Generally API 5L refers to API 5L mild steel pipe ,which is out of the ground the oil, gas, water, transported by pipeline to pipe oil and gas industry companies.

OCTG are mainly used for oil and gas well drilling and transportation. It includes oil drilling pipe, oil casing, oil extraction pipe. Oil drill pipe is mainly used to connect drill collars and drill bits and transmit drilling power. The oil casing is mainly used to support the well wall during the drilling process and after the well completion, so as to ensure the drilling process and the normal operation of the entire oil well after the well completion. The oil suction pipe mainly transports the oil and gas at the bottom of the oil well to the surface.

During welding, for the part where there is no complete fusion between the weld bead and the base metal or between the weld bead and the weld bead, the incomplete fusion can be divided into groove incomplete fusion, weld bead incomplete fusion and weld root incomplete fusion. According to the different components, it can be divided into white incomplete fusion and black incomplete fusion.

The straight seam steel pipe adopts a small specification model, which can avoid crack and deformation. The welding current is 20% lower than that of high carbon steel. In order to ensure the ignition of electric arc, DC reverse connection is adopted. In multi-layer welding, the temperature shall be controlled. After welding, forced water cooling can be adopted without arc outside the groove. The wire joints shall be connected correctly, and the weld deformation can only be corrected by cold drawing.

The stress distribution in the welded joint is complex and uneven. The stress value at some points is much larger than the average stress value, which is called stress concentration. There are many reasons for stress concentration. The existence of process defects in the weld is one of the more important factors.

Phenomenon: This is a common problem, which is not beautiful and harmful. Splashes will increase the hardened structure on the surface of the material and produce hardening and other defects.

Post weld heat treatment can eliminate residual stress, prevent deformation, improve the performance of base metal and welded components, soften heat affected zone, increase weld ductility, improve toughness, discharge harmful hydrogen, improve creep performance and fatigue strength.

During DC arc welding, the phenomenon of partial blow caused by electromagnetic force is called magnetic partial blow, which has an adverse impact on the welding process and quality. Only by overcoming it can we ensure the welding quality.

Steel pipe concrete structure is a novel composite structure made of concrete filled steel tube formed. Because steel concrete structure to more effectively play two materials steel and concrete respective advantages, while overcoming the disadvantages of steel structures is prone to local buckling.

Using the appropriate lubricant for stainless steel drawing had a significant effect. A layer of lubricant can have a certain toughness and elongation of the film between the convex and concave mold is formed, which is conducive to the stainless steel deep drawing.