Coating structure of a metal pipe and method of coating a metal pipe

A coating structure of a metal pipe comprising:

• a zinc or zinc-nickel plating layer formed on the outer surface of a metal pipe;
• a coating layer predominantly composed of a chromium compound, and a phosphoric acid compound, which are derived from a solution comprising said chromium compound and said phosphoric acid compound, and formed on the zinc or zinc-nickel plating layer, wherein said phosphoric acid compound is at least one substance selected from a group consisting of oxyacid of phosphorus, oxysalt of phosphorus, anhydride of oxyacid of phosphorus and anhydride of oxysalt of phosphorus;
• an epoxy resin layer containing an epoxy resin formed on said coating layer;
• and
• a polyvinylidene fluoride layer formed on said epoxy resin layer.

A coating structure for a metal pipe comprising:

• a zinc or zinc-nickel plating layer formed on the outer surface of a metal pipe;
• a coating layer predominantly composed of a chromium compound and a phosphoric acid compound which are derived from a solution comprising said chromium compound and phosphoric acid compound, and formed on the zinc or zinc-nickel plating layer, wherein said phosphoric acid compound is at least one substance selected from a group consisting of oxyacid of phosphorus, oxysalt of phosphorus, anhydride of oxyacid of phosphorus and anhydride of oxysalt of phosphorus;
• an epoxy resin layer containing an epoxy resin formed on said coating layer;
• a polyamide resin layer formed on said epoxy resin layer;
• and
• an outer resin layer containing polypropylene and polyethylene formed on said polyamide resin layer.