... steel tubes Thickness: SCH 20 to SCH 140 (1.73-36.5mm) Standard: API 5L, API 5CT, ASTM A106.TM A106. welded steel ... : 6 to 18mm ( 0.236-0.708 inch)Welded Steel Pipe Steel Grade: A, B, X42, X46, X52, X56, X60 ... middle straight seam steel pipe production line and four production lines ofφ219-φ2032 bifilar double-side spiral welding pipes ... ,coal gas, natural gas. Heat power. Etc. welded steel tubes