Why do spiral welded steel pipes develop misalignment

In production practice, spiral welded steel pipes are often downgraded due to excessive misalignment. Therefore, it is necessary to analyze the causes of misalignment and preventive measures. The camber of the steel strip is the primary factor causing misalignment in spiral welded steel pipes. During spiral forming, the camber of the steel strip continuously changes the forming angle, leading to changes in the weld gap, resulting in gaps, misalignment, and even overlap.

When the weld reinforcement of the spiral welded steel strip at both ends is large, improper handling during forming can easily cause significant misalignment.

Poor welding conditions at the edge of the steel strip are another important cause of misalignment.

(1) Raw materials, namely steel strip coils, welding wire, and flux, must undergo rigorous physical and chemical testing before use.

(2) For butt welding of the steel strip ends, single-wire or double-wire submerged arc welding is used. After being rolled into spiral welded steel pipes, automatic submerged arc welding is used for repair welding. 

(3) Before forming, the strip steel undergoes leveling, edge trimming, and edge planing. The surface of the spiral steel pipe is then cleaned, conveyed, and pre-bent.

(4) A weld gap control device is used to ensure that the weld gap of the spiral steel pipe meets welding requirements. The diameter of the spiral steel pipe, misalignment, and weld gap are all strictly controlled.

(5) External or internal control roller forming is used.

(6) An electric contact pressure gauge is used to control the pressure of the hydraulic cylinders on both sides of the conveyor, ensuring stable conveying of the strip steel.

(7) After being cut into individual spiral steel pipes, the first three pipes of each batch undergo a strict first-pass inspection system. The mechanical properties, chemical composition, fusion status, surface quality of the spiral steel pipe, and non-destructive testing are checked to ensure the pipe-making process is qualified before formal production begins.

(8) An air plasma cutting machine is used to cut the spiral steel pipe into individual pieces.

(9) Both internal and external welding are performed using electric welding machines with single-wire or double-wire submerged arc welding to obtain stable welding specifications.

(10) All welds are inspected using an online continuous ultrasonic flaw detector, ensuring 100% non-destructive testing coverage of the spiral welds. If defects are found, an automatic alarm is triggered, and a mark is applied, allowing production workers to adjust process parameters and eliminate defects promptly.

(11) Areas with continuous ultrasonic flaw detection marks on the weld are manually inspected using ultrasonic and X-ray methods. If defects are found, they are repaired and then subjected to non-destructive testing again until the defects are confirmed to be eliminated.