Abstract: In an exhaust gas purification apparatus or other apparatuses that are supplied with ammonia generated from a urea aqueous solution and causes selective reduction and purification of nitride oxides, a shot peening treatment is applied to a welded portion of its exhaust pipe which is made of a ferritic stainless steel plate and through which exhaust gas containing ammonia and hydrogen passes. By shot peening the welded portion of the exhaust pipe, a tensile residual stress in the welded portion of the exhaust pipe can be replaced with a compressive residual stress, and further the diameter of metal crystal grains in the welded portion can be reduced. In this way, the durability of the exhaust pipe can be improved.

Abstract: In an exhaust gas purification apparatus or other apparatuses that are supplied with ammonia generated from a urea aqueous solution and causes selective reduction and purification of nitride oxides, a shot peening treatment is applied to a welded portion of its exhaust pipe which is made of a ferritic stainless steel plate and through which exhaust gas containing ammonia and hydrogen passes. By shot peening the welded portion of the exhaust pipe, a tensile residual stress in the welded portion of the exhaust pipe can be replaced with a compressive residual stress, and further the diameter of metal crystal grains in the welded portion can be reduced. In this way, the durability of the exhaust pipe can be improved.