We manufacture four steel grades (J55, K55,N80, L80 and P110), six ... 4", 4-1/2") of tube. API spiral steel pipe There are four steel grades (J55, K55,N80, L80 and P110), two ... series (prestressed anti-hydrogen one and high-vacuum one)and three sizes (41/2 ", 31/2 " and small caliber) ... the leading level at home. Two steel grades (J55 and N80)and three specifications of workover casings are available. ...