Reasons for the misalignment of spiral steel pipes

In production practice, steel pipes are often degraded due to wrong edges and excessive tolerances. Therefore, it is necessary to analyze the causes of the misalignment of spiral steel pipes and their preventive measures.

The sickle bend of the steel strip is the main factor causing the misaligned edges of the steel pipe. In the forming of spiral welded pipes, the sickle bend of the steel strip will continuously change the forming angle, causing the weld gap to change, resulting in seams, misaligned edges, and even overlapped edges. When the weld reinforcement of the head and tail butt welding of the steel strip is large, if it is not handled properly during over-forming, it is easy to cause large misalignment. Poor edge condition of the steel strip is another important reason for misalignment.

(1) The raw materials are steel strip coil, welding wire, and flux. They must undergo strict physical and chemical inspections before being put into use.
(2) For the head-to-tail butt joint of the steel strip, single-wire or double-wire submerged arc welding is used, and automatic submerged arc welding is used for repair welding after being rolled into a steel pipe.
(3) Before forming, the strip steel undergoes leveling, trimming, planing, surface cleaning, transportation, and pre-bending.
(4) A weld gap control device is used to ensure that the weld gap meets the welding requirements. The pipe diameter, offset amount, and weld gap are all strictly controlled.
(5) Adopt external control or internal control roller forming.
(6) Electric contact pressure gauges are used to control the pressure of the cylinders on both sides of the conveyor to ensure smooth transportation of the strip.
(7) After cutting into individual steel pipes, the first three steel pipes in each batch must undergo a strict first inspection system to check the mechanical properties, chemical composition, fusion status of the welds, the surface quality of the steel pipes, and non-destructive testing to ensure the pipe making process Only after passing the test can it be officially put into production.
(8) Use an air plasma cutting machine to cut the steel pipe into individual pieces.
(9) Both internal and external welding use electric welding machines for single-wire or double-wire submerged arc welding to obtain stable welding specifications.
(10) All completed welds have been inspected by an online continuous ultrasonic automatic flaw detector, ensuring 100% non-destructive testing coverage of spiral welds. If there is a defect, it will automatically alarm and spray mark, so that production workers can adjust the process parameters at any time to eliminate defects in time.
(11) The areas with continuous sonic flaw detection marks on the welds will undergo manual ultrasonic and X-ray re-examination. If there are indeed defects, they will be repaired and then undergo non-destructive inspection again until it is confirmed that the defects have been eliminated.