PURPOSE: To execute the lining of the coat excellent in the peeling resistance and the corrosion resistance on the inner surface of the faucet part as the piping joining part by forming an Al spray-coated layer and/or an iron oxide layer on the inner surface of the faucet of a cast iron tube as cast, and then, executing annealing.

CONSTITUTION: The Al spray-coated layer 2 of 30-200μm thickness is formed by executing the Al spray coating on the inner surface of the faucet part 1 and the flange end surface of the cast iron tube as cast. Then, red iron oxide (powder of Fe2O3) which is slurried with water is coated thereon to form the Fe2O3 layer. This cast iron tube is heated and annealed in the oxidizing atmosphere in an annealing furnace at the temperature of e.g. 980°C, the Al spray- coated layer is oxidized and converted into the Al2O3 layer of fine structure. Lining of the coat of Al2O3 and Fe2O3 excellent in the resistance and the corrosion resistance is executed on the inner surface of the faucet part as the piping joining part, and the water-tightness at the joining part is improved thereby.