... GB/T3091-2001 , BS 1378, ASTM A53-2007Materials: Q195, Q215, Q235, Q295, Q345, 10 #, 20#, 16Mn ect.Thickness ... steel gradeInches mmtolerance mmtoleranceQ195, Q215, Q235, Q295, Q345, 10#, 20#, 16Mn etc.1/2"21.3 ... HENGJI Steel have 12 ERW pipe production lines and 2 hot-dipped galvanized pipe production lines, provding ... following GB/T 13793 and SY/T 5768 for domestic market and ASTM A53 or API Spec ...