Metallic components for use in corrosive environments and method of manufacturing

Abstract

The present invention relates to a metallic component and method of manufacture of the component for use in a corrosive environment, such as components used in fossil fuel recovery or used in chemical facilities. The components comprise at least one metallic portion having a deep, stable layer of compressive stress for providing life extension and mitigation of fatigue and corrosion related failures. Preferably, the layer of compressive stress has a depth that exceeds the depth of any surface irregularities.

1 . A method of improving the properties of a metallic component for use in a corrosive environment comprising the steps of:
 identifying at least one portion of the component that is expected to be exposed to a corrosive environment;   determining a desired compressive stress distribution for said at least one portion of the component that is expected to be exposed to a corrosive environment;   inducing said desired compressive stress distribution within at least a portion of the surface of a component.   
     
     
         2 . The method of  claim 1  wherein said desired compressive stress distribution having a magnitude, depth, and cold work effective to mitigate SCC and H 2 S cracking of the component during use in a corrosive environment. 
     
     
         3 . The method of  claim 1  wherein the corrosive environment is identified and wherein the desired compressive stress distribution is determined for the identified corrosive environment. 
     
     
         4 . The method of  claim 1 , wherein said compressive stress distribution is induced using a CNC or robotically controlled burnishing and effective to impart the desired compressive stresses in a controlled manner. 
     
     
         5 . The method of  claim 1  wherein the step of inducing the desired compressive stress distribution includes using a hydraulically supported burnishing apparatus. 
     
     
         6 . The method of  claim 1  wherein the step of inducing the desired compressive stress distribution includes the steps of determining burnishing parameters to provide a smooth surface along the at least one portion of the surface of the component such that surface irregularities that can become crack or corrosion pit initiation sites are placed in compression 
     
     
         7 . The method of  claim 6  wherein said burnishing parameters include the smoothness of the burnishing member that will be used for inducing compressive stress within the at least one portion of the surface of the component, the diameter of the of the burnishing member, the force with which the burnishing member will be pressed against the at least one portion of the surface of the component, and the pattern of burnishing. 
     
     
         8 . The method of  claim 1  further comprises the step of identifying the material properties of the component, the applied loads expected to be applied to the component, the environment in which the component is expected to operate, and the known causes Of failure for similar components. 
     
     
         9 . The method of  claim 1  further comprising the step of enhancing the smoothness of the surface along the at least a portion of the surface of a component such that surface irregularities that can become crack or corrosion pit initiation sites are reduced or eliminated. 
     
     
         10 . The method of  claim 1  wherein the desired compressive stress has a magnitude and depth of compression that extends to a depth of at least nominally of about 0.5 mm such that the sum of residual and applied stress never exceeds the threshold for SCC in the corrosive environment of the application or the fatigue endurance limit of the material. 
     
     
         11 . The method of  claim 1  wherein the induced desired compressive stress has a depth of compression that incorporates a majority of surface irregularities along the at least one portion of the surface of the component. 
     
     
         12 . The method of  claim 1  wherein the desired compressive stress distribution has a depth of penetration that penetrates entirely through the at least a portion of the surface of a component. 
     
     
         13 . The method of  claim 1  wherein the compressive stress distribution within at least a portion of the surface of the component has a depth that exceeds the depth of any surface irregularities. 
     
     
         14 . A component for use in a corrosive environment comprising:
 at least one portion of the component having a metallic surface;   a compressive stress distribution within said surface;   wherein the depth of said compressive stress distribution is such that it exceeds a majority of surface irregularities along said surface and having an amount of cold work induced within said surface that is less than the amount necessary to damage the crystalline structure along said surface and to create slip bands, dislocations, and twinning such that said surface is more susceptible to stress corrosion.   
     
     
         15 . The metallic component of  claim 14  wherein the said surface has a depth of compression is at least about 1 mm. 
     
     
         16 . The metallic component of  claim 12  wherein said stress distribution has a magnitude and depth of compression at least as great as the sum of any residual and applied stress anticipated within said at least one portion. 
     
     
         17 . The metallic component of  claim 12  wherein said stress distribution has a depth of compression that does not exceed the threshold for SCC in the expected corrosive environment of the application of the component. 
     
     
         18 . The metallic component of  claim 12  wherein said at least one portion has a depth and said compressive stress distribution penetrates through the entire depth of the at least one portion.