During the welding process, if the interlayer temperature is too high, the grains will be elongated and t8/5 will be increased. It cannot be normalized during on-site welding, and the original strength and toughness of the steel pipe will be lost. Therefore, the interlayer temperature must be strictly controlled during the welding process to prevent grain elongation.

Lamellar tearing usually occurs in the welding of thick-walled seamless pipes. The main reason is that the MnS inclusions in the steel pipe develop into cracks and then tear under the tensile stress perpendicular to the plate surface, resulting in low plastic failure of the structure.

Submerged arc welded straight seam steel pipe (LSAW pipe) is a kind of steel pipe used in oil and gas pipelines with large consumption and high reliability. The forming unit forms include UOE, RBE, JCOE, etc.

Petroleum pipe is a seamless steel pipe suitable for furnace tubes, heat exchangers and pipes in petroleum refineries. Petroleum pipe is a long strip of steel with a hollow section and no joints around it, and petroleum cracking pipe is an economical cross-section steel.

For large-diameter spiral steel pipe (SSAW pipe), if the outer protective pipe is polyethylene pipe, there is no need to make anti-corrosion polyethylene. This kind of steel pipe is odorless, non-toxic, feels like wax, and has excellent low temperature resistance (the lowest operating temperature can reach -70~-100°C). Good chemical stability, corrosion resistance to most acids and bases (not resistant to acids with oxidizing properties), insoluble in common solvents at room temperature, and low water absorption. However, because it is a linear molecule, it can be slowly dissolved in some organic solvents without swelling, and has excellent electrical insulation performance.

Spiral steel pipe (SSAW pipe) is a welded steel pipe made of strip steel coil as raw material, extruded at regular temperature, and welded by automatic double-wire double-sided submerged arc welding process. Spiral steel pipe is mainly used in water supply engineering, octg pipe, chemical industry, electric power industry, agricultural irrigation, urban construction