... /8 ", 3-1/2", 4", 4-1/2") of tube. welded round tube There are four steel grades (J55, K55,N80, L80 ... . There are two series (prestressed anti-hydrogen one and high-vacuum one)and three sizes (41/2 ", 31/2 " and small ... six items in total. The annual production capacity of high-vacuum tubing is 200 thousand meters, and prestressed anti-hydrogen one ...