Abstract:
A method and an apparatus for controlling the rate of pressure applied to an air controlled device. The apparatus includes a flow restrictor, a regulator, and a dome loaded regulator. The regulator is configured to be operatively connected to a pressure source and is set to a first selected pressure. The flow restrictor is arranged to control the rate of applying pressure to the air controlled device after the first pressure is reached. The dome loaded regulator is in communication with the regulator and the flow restrictor such that the regulator and the flow restrictor alternately determine the flow rate from the pressure source to the air controlled device. The method includes setting a predetermined parameter and automatically reducing the rate of applying pressure to the air controlled device after the predetermined parameter is reached.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the priority, pursuant to 35 U.S.C. §119(e), of U.S. Provisional Application No. 60/507,331, entitled, “A Method and Apparatus for Controlling the Rate of Pressure Applied to a Cathead Clutch,” filed on Sep. 30, 2003. That application is incorporated by reference in its entirety. 
     
    
     BACKGROUND OF INVENTION  
       [0002]     Background Art  
         [0003]     Compressed air is commonly used to actuate equipment and provide force for various functions. One function common to the oil field is to control the engagement of a cathead clutch. A cathead is a power driven rotating drum used to wind and unwind cable (e.g. braided wire or chain) on a drilling rig. The cable used with the cathead is commonly referred to as the “catline.” The catline that is wound around the drum can be used for various functions on the drilling rig, such as moving heavy objects and applying torque to a threaded connection.  
         [0004]     A simplified representation of making up a connection using a cathead is shown in  FIG. 1 . To apply torque, tongs  103 ,  104  are typically attached to the two tubular pieces  101 ,  102  to be connected. One tubular piece  101  is held fixed by connecting the tong  104  to a fixed object  108  using a cable  105 , while the other tong  103  is connected to the catline  107  wrapped around the drum on the cathead  106 . Air pressure from a pressure source (not shown) is used to actuate a cathead clutch (not shown) to turn the cathead  106 , which pulls on the catline  107 . The tension in the catline  107  multiplied by the distance from the center of the tubular piece  102  to the attachment point  103   a  (“tong length”) on the tong  103  is the torque applied to the connection. The cathead  106  used to make-up connections is commonly referred to as the “make-up cathead,” while a cathead used for disconnecting tubular pieces  101 ,  102  is commonly referred to as the “breakout cathead.” Typically, a drilling rig will have both a make-up cathead  106  and a breakout cathead (not shown) located on opposite sides of the draw works  110 .  
         [0005]     To measure the amount of torque applied to a connection, an instrument (e.g. load cell) for measuring the tension in the catline may be used. In some cases, the tension is displayed on a gauge and the user multiplies the tong length to estimate the torque on the connection. A more common practice is to measure the linear strain in the catline and view an indicating meter calibrated to display units of torque (e.g. ft*lbs). Indicating meters for use on drilling rigs are usually designed such that they are not significantly affected by vibration and changes in temperature.  
         [0006]     After the desired amount of torque has been achieved, the operator of the cathead will release the air pressure. Alternatively, the operator may use a system that automatically shuts off the air supply and vents to disengage the cathead clutch when the desired torque is reached. One such torque control system is Smith Services (Houston, Tex.) Model 2000 Tru-Torque Automatic Torque-Controlled System.  
         [0007]     A common problem experienced with systems controlled by air pressure is that the rate of applying the pressure is difficult to control. In the scenario of using a air pressure to actuate a cathead clutch, an operator commonly controls the air flow with a throttle like control. The operator will commonly have to rely on “touch” and experience to control the rate of applying pressure. When pressure is applied too quickly, time delays in the actuation of the torque control system may cause the connection to be damaged by too much torque. With cathead clutches (and other clutches), heavy use can overheat the clutch causing slippage and inconsistent rates of applying torque. Consistent application of torque while preventing too much torque from being applied is useful for making up connections dependably and quickly.  
         [0008]     What is needed is a system for controlling the rate of pressure applied from a pressure source to an air controlled device.  
       SUMMARY OF INVENTION  
       [0009]     In one aspect, the present invention relates to an apparatus for controlling the rate of applying pressure to an air controlled device. The apparatus includes a regulator, a flow restrictor, and a dome loaded regulator. The regulator is configured to be operatively connected to a pressure source and is set to a first selected pressure. The flow restrictor is arranged to control the rate of applying pressure to the air controlled device after the first pressure is reached. The dome loaded regulator is in communication with the regulator and the flow restrictor such that the regulator and the flow restrictor alternately determine the flow rate from the pressure source to the air controlled device.  
         [0010]     In another aspect, the present invention relates to an apparatus for controlling a rate of applying pressure to an air controlled device. The apparatus includes a pressure inlet in communication with a pressure source, a means for setting a first predetermined pressure, a means for controlling the rate of applying pressure after the first predetermined pressure is reached, and a pressure outlet in communication with the air controlled device. The rate of applying pressure after reaching the first predetermined pressure is lower than an initial rate of applying pressure.  
         [0011]     In another aspect, the present invention relates to a method of controlling a rate of applying pressure to an air controlled device. The method includes setting a predetermined parameter and automatically reducing the rate of applying pressure to the air controlled device after the predetermined parameter is reached.  
         [0012]     In another aspect, the present invention relates to a method of making up a connection. The method includes engaging a first tong with a first tubular piece and a second tong with a second tubular piece. Both tubular pieces have threaded connections formed thereon and are adapted to connect to each other. A catline is connected to the second tong and attached to a cathead. To apply torque to the second tubular piece using the second tong, a cathead clutch is engaged to apply a pull on the catline at a first rate. Then, pull at a second rate is automatically applied on the catline. The second rate is slower than the first rate.  
         [0013]     Other aspects and advantages of the invention will be apparent from the following description and the appended claims. 
     
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0014]      FIG. 1  shows a setup for making up a connection.  
         [0015]      FIG. 2  shows a schematic layout of an apparatus for controlling a rate of applying pressure to an air controlled device in accordance with an embodiment of the present invention.  
         [0016]      FIG. 3  shows a graph of a rate of applying pressure to an air controlled device in accordance with an embodiment of the present invention.  
         [0017]      FIG. 4  shows a schematic layout of an air over hydraulics system in accordance with an embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0018]     In one aspect, the present invention provides an apparatus for applying pressure from a pressure source to an air controlled device. More specifically, embodiments of the present invention initially apply a relatively high rate of pressure until reaching a desired pressure, and then apply pressure at a reduced rate. In another aspect, embodiments of the present invention provide methods for applying pressure to an air controlled device.  
         [0019]     As discussed above, rapidly applying torque to a connection has the risk of damaging a connection in the time that lapses from reaching the desired torque to the automatic or manual release of the pressure. Choking off the line providing pressure would reduce this risk, but at the same time greatly increases the amount of time spent making up connections. Further, the initial application of pressure locks the tongs in place by loading them. Slowly applying pressure before locking the tongs could cause the tongs to slip out of place, or could require personnel to hold the tongs in place during initial loading, which decreases safety.  
         [0020]     A method in accordance with an embodiment of the invention is to initially apply pressure rapidly to the air controlled device up to a selected amount of pressure below the maximum expected for applying torque to the connection or for controlling another air controlled device. After reaching that selected pressure, the rate of applying pressure could be automatically decreased such that increases in torque are gradual towards the end of the operation.  
         [0021]     In  FIG. 2 , a schematic layout of an apparatus for controlling the rate of applying pressure to an air controlled device in accordance with one embodiment of the present invention is shown. In  FIG. 2 , the apparatus  10  has an inlet  56  in communication with a pressure supply  22 . In this particular embodiment, a proportional control  24  is included for an operator to exercise some manual control over the rate of applying pressure. When the proportional control  24  is activated to allow pressurized air from the pressure supply  22  to flow, the pressurized air flows through line  55  into the apparatus  10 . The pressurized air flow exits the apparatus  10  through line  14  and outlet  57  to control the air controlled device  20 . In other embodiments, the apparatus may be directly connected to the supply source  22  and air controlled device  20 . In another embodiment, inlet  56  and outlet  57  may have quick disconnects adapted to easily connect to other devices with which the apparatus  10  will operate.  
         [0022]     In this embodiment, the apparatus  10  includes a regulator  28 , a flow restrictor  30 , a dome loaded regulator  32 , and one way check valves  5 ,  6 . The apparatus  10  is configured to control the rate of air supplied from the supply source  22  to the air controlled device  20  via line  52 . Initially, flow through the dome loaded regulator  32  is controlled by pressure traveling through regulator  28 , check valve  5 , and line  51 . For example, if 50 psi is applied through line  51 , only 50 psi will pass through the dome loaded regulator  32 . In other embodiments, the ratio may be different. For example, the dome loaded regulator  32  could be configured to allow 25 psi to pass through when 50 psi is applied to the dome loaded regulator  32  through line  51 .  
         [0023]     The regulator  28  may be set to a selected pressure to only allow flow through line  51  up to that selected pressure. Because flow is not significantly restricted prior to reaching the selected pressure, the dome loaded regulator  32  will allow a relatively high rate of supplying air to the air controlled device  20 . This rapidly actuates the air controlled device  20 . If the air controlled device  20  is a cathead clutch, the cathead clutch would quickly activate to tighten the catline and apply torque to the connection. After reaching the selected pressure, regulator  28  prevents applying increased pressure through line  51 . At that point, the increasing pressure may flow through flow restrictor  30  and line  50  to control the dome loaded regulator  32 . This decreases the rate of pressure applied to the air controlled device  20 . In this embodiment, the flow restrictor  30  is shown as a needle valve that is adjustable by an operator. In another embodiment, the flow restrictor  30  may be an orifice plate. One of ordinary skill in the art will appreciate that alternative flow restrictors (both adjustable and fixed) known in the art may be used. A needle valve provides an adjustment that an operator can make to adapt the apparatus  10  to the specific situation. An orifice plate with changeable orifice sizes may be used to similarly provide an adjustment.  
         [0024]     Continuing with  FIG. 2 , as air flows through the flow restrictor  30 , check valve  5  prevents the air pressure from reversing through line  51 . Check valve  6  is arranged to only allow flow from line  14  to pass through to line  52 . Because of this, when the system is deactivated, pressurized air in the air controlled device  20  is able to release by rapidly dumping air through check valve  6  to return to the supply source  22  or vent to the atmosphere. This arrangement bypasses the flow restrictions of the dome loaded regulator  32  and flow restrictor  30 .  
         [0025]     The system may be deactivated in several ways. In one embodiment, the proportional control  24  is shut off, which vents the air to atmosphere. Pressurized air in the air controlled device  20  and apparatus  10  would rapidly vent to the atmosphere. In another embodiment designed to be used with a cathead clutch to make up connections, the apparatus  10  may be connected to a torque control device. Upon reaching a desired torque, the torque control device could actuate a valve to divert air from the cathead clutch and release it. One of ordinary skill in the art will appreciate that apparatus  10  may be adapted to work with many air controlled devices and peripherals for controlling them without departing from the scope of the invention.  
         [0026]     Turning to  FIG. 3 , a graph showing the rate of increasing pressure in accordance with an embodiment of the present invention is shown.  FIG. 3  shows pressure plotted against time. Time T1 is the amount of time that passes prior to reaching a selected pressure A. The pressure during T1 rapidly increases. After reaching the selected pressure A, the pressure increases more gradually over the time period T1. One of ordinary skill in the art will appreciate that embodiments of the invention may be modified or adjusted to have different lengths of time periods T1, T2 and different rates of pressure increase without departing from the scope of the present invention.  
         [0027]     Applying  FIG. 3  to the apparatus  10  shown in  FIG. 2 , time T1 would correspond with the initial application of pressure when the air flow passes freely through regulator  28 . Regulator  28  blocks air flow after the selected pressure A is reached. This causes air flow to pass through the flow restrictor  30 , which reduces the flow rate (and the rate of pressure increase) as shown during time T2 in  FIG. 3 . In the example application of using apparatus  10  to control a cathead clutch for making up a connection, during time T1, the cathead clutch would activate rapidly to begin pulling the catline and tighten the connection. During time T2, the pressure and corresponding increase in torque applied to the connection would be more gradual. The more gradual increase in torque advantageously reduces the risk of applying too much torque prior to deactivating the cathead clutch. Further, the rapid activation of the cathead clutch during time T2 reduces the amount of time used to make up the connection.  
         [0028]     Note that  FIG. 2  is for illustration only. One of ordinary skill in the art will appreciate that various modifications of the apparatus  10  are possible to achieve the pressure profile shown in  FIG. 3  without departing from the scope of the present invention. For example, the regulator  28  and flow restrictor  30  may be combined in a single mechanism such that the combing regulator/flow restrictor begins to restrict flow at a selected pressure.  
         [0029]     In some embodiments of the invention, the rate of air flow through the flow restrictor (shown as  30  in  FIG. 2 ) can be adjusted to control the rate of air flow after reaching the selected pressure A. In some embodiments, selected pressure A may be adjusted by the user by selecting a regulator ( 28  in  FIG. 2 ) with an adjustment feature. Being able to adjust selected pressure A and/or the rate of air flow through the flow restrictor allows for an operator to adapt the apparatus to the supply source, the air controlled device to be controlled, and any additional equipment that may be connected to the apparatus. In the example application of engaging a cathead clutch for making up a connection, an embodiment of the invention with an adjustable regulator and flow restrictor could be adapted for the air pressure to be supplied from the pressure source, the torque to be applied to the connection, and to the maximum pull that the cathead can achieve. In some embodiments, adjustment to the regulator and flow restrictor may be performed by hand or with readily available hand tools such as a screw driver.  
         [0030]     While the above embodiments have only shown a single change in the rate of applying pressure, one of ordinary skill in the art that an apparatus could be similarly designed to have two or more changes in the rate of applying pressure. This may be accomplished by adding a second regulator with a selected pressure B in line (or in parallel) with a second flow restrictor allowing a different flow rate than the other flow restrictor.  
         [0031]     In one embodiment, the air controlled device  20  may be a piston  410  connected to a hydraulics system  420 , as shown in  FIG. 4 . This arrangement is commonly referred to as an “air over hydraulics” system. The apparatus  400  may control the amount of pressure applied to the piston  410 , which controls pressure in the hydraulics system  420 . In one embodiment, the piston  410  may control flow through a dome loaded regulator (not shown) in the hydraulics system  420 .  
         [0032]     Embodiments of the invention offer one or more of the following advantages. Embodiments of the invention having only mechanically actuated components (e.g.  FIG. 1 ) are able to be put in line with already existing equipment to provide a simple apparatus for controlling pressure. Such an embodiment does not require extra power or controls and can be adapted to plug into an already existing pressure line. Further, limiting the use of electronically actuated components is useful for harsher environments. For example, many components for use in the oilfield must be explosion proof (i.e. not provide an ignition source). Mechanically actuated components do not require extra preparation to not provide ignition sources. Embodiments of the invention that only have mechanically actuated components inherently meet this requirement. Additional electrically actuated components used in accordance with some embodiments of the invention may require modifications to meet this requirement.  
         [0033]     While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.