Compared with traditional pipe, seamless steel pipe has lighter material, high strength, good resistance, can withstand high internal pressure, is sensitive to production, and can be used in messy or harsh geological conditions. However, there are drawbacks in the use process, mainly because the internal and external anti-corrosion treatment is more troublesome. The first is the problem of anti-corrosion of the outer wall.

The welding process of the erw pipe is to use the skin-receiving principle generated by the high-frequency current to heat the edge of the hot-rolled coil to a molten state, and then perform welding by a mechanical extrusion method.

Fatigue: A phenomenon in which a metal material is below the ultimate strength and is subjected to an alternating load (that is, a load whose shape and direction are repeatedly changed) for a long period of time, and suddenly breaks without significant plastic deformation, and is called fatigue. The fatigue index includes fatigue limit and fatigue strength.

ERW pipe standard are as follows:
API 5L, ASTM A53 B, ASTM A178, ASTM A500/501, ASTM A691, ASTM A252, ASTM A672

(1) Domestic casing according to SY/T6194-96, the length of the casing is not fixed, and its range is 8-13m. However, casings not shorter than 6 m can be supplied, and the number must not exceed 20%.
(2) The inner and outer surfaces of the casing shall be free from folding, hairline, separation, cracking, rolling and crusting. These defects should be completely removed and the depth of removal should not exceed 12.5% of the nominal wall thickness.

Stainless steel is referred to as stainless steel, it is composed of stainless steel and acid steel two parts, in short, can resist atmospheric corrosion of steel called stainless steel, and can resist the corrosion of chemical media steel called acid steel. Generally speaking, chromium content Cr more than 12% steel has the characteristics of stainless steel according to the microstructure of stainless steel after heat treatment can be divided into five categories: ferritic stainless steel, martensitic stainless steel, austenitic stainless steel, austenitic - ferritic biphase stainless steel and precipitation hardened stainless steel.