Abstract:
The present invention is directed to a method of extending the life of thin walled tubing by austempering the tubing in a controlled continuous run process involving heating, quenching, and cooling the tubing pursuant to predetermined process parameters. The invention is also directed to a process for austempering tubing having a welded seam and for relieving residual stress in the weld. The invention is further directed to the product of the above processes as well as an austempered weld stress relieved thin walled tubing and such tubing in combination with other apparatus with which it is suitable for use in the production of hydrocarbons.

Description:
RELATION TO OTHER APPLICATIONS  
       [0001]     This application is a divisional of U.S. patent application Ser. No. 10/943,575, filed Sep. 17, 2004 and still pending. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field Of The Invention  
         [0003]     The present invention is directed to a method of extending the life of thin walled tubing by austempering the tubing in a controlled process involving heating, quenching, and cooling the tubing pursuant to predetermined process parameters. The invention is also directed to a process for austempering tubing having a welded seam and for relieving residual stress in the weld. The invention is further directed to the product of the above processes as well as an austempered weld stress relieved thin walled tubing and such tubing in combination with other apparatus with which it is suitable for use in the production of hydrocarbons.  
         [0004]     2. Description of the Prior Art  
         [0005]     As each instance tubing is rolled on or off a coil tubing reel, it is permanently elongated. The elongation accumulates until exhausted and the tubing breaks. Hence, elongation is a significant property of the tubing material.  
         [0006]     The second significant property of tubing material is strength or hardness. This quality resists dilation stresses of pressure and tension stresses of deployments in deep wells.  
         [0007]     A characteristic of steel is decreasing elongation with increasing hardness. Metallurgically, an ideal coil tubing is a paradox: hard for strength in deep or high pressure wells, ductile for repetitive reeling.  
         [0008]     Present technology coil tubing steels have a martensitic structure. Martensite has unfavorable hardness versus elongation trade-off. On the other hand, austempered steels have a bainitic structure. Bainitic structured steels are not only hard, but also retain commendable elongation.  
         [0009]     Austempering of steel is known in the prior art; however, it is typically accomplished in a non-continuous batch process which is unsuitable for coil tubing milling.  
         [0010]     Represented by  FIG. 1  is the current technology to continuously mill steel tubing: metal strip is introduced to a tube formation device, the seam welded and scarfed, and the formed tubular annealed, e.g., by heating. The tubing is chilled by a cooling apparatus and then travels through additional formation devices, e.g., sizing rolls. The tubular may then be heated and cooled again and taken up, e.g., on a reel. By welding the butts of the strip stock at the front end of the process, very long lengths of tubing can be milled.  
         [0011]     In the continuous tube milling process, the sizing operation in  FIG. 1  work-hardens the tubing increasing the strength. The thermal processes depicted in  FIG. 1  are either palliatives for problems caused by welding, or to soften tubing to the desired grade after work-hardening. The thermal processes used in present tubing milling technology do not harden the tube.  
       SUMMARY OF THE INVENTION  
       [0012]     The present inventions are directed toward an apparatus and methods useful for increasing the strength of the tubing while maintaining the elongation of thin walled tubing by austempering the thin walled tubing. The present invention is further directed toward a method for austempering thin walled tubing comprising a welded seam and for stress relieving the welded seam. The present invention is also directed toward a product produced by the methods and/or processes described above. The present invention is also directed toward a thin walled austempered tubing comprising a stress relieved welded seam. 
     
    
     DESCRIPTION OF THE DRAWINGS  
       [0013]      FIG. 1  is a schematic overview of a prior art system.  
         [0014]      FIGS. 2 and 2   a  are schematic overviews of an exemplary apparatus for practicing the present inventions&#39; methods.  
         [0015]      FIG. 3  is a view in partial perspective of a section of austempered tubing.  
         [0016]      FIG. 4  is a schematic view of an exemplary deployment of austempered tubing in a well.  
         [0017]      FIG. 5  is a block diagram of a first method of the present invention.  
         [0018]      FIG. 6  is a block diagram of a second method of the present invention.  
         [0019]      FIG. 7  is a block diagram of a third method of the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0020]     Referring now to  FIG. 2 , exemplary apparatus  10  for austempering thin walled tubing according to the methods of the present inventions comprises heater  20 , low temperature reservoir  30 , and cooler  40 . Apparatus  10  is adapted to be used with continuous runs of tubing  12  while practicing the methods of the present invention. As used herein, a continuous run is one which processes a length of around 200 feet or more in a single processing procedure.  
         [0021]     Metallic tubing  12  has a wall thickness of less than 0.25 inches, preferably around 0.120 inches. In an embodiment, metallic tubing  12  comprises a steel alloy with a carbon content greater than or equal to 0.25 and less than or equal to 0.45 and may comprise 4130 alloy steel. Metallic tubing  12  may be supplied from source  15  of a substantially continuous supply of metal, e.g. a rolled strip, and formed into a tubular at tube former  90 . Seams created by tube formation may be welded at seam welder  91  and the formed seam scarfed at scarfer  92 .  
         [0022]     Heater  20  is adapted to accept a section of metallic tubing  12  and heat the section to a high temperature in the range of 1300-1600° F. Heater  20  may comprise an induction heater and/or a flame or the like, or a combination thereof. Heater  20 , e.g. an induction heater, may be located proximate to or within low temperature reservoir  30 .  
         [0023]     Low temperature reservoir  30  is adapted to accept a moving section of metallic tubing  12  as part of a continuous run process and to reduce the temperature of the section of metallic tubing to a first low temperature in the range of 500-1000° F. in a time period of less than 3 seconds. Low temperature reservoir  30  as used for quenching may comprise a molten salt bath. Moving may be accomplished by numerous equivalent means including by using rollers.  
         [0024]     Cooler  40  is adapted to cool a section of metallic tubing  12  to a second low temperature below 100° F. Cooling may be accomplished by numerous equivalent means including by forced convection. Additional coolers may be present, e.g. water cooler  93 , as is practiced in the art.  
         [0025]     Additional processing may occur after the second cooling. For example, austempered metallic tubing  12  may be sized at sizing rollers  94  and cooled further by coolers  96  and  97 .  
         [0026]     Austempered metallic tubing  12  may then be taken up, e.g. at takeup reel  17 .  
         [0027]     Austempered thin walled welded tube  12  may be coiled on a reel, e.g., takeup reel  17 , which may be further mounted on ship  16  ( FIG. 2   a ).  
         [0028]     Referring to  FIG. 3 , austempered thin walled welded tube  12  may comprise first end region  12   a  adapted to be attached to device  19 , e.g. a motor, an overshoot jar, an intensifier, a landing nipple, a plug catcher, a casing scraper, a snake pin, a downhole tool, a valve, or the like. Austempered thin walled welded tube  12  may further comprise second end region  12   b  opposite first end region  12   a  which may be adapted to be further connected to device  18 , e.g. a pump.  
         [0029]     Austempered, thin walled, and stress relieved welded tubing  12  may be produced by any of the exemplary methods described herein. Moreover, thin walled welded tube  12  produced by any of the exemplary methods described herein may comprise an austempered cylindrical body created as part of the continuous run processes of those methods where the austempered cylindrical body comprises first seam edge  12   c , second seam edge  12   d , and a wall having a thickness of less than 0.25 inches. Thin walled welded tube  12  may further comprise stress relieved welded seam  12   e  joining the first and second seam edges.  
         [0030]     Referring now to  FIG. 4 , in an exemplary embodiment thin walled welded tube  12  is unspooled from takeup reel  17 . One end of thin walled welded tube  12  is connected to pump  18  and the other end deployed through well casing  90  and/or production tubing  91 , terminating in tool  19 .  
         [0031]     In the operation of exemplary embodiments, referring now to  FIG. 5 , in a first exemplary method for austempering thin walled tubing, a section of metallic tubing  12  ( FIG. 2   a ) is heated to a high temperature in the range of 1300-1600° F. in heater  20  ( FIG. 2   a ). The section of metallic tubing  12  has a wall thickness of less than 0.25 inches, preferably around 0.120 inches.  
         [0032]     After being heated, the section of heated metallic tubing  12  ( FIG. 2   a ) is moved from heater  20  ( FIG. 2   a ) to low temperature reservoir  30  ( FIG. 2   a ) as part of a continuous run process. While in low temperature reservoir  30 , the section of metallic tubing  12  is quenched to reduce the temperature of the section of metallic tubing  12  to a first low temperature in the range of 500-1000° F. in a time period of less than 3 seconds. Processing the section of metallic tubing  12  may comprise a time-temperature-transformation curve where the start of conversion to austentite-ferrite is at least 0.75 seconds after quenching in low temperature reservoir  30 .  
         [0033]     The section of metallic tubing  12  ( FIG. 2   a ) is allowed to transform to bainite and then moved out of low temperature reservoir  30  ( FIG. 2   a ) as part of the continuous run process and cooled to a second low temperature below around 100° F. Cooling may be by forced convection, e.g. at cooler  40  ( FIG. 2   a ).  
         [0034]     In a second exemplary method, referring to  FIG. 6 , a further exemplary method for austempering thin walled coiled tubing  12  ( FIG. 2   a ) comprises extending a section of thin walled metallic tubing  12  having a wall thickness of less than 0.25 inches from a coil mounted about reel  15  ( FIG. 2   a ) into heater  20  ( FIG. 2   a ) as part of a continuous run process. The section of metallic tubing  12  is heated to a high temperature in the range of 1300-1600° F. in heater  20  and then moved from heater  20  to low temperature reservoir  30  ( FIG. 2   a ) as part of the continuous run process. In low temperature reservoir  30 , the section of metallic tubing  12  is quenched in low temperature reservoir  30  to reduce the temperature of the section of metallic tubing  12  to a first low temperature in the range of 500-1000° F. in a time period of less than around 3 seconds.  
         [0035]     The section of metallic tubing  12  ( FIG. 2   a ) is allowed to transform to bainite and then the section of metallic tubing  12  transformed into bainite is moved out of low temperature reservoir  30  ( FIG. 2   a ) as part of the continuous run process and cooled to a second low temperature below around 100° F., e.g. at cooler  40  ( FIG. 2   a ).  
         [0036]     After it reaches the second low temperature, the section of metallic tubing may be coiled, e.g. about reel  17  ( FIG. 2   a ).  
         [0037]     In a third exemplary method, referring now to  FIG. 7 , a section of thin walled metallic tubing  12  ( FIG. 2   a ) having a welded seam and a wall thickness of less than 0.25 inches is extended from a coil mounted about reel  15  ( FIG. 2   a ) into heater  20  ( FIG. 2   a ) as part of a continuous run process. The section of metallic tubing  12  is heated to a high temperature in the range of 1300-1600° F. in heater  20  ( FIG. 2   a ) and then moved from heater  20  to low temperature reservoir  30  ( FIG. 2   a ) as part of the continuous run process. In low temperature reservoir  30 , the section of metallic tubing  12  is quenched to reduce the temperature of the section of metallic tubing  12  to a first low temperature in the range of 500-1000° F. in a time period of less than around 3 seconds.  
         [0038]     The section of metallic tubing  12  ( FIG. 2   a ) is then allowed to transform to bainite. The section of metallic tubing  12  transformed to bainite is then moved out of low temperature reservoir  30  ( FIG. 2   a ) as part of the continuous run process cooled to a second low temperature below around 100° F., e.g. at cooler  40  ( FIG. 2   a ).  
         [0039]     The foregoing disclosure and description of the inventions are illustrative and explanatory. Various changes in the size, shape, and materials, as well as in the details of the illustrative construction and/or a illustrative method may be made without departing from the spirit of the invention.