Abstract:
A system and method for heat treating a tubular. In one embodiment, a system for heat treating a tubular includes a first coil and a second coil. The first coil is configured to circumferentially surround the tubular and induce, from without the tubular, current flow in a cylindrical portion of the tubular adjacent the first coil. The second coil is configured to be inserted into a bore of the tubular and induce, from within the tubular, in conjunction with the first coil, current flow in the cylindrical portion of the tubular.

Description:
BACKGROUND 
       [0001]    The fabrication and manufacture of goods from metals often results in the metals having a less than desirable metallurgical condition. To convert the metals to a desired condition, it is common to heat treat the metals. In heat treating, an object, or portion thereof, is heated to a suitably high temperature and subsequently cooled to ambient temperature. The temperature to which the metal is heated, the time of heating, as well as the rate of cooling, may be selected to develop the intended physical properties in the metal. For example, for normalization, steel is to be heated to a temperature above the critical range, to about 1600 degrees Fahrenheit and then cooled slowly, while tempering of steel also requires uniformly heating to a temperature below the critical range to a specified temperature, holding at that temperature for a designated time period then cooling in air or liquid. 
         [0002]    Inductive heating is one method for producing heat in a localized area of a metallic object. In inductive heating, an alternating current electric signal is provided to a coil disposed near a selected location of the metallic object to be heated. The alternating current in the coil creates a varying magnetic flux within the metal to be heated. The magnetic flux induces current flow in the in the metal, which, in turn, heats the metal. 
       SUMMARY 
       [0003]    A system and method for heat treating a tubular are disclosed herein. In one embodiment, a system for heat treating a tubular includes a first coil and a second coil. The first coil is configured to circumferentially surround the tubular and induce, from without the tubular, current flow in a cylindrical portion of the tubular adjacent the first coil. The second coil is configured to be inserted into a bore of the tubular and induce, from within the tubular, in conjunction with the first coil, current flow in the cylindrical portion of the tubular. 
         [0004]    In another embodiment, a method for heat treating a tubular includes positioning a first coil to encircle a portion of a tubular to be heat treated. A second coil is positioned within a bore of the tubular at a location of the portion of the tubular to be heat treated. The portion of the tubular is heat treated by inducing current flow about an exterior cylindrical wall and an interior cylindrical wall of the portion of the tubular via the first coil and the second coil. 
         [0005]    In a further embodiment, inductive heat treatment apparatus includes an exterior induction coil, an interior induction coil, and a controller coupled to the exterior induction coil and the interior induction coil. The exterior induction coil is configured to surround an outside diameter of a tubular. The interior induction coil is configured to occupy a bore of the tubular. The controller is configured to simultaneously energize the exterior induction coil and the interior induction coil to concurrently heat treat a selected cylindrical portion of the tubular from exterior and interior of the tubular. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    For a detailed description of exemplary embodiments of the invention, reference is now be made to the figures of the accompanying drawings. The figures are not necessarily to scale, and certain features and certain views of the figures may be shown exaggerated in scale or in schematic form, and some details of conventional elements may not be shown in the interest of clarity and conciseness. 
           [0007]      FIG. 1  shows a schematic diagram of a system for heat treating a tubular in accordance with principles disclosed herein; 
           [0008]      FIG. 2  shows a block diagram of a controller for managing heat treatment of a tubular in accordance with principles disclosed herein; 
           [0009]      FIG. 3  shows a cross sectional view of a wall of a tubular heat treated in accordance with principles disclosed herein; and 
           [0010]      FIG. 4  shows a flow diagram for a method for heat treating a tubular in accordance with principles disclosed herein. 
       
    
    
     NOTATION AND NOMENCLATURE 
       [0011]    Certain terms are used throughout the following description and claims to refer to particular system components. In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . .” Also, the term “couple” or “couples” is intended to mean either an indirect or direct connection. Thus, if a first device couples to a second device, that connection may be through direct engagement of the devices or through an indirect connection via other intermediate devices and connections. Further, the term “software” includes any executable code capable of running on a processor, regardless of the media used to store the software. Thus, code stored in memory (e.g., non-volatile memory), and sometimes referred to as “embedded firmware,” is included within the definition of software. The recitation “based on” is intended to mean “based at least in part on.” Therefore, if X is based on Y, X may be based on Y and any number of other factors. The term “approximately” means within plus or minus 10 percent of a stated value. 
       DETAILED DESCRIPTION 
       [0012]    In the drawings and description that follow, like parts are typically marked throughout the specification and drawings with the same reference numerals. The present disclosure is susceptible to embodiments of different forms. Specific embodiments are described in detail and are shown in the drawings, with the understanding that the present disclosure is to be considered an exemplification of the principles of the disclosure, and is not intended to limit the disclosure to that illustrated and described herein. It is to be fully recognized that the different teachings and components of the embodiments discussed below may be employed separately or in any suitable combination to produce desired results. 
         [0013]    In manufacture of tubulars, such as those employed in drilling of subsurface formations (e.g., tubulars used in a drill string), heat treating may be applied to improve the metallurgical characteristics of selected portions of the portions of the tubular. For example, portions of the tubular along weld lines may be heat treated to relieve internal stresses caused by the welding. 
         [0014]    In conventional post-weld heat treating of drill string tubulars, a selected portion of the wall of the tubular is heated from one side (e.g., heat is induced from the outer surface of the tubular) and the metal of the tubular conducts the heat to the opposing side of the tubular wall. When examined metallurgically, such heating (heating via an induction coil disposed about the outer diameter (OD) of the tubular) may produce a heat affected zone that is substantially wider at the OD of the tubular wall than at the inner diameter (ID) of the tubular wall. Such heat treating may be difficult to control. If the heat treatment is too shallow, less than the entire thickness of the tubular wall may be heat treated. If the heat treatment is too deep, the length of the heat treated region (along the tubular) may be greater than desired. 
         [0015]    Embodiments of the present disclosure include a system for heat treating a tubular that simultaneously provides inductive heating about 360 degrees of the outer and inner surfaces of a tubular. By providing inductive heating from both the exterior and the interior of a tubular, embodiments provide a better controlled heat treatment with a narrower heat affected zone, resulting in higher product quality. Additionally, by heating from both without and within, embodiments reduce the time required to heat treat the tubular, thereby improving manufacturing throughput and reducing overall production cost. 
         [0016]      FIG. 1  shows a schematic diagram of a system  100  for heat treating a tubular  106  in accordance with principles disclosed herein. The system  100  includes a first induction coil  102 , a second induction coil  104 , a controller  110 , and a pyrometer  112 . The first induction coil  102  is positionable about the tubular  106 , such the first induction coil  102  surrounds a cylindrical portion of the tubular  106 , and is configured to inductively heat the cylindrical portion of the tubular  106  from the exterior. The second induction coil  104  is positionable within the inner bore of the tubular  106 , and configured to inductively heat a cylindrical portion of the tubular  106  from the interior. Some embodiments of the coil  104  may be capable of inductively heating any selected portion of the tubular  106 . Other embodiments of the coil  104  may be capable of inductively heating a portion of the tubular  106  at a location up to 48 inches from the end of the tubular  106 . 
         [0017]    In operation, the first and second inductive coils  102 ,  104  are positioned to inductively heat a same cylinder of the tubular  106 . For example, in  FIG. 1 , the coils  102 ,  104  are centered on the weld line  108  joining segments  118  and  120  of the tubular  106 . The tubular  206  may be, for example, a drill pipe, a drill collar, a downhole tool housing, or any other tubular employed in drilling or production of subsurface formations. 
         [0018]    The coils  102 ,  104  may be generally toroidal in shape, and formed of one or more turns of copper tubing that provides a conductive path for current that energizes the coil, and a channel for pumping coolant through the coil. Each of the coils  102 ,  104  may be wrapped in a refractory material that provides a housing for the coil. In some embodiments, the coil  102  includes nine turns and the coil  104  includes eleven turns. The number of turns may differ in other embodiments of the coils  102 ,  104 . 
         [0019]    The controller  110  is coupled to coil  102  via tubing  114  that provides a path for current and cooling flow. Similarly, controller  110  is coupled to coil  104  via tubing  116 . The controller  110  manages the operation of the coils  102 ,  104  to heat treat the tubular  106 . More specifically, the controller  110  controls flow of alternating current (AC) to the coils  102 ,  104 , thereby controlling the heating of the tubular  106 . The pyrometer  112  is coupled to the controller  110 . The pyrometer  112  measures the temperature of the portion of the tubular  106  heated by the system  100 . In some embodiments, the pyrometer  112  is an optical pyrometer. The pyrometer  112  may be focused on the exterior surface of the tubular  106 . The controller  110  may determine current values and/or heating intervals based on the temperature measurement values provided by the pyrometer  112 . For example, if inductive heating has increased the temperature of the tubular  106  to a predetermined value, the controller  110  may set the current to the coils  102 ,  104  to maintain the tubular  106  at the attained temperature for a predetermined time interval. 
         [0020]    Some embodiments of the controller  110  may include multiple sub-controllers that cooperatively control the coils  102 ,  104  to inductively heat a selected portion of the tubular  106 . For example, a first sub-controller may manage operation of the coil  102  in cooperation with a second controller that manages operation of the coil  104 . 
         [0021]      FIG. 2  shows a block diagram of the controller  110  in accordance with principles disclosed herein. The controller  110  includes a processor  202 , storage  204 , an ID coil power supply  210 , an OD coil power supply  212 , and a cooling system  214 . The processor  202  is coupled to the ID coil power supply  210 , the OD coil power supply  212 , and the coil cooling system  214  to monitor and control the operation of the system  100 . The controller  110  may also include various other components, such as display devices (e.g., a monitor), operator control devices (a keyboard, mouse, trackball, etc.), and/or other components that have been omitted from  FIG. 2  in the interest of clarity. In some embodiments of the controller  110 , the processor  202  and the storage  204  may be embodied in a programmable logic controller or other computing device. 
         [0022]    The OD coil power supply  212  includes a solid-state high frequency power supply that provides power to the coil  102 . Some embodiments of the power supply  212  may include integrated gate bipolar transistor (IGBT) drivers to provide current to the coil  102 . The OD coil power supply  212  is controllable by the processor  202  to provide any of wide range of frequencies of AC to the coil  102 , and to provide any of a specified power, current, and/or voltage to the coil  102 . The OD coil power supply  212  may also be controllable by the processor  202  to sweep a range of frequencies for determination of a resonant frequency of the circuit comprising the coil  102  and the tubular  106 . In some embodiments of the system  100 , the OD coil power supply  212  is controllable by the processor  202  to provide approximately 180 hertz (Hz) AC and/or at least approximately 150 kilowatts of power to the coil  102 . 
         [0023]    The ID coil power supply  210  is similar in structure and operation to the OD coil power supply  212 , and provides power to the coil  104 . Like the OD coil power supply  212 , the ID coil power supply  210  is controllable by the processor  202  to provide any of wide range of frequencies of AC to the coil  104 , and to provide any of a specified power, current, and/or voltage to the coil  104 . The ID coil power supply  210  may be controllable by the processor  202  to sweep a range of frequencies for determination of a resonant frequency of the circuit comprising the coil  104  and the tubular  106 . 
         [0024]    To avoid interference in the operation of the coils  102 ,  104 , the ID coil power supply  210  may provide AC to the coil  104  at a substantially different frequency than the frequency at which AC is provided to the coil  102  by the OD coil power supply  212 . For example, in some embodiments, the frequency of current provided to the coil  104  may be substantially higher than the frequency of current provided to the coil.  102 . In some embodiments of the system  100 , the ID coil power supply  210  is controllable by the processor  202  to provide AC to the coil  104  at a frequency in a range of from approximately 3 kilohertz (KHz) to approximately 10 KHz, and/or to provide at least approximately 125 kilowatts of power to the coil  104 . 
         [0025]    The cooling system  214  provides cooling to the coils  102 ,  104 , and/or the power supplies  210 ,  212 . In some embodiments, the cooling system  214  includes a water recirculating system that provides water cooling to the coils  102 ,  104 , and/or the power supplies  210 ,  212 . For example, the cooling system  214  may pump water through the copper tubing of the coils  102 ,  104 . The cooling system  214  may provide approximately 90 gallons per minute water to cool the coils  102 ,  104 , where the water temperature is no more than 90 degrees Fahrenheit and above the dew point. 
         [0026]    The processor  202  is a device that executes instructions to manage the heat treatment of tubular  106 . Suitable processors include, for example, general-purpose microprocessors, digital signal processors, and microcontrollers. Processor architectures generally include execution units (e.g., fixed point, floating point, integer, etc.), storage (e.g., registers, memory, etc.), instruction decoding, peripherals (e.g., interrupt controllers, timers, direct memory access controllers, etc.), input/output systems (e.g., serial ports, parallel ports, etc.) and various other components and sub-systems. 
         [0027]    The storage  204  is a computer-readable storage device that stores instructions to be executed by the processor  202 . When executed the instructions cause the processor  202  to perform the various heat treatment management operations disclosed herein. A computer readable storage device may include volatile storage such as random access memory, non-volatile storage (e.g., FLASH storage, read-only-memory, etc.), or combinations thereof. Instructions stored in the storage  204  may cause the processor  202  to enable flow of current to the coils  102 ,  104 , control values of current, voltage, and/or power provided to the coils  102 ,  104 , control coolant flow to the coils  102 ,  104 , etc. 
         [0028]    The storage  404  includes a heat treatment control logic module  206 , and tubular parameters  208 . The processor  202  executes instructions of the heat treatment control logic module  206  to manage heat treatment of the tubular  206 . The tubular parameters  208  may include parameter values for heat treating a number of different tubulars (e.g., tubulars of different types, materials, wall thicknesses, etc.) The values of the tubular parameters  208  may be entered by an operator for future retrieval, and selected by the operator for application to a particular tubular. The parameter values may include minimum and/or maximum power levels for pre-heating and soaking, set point temperature of OD heating, etc. 
         [0029]    The heat treatment control logic module  206  may control the heat treatment of the tubular  106  using a proportional-integral-derivative (PID) control loop, or other control methodology, with temperature feedback provided via the pyrometer  112 . The processor  202 , via execution of the heat treatment control logic module  206 , controls the power provided to both of the coils  102 ,  104 . For example, as the temperature of the exterior surface of the tubular  106  approaches or reaches a predetermined set point temperature during heat treatment, the processor  202  may reduce or disable current flow to the coils  102 ,  104 . 
         [0030]      FIG. 3  shows a cross sectional view of a wall of the tubular  106  heat treated in accordance with principles disclosed herein. By heating the wall of the tubular  106  proximate the weld line  108  from both the outer and inner surfaces of the wall, the width of the heat affected zone  302  is reduced relative to application of inductive heating from a single surface of the tubular  106 . Additionally, the system  100  provides a more uniform heat affected zone  302  than is provided using single coil inductive heating. As shown in  FIG. 3 , operation of the system  100  produces a heat treated zone  302  having a shallow parabolic outline with the vertex facing the weld line  108 . In some embodiments, the vertex is located in a center third of the wall of the tubular  106  in accordance with the balanced heating provided by the coils  102 ,  104 . Furthermore, the system  100  can produce the superior heat treatment result shown in  FIG. 3  in significantly less time than would be required to produce an inferior result using a single coil. 
         [0031]      FIG. 4  shows a flow diagram for a method for heat treating a tubular in accordance with principles disclosed herein. Though depicted sequentially as a matter of convenience, at least some of the actions shown can be performed in a different order and/or performed in parallel. Additionally, some embodiments may perform only some of the actions shown. In some embodiments, at least some of the operations of the method  400 , as well as other operations described herein, can be implemented as instructions stored in a computer readable storage device  204  and executed by the processor  202 . 
         [0032]    In block  402 , parameter values to be applied to heat treatment of the tubular  106  are selected. In some embodiments, the parameter values for a number of different tubulars are stored in the storage device  204 , and selected by identifying the tubular to be heat treated. For example, an operator of the system  100  may select a tubular to be heat treated via a user interface of the controller  110 . 
         [0033]    In block  404 , the coil  102  is positioned around the outer diameter of the tubular  106 . In some embodiments of the system  100 , the coil  102  may stationary and the tubular  106  inserted into a central opening of the coil  102  such that the coil  102  surrounds the circumference of the tubular  106 . In other embodiments, the coil  102  may be portable and moved into position about the tubular  106  such that the coil  102  completely surrounds the outer diameter of a portion or segment of the tubular  106  to be heat treated. For example, the coil  102  may be centered about the weld line  108 . 
         [0034]    In block  406 , the coil  104  is inserted into an end of the tubular  106  to a location that is radially aligned with the coil  102 . For example, both the coil  102  and the coil  104  may be centered on the weld line  108  for heat treating of the welded portion of the tubular  106 . 
         [0035]    In block  408 , the controller energizes the coils  102 ,  104  by providing AC current to the coils  102 ,  104  at selected frequencies, power, voltage, and/or current levels. The frequency of current provided to the coil  104  may be higher than the frequency of current provided to the coil  102 . For example, approximately 180 Hz AC may be provided to coil  102 , and AC in a range of approximately 3 KHz to 10 KHz may be provided to coil  104 . The energized coils  102 ,  104  inductively heat the tubular  106 . For example, the coils  102 ,  104  may inductively heat a cylindrical portion of the tubular  106  to a temperature of 2000 degrees Fahrenheit or higher. 
         [0036]    In block  410 , the controller  110  is monitoring the temperature of the tubular  106  via the pyrometer  112 . The controller  110  may continue to provide current to the coils  102 ,  104  at a level that increases the temperature of the portion of the tubular  106  being heat treated until the temperature of the tubular reaches or approaches a specified set point temperature for heat treatment of the tubular  106 . The set point temperature may be provided as one of the parameter values selected in block  402 . 
         [0037]    In block  412 , the controller  110  reduces current flow to the coils  102 ,  104  to a level that maintains the tubular  106  at the set point temperature, and allows the tubular  106  to temperature soak for a predetermined soak time period. The predetermined soak time period may be provided as one of the parameter values selected in block  402 . 
         [0038]    In block  414 , the controller  110  deactivates the coils  102 ,  104  by disabling current flow to the coils  102 ,  104 . The coil  104  is extracted from the bore of the tubular  106  in block  416 , and the coil  102  is removed from around the tubular  106  in block  418 . 
         [0039]    The above discussion is meant to be illustrative of various embodiments of the present invention. Numerous variations and modifications will become apparent to those skilled in the art once the above disclosure is fully appreciated. It is intended that the following claims be interpreted to embrace all such variations and modifications.