What are the manufacturing processes for API 5L X52 grade pipes?

The steps to manufacture API 5L X52 grade pipes are as follows:
For raw materials, select high-quality pig iron and scrap steel, strictly inspect and pre-treat, and select low sulfur and phosphorus purity. Use electric arc furnace or oxygen converter for smelting, accurately control the furnace temperature and atmosphere, and adjust the content of carbon, manganese and other elements in the molten steel. After ladle refining, argon blowing and vacuum treatment are used to remove impurities and fine-tune, and continuous casting is used to obtain steel billets or mold casting into steel ingots. Continuous casting is efficient and has stable quality, and mold casting is suitable for special needs.
During rolling, the billet (ingot) is first heated to 1000-1200℃ for plasticization. To make seamless pipes, perforate them into rough pipes (oblique rolling, extrusion perforation method), and then use the pipe rolling machine to select the roller hole type and parameters according to the specifications for rolling, reduce the outer diameter and wall thickness, and then sizing and straightening to ensure dimensional accuracy and straightness.
In terms of welding, high-frequency resistance welding is used to make straight seam welded pipes. After bending the steel strip, high-frequency current is passed through it, and the butt joint is heated and melted, and pressure welding is applied to the butt joint. The speed is fast and the weld is excellent. Submerged arc welding (straight seam, spiral type) relies on arc melting of welding wire and weldment under granular flux to form a weld. It has a large penetration depth and high strength and is used for large-diameter thick-walled pipes.
In terms of heat treatment, normalizing is heated to supercritical temperature and then air-cooled to refine the grains and improve performance; tempering is heated to a low temperature range and cooled after quenching or normalizing to eliminate internal stress and adjust hardness and toughness; for high strength and toughness, martensite structure is quenched and then tempered to optimize performance.
In terms of surface treatment, pickling removes oxide scale and rust from pipes to clean the surface; galvanizing increases corrosion resistance and prolongs service life, and is used in places with high corrosion protection requirements; painting (epoxy, polyurethane paint, etc.) strengthens corrosion resistance and has decorative and identification functions.