Fatigue Index and Process Flow of Double-sided Submerged Arc Welded Spiral Steel Pipe

Fatigue Index of Double-sided Submerged Arc Welded Spiral Steel Pipe

Fatigue: Metal materials under the ultimate strength, long-term bearing the role of alternating loads (that is, the size and direction of repeated changes in the load), without significant plastic deformation and sudden fracture phenomenon, known as fatigue. Fatigue index includes fatigue limit and fatigue strength.

FATIGUE LIMIT: The maximum stress that a metal material can bear under repeated or alternating stresses is called the fatigue limit when the cycle (N) stress cycle does not break.

Fatigue strength: The maximum stress that a metal material can bear when it breaks after several cycles (N) under repeated or alternating stresses is called fatigue strength. At this time, N is called the fatigue life of materials. There is no obvious fatigue limit for some metal materials under repeated or alternating stresses, which is commonly expressed as fatigue strength.

Technological process

After the steel plate enters the production line, the ultrasonic inspection of the whole plate is carried out first.

Milling: Double-sided milling of steel plate edges by a milling machine to achieve the required width, parallelism and groove shape.

Pre-bending edge: Pre-bending edge by using pre-bending machine, so that the edge of the plate has the required curvature;

Forming: In JCO forming machine, first half of the pre-bended steel plate is stamped into "J" shape by several steps, then the other half of the steel plate is also bent into "C" shape, and finally the "O" shape of the opening is formed.

Pre-welding: to make the formed steel pipe seam and use gas shielded welding (MAG) for continuous welding;

Internal welding: Longitudinal multi-wire submerged arc welding (up to four wires) is used to weld the inside of the straight seam steel pipe; g. External welding: Longitudinal multi-wire submerged arc welding is used to weld the outside of the spiral submerged arc welding steel pipe;

Ultrasound inspection I: 100% inspection of inner and outer welds and base metal on both sides of welds of spiral steel pipe;

X-ray inspection I: 100% X-ray industrial television inspection of internal and external welds, and image processing system to ensure the sensitivity of flaw detection;

Diameter enlargement: The whole length of straight seam steel tube is enlarged to improve the dimensional accuracy of steel tube and the distribution of internal stress of steel tube.

Hydraulic test: The expanded steel pipe is inspected one by one on the hydraulic test machine to ensure that the test pressure meets the standard requirements. The machine has the function of automatic recording and storage.

Chamfering: The qualified steel pipe will be processed to meet the required pipe end groove size;

Ultrasound Inspection II: Ultrasound Inspection is carried out one by one again to inspect the possible defects of longitudinal welded steel pipe after diameter enlargement and water pressure.

X-ray inspection II: X-ray industrial television inspection and photography of weld seam of pipe end after diameter enlargement and hydraulic test.

Tube end magnetic particle inspection: This inspection is carried out to find the defect of the tube end.

Anti-corrosion and coating: qualified steel pipes are anticorrosive and coated according to user's requirements.

In addition to the above testing items, according to API standards and other relevant standards and the special requirements of some users, it is necessary to carry out damage inspection and other tests on steel plates and steel pipes, including sampling inspection of physical and chemical properties of raw materials and 100% appearance inspection of steel plates.