Q1: What are the key steps in the production process of A335 steel pipe?
The production process includes steelmaking (arc furnace or converter), continuous casting or die casting into billets, hot rolling and perforation into rough tubes, cold drawing or hot extrusion forming, heat treatment (normalizing + tempering), straightening, non-destructive testing (UT/RT), water pressure testing, etc. Among them, the hot rolling process affects the grain size, and cold drawing can improve the dimensional accuracy. High-end steel grades such as P91 require strict control of the rolling temperature. Finally, the whole process quality inspection is required according to the ASTM A335 standard.
Q2: Why must A335 steel pipe be heat treated?
Heat treatment (usually normalizing + tempering) can eliminate cold working stress, homogenize the structure, and improve toughness and high temperature performance. For example, the normalizing temperature of P22 steel is 900-950°C and the tempering temperature is 650-700°C. If not heat treated, residual stress may cause cracking in service. Some grades (such as P91) also require accelerated cooling to obtain martensitic structure. Hardness testing is required after heat treatment to verify the effect.
Q3: What are the advantages of hot extrusion process in A335 production?
Hot extrusion is suitable for high-alloy steel (such as P92), which can reduce the risk of cracks in traditional rolling. Extrusion can form complex cross-sections in one go and improve material utilization. Deformation is more uniform at high temperature (1200°C) and reduces internal defects. However, the equipment cost is high and it is suitable for small batches of high value-added products. After extrusion, it is necessary to expand the diameter or cold roll to accurately control the size.
Q4: How to control inclusions in the production of A335 steel pipes?
Use out-of-furnace refining (such as LF furnace, VD vacuum degassing) to reduce sulfur and phosphorus content. Use protective slag to prevent oxidation during continuous casting. Ultrasonic detection of steel billets before rolling to remove defects. High-grade steel pipes (such as P91) require non-metallic inclusion ratings ≤1.5. Regular sampling and metallographic analysis are required during production to ensure purity.
Q5: How to ensure the dimensional accuracy of A335 steel pipe?
The cold rolling process can control the outer diameter tolerance to ±0.1 mm and the wall thickness tolerance to ±10%. Use a laser diameter gauge for online monitoring. The straightening machine eliminates the curvature (usually required to be ≤1.5 mm/m). The sizing process ensures that the roundness error is less than 0.5%. The final inspection must comply with the ASTM A530 dimensional standard, and the ovality and wall thickness uniformity are measured by sampling.
