| 摘要 |
An exhaust gas purification apparatus includes a SCR converter selectively reducing and purifying NOx in exhaust gas upon being supplied with ammonia generated from urea aqueous solution and an injection nozzle injection-supplying the urea aqueous solution on exhaust gas upstream side of the SCR converter. At least a part of an exhaust pipe located between the injection nozzle and the SCR converter has a double-pipe structure including inner and outer pipes, each having a welded portion, and the welded portion of the outer pipe was welded from an inside of the outer pipe. Thus, the outer pipe has fine welded portion on an inner peripheral surface where a welding temperature is high and the coarse welded portion on an outer peripheral surface where the welding temperature is low, resulting in an ordered atomic arrangement and thus improved corrosion resistance of the inner peripheral surface, which may be exposed to ammonia. |
