To maintain interface adhesion between a coat layer and a metal layer and improve heat and water resistance of the coat layer by forming a coat layer to be formed on a surface of a metal pipe out of a resin composition in which specified quantities of specified two kinds of antioxidant are added.

A coat layer formed on a surface of a metal pipe is formed of a resin composition. The resin composition is formed by mixing in 100 pts.wt. of polyolefin resin, 0.05-0.3 pts.wt. of hindered amine antioxidant of poly[{6-(1,1,3,3-tetramethylbutyl)amino-1,3,5-triazine-2,4-diyl} {2,2,6,6-tetramethyl-4- piperidine)imino}hexamethylene{2,2,6,6-tetramethyl-4-piperidiene)imino}] and 0.05-0.3 pts.wt. of hindered phenol antioxidant of pentaerthrityl-tetrakis [3-(3,5-di- t-butyl-4-hydroxyphenyl)propionate]. Accordingly, the coat layer is excellent in interface adhesion property and heat oxidation preventing property and can be used for heat and water resisting pipe.