... manufacturer.we already passed *ISO certificate, and API 5L and API 5CT cetificate.* our products are seamless steel pipe ... 14mm STANDARD GB3091-2001 GB9711.1 GB9711.2 API5L API 5CT MATERIAL ST37,ST44,ST52, Q235B/Q345B/L245 ... /L290/L360/L415/L485/20# API 5L.B/X42/X52/X60/X70 etc*SEAMLESS STEEL ... GB/T8163-1999 GB3087-1999 GB5310-1999 API5L API 5CT MATERIAL ST37,ST44,ST52,Q345B/20#/45#/ ...