What is the difference between hot rolling and cold drawing of seamless carbon steel pipes?
Hot rolled pipes are rolled and formed at above 1200℃, with large dimensional tolerance but high production efficiency, and are suitable for large diameter thick wall pipes. Cold drawn pipes are drawn through dies at room temperature, with precise dimensions and smooth surface, but the cost is high. Hot rolled pipes require subsequent straightening and descaling, while cold drawn pipes require annealing to eliminate work hardening. The choice between the two depends on the accuracy requirements (such as cold drawn pipes for hydraulic cylinders).
What is the production process of high frequency welded (ERW) carbon steel pipes?
ERW pipes first roll the steel strip into a cylinder, heat the edge with high frequency current and weld under pressure. The process includes: uncoiling → flattening → forming → welding → deburring inside and outside → cooling → sizing → cutting. Online non-destructive testing (such as eddy current or ultrasonic) is required after welding. ERW pipes are low cost and high efficiency, but the weld quality is a key control point (must comply with API 5L Appendix R).
What are the respective advantages of spiral welded pipes and straight seam welded pipes?
Spiral welded pipes are welded by spiral coiling of steel strips, which can produce ultra-large diameter pipes (such as more than 3 meters) with uniform stress distribution in the weld. Straight seam welded pipes (such as LSAW) are welded by direct welding of steel plates, with stronger wall thickness capacity (up to 100mm), suitable for high-pressure scenarios. Spiral pipes have high material utilization, but it is difficult to control ovality; straight seam pipes have better dimensional accuracy, but the equipment investment is high.
What are the surface treatment processes for carbon steel pipes?
Common treatments include sandblasting (rust removal), pickling (removal of oxide layer), galvanizing (rust prevention), painting (such as epoxy resin) and PE/3PE anti-corrosion (for buried pipes). Galvanizing is divided into hot dip and electroplating, and 3PE combines three layers of protection of fused epoxy, adhesive and polyethylene. The choice depends on the environment (such as cathodic protection + coating for seawater environment).
How to control residual stress in carbon steel pipe manufacturing?
Residual stress originates from cold working or welding, which may cause deformation or cracks. Control methods include: heat treatment (such as overall annealing), mechanical vibration aging, natural aging placement or pre-stretching process. Welded pipes need to optimize welding parameters and sequence, and cold-drawn pipes need to control deformation. Residual stress detection can be done by X-ray diffraction or drilling.
