| 摘要 |
PURPOSE:To obtain a steel pipe having an outer face coated with plastic whose inner and outer faces are excellent in corrosion resistance by galvanizing the inner and outer faces of the steel pipe and thereafter shot-blasting the galvanized layer of the outer face to peel this layer and regulating surface roughness to the prescribed thickness and thereafter applying chromic acid thereto and furthermore applying primer to form a primer layer. CONSTITUTION:A steel pipe 1 is immersed in a galvanizing tank and galvanized layers 2a, 2b are formed on the inner and outer faces of the steel pipe 1. Thereafter the galvanized layer 2b of the outer face is peeled by a shot blasting device until surface roughness is regulated to 20-100mum in Rz. Chromic acid is applied to this surface and a chromate layer 3 is formed to enhance adhesive property and thereafter a primer layer 4 is provided. This primer layer 4 is formed by application of thermosetting resin e.g. such as epoxy resin. Preferably thermosetting resin such as epoxy resin having a fast-curing type at the comparatively low temp. is applied. Further when surface roughness is not regulated to <=100mum in Rz, the adhesive property to the primer layer is not enhanced. It is unprofitable in an economical aspect that roughness is regulated to 20mum in Rz. |
