| 摘要 |
Impregnation of water and oil into a coating film can be positively shut off, the coating film can be brought into closer contact, and corrosion resistance and chemical resistance can be significantly increased. A plating layer (4) is formed on the outer peripheral surface of a metallic blank tube (2), and a coating film (5) is formed on the plating layer (4) by a chemical conversion treating of a hard-to-dissolving chromium-free coating type or at least one intermediate coat layers (7a, 7b) are formed between a primary coat layer (6) and a top coat layer (8).
|
