1, Seamless carbon tubes 2,OD:20-325mm 3, W.T.:2-50mm 4, Certificate: ISO9001, API 5L 1, Seamless carbon tubes2,OD:20 ... : (GB/T8162-2008): (GB/T8163-2008), fluid tubes, in the low-pressure boiler tubes: (GB/T3087-2008), high pressure boiler tube: (GB ...