WO2011115667A1

WO2011115667A1 - Metallic components for use in corrosive environments and method of manufacturing

Info

Publication number: WO2011115667A1
Application number: PCT/US2011/000469
Authority: WO
Inventors: Jeremy E. Scheel; Douglas J. Hornbach; Paul S. Prevey
Original assignee: Scheel Jeremy E; Hornbach Douglas J; Prevey Paul S
Priority date: 2010-03-15
Filing date: 2011-03-15
Publication date: 2011-09-22
Also published as: CA2804466A1; US20110223443A1

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.

Description

METALLIC COMPONENTS FOR USE IN CORROSIVE ENVIRONMENTS AND METHOD

OF MANUFACTURING

[0001] This application claims the benefit of U.S. Provisional Application No. 61/340,282, filed March 15, 2010.

Technical Field

[0002] The present invention relates generally to metallic components used in a corrosive environment, such as components used for fossil fuel recovery that have improved properties and methods of manufacturing such components. More specifically, the present invention are new and novel metallic components for use in corrosive environments such as components used for fossil fuel recovery, and methods of manufacture, whereby the components have improved properties for mitigating or preventing the deleterious effects of stress corrosion cracking (SCC) and fatigue on the useful life of the metallic components. Such components are typically used in recovery and distribution of fossil fuels or used in chemical plant applications.

Background

[0003] In the recovery and distribution of fossil fuels and the operation of petrochemical refineries and other types of chemical plants, failure of metallic components is often a result of the combination of stress as well as one or more corrosive elements, such as hydrogen sulfide, H₂S, ammonia, or chlorine, to which the component is exposed in service. The elevated temperatures, pressures, and applied stresses, either static or alternating, to which such components are exposed, contribute to their degradation and the rate at which corrosive related failure processes occur, especially SCC and corrosion fatigue. The life of metallic components in these environments and applications is often limited, and premature component failures restrict production and increase operational costs.

[0004] In oil and natural gas well drilling to recover fossil fuels, the depth to which drilling can be performed is limited by the materials available for the drill pipe, tubing, and casing, generally referred to as Oil Country Tubular Goods (OCTG). In offshore drilling, the material strength of the OCTG and drill components limits the depth of water and thus the distance from shore that is accessible. The pipe used for distribution of the fossil fuel is generally known as Line Pipe Tubular Products (LPTP). As used herein, OCTG, LPTP and drill and drill rig products and components will collectively be referred to as Fuel Recovery Components. Line Pipe Tubular Products may be fabricated as either seamless or welded, with the seamless generally used for the most demanding applications. It is well known that the strength of Fuel Recovery Components formed from metallic materials, such as steel alloys, can be increased by various heat treatment procedures, and a variety of heat treatable Fuel Recovery Components are available having a range of strengths (including the yield, ultimate, and fatigue strengths). The toughness of the alloy in stress corrosion cracking, given by the parameter K|_Scc, is a measure of the resistance to cracking, and generally is reduced as the yield and ultimate strength are increased by heat treatment. Therefore, the strength of metallic material that can be used in a SCC prone environment, such as environments that Fuel Recovery Components often operate in, is limited.

[0005] The weight of various Fuel Recovery Components, such as pipe hanging from a drill platform in well drilling operations, is often a primary source of applied stress. In horizontal drilling, now used for both oil and gas machinery with minimal environmental impact, a significant bending stress is applied to the Fuel Recovery Components (such as a pipe, tubing, casing, or coupling) in the transition from vertical to horizontal drilling. Higher strength steel drill pipes, distribution pipes, and casing allow deeper wells and drilling in deeper water, providing a major economic advantage in tapping deep oil and gas fields both on land and off-shore. However, when the oil or gas wells are "sour" with H₂S present, or when the stressed pipe is exposed to seawater during offshore drilling or subsurface salt-water deposits containing dissolved chlorine, the pipe and casing are subject to SCC. It is then a common practice to limit the strength of steel pipe, tubing, casing and other Fuel Recovery Components because the softer, weaker material is not susceptible to SCC. Expensive SCC "down hole" failures are avoided at the cost of limiting the possible range of drilling.

[0006] The failure of Fuel Recovery Components as well as components used in a wide variety of chemical plant applications generally results in major economic loss, if not catastrophic damage impacting public safety. It is well known that failure of such metallic components is most commonly caused by the mechanisms of SCC or fatigue. SCC occurs from the surface being exposed to a corrosive media to which the alloy is susceptible under a primarily constant steady state applied tensile stress exceeding a tensile stress threshold specific to the alloy and the environment. Fatigue failures occur under the influence of alternating applied stress, generally accompanied by a steady mean stress, and often originate from a surface flaw such as a corrosion pit, SCC, or scratch. Corrosion fatigue is a combination of fatigue failure in the presence of a corrosive environment, in effect adding a SCC component to failure under cyclic loading. [0007] There are several current chemically-based practices that are used to attempt to prevent or reduce SCC and corrosion fatigue failure in metallic components that are used in fossil fuel and chemical applications:

1 ) use alloys with enhanced corrosion resistance such as stainless steels;

2) use sacrificial anodes to cathodically protect the metallic components;

3) chemically alter the environment of the component with alkaline substances or other protective fluids;

4) paint, plate, or coat components to shield the metallic surfaces from the corrosive environment; and

5) limit the strength of the steels used and applied stress levels.

[0008] All of these chemistry or coating-based methods have limitations, or have shown limited improvement in performance at relatively high implementation costs to the end-user. Components formed from corrosion resistant alloys are relatively expensive and often are not cost effective. Cathodic protection offers only temporary benefit by redirecting the corrosion process to the sacrificial material until it is consumed. Adding chemicals to neutralize corrosive elements, often known as 'down-hole' injection, also offers only a temporary solution because the chemicals will eventually diffuse away or be consumed in reaction. Paint and coatings will peal, wear away, or be scraped off eventually exposing the surface to the corrosive environment, and generally cannot be renewed on the casing and components installed down in the well. Reducing the strength of the material and designing for lower applied stresses provides a long-term solution but limits performance, as noted above.

[0009] Mechanical methods have been used or proposed that are designed to place the surface layer that will be in contact with the corrosive media in a state of residual compression in an attempt to mitigate either SCC or fatigue. Such methods include shot peening, laser shock processing (LSP), low plasticity burnishing (LPB), and deep rolling.

[0010] Shot peening has been widely used in many industries for decades to introduce a relatively shallow surface layer (<0.5 mm) of residual compression in metallic components, and has been used to reduce the susceptibility of such components to SCC. However, because it is a random impact process, shot peening severely cold works the surface in order to cover the surface with impact dimples and produce the compressive layer. The beneficial compressive residual stresses in the highly cold worked surface are then known to be susceptible to rapid thermal relaxation at relatively lower service temperatures and is therefore unacceptable for certain components. Further, the relatively shallow cold worked residual compression layer is also susceptible to loss of compression by tensile overload in work hardening materials, again making the method unacceptable for certain components. Shot peening also produces a roughened dimpled surface that makes it more difficult to detect a crack or flaw using nondestructive inspection (NDI) methods such as ultrasonic and eddy current means, again making it unacceptable for certain applications.

[0011] LSP has been proposed for oil, gas, and petrochemical weld applications. LSP can produce relatively deep (~1 mm) compression, but is prohibitively expensive for components having large surface areas needing treatment. Further, LSP requires an ablative coating to be applied along the surface of the component being treated that generates post-processing debris that must be removed, thereby adding additional cost. In addition, LSP requires repeated shocking cycles to achieve a 1 mm deep compressive layer, thereby adding additional cost and process time. Also, LSP has been known to damage the surface in three ways that have been shown to contribute to component failure. First, internal cracking can occur due to superposition of echoing shock waves. Second, LSP shock waves are known to cause twinning in some crystals, like in titanium alloys, that are associated with subsequent fatigue crack initiation. Third, LSP is known to produce laser burns and local areas of residual tension that occur if the ablative coating is breached so that the laser strikes the bare metal surface; surface tension from such burns will exacerbate SCC. Accordingly, components treated using LSP often require post-processing inspection that can significantly increase cost and processing time. Components that have been damaged by the LSP process often require additional processing or must be scrapped, thereby further increasing cost and processing time. Further, denting of the surface at each shock point by LSP may also require refinishing operations. Like shot peening, the dented surface reduces the effectiveness of eddy current and ultrasonic NDI techniques that are vital to monitor the integrity of critical components.

[0012] Deep rolling, a form of roller or ball burnishing, has also been proposed to introduce a layer of compression and cold work deeper than that provided by shot peening and improves the surface finish of the treated area. Deep rolling creates a highly cold worked surface in the area being treated in order to mechanically strengthen the surface material while introducing compression. The depth and magnitude of cold work along the surface typically exceeds that produced by shot peening. Cold working, however, is well known to increase the susceptibility of metals to SCC. Annealing or tempering to reduce or eliminate cold work and reduce hardness is a common remedy used to reduce such susceptibility to stress corrosion cracking. However, such processes increase processing time and cost and may be difficult to perform on certain components. Accordingly, deep rolling suffers from the conflicting influences of the detrimentally increased cold working of the surface as the beneficial residual compression is introduced.

[0013] Both SCC and fatigue failures are well known to initiate from very small surface irregularities such as surface cracks, small crevices, flaws, scratches, persistent slip bands, even crystal twin boundaries created by deformation, and the like. Such surface irregularities are known to serve as sites of increased ion concentration, exacerbating SCC. The surface irregularities are also points of stress concentration that are well known to serve as fatigue crack initiation sites. Cold working, such as by shot peening and deep rolling, is known to damage the crystalline structure, creating slip bands, dislocations, and twinning that make the surface more susceptible to chemical attack. Work hardening, like hardening by heat treatment, makes metals more susceptible to SCC. Further, deforming the surface to introduce residual compression in ways that increase the surface irregularities, such as by shot peening and LSP, is also known to create local sites for SCC and fatigue initiation.

[0014] Accordingly, a need exists for corrosive resistant components, such as Fuel Recovery Components as well as components for use in a wide variety of chemical plant applications where SCC failures occur, that have improved properties for mitigating or preventing the deleterious effects of SCC and fatigue on useful life. A practical, inexpensive method is needed for introducing a relatively deep, stable layer of beneficial compressive stress along and into the surface of such components that protects against or reduces SCC, fatigue, corrosion fatigue and related failure modes, and provides an improved surface finish with low cold working, so that the metallic materials forming the components can be used at their full available strength.

Disclosure of Invention

[0015] The present invention relates generally to corrosive resistant components, such as Fuel Recovery Components as well as components used in a wide variety of chemical plant applications, and their method of manufacture. Such corrosive resistant components have improved stress corrosion and fatigue properties for mitigating or preventing the deleterious effects of SCC and fatigue on useful life of the metallic components.

[0016] The preferred method of the invention disclosed herein dramatically improves the SCC, corrosion fatigue, and general fatigue performance of metallic components used in a wide variety of applications, such as fossil fuel recovery and chemical plant applications, manufactured from traditional low-cost alloys, such as carbon steel, without altering either the alloy chemical composition or the geometry of the component. The invention puts the surface of the metallic component that is in contact with the corrosive environment, and the layer of material immediately below the surface, into a state of high residual compression with controlled low cold working to a sufficient depth to encompass the surface irregularities. In a preferred embodiment, the components include tubular products such as pipe, tubing, casing, and couplings, having the outside, or inside, or both surfaces processed using various machine tools or robots commonly available that can be used to position and move the burnishing tools to cover all or a portion of the surface being treated. In a preferred embodiment of the invention, a preferred method includes a surface treatment which is performed in a single automated operation during initial manufacture or during repair and overhaul of existing components. [0017] In a preferred embodiment of the invention, a layer of compression is created using one or more ball or roller burnishing tools and normal forces and tool positioning that produce a relatively uniform layer of compression extending to a depth of about 1 mm or more, so that the surface being treated when in contact with a corrosive media and any surface irregularities, such as discussed above, are confined in a layer of compressive residual stress. The magnitude of the residual compression is generally on the order of the yield strength of the alloy so that the surface layer remains in compression under any applied tensile stresses experienced by the component during service, and the stress at the surface in contact with the corrosive environment never exceeds the critical tensile threshold for SCC. In a preferred embodiment, scratches and other surface irregularities are maintained in compression, even under external applied tensile loading during service, thereby fatigue initiation is prevented or significantly reduced.

[0018] In another preferred embodiment of the invention, the position and force applied to one or more tools during the burnishing process is controlled to develop a specified level of low cold work while introducing a layer having a desired magnitude of compression. The layer of compression is of a magnitude and depth such that the sum of residual and applied stress at the surface and to a depth of at least nominally about 0.5 mm never exceeds the threshold for SCC in the specific corrosive environment of the application or the fatigue endurance limit of the material. In a preferred embodiment, the depth of compression is chosen so that the all or a majority of surface irregularities that may operate as sites of crack initiation are confined within the depth of the compressive layer.

[0019] Processing by the method of this invention allows inexpensive steel or alloy to be used for components that operate in a corrosive environment, such as Fuel Recovery Components as well as components used in a wide variety of chemical plant applications (such as piping, casing, couplings and related components), that are normally restricted to use only in applications not subject to SCC, to then be placed in service in corrosive environments, such as in "sour" wells, and applications previously requiring more costly alloys, such as stainless steels. Inexpensive steels processed by the method of this invention can then be used at their optimum temper and strength to allow higher applied stresses in service allowing drilling of deeper wells at lower cost.

[0020] In a preferred embodiment, the surface finish is improved by burnishing with a finely finished tool to both reduce surface irregularities while enhancing the detection limits of NDI. Improved NDI detection limits reduce inspection costs and allow more reliable detection of flaws. Elimination or the reduction of surface irregularities improves both SCC and fatigue resistance, as noted above.

Brief Description of the Drawings

[0021] The foregoing and other features of the invention will be best understood with reference to the following detailed description of a specific embodiment of the invention when read in conjunction with the accompanying drawings, wherein:

[0022] FIG. 1 is a plot of the subsurface residual stress and diffraction peak width distributions produced by the burnishing method of the subject invention in low cost P110 casing coupling material. The residual stress shown is additive to the applied stress in service;

[0023] FIG. 2 is a bar chart comparing the surface roughness measured on the surface of P110 steel coupling stock as-manufactured versus after-processing showing the improved finish with the method of the current invention; [0024] FIG. 3 is a bar chart showing failure by SCC in the National Association of Corrosion Engineers' (NACE) 1% H₂S solution of as-manufactured P110 coupling stock samples after only 10 hour exposure, and showing that exposure for over 420 hours did not break the same P110 material after processing with the method of the invention;

[0025] FIG. 4 is a schematic illustration showing the relationship between the burnishing apparatus and control system for properly inducing a desired stress distribution along and into the surface of a component;

[0026] FIG. 5 is a flow diagram illustrating a preferred method of the subject application;

[0027] FIG. 6 is a schematic illustration of a portion of a component being manufactured using the method of the subject invention; and

[0028] FIG. 7 is a schematic illustration of the surface of the component shown in FIG. 6 illustrating various surface irregularities.

Best Mode for Carrying Out the Invention

[0029] Referring to FIG. 1 , the "as-received" subsurface residual stress distributions created by the current methods of manufacturing components used in a corrosive environment, such as Fuel Recovery Components as well as components used in a wide variety of chemical plant applications (including, but not limited to pipe, tubing, casing and OCTG), is shown in comparison to the beneficial high magnitude deeper compressive residual stress layer created by a preferred method of the current invention. The residual stress is shown in both units of the common engineering usage in the United States, where 1 ksi = 1000 psi, and in SI units of MPa. Prior art manufacturing methods used for such typical components, such as OCTG products, provide only relatively shallow compression, generally less than -30 x 10³ psi (-30 ksi or -200 MPa) extending to a depth of only about 0.020 in. (0.5 mm), such as in the example shown. The prior art practice does not attempt to control or optimize in any way the state of residual stress on the surface of the products. The deeper and higher magnitude compressive residual stress distribution produced by the method of the present invention is shown as "LPB" in FIG. 1. The method of the invention introduces compression of much higher magnitude, nominally -100 ksi (- 700 MPa), approaching the yield strength of the material and extending to a depth greater than about 0.040 in. (1mm). In a preferred embodiment of the invention, the depth of compression produced by the method of the subject invention exceeds the depth of any surface irregularities.

[0030] Referring to FIG. 3, SCC of P110 casing material loaded as U-bend samples in tension in a "sour" H₂S solution is shown as having been eliminated after processing by the method of the subject invention. As-manufactured casing material failed in only 10 hours. In a preferred embodiment of the present invention, SCC and failure from fatigue or corrosion fatigue damage is mitigated by introducing a layer of compressive residual stress using a process of LPB. Inducing a compressive stress distribution along a surface by LPB is shown and described in U.S. Patent Nos. 5,826,543 and 6,415,486, which are incorporated herein by reference.

[0031] Referring to the bottom of FIG. 1 , the method of the invention creates a desired compressive stress distribution by deforming the material a minimal amount to achieve the required compression. LPB produces less than approximately 5% cold work while creating a depth and magnitude of compression comparable to LSP or deep rolling. It has been found that using LPB for components used in a corrosive environment, such as Fuel Recovery Components as well as components used in a wide variety of chemical plant applications, provides the desired compressive stress distribution along and into the surface being treated without the increased susceptibility to SCC and corrosion fatigue caused by cold working of the surface such as by shot peening or deep rolling and without the detrimental effects often caused by laser shock peening.

[0032] Referring to FIG. 2, processing by the method of the invention has been shown to improve the surface finish from about 204 to about 90 micro-inches, reducing the roughness of the surface being treated. In the preferred embodiment, the method of the subject invention improves the surface finish by rolling a hardened ball or roller having a generally smooth surface along the surface of the component. The surface produced by the subject invention depends upon the burnishing parameters selected, such as the smoothness of the hardened ball or roller, the ball or roller diameter, and the force with which it is pressed against the surface of the piping or other component. In a preferred embodiment, the selected burnishing parameters are selected to produce a smooth surface effective for improving detection limits for NDI and elimination or reduction of surface irregularities that can become fatigue crack or corrosion pit initiation sites.

[0033] In another preferred embodiment, as illustrated in FIG. 4, the method uses a burnishing apparatus 100 having a constant volume flow of fluid 102 to support a hydrostatic burnishing member 104 (such as shown or taught in U.S. Patent No. 6,415,486 which is incorporated herein by reference) that rolls along a surface portion 106 of the component 108 being treated with sufficient force to induce compressive stress 110 having a desired magnitude and depth of compression and also allows large surface areas of components, such as Fuel Recovery Components as well as components used in a wide variety of chemical plant applications, to be processed rapidly with minimum down time and tool costs.

[0034] Another embodiment of the method of the subject invention, as shown in FIG. 4, a computer numerically controlled (CNC) apparatus 112 is used to position one or more burnishing members 104 of a burnishing apparatus 100 to guide the members 104 in a predetermined pattern along the surface portion 106 of the component 108 being treated with sufficient, but not necessarily constant pressure, to create a desired distribution of compressive residual stress 110 on and into the surface portion 106 of the component 108.

[0035] A further embodiment of the method utilizes a means of rotating the component 114 being processed in the manner of a lathe or similar means, while one or more burnishing apparatuses are held at fixed angular positions and are positioned down the length of the rotating component in a helical pattern to cover at least a portion of the outside or inside surface.

[0036] Referring to FIG. 5, a preferred embodiment of the method of the present invention is shown whereby components expected to operate in a corrosive environment are identified (step 200). One or more surface portions of one or more of the identified components are identified and selected for receiving a surface treatment (step 202), such as burnishing. The environment that the surface portions will be exposed to, as well as various operating applied, static, and alternating stresses expected to be encountered, are identified (step 204). A stress distribution for each surface portion is then determined based upon the geometry of the component; the material forming the component along the surface portion being treated; the environment to which the component will be exposed; the use of the component; and the temperatures, pressures, and applied, static, and alternating stresses to which the component is expected to be exposed during service (step 206). Burnishing parameters, such as the smoothness of the burnishing member, the diameter of the burnishing member, the force with which the burnishing member is pressed against the surface being treated, and the pattern of burnishing are then determined based on the desired stress distribution (step 208). In a preferred embodiment of the invention, the burnishing parameters are selected such that a relatively uniform layer of compression is induced along the surface portion and extending to a depth sufficient such that the surface being treated when in contact with a corrosive media and any surface irregularities are confined in a layer of compressive residual stress. In another preferred embodiment of the invention, the burnishing parameters are also selected such that the magnitude of the residual compression induced along and into the surface portion is generally on the order of the yield strength of the alloy forming the surface portion of the component so that the surface layer remains in compression under any applied tensile stresses expected to be experienced by the component during service. In another preferred embodiment of the invention, the burnishing parameters are selected such that in operation of the component, the stress at the surface in contact with the corrosive environment never exceeds the critical tensile threshold for SCC. In another preferred embodiment, the burnishing parameters are selected such that surface irregularities along the surface portion are maintained in compression, even under external applied tensile loading during service of the component, thereby reducing or eliminating fatigue initiation. The method further comprises the step of performing a burnishing operation along the one or more of the identified surface portions using the determined burnishing parameters to induce the desired stress distribution along and into the identified surface portions (step 210). In a preferred embodiment, the burnishing operation is performed such that the amount of cold work induced along the surface portions is less than about 5%. In a preferred embodiment, the burnishing parameters are fed into a computer control system that cooperates with a burnishing apparatus (such as a CNC system) for performing the burnishing operation (step 212). Inspecting the treated component for surface irregularities (step 214) is performed after burnishing.

[0037] It should be understood that the method of the subject invention will improve the SCC and H₂S cracking resistance of metallic components formed of less expensive alloys to allow them to be used in chloride or sulfide corrosive environments such as Fuel Recovery Components and chemical plant applications, where they cannot currently be used. It should also be understood that the method of the subject invention may be integrated into any existing production or repair processing platform / delivery system to allow for processing of both new production components as well as repair / life extension of existing components. It should also be understood that the method of the subject invention may be used on various components used in corrosive environments such as most or all metallic components used in a fossil fuel recovery where any environmentally assisted cracking is expected or may occur.

[0038] Referring to FIGs. 4, 6, and 7, a schematic cross-section of a surface portion 106 of a metallic component used in a corrosive environment 108, such as Fuel Recovery Components or components used in chemical plant applications having an outer surface 116 and an inner surface 118 is shown (FIG. 6). In a preferred embodiment, the component is in the form of a pipe, tube, casing, coupling, or other similar component. The surface portion 106 of the component 108 has a compressive residual stress distribution 110 induced therein. The depth D of compression is such that it exceeds any surface irregularities 120. In another preferred embodiment, the surface portion 106 has less than approximately 5% cold work. In another preferred embodiment of the invention, the residual stress distribution extends through the entire thickness D of the surface portion 106.

[0039] It should be understood that the component 108 can include a plurality of surface portions 106 or that the entire component can include one or more surface portions 106. It should also be understood that each surface portion can have its own unique compressive stress distribution or a plurality of residual stress distributions can be utilized.

[0040] It should be understood that one or both of the inside and outside surface portions can be treated to improve the surface finish and produce a depth of compression is such that all or a majority of surface irregularities, such as flaws, corrosion pits, persistent slip bands, and the like that may operate as sites of crack initiation are confined within the depth of the compressive layer. In another preferred embodiment, the depth of the residual stress distribution in the surface portion extends to a depth of at least to about 1 mm. In another preferred embodiment of the invention, the residual stress in the surface portion is of a magnitude and depth such that the sum of residual and applied stress at the surface and to a depth never exceeds the threshold for SCC in the corrosive environment of the application or the fatigue endurance limit of the material forming the portion of the component.

[0041] It should now be apparent to one skilled in the art that the subject invention provides corrosive resistant components that can be used at their full available strength due to improved properties that mitigate or prevent the deleterious effects of stress corrosion cracking and fatigue. Further, that the invention is a practical, inexpensive method of introducing a relatively deep, stable layer of beneficial compressive stress along and into the surface of Fuel Recovery Components, as well as components for use in a wide variety of chemical plant applications, that protects against or reduces SCC, fatigue, corrosion fatigue and related failure modes with an improved surface finish, and low cold working.

[0042] While the methods and components described herein constitute preferred embodiments of the invention, it is to be understood that the invention is not limited to the precise method and components, and that changes may be made therein without departing from the scope of the invention which is defined in the appended claims.

[0043] What is claimed is:

Claims

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 H₂S 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 that penetrates through the entire depth of the at least one portion.