... :Structure 4)Certification:ISO9001:2000 Hot-dip Galvanized steel pipe 1)Thickness:2.77-6.02mm 2)OD:21. ... )Production:Has the following production steps:a. Round preparation, b. Heating, c. Hot perforation, d. Cutting head, e. Pickling, f. ... transport and water supply projects; building, central air-conditioning pipe, fence, threading pipe, rolling doors, metal frame, support tube, furniture, sports ...