tracking are troublesome, so the probability of exceeding the standard of weld defects is higher than that of straight seam submerged arc steel pipe. The emphasis of this heating operation is to average the billet to a temperature suitable for processing. Because the perforation has a great influence on the quality, that is to say, the temperature during the elbow processing is an important condition affecting the quality, so it is usually necessary to control the billet temperature during the perforation processing.

  The stagger amount of spiral steel pipe weld is countless in 1.1-1.2mm, which is less than 10% of the thickness according to the international conventional stagger amount. If the pipe wall thickness is small, the stagger amount is difficult to meet the requirements, while the straight seam submerged arc spiral steel pipe has no such problem.

  Therefore, the countermeasure to eliminate this defect is to eliminate the rust, oil, moisture and other substances of welding wire and weld firstly, and then to dry the flux well to remove the moisture. In addition, it is also useful to increase the current, reduce the welding speed and slow down the solidification speed of molten metal. The stack thickness of flux is usually 25-45mm. When the particle size of flux is large and the density is small, the stack thickness is large, otherwise it is small; when the current is high and the welding speed is low, the stack thickness is large, otherwise it is small. In summer or when the air humidity is high, the recovered flux should be dried before use. When welding the plate with strong sulfur segregation zone, the sulfide in the sulfur segregation zone enters into the weld metal and cracks occur. This is due to the presence of hydrogen in iron sulfide and steel with low melting point in the sulfur segregation zone.

  Therefore, in order to prevent this situation, semi steel or steel with less sulfur segregation band is used. Secondly, it is necessary to clean and dry the weld surface and flux. Steel plate surface treatment. In order to prevent the uncoiled and leveled scrap iron and other sundries from entering the forming process, the plate surface cleaning device shall be equipped.

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