PURPOSE: To improve the resistance to nitric acid at a weld zone by a protective layer to improve the resistance to nitric acid after welding by forming the above-mentioned protective layer before welding on a groove of stainless steels containing Mo and then, performing welding by using a welding rod of stainless steel containing Mo.

CONSTITUTION: Material to constitute the vessel, etc., is made of the stainless steel containing Mo and welding is performed on the welding groove of this material by using the welding rod made of the stainless steel of the same quality as this material. Before this welding, the protective layer to improve the resistance to nitric acid is provided. As this protective layer, Y308L, etc., not containing Mo as a build-up layer 14 and a lip layer 15 is formed by welding as the welding rod. Since this protective layer does not contain Mo, the resistance to nitric acid can be improved after welding of materials 10 and 11. Consequently, it is snot necessary to increase the plate thickness of the materials and the weight and cost of the vessel, etc., can be also reduced.