Abstract:
The level winding system described has a storage reel, a knuckle boom and a roller guide head for control the winding and unwinding of coiled tubing from the storage reel. The knuckle boom has a crane attached to a rotatable, elevatable, and extendible boom with an attached roller guide head. The described level winding system is easy to control, robust, very adaptable to different rig geometries and tubing sizes, and easy to maintain.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]    The present application, pursuant to 35 U.S.C. 111(b), claims the benefit of the earlier filing date of provisional application Serial No. 60/303,184 filed Jul. 5, 2001, and entitled “Coiled Tubing Level Wind System.” 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates to the level winding on a reel of coiled tubing for use in drilling, production, and servicing of wells used for production of petroleum products. The invention is used to ensure that the tubing is stored on the reel in a manner, which will cause it to lie on the reel in a compact pattern and unspool without risk of binding.  
         BACKGROUND OF THE INVENTION  
         [0003]    When continuous coiled tubing is to be used in a well as a service tubing string, a production string, or a drill string, it must be taken from a reel, forced into the well, manipulated, withdrawn from the well, and stored back on its reel. Tractive means, commonly termed coiled tubing injectors, are used to force the tubing into or out of the wellhead. The tubing is generally under relatively low tension between the tractive means and the storage reel. When the tubing is respooled onto a reel located close to the tractive means, level winding is essential to ensure that the tubing will load densely onto the reel. Additionally, level winding prevents unstable local stack-ups of tubing, which can result in binding of the tubing when it is pulled from the reel. Lastly, level winding minimizes the tendency to overstress and dent or kink tubing where it crosses a lower layer of tubing at a large angle.  
           [0004]    To date, four basic types of level winding schemes have been used for coiled tubing. The first and most common type utilizes a ball reverser or similar pawl-type reverser which has a shaft with two intersecting coaxial grooves, one being right-handed and the other being left-handed, cojoined at both opposed travel limits by turnaround sections. A swiveling tracking pawl or a special ball nut constrained to follow a separate linear track parallel to and offset from the shaft axis is used as a follower to follow the path of the rotating shaft. See for example the 1997 Flennor Division of Norco, Inc. Catalog “Ball Reverser”. A tubing guide, typically with rollers constraining the tubing on three or four sides, is mounted to the follower to compel the tubing to follow the track of the follower. While the reverser shaft is rotated in a fixed ratio to the turns of the drum, the nut or tracking pawl is caused to reciprocate on its linear track. The turnarounds for the reverser are typically located slightly inside of the flanges of the take-up reel. This type of system is offered by Hydrarig, Inc. of Fort Worth, Tex. and others. In some cases, an independently controlled hydraulic cylinder is used to displace the tubing guide relative to the follower so that control of the winding can be varied as necessary with the different tubing sizes and attendant bending stiffness variations. Level wind systems using reversers are generally expensive and easily damaged. Additionally, because they are directly driven, the drive ratio between the reel and the reverser shaft must be changed for each size of tubing, which is used on the reel.  
           [0005]    A second type of level winding system for coiled tubing rigs is shown in Gipson U.S. Pat. No. 4,673,035 and used by Precision Drilling, Inc. of Brady, Tex. For this system, the entire reel is reciprocated by means of one or more hydraulic cylinders in the direction of the rotational axis of the reel to effect level winding.  
           [0006]    A third type of reciprocating device, offered by Amacoil, Inc. of Aston, Pa. is used for certain level winds outside of the coiled tubing industry. This device utilizes rings mounted in a linearly reciprocable follower, which bear on and are rotated by a smooth cylindrical shaft. The Model RG, shown in the “Amacoil/Uhing Linear Actuators” 2001 Catalog, rotates the shaft in a manner similar to that used by ball reversers. Means is provided for controlling the pitch for the device by altering the axial orientation of the follower rollers relative to the smooth shaft axis. A reverser mechanism triggered by abutment contact at either end of the travel is provided with the Model RG reciprocator. While this device might be satisfactory for the smallest sizes of coiled tubing, the forces deliverable by the device appear to be insufficient for use with the largest sizes of coiled tubing. Additionally, the pitch of the rings must be very carefully set in order to obtain accurate reciprocation whenever the tubing size is changed.  
           [0007]    A fourth type of level wind device uses guide rollers reciprocated by either a hydraulic cylinder or a screw/nut combination driven by a rotary motor. Alternately, a linear electric motor could be used for cases when only limited forces are required. Several types of variants of this type of device have been developed for use with pipe reel barges and for other level wind applications. The earliest systems utilized direct manual control of the reciprocation. Direct mechanical control of switches or hydraulic valves was used for older automatic systems to reverse the direction of the traveler. Newer systems can use preprogrammed electronic controls either with or without feedback sensors. These systems require separate support structures, protection from mechanical damage, and for electronic systems, protection from lightning damage.  
           [0008]    Thus, a need exists for a simpler level winding system with enhanced flexibility to permit it to better control the winding for large ranges of reel core diameters and outer diameters and tubing sizes.  
         SUMMARY OF THE INVENTION  
         [0009]    The invention contemplates improved flexibility of the level winding system to permit it to better control the winding for large ranges of reel core diameters and outer diameters and tubing sizes. The present invention avoids some of the disadvantages of the level wind means discussed above by adapting an inexpensive small crane included with the coiled tubing rig to serve as a level wind device. This new means is easy to control, robust, very adaptable to different rig geometries and tubing sizes, and easy to maintain.  
           [0010]    One aspect of the invention is a level winding rotationally mounted and axially extensible knuckle boom for use with a coiled tubing injector, the knuckle boom comprising (a) slewing means for controllably slewing about a vertical axis; (b) elevating means for controllably elevating and lowering the boom; (c) extension means for controllably extending and retracting the boom; and (d) guide roller means for guiding a tubing during the tubing winding or unwinding onto or off of a storage reel, said guide roller means mounted on an outer end of said boom; whereby the boom is selectably controlled so that the tubing alignment is controlled by the roller guide means as the tubing is wound or unwound onto or off of the storage reel.  
           [0011]    Another aspect of the present invention is A level winding system for use with a coiled tubing injector unit comprising (a) a tubing storage reel; (b) a crane having a boom, said crane comprising a rotating element for controllably rotating the boom about a vertical axis, a hydraulic cylinder for controllably elevating and lowering the boom, and an extension element for controllably extending and retracting the boom; and (c) a guide roller element for guiding a tubing during the tubing winding or unwinding onto or off of the tubing storage reel, said guide roller element mounted on an outer end of said boom and comprising a roller bracket, a horizontal roller and an opposed pair of substantially parallel orthogonal rollers, wherein the axes of the orthogonal rollers are substantially perpendicular to the axis of the horizontal roller; whereby the roller guide element is positioned by the crane and the boom as the roller guide element guides the tubing onto or off of the storage reel.  
           [0012]    Yet another aspect of the present invention is a level winding system comprising a reel holding a coiled tubing, said tubing wound and unwound from the reel by the level winding system; a roller guide head proximal to the reel and comprising multiple rollers, said rollers partially or fully surround the tubing to partially constrain the lateral movement of the tubing; and roller guide head manipulation element comprising a crane, a plurality of crane actuators and a crane control device.  
           [0013]    The foregoing has outlined rather broadly several aspects of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and the specific embodiment disclosed might be readily utilized as a basis for modifying or redesigning the structures for carrying out the same purposes as the invention. It should be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    The novel features which are believed to be characteristic of the invention, both as to its organization and methods of operation, together with the objects and advantages thereof, will be better understood from the following description taken in conjunction with the accompanying drawings, wherein:  
         [0015]    [0015]FIG. 1 is an oblique view of a coiled tubing rig reel using the level wind system of this invention in the process of level winding;  
         [0016]    [0016]FIG. 2 shows a side profile view of the reel and the level wind system if FIG. 1 with the boom extended fully for controlling the outer wraps on the reel;  
         [0017]    [0017]FIG. 3 illustrates a side view of the level wind system of FIG. 2, but with the boom retracted;  
         [0018]    [0018]FIG. 4 is an oblique view of a partial longitudinal vertical cross-section of the level wind system of FIG. 3 showing the internals of the boom extension means  
         [0019]    [0019]FIG. 5 shows an oblique view of the guide head with its rollers for contacting and urging the coiled tubing into the desired alignment;  
         [0020]    [0020]FIG. 6 is a longitudinal vertical section through the middle of the boom of FIG. 3;  
         [0021]    [0021]FIG. 7 shows an oblique view of an alternate guide head with rollers for contacting and urging the coiled tubing on all sides;  
         [0022]    [0022]FIG. 8 shows a simple manually controlled hydraulic circuit for controlling the operation of the level winding of the coiled tubing; and  
         [0023]    [0023]FIG. 9 shows an oblique view of an alternate guide head with rollers for contacting and urging the coiled tubing on all sides.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0024]    The present invention provides an adaptation of a small hydraulic slewing crane having an extendable and elevatable boom configured to guide the coiled tubing of a coiled tubing service rig onto and off of a storage reel for deployment in a well. This guiding operation is termed level winding, since it involves laying the tubing in smooth, uniform layers on the reel so that the tubing is stored compactly, without overstress at the tubing crossings, and without risk of tubing binding during unreeling.  
         [0025]    Referring now to the drawings, and initially to FIGS. 1 and 2, it is pointed out that like reference characters designate like or similar parts throughout the drawings. The Figures, or drawings, are not intended to be to scale. For example, purely for the sake of greater clarity in the drawings, wall thickness and spacing are not dimensioned as they actually exist in the assembled embodiment.  
         [0026]    [0026]FIGS. 1 and 2 show the elements of the tubing storage assembly  10  of a coiled tubing rig in their relative operating positions, but without the mounting base or trailer and without the injector. The coiled tubing rig is not shown for the sake of clarity. The level wind mechanism of this invention is applicable to a variety of rig arrangements, such as those shown in Butler U.S. Pat. No. 5,937,943 or Andreychuk U.S. Pat. No. 6,003,598. The horizontal axis reel  11  holds a supply of continuous, reeled-up coiled tubing  12 , the entering portion  13  of which is shown extending upwardly to an unshown injector assembly. Located in close proximity to the reel  11  on rig deck  14  is the level wind unit  15 . Level wind unit  15  consists of a hydraulic slewing crane  16  supporting a roller guide head  80 . The vertical pedestal  17  of crane  16  is positioned on the rig deck  14  and/or crossbeams of the rig foundation in the midplane between the vertical flanges of reel  11  and close enough to the reel periphery so that it can extend roller guide head  80  over the reel.  
         [0027]    Pedestal  17 , shown in FIG. 3, is a vertical hollow tube having a bottom transverse flange  18  suitable for welding or bolting to deck  14  and an upper gusseted transverse flange  19  which supports large diameter high moment capacity slewing bearing  22 . Slewing bearing  22  shown in FIG. 4, which is annular and of ball or roller construction, is bolted on its outer race flange to flange  19  with bolts  23 . The inner race flange of bearing  22  is bolted to slewing head  26 .  
         [0028]    Slewing head  26  consists of core tube  27 , integral upper transverse flange  28 , boom bracket  29 , and elevating cylinder bracket  37 . Core tube  27  extends downwardly a short distance below the level of rig deck  14 . The inner race flange of slewing bearing  22  is bolted to the lower side of flange  28  to support slewing head  26  so that it can be pivoted about its vertical axis. Boom bracket  29  consists of two identical boom pin plates  30  which are welded perpendicular to the horizontal upper surface of flange  28  parallel and symmetrically spaced apart from the vertical axis of slewing head  26 . A pin hole  32  extends through each boom pin plate  30  to support coaxial boom hinge pin  33 . Transverse stiffener plate  34  is welded to both the boom pin plates  30  and the flange  28  to strengthen and rigidize boom bracket  29 . Elevating cylinder bracket  37  consists of two identical parallel symmetrically spaced apart cylinder bracket plates  38  on the forward side of boom bracket  29 . Cylinder bracket plates  38  are welded both to flange  28  and plate  34  and have elevating cylinder pin holes  39  for mounting coaxial first elevating cylinder pin  40 .  
         [0029]    At the lower end of core tube  27  of slewing head  26  is the rotator assembly  45 . The rotator assembly consists of two horizontal parallel but opposed hydraulic cylinders  46  having mounting eyes both on the rod end and on the cylinder end. Each cylinder end eye is connected to the unshown rig frame at fixed cylinder axis  47  by a pin (unshown), while cylinder rod end pins  48  are mounted in the rod end eyes and thereby are connected to eccentric arms  49 . Each of the two eccentric arms  49  is formed of a semicylindrical half collar having opposed projecting ears, which are in a vertical plane slightly offset to the half collar side from the vertical diametral plane. The inner diameter of the half collars is that of the core tube  27 . One or more through holes in each ear permit clamping the eccentric arms to the lower end of core tube  27  of slewing head  26  with bolts  50  connecting the two eccentric arms  49 . Radially projecting outwardly from each half collar is a horizontal plate welded to the half collar and having at its outward end a vertical axis pin hole through which the cylinder rod end pins  48  are engaged.  
         [0030]    The boom assembly  55  is mounted to the boom bracket  29  of the slewing head  26 . Boom assembly  55  consists of boom socket tube  56 , boom middle tube  75 , and boom inner tube  76 . Boom socket tube  56  is a substantially rectangular steel tube having radiused edges between the flats of the tube and one end closed by a bolted-on end plate. Two identical reinforcing cheek plates having horizontal axis boom pivot eye holes  57  are symmetrically welded to the sides of the boom socket tube  56  near the closed end. Boom pivot eye holes  57  are located on the lower side of boom socket tube  56  and horizontal boom hinge pin  33  engaged with holes  57  connects the boom socket tube to slewing head  26 . On the underside of boom socket tube  56  further outward from the location of boom pivot eye holes  57  in the direction away from the closed end of tube  56  is boom elevator bracket  58 . Boom elevator bracket  58  consists of two identical parallel vertical plates having horizontal axis boom elevator bracket eye  59  through pin holes symmetrically welded to the bottom of tube  56 . Hydraulic boom elevator cylinder  60  is connected through a horizontal eye on the back end of cylinder  60  to elevating cylinder bracket  37  by means of first elevating cylinder pin  40 . Cylinder  60  is connected to boom elevator bracket  58  at its rod end by boom elevator cylinder rod end pin  61  which also passes through elevator bracket eye  59 . Adjacent the closed end of boom socket tube  56  are horizontal axis extension cylinder mounting eyes  62  which penetrate concentrically through the vertical sides of tube  56 . Boom extension cylinder  65  is mounted inside boom socket tube  56  by means of pinning boom extension cylinder rod end eye  66  to eyes  62  by means of boom extension cylinder rod end pivot pin  67 . The cylinder end of boom extension cylinder  65  is fitted with horizontal boom extension cylinder outer end pivot eye  68  and inserted outer end pivot pin  69 .  
         [0031]    As shown in FIG. 6, boom middle tube  75  and boom inner tube  76  are also constructed of rectangular cross-section steel tubes similar to that used for boom socket tube  56 . However, boom middle tube  75  is selected to be a close sliding fit to the interior of socket tube  56 , and boom inner tube  76  is similarly chosen to be a close sliding fit to the interior of middle tube  75 . The outer end of boom inner tube  76  has a transverse plate outer end mounting flange  77  welded onto the tube. Mounting flange  77 , which has multiple drilled and tapped mounting holes in its face, does not project beyond the outer periphery of tube  76 . Close to the outer end of inner tube  76  at midheight in the vertical tube walls are horizontal coaxial cylinder mount eyes which are engaged by boom extension cylinder outer end pivot pin  69  so that the boom extension cylinder  65  is thereby attached.  
         [0032]    Roller guide head  80 , shown in FIG. 5, projects outwardly from the outer end of boom inner tube  76 . Roller guide head  80  consists of roller bracket  81  and a set of rollers  84  and  86  mounted thereto. Roller bracket  81  has back plate  82  which has two mirror image trapezoidal side plates  83  symmetrically spaced apart from the middle of back plate  81  and welded perpendicular to plate  82 . Back plate  82  has multiple bolt holes in a pattern corresponding to that on the outer end mounting flange  77  of inner tube  76 . The outer tip of each of trapezoidal side plates  83  has an inwardly projecting tab which is parallel to back plate  82  and has a central through hole normal to back plate  82 . Drilled and tapped into back plate  82  and coaxial with the through hole in the tab of each side plate  83  are two side roller shaft mount holes. Identically offset from the back plate and parallel to it are two horizontal roller shaft mount holes near the comers of side plates  83  adjacent back plate  82 . The horizontal roller shaft mount holes of one side plate  83  are tapped. Two horizontal axis rollers  84  and two side rollers  86  are each mounted to roller bracket  81  by a coaxial horizontal roller shaft  85  and side roller shaft  87 , respectively. The roller shafts  85  and  87  have hex heads, long cylindrical shanks, and threaded tips which may be threadedly engaged in the tapped holes in roller bracket  81 . Rollers  84  and  86  typically are provided with internal roller bearings at each end which are supported by shafts  85  and  87 . The rollers  84  and  86  may be coated with rubber or other coatings which will distribute any load applied to the tubing passing over the rollers and thereby avoid permanently distorting the tubing. Roller bracket  81  is attached to outer end mounting flange  77  of inner tube  76  by multiple mounting bolts passing through the mounting bolt holes of back plate  82  and threadedly engaged in the tapped holes in the flange  77 .  
         [0033]    Referring to FIG. 8, the simple manually controlled hydraulic system  89  for manipulating the crane as a level winding mechanism is shown. Pump  90 , typically a small piston pump, draws hydraulic fluid from tank  91 . The output from pump  90  flows to a tee connection, where one leg supplies the control valves and cylinders and the other goes to a system relief valve  92 . System relief valve  92  avoids dead-heading of the pump and the consequent damage. Boom elevator cylinder  60  is controlled by control valve  93  and the combination of check valve  94  and piloted relief valve  95 . The combination of check valve  94  and piloted relief valve  95  are located on the piston side flow line of cylinder  60  to function as a cylinder lock valve to avoid release of the load due to external leaks or internal leaks in control valve  93 . The piston side of boom elevator cylinder  60  is the side loaded by the weight and other vertical load components of the boom. Control valve  93  is a three-position, four-way, spring-centered, manually operated valve with the cylinder ports blocked and the pressure directed to tank  91  in the center position. Slewing cylinders  46  are run in parallel and are controlled by control valve  99 , which is identical to control valve  93 . Boom extension cylinder  65  is controlled by control valve  105  and the combination of check valve  106  and piloted relief  107 . Valves  105 ,  106 , and  107  are respectively identical to valves  93 ,  94 , and  95  in construction and operation. The combination of check valve  106  and piloted relief valve  107  are located on the piston side flow line of cylinder  65  to function as a cylinder lock valve to avoid release of the load due to external leaks or internal leaks in control valve  105 . The piston side of boom extension cylinder  65  is the side loaded by the weight and other axial load components of the boom.  
         [0034]    Alternate roller guide head  200 , shown in FIG. 7, is substantially the same as roller guide head  80 , but with the addition of an additional outside roller for ensuring that the tubing cannot jump out of the guide head due to erratic reel or injector operation. Alternate roller guide head  200  projects outwardly from the outer end of boom inner tube  76 . Alternate roller guide head  200  consists of roller bracket  201  and a set of rollers  204 ,  206 , and  208  mounted thereto. Roller bracket  201  has back plate  202  which has two mirror image side plates  203  symmetrically spaced apart from the middle of back plate  201  and welded perpendicular to back plate  202 . Back plate  202 , which is identical to back plate  82  of roller guide head  80 , has multiple bolt holes in a pattern corresponding to that on the outer end mounting flange  77  of inner tube  76 . The side plates  203  are similar to those of roller guide head  80 , but onto their basic trapezoidal profile on the outer side an ear is extended coplanar with the side plate and parallel to bottom plate  202 . The outer tip of each of trapezoidal side plates  203  has an inwardly projecting tab which is parallel to back plate  202  and has a central through hole normal to back plate  202 . Drilled and tapped into back plate  202  and coaxial with the through hole in the tab of each side plate  203  are two side roller shaft mount holes. Identically offset from the back plate and parallel to it are two horizontal roller shaft mount holes near the corners of side plates  203  adjacent back plate  202 . The projecting coplanar ears near the outer end of side plates  203  have central horizontal axis holes for the mounting of a horizontal axis keeper roller. The horizontal roller shaft mount holes and the keeper roller shaft mount holes of one side plate  203  are tapped. Two horizontal axis rollers  204 , two side rollers  206 , and outside keeper roller  208  are each mounted to roller bracket  201  by a coaxial horizontal roller shaft. Horizontal roller shafts  205  are used for both horizontal rollers  204  and outside keeper roller  208 , while side roller shafts  207  are used for side rollers  206 . The roller shafts  205  and  207  have hex heads, long cylindrical shanks, and threaded tips which may be threadedly engaged in the tapped holes in roller bracket  201 . Rollers  204 ,  206 , and  208  typically are provided with internal roller bearings at each end which are supported by shafts  205  and  207 . The rollers  204 ,  206 , and  208  may be coated with rubber or other coatings which will distribute any load applied to the tubing passing over the rollers and thereby avoid permanently distorting the tubing. Roller bracket  201  is attached to outer end mounting flange  77  of inner tube  76  by multiple mounting bolts  88  passing through the mounting bolt holes of back plate  82  and threadedly engaged in the tapped holes in the flange  77 .  
         [0035]    [0035]FIG. 9 shows a second alternative roller guide  300 , which may be used in place of either roller guide  80  or  200 . Roller guide head  300  consists of a frame  302 , which is made by bending a rectangular steel plate into a symmetrical vee with an included angle of approximately 90° to 135°. Frame  302  is mounted symmetrically on the outer end of the boom inner tube  303 . Boom inner tube  303  is similar to boom inner tube  76 , but does not have the transverse flange at its outer end. First roller  305 a has interior roller bearings corresponding to those of the rollers in the other embodiments and is mounted by first roller pedestal  306  and second roller pedestal  307 , which are supported on frame  302 . Shaft  308  is supported in pedestals  306  and  307  and serves to mount roller  305   a.  First roller  305   a  is parallel to one interior side of the vee of frame  302 , while second roller  305   b  is similarly supported by its respective first and second roller pedestals  306  and  307  and shaft  308 , but second roller  305   b  is mounted on the other interior face of the vee. Keeper roller  312  is constructed similarly to rollers  305   a,b,  but is typically slightly longer than rollers  305   a,b.  Keeper roller  312  is mounted at the outer tips of the vee by its roller pedestals  306  and a keeper roller shaft  313 . The roller configuration of the roller guide embodiment  300  thus forms a triangular guide for tubing  301  passing through the roller guide.  
         [0036]    Operation of the Invention:  
         [0037]    The operation of this invention is described herein for the reeling in of the coiled tubing when the level winding is critical. Level winding is less critical for unreeling and in some cases may be avoided for unreeling.  
         [0038]    The crane  16  is rotated about its vertical axis in the center of its pedestal  17  in the following manner. The slewing control valve  99  for the rotator cylinders  46  is shifted so that, for rotation which is counterclockwise when viewed downwardly, hydraulic fluid from pump  90  is applied to the piston side of the cylinders, causing the rod to extend and fluid from the rod end to return to tank  91  through the return port of valve  99 . For clockwise motion, the control valve  99  is shifted so that fluid is applied to the rod side of the cylinders, causing the rod to retract and fluid from the piston end of cylinders  46  to return to tank  91  through the return port of valve  99 . The forces and motion applied to the rod are reacted against by the rig structure through the pins joining cylinders  46  to the rig structure at fixed cylinder axes  47 . The rod force is transferred to the eccentric arms  49  through the cylinder rod end pins  48  and thence to the lower end of the core tube  27  of slewing head  26  by means of friction induced between the half collars of the eccentric arms and the core tube by the clamping action of clamp bolts  50 . Since the rod forces acting on core tube  27  are of equal magnitude but opposite direction and are eccentric from the vertical axis of the crane  16 , a pure force couple is induced on core tube  27  and the boom assembly  55 . A minor portion of this couple will be expended to overcome friction and to overcome inertia if moving. However, most of this couple will result in lateral forces being applied to the coiled tubing  13  by one of the side rollers  86  of the roller guide head  80 . These lateral forces provide the primary guidance for ensuring that the tubing is laid in uniformly on the reel during rewinding.  
         [0039]    The boom assembly  55  of crane  16 , which is pivoted about boom hinge pin  33  mounted in the boom mounting pin hole of slewing head  26  and engaged in boom pivot eye  57  of the boom socket tube  56 , is caused to raise or lower in the following manner. The boom elevation control valve  93  for the boom elevator cylinder  60  is shifted to cause fluid from pump  90  to be applied to the piston side of the cylinder to extend the rod and raise the boom. The static cylinder end of boom elevator cylinder  60  reacts on the elevating cylinder bracket  37  through first elevating cylinder pin  40  while the rod end of the cylinder reacts on boom elevator bracket  58  of boom socket tube  56  of boom assembly  55  through boom elevator cylinder rod end pin  64 . The weight of boom assembly  55  and any loads applied to the horizontal axis rollers  84  of roller guide head  80  by the tubing  13  are reacted against by the boom elevator cylinder  60  and the boom hinge pin  33 . By raising the boom sufficiently, the horizontal rollers  84  can exert a normal force on the tubing causing it to be lifted, if necessary.  
         [0040]    The boom assembly  55  can be extended or retracted in the following manner. The boom extension control valve  105  is shifted to cause hydraulic fluid from pump  90  to be applied to the piston side of the boom extension cylinder  65  to extend the boom. As this is happening, the fluid from the rod side of cylinder  65  is returned to tank  91  through the return ports of valve  105 . The fluid entering the piston end of cylinder  65  freely passes through check valve  106 . To retract the boom, the boom extension control valve is shifted to cause fluid from pump  90  to be applied to the rod side of the cylinder  65  to cause the rod to retract and retract the boom. The fluid on the piston side of cylinder  65  is permitted to outflow from the cylinder when the pressure applied to the rod side of the cylinder. The pilot operated relief valve  107  opens so that the return flow can pass to tank  91  through the return port of valve  105 . The rod end of the boom extension cylinder  65  reacts against boom extension cylinder mounting  62  of boom socket tube  56  through boom extension cylinder rod end pivot pin  67  and boom cylinder rod end eye  66 . The cylinder end of boom extension cylinder  65  reacts against the boom inner tube  76  through boom extension cylinder outer end pivot pin  69  engaged in cylinder mount eyes of boom inner tube  76  and boom extension cylinder outer end pivot eye  68 . The loads on the boom extension cylinder are primarily friction and the axial component of the weight vector, but in some cases, tubing  13  reactions on the horizontal axis rollers  84  also impact the cylinder loads.  
         [0041]    The following description describes the operation of the level winder during rewinding. If the tubing  13  is not already fed through the roller guide head  80 , then that is done after the roller guide head  80  or  200  is aligned with the desired starting position of the tubing on the reel  11 . Alternate roller guide head  200  functions identically to roller guide head  80 , but the outside keeper roller  208  is only mounted after the tubing  13  is positioned between the other rollers. The keeper roller functions to ensure that tubing  13  cannot disengage from the roller guide head. Alignment of the roller guide head  80  or  200  involves the following steps. First, the boom assembly  55  is elevated sufficiently to ensure clearance above the reel and then the boom is extended outwardly to locate it properly above and ahead of the winding surface of the current tubing layer. The boom and roller guide head must always be clear of the flanges of reel  11 . Some care is necessary, since the bending strength in the tubing and the residual bending stresses resulting from its passage through the overbend between the wellhead and the reel cause the tubing to follow a curved path, even under tension. As the reel  11  is rotated, drawing tubing  13  onto its drum surface or the surface of the tubing  12  which is already spooled, the boom assembly  55  is continuously slewed with a slight lag to cause a side roller  86  to bear on the tubing  13  near the touchdown point on the reel. This force applied by the side roller and controlled by the slewing of the boom in turn causes tubing  13  to bear against the last turn laid on the reel. When a side flange of the reel  11  is reached, it is necessary for the slewing action to be halted until the tubing  13  climbs on top of the previous layer, thereby beginning a new layer. After the first tubing wrap on the new layer is complete, the slewing is reversed in direction and, slightly lagging to ensure tight packing of the wraps in the layer, proceeds toward the opposite flange. In general, it is advisable to avoid exerting much force or to exert no force on the tubing  13  with the horizontal axis rollers  84 , as this lateral force could excessively work the tubing and thereby shorten its fatigue life. Similarly, if alternate roller guide head  200  is used, the outside keeper roller should only contact the tubing in the event of the tubing trying to lift out of the roller guide head.  
         [0042]    The control of the three hydraulic valves operating the crane  16  readily can be done manually, or the controls could be computerized with proportional solenoid valves replacing control valves  93 ,  99 , and  105  and with a prerecorded pattern for each tubing size. In order to properly spool the tubing automatically, at a minimum a footage sensor and/or a reel turn count sensor would be required. Roller load sensors might also be required. Typically, any automatic control system would be provided with manual overrides. Generally, the slewing adjustments are made much more than those for boom extension or boom elevation.  
         [0043]    The advantages of this invention accrue from the inexpensive, reliable construction of the crane and its simple, insensitive manual control. If automatic control is desired, it too can be made relatively simple and inexpensive. The maintenance of the crane is simple, inexpensive, and uses commonly available parts. An additional advantage of this invention is that the crane also may be utilized for lifting purposes by either replacing the roller guide head or providing separate lifting means with a permanently mounted roller guide head.  
         [0044]    As will be understood readily by those skilled in the art, various changes in the configuration of this invention can be made without departing from the spirit of the invention. For example, a single cylinder could slew the boom using a chain with idler sprockets and a double-ended cylinder. Similarly, a hydraulic motor could be used to slew the crane. Likewise, other ways of extending or elevating the boom could be utilized, as will be recognized easily by those skilled in the art. These modifications do not constitute a departure from the spirit of this invention.