... stable quality. Product Name Seamless Steel Tubes for Boiler, Pressure Vessel & Heat ExchangerAmerican Standard ASTM A53,ASTM A106,ASTM A333,ASTM A334 ... , C; GR1,GR6; GR.A-1,GR.CChinese Standard GB 3087,GB 5310,GB 6479,GB 9948,GB 18248,GB/T 18984Grade 10,20,20G,16Mn,37Mn,12CrMo ...