Exhaust gas purification apparatus and method for increasing corrosion resistance of exhaust gas purification apparatus

Abstract

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.

What is claimed is: 
     
         1 . An exhaust gas purification apparatus comprising:
 a selective catalytic reduction converter which is disposed in an exhaust pipe of an engine and that selectively reduces and purifies nitrogen oxide contained in exhaust gas upon being supplied with ammonia generated from a urea aqueous solution; and   an injection nozzle that supplies by injection the urea aqueous solution on an exhaust gas upstream side of the selective catalytic reduction converter,   wherein at least a part of the exhaust pipe located between the injection nozzle and the selective catalytic reduction converter has a double-pipe structure including an inner pipe and an outer pipe, each of which has a welded portion, wherein the welded portion of the outer pipe is produced by welding performed from an inside of the outer pipe.   
     
     
         2 . The exhaust gas purification apparatus according to  claim 1 , wherein the welding comprises tungsten inert gas welding. 
     
     
         3 . The exhaust gas purification apparatus according to  claim 1 , wherein each of the inner pipe and the outer pipe has a welded portion extending in a direction in which an axis thereof extends. 
     
     
         4 . The exhaust gas purification apparatus according to  claim 1 , further comprising an oxidation catalytic converter disposed on an exhaust gas downstream side of the selective catalytic reduction converter and that oxidizes ammonia. 
     
     
         5 . The exhaust gas purification apparatus according to  claim 1 , further comprising a diesel particulate filter disposed on the exhaust gas upstream side of the selective catalytic reduction converter and that collects and removes particulate matter contained in the exhaust gas. 
     
     
         6 . The exhaust gas purification apparatus according to  claim 5 , further comprising a diesel oxidation catalytic converter disposed on an exhaust gas upstream side of the diesel particulate filter and that oxidizes nitrogen monoxide contained in the exhaust gas to nitrogen dioxide. 
     
     
         7 . A method for increasing corrosion resistance of an exhaust gas purification apparatus in which at least a part of an exhaust pipe located between a selective catalytic reduction converter, that selectively reduces and purifies nitrogen oxide contained in an exhaust gas upon being supplied with ammonia generated from a urea aqueous solution, and an injection nozzle, that supplies by injection the urea aqueous solution on an exhaust gas upstream side of the selective catalytic reduction converter, has a double-pipe structure including an inner pipe and an outer pipe, each of which has a welded portion,
 the method comprising the step of   producing the welded portion of the outer pipe by welding performed from an inside of the outer pipe.   
     
     
         8 . The method for increasing corrosion resistance of the exhaust gas purification apparatus according to  claim 7 , wherein each of the inner pipe and the outer pipe is welded by tungsten inert gas welding. 
     
     
         9 . The method for increasing corrosion resistance of the exhaust gas purification apparatus according to  claim 7 , wherein each of the inner pipe and the outer pipe is welded in a direction in which an axis thereof extends.