Abstract:
A method for making a downhole tool material for a hydrocarbon well that includes solution heat treating a precipitation hardening nickel alloy; cold working the alloy following the solution heat treating; aging the alloy following the cold working and the material made therefrom.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    In the hydrocarbon recovery industry, tools utilized in connection with all aspects of fluid production are at least potentially exposed to very harsh conditions. Such conditions can be natural, such as high temperature and pressure and some can be due to the fluids such as CO2, H2S, chloride ions, and acid stimulation. It will be appreciated that such conditions are exemplary only and that other conditions contributing to material stress, corrosion, and/or environmental cracking whether natural or induced are equally implicated. 
         [0002]    Because of the conditions under which downhole tools must operate it is conventional knowledge that very high strength and highly corrosion resistant materials must be used. Such properties are found in exotic and high cost alloy materials. While such materials are known and would function well for their intended purposes, they are very costly and usually not available in the sizes required. 
         [0000]    At the very high strengths desired, very few materials meet material requirements for corrosion and environmental cracking resistance, particularly according to NACE MR0175 specification. The combination of very high strength, very high corrosion resistance, relatively heavy wall thickness, and dimensional uniformity has only been previously available in exotic alloys such as MP35N and Elgiloy. 
       SUMMARY 
       [0003]    A method for making a downhole tool material for a hydrocarbon well that includes solution heat treating a precipitation hardening nickel alloy; cold working the alloy following the solution heat treating; aging the alloy following the cold working and the material made therefrom. 
     
    
     DETAILED DESCRIPTION 
       [0004]    The material limitations and costs associated with producing ultra high performance downhole tools as noted above can be reduced by a method of making downhole tools as described hereunder. Through the employment of certain processing steps in a certain order, much less expensive to procure precipitation hardening nickel alloys can be enhanced primarily with respect to strength to a level that renders them acceptable for use as ultra high performance downhole tools. Currently, as will be recognized by one of ordinary skill in the art, there are limitations to the strength of these suitable corrosion resistant alloys utilized in high pressure or highly corrosive environments within a wellbore. Materials as described herein and processed herein will exceed the current limitations for these alloys thereby improving overall strength and facilitating a greater freedom as to component shape, and size, and/or allowing significantly higher performance (e.g. burst, tensile) rating for the overall tool. 
         [0005]    Precipitation hardening nickel alloys such as 725 (UNS NO7725) and 625 plus (UNS NO7716) have been successfully used for the downhole environment in severely corrosive environments up to minimum yield strengths of ˜130-140 ksi. This strength is the peak achievable using a solution treat and age heat treatment, as required for compliance to NACE MR0175. Strength levels for the identified alloys can be further enhanced to minimum yield strength of approximately 160 ksi or higher when subjected to the processing steps as taught herein. 
         [0006]    In accordance with the method disclosed herein, precipitation hardening nickel alloys can now be made to possess a higher minimum yield strength and maintain high corrosion resistance. 
         [0007]    In order to achieve the benefits set forth above, precipitation hardening nickel alloy is subjected to a solutionizing heat treatment at a temperature range of from about 1600F to about 2000F and for a period of time of from about 30 minutes to about four hours. The solutionizing will allow grain growth and cause small precipitates of various phases to dissolve within the matrix. A variety of time and temperature profiles could be used, with the stipulation that the precipitates are dissolved. Following the heat treatment, and instead of other processes such as precipitation hardening, the material, in accordance with the method hereof is subjected to a flow forming process thereby introducing a substantial amount (between about 20% to about 90%) of cold work into the material, or in other words the material is strengthened due to plastic deformation of the material. In a flow forming process a blank of material is cold worked using rollers that transfer extreme compressive forces to “flow” the material to match a prescribed form during a spinning process. Externally applied heat is not used in the process but it is noted that the forming itself can cause the target material to increase in temperature due to the flow forming process. The flow forming process, in addition to strengthening the material through cold work affords a near net shape capability, which reduces machining and material waste. 
         [0008]    The now cold worked material is then direct aged to further increase its strength. The aging is performed at a lower temperature of about 1000° F. to about 1500° F. for about 2 to about 25 hours to minimize loss of the strength component attributable to strain hardening. Final machining tends to hold tolerances better due to the aging process as there is lower internal residual stress in materials prepared by the method hereof so that distortion during machining is minimized. 
         [0009]    Through use of the method described herein, the comparatively less expensive materials can be modified to exhibit required properties of strength and corrosion resistance sufficient to either equal or exceed current requirements for service. 
         [0010]    While preferred embodiments have been shown and described, modifications and substitutions may be made thereto without departing from the spirit and scope of the invention. Accordingly, it is to be understood that the present invention has been described by way of illustrations and not limitation.