The forming method for spiral submerged arc welded pipes is the upper-coiling method.
In the upper-coiling process, the elevation of the lower surface of steel pipes of various specifications remains unchanged, making the auxiliary equipment simpler and easier to manufacture, with less civil engineering work required. However, the height of the outer welding head needs to be adjusted according to the change in the outer diameter of the steel pipe. During upper coiling, the internal welding head is located near the strip steel inlet, facilitating the easy replacement of parts such as contact tips, without the need to cut holes in the steel pipe, thereby saving both steel material and time.
The welding at the biting point facilitates the application of advanced technology for automatic control of weld gap to ensure welding quality. Additionally, it is easier to remove scale from the inner and outer pressing rollers and replace spare parts. Therefore, the upper-coiling method is widely adopted in most spiral submerged arc welded pipe production lines.
The lower-coiling method has been largely phased out since the 1980s.
Analysis of Causes for Intermittent Tightness or Looseness, Internal Tightness and External Looseness, or Open Seam Defects in Forming Seams
(1) Uneven working width of strip steel or poor edge condition of strip steel can easily lead to intermittent tightness or looseness in the forming seam.
(2) Insufficient height of the welding pad roller can easily cause internal tightness and external looseness in the forming seam.
(3) The absence of a groove or the presence of an inverse groove (wider at the top and narrower at the bottom) on the edge of the strip steel can result in internal tightness and external looseness in the forming seam.
(4) Inappropriate shape of the vertical roller (usually using a slanted vertical roller at the entrance of the former) can cause damage to the lower edge of the strip steel, leading to internal tightness and external looseness in the forming seam.
(5) Poor delivery condition of the strip steel can easily result in internal tightness and external looseness, or intermittent tightness and looseness in the forming seam.
(6) Open seams are typically caused by severe insufficient deformation of the strip steel, rapid changes in working width, or long-distance welding deviation during internal welding.
Spiral steel pipes are primarily used in water supply projects, petrochemical industries, chemicals, electricity, agricultural irrigation, and urban construction. For liquid transportation: water supply and drainage. For gas transportation: natural gas, steam, liquefied petroleum gas. Structural applications include: piling pipes and bridges; used in docks, roads, building structures, etc.
