Abstract:
The method of preventing over tension to an umbilical wrapped on the spool of an offshore reel when the umbilical is being normally deployed or retrieved or when the umbilical is unexpectedly pulled from the spool on the reel, comprising providing a main disk, mounting the main disk on the spool of the reel with a slip connection which will be automatically controlled, connecting motor power for the reel to the main disk, connecting brakes to the main disk, such that when the diameter of deployment varies the slip connection torque will be automatically adjusted and prevent the umbilical from being subjected to tension higher than the desired amount.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     N/A 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     N/A 
     INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISK 
     N/A 
     BACKGROUND OF THE INVENTION 
     The field of this invention of that of umbilical reels which store and handle hose and/or electric and/or fiber optic control lines for deepwater offshore service. These reels typically pay out these lines, called umbilicals, and mechanics clamp the umbilical to a drilling riser or other pipe string being run to the seafloor. The actual weight of the umbilical is typically supported once it leaves the reel and in the water by the riser or pipe to which it is clamped. Typically these reel units have to be closely monitored to insure that excessive tension which can destroy the umbilical is not encountered as it is being deployed or in the event of unexpected movement of the riser or pipe to which it is clamped. 
     When the drilling riser or other pipe string is lowered, an operator will rotate the spool to allow umbilical to be paid off in accordance with the downward movement of the riser or pipe. In some cases, the motor can be left in the take up mode, and the umbilical simply be pulled off the spool against a relatively constant torque provided by the motor power. 
     The spool portion of a reel can typically be locked into position by the brakes, the motor, or a manual locking pin. 
     A danger to the umbilical or reel can occur in the event that the drilling riser or other pipe string to which the umbilical is attached is lowered while the reel spool is locked in position. The reel spool can be locked in position because someone forgot to release the locking pin, the brakes are set, or the motor is locked. When this happens, an umbilical worth hundreds of thousands of dollars can be destroyed by the excessive tension and personnel can be injured. 
     Alternately, if the riser and umbilical are being deployed and the air pressure which runs the reel is lost, the failsafe brakes will automatically lock creating a chance that excessive tension will destroy the umbilical before the condition is recognized. 
     A slip clutch has sometimes been added to the reel to allow the spool to turn when a relatively fixed preset tension limit on the umbilical is exceeded. The spool holds several layers of umbilical and as successive layers of umbilical are deployed the spooling diameter decreases and this effect causes the tension on the umbilical to increase because the preset torque remains fixed. As offshore services are required in deeper water the length of umbilical deployed from the reels increases and this causes the diameter differential between a fully loaded spool and a fully deployed spool to increase thus multiplying the maximum tension on the umbilical during deployment. A fixed preset torque which provides a tension of 1,000 pounds on the umbilical when the spool is fully loaded can vary to over 3,000 pounds when the spool is nearly empty. 
     BRIEF SUMMARY OF THE INVENTION 
     The object of this invention is to provide a method for automatically controlling the slipping torque on a motorized offshore reel to provide a constant tension on an umbilical as it is being deployed. 
     A second object of the present invention is to provide a method of counting the revolutions of the spool during the umbilical deployment, determining the current radius to the cable being deployed, and automatically controlling the slipping torque in a fashion to maintain a constant tension limit on the umbilical. 
     A third object of the present invention is to utilize said means for automatically controlling slippage torque to apply maximum torque in an emergency. 
     Another object of the present invention is to provide means to calibrate the slipping torque on the reel in actual field conditions. 
    
    
     
       BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  is a view of a reel of this invention on the deck of a deepwater floating vessel, showing the umbilical clamped to a drilling riser. 
         FIG. 2  is an end view of a reel of this invention. 
         FIG. 3  is a front view of a reel of this invention. 
         FIG. 4  is a section of a slip clutch assembly of this invention. 
         FIG. 5  is a section of a slip clutch assembly with a schematic of the torque adjustment system of this invention. 
         FIG. 6  is a section of a reel of this invention showing the forces and diameters that cause the umbilical tension to vary during deployment. 
         FIG. 7  is a schematic of the motor controller and the motor operating system. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a vessel  1  floating on the ocean  3  and having a drilling riser  5  extending down toward a blowout preventer stack  7 . The blowout preventer stack  7  is landed on a subsea wellhead  9  which is in turn landed on the seafloor  10 . Casing  12  extends into the seafloor below the subsea wellhead  9  for the purpose of drilling an oil or gas well. 
     Reel  14  is positioned on the deck  16  of vessel  1  with umbilical  18  extending over pulley or sheave  20  and going down the side of the riser  5 . Riser  5  is a series of jointed pipes and as they are sequentially connected and lowered into the ocean to lower the blowout preventer stack  7 , clamps  22  secure the umbilical  18  to the drilling riser  5 . The riser  5  and blowout preventer stack  7  may weigh as much as 650,000 lbs. When lowered with the umbilical  18  attached, if the rotation of the reel  14  is stopped, the full 650,000 lb. load can be put on the umbilical, destroying it. An even worse consequence is that the pulley or sheave  20  can be pulled down from its mounting and injure personnel on the deck. 
     Referring now to  FIG. 2 , reel  14  is shown with a frame  30  and a spool  32 . Main disk  34  is shown mounted to the spool  32  by four slip clutch assemblies  36 . As will be seen later, the slip clutch assemblies  36  provide a preset friction grip on the main disk  34  to withstand torque as the spool  32  rotates, but will be allowed to slip if the preset friction grip is exceeded when a large tension on the umbilical  18  is encountered. A slip torque controller  37  is located on the side of the spool  32  which automatically adjusts the control pressure to the slip clutch assemblies  36  as the spool  32  rotates allowing the friction grip on the main disk  34  to vary to maintain a relatively constant slip tension on the umbilical  18  as successive layers of umbilical  18  leave the reel  14  at different distances from the spool  32  centerline. 
     Motor  38  is shown with gear  40  (shown through the motor for clarity) engaging the outer gear profile  42  on the perimeter of main disk  34 . Gear  40  and the outer gear profile  42  are positively engaged such that if the motor  38  does not turn, the main disk  34  cannot rotate. Alternately, the connection between the motor and the main disk can be by roller chain and sprocket profiles, as is well understood in the industry. A motor torque controller  43  is located next to the motor  38  which adjusts the air pressure to the motor  38  as the spool  32  rotates to maintain a relatively constant tension on the umbilical  18  as the umbilical  18  leaves the reel  14 . 
     Brake assemblies  44  and  46  are caliper or disk brake assemblies which are spring loaded to engage when air pressure is released. If the air pressure is released from these brakes, the brakes will close and the main disk  34  will not rotate about the centerline of spool  32 . 
     Spool  32  rotates on main bearings  48 . Panels  50 ,  52 , and  54  provide valves for remote control functions at the end of the umbilical. Levelwind  56 , as will be seen in  FIG. 3 , has gear  58  to receive motive power from the main disk  34  and a manual clutch and handle  59  which allows for adjustment of the wrapping position of the umbilical. 
     Locking pin  60  is engaged in locking pin socket  61  which is fixed to a leg  62  of the reel frame  30 . Locking pockets  62  are provided on the side of spool  32  for engaging locking pin  60  to positively stop the rotation of the spool  32 . When locking pin  60  is an instrumented load pin, it can be engaged and give a positive reading of the torque output of the motor. 
     Locking pin  65  is engaged in locking pin socket  66  which is fixed to the motor mount  67  on the frame  30 . One or more holes  68  are drilled through the main disk  34 . When locking pin  65  is engaged in a hole  68 , the main disk  34  will not rotate. When locking pin  65  is an instrumented load pin, it can be engaged to give a positive reading of the slipping force when the umbilical  18  is pulled, as long as the brakes  44  and  46  are released and the motor  38  is allowed to free wheel. 
     Referring now to  FIG. 3 , levelwind  56  is shown having on a pair of diamond pattern screws  70  and  72  much like on an ordinary fishing reel. Level wind carriage  74  contains rollers  76  for controlling the position of the umbilical  18  (not shown) when it is being reeled in. Spool  32  has side flanges  78  and  79 . 
     Referring now to  FIG. 4 , a slip clutch assembly  36  is shown with brake pads  80  and  82  which will be utilized to friction clamp onto the main disk  34 . Piston  84  cooperates with conical springs  85  to manually preload the brake pad  80  onto the main disk  34 . Main disk  34  is pushed against brake pad  82  and imparts the same load to brake pad  82 . Cylinder head  86  seals the cylinder  87  allowing the piston  84  to be operated. 
     Pressure in pressure port  90  controls the air pressure in chamber  91  to increase the friction load of brake pad  80  onto main disk  34  and therefore of main disk  34  onto brake pad  82 . This allows the friction grip on the main disk  34  to be increased when a higher slipping load is desired. 
     Pressure in pressure port  90  controls the air pressure in chamber  91  to increase the friction load of brake pad  80  onto main disk  34  and therefore of main disk  34  onto brake pad  81 . This allows the friction grip on the main disk  34  to be increased when a higher slipping load is desired. 
     Bolts  92  attach bracket  93  to bracket  94  in a portion in front of and behind the cylinder  87  (not shown). Slots  95  allow for position adjustment of bracket  93  relative to bracket  94  in a first direction. Bolts  96  bolt bracket  94  to the side flange  78  of the spool. Slot  98  allows for adjustment of the slip clutch assembly  36  along the surface of the side flange  78  of the spool generally in a direction 90 degrees to the adjustment allowed by slots  95 . 
     Referring now to  FIG. 5 , is a section of a slip clutch assembly  36  with a schematic of the torque controller  37  system which contains a revolution counter  100 , a computer  102 , a pressure transducer  104 , electric lines  105 , two pressure increase valves  106  and  108 , a vent valve  110 , and an emergency shut down button  112 . The revolution counter  100  can count the spool  32  revolutions by sensing a passing object, sensing gravity or other means. An air storage tank  113  and connecting air lines  114  will be pressurized prior to operations. 
     With specific input information on the diameter of spool  32 , the width of spool  32  and the diameter of umbilical  18 , the row number of the current umbilical being paid off, the number of umbilical wraps on that row, and the desired tension, the computer  102  can calculate the pressure for port  90  required to generate the desired torque. The computer  102  will read the current pressure as indicated on the pressure transducer  104  and compare it to the desired pressure. 
     The computer  102  will then either send an electronic signal to open the vent valve  110  to reduce the pressure in port  90  or pressure increase valve  106  to increase the pressure to match the desire. Alternately, a pressure regulator as is well understood in the industry may be controlled to maintain the desired pressure in port  90  to produce the required torque on the spool  32  to keep the umbilical  18  tension stable. 
     If an emergency occurs and emergency shut down button  112  is pushed, it will lock brake pads  80  and  82  on the main disk  34  by putting pressure into port  88  on therefore on the opposite side of the piston  84 . This will have the air pressure loading adding to the conical spring  85  loading for an increased friction loading on the main disk  34 . 
     Referring now to  FIG. 6 , a section through the reel is generally taken as indicated by section “ 6 - 6 ” on  FIG. 2 . The slip clutch assemblies are indicated as being mounted at a radius  120  from the centerline of the reel. The umbilical  18  is shown to be paid off at a radius  116  on a full reel and at a radius  118  on a near empty reel. The spool  32  is shown to be 21 umbilical wraps wide. The objective is to control the friction grip on the main disk  34  at the radius  120  such that the slip tension on the umbilical  18  will be the same at the full reel radius of  116  or the empty reel radius of  118 . As the radii are different in these situations, the problem is most easily understood in terms of torques about the rotational centerline of the spool. 
     As a real life example, the problem will be demonstrated in terms of a desired umbilical tension of 1000 lbs., an outer radius  116  of 45 inches, and inner radius  118  of 15 inches, a slip clutch assembly radius  120  of 30 inches, area of piston  84  energized by air is 1.5 sq. in. rig air supply will be at least 120 p.s.i., and a sliding coefficient of friction of 0.3. 
     The torque generated by the umbilical on the full reel is 45 inches times 1,000 lbs. or 45,000 in-lbs. The total resisting force on the slip assemblies will be determined by 45,000 in-lbs./30 inches or 1,500 lbs. Sliding friction is calculated by the normal force (perpendicular to the surface) time the coefficient of friction. This means that the total normal force will need to be 1,500 lbs./0.3=5,000 lbs. The normal force is divided up between four slip clutch assemblies with friction on two sides each, so the individual required normal force is 5,000 lbs./8=625 lbs. This means that the conical springs  85  as seen on  FIG. 4  need to be designed to output 625 lbs. in each of the slip assemblies  36 . 
     The torque generated by the umbilical on a nearly empty reel is 15 inches times 1,000 lbs. or 15,000 in-lbs. The total resisting force on the slip assemblies will be determined by 15,000 in-lbs./30 inches or 500 lbs. This means that the total normal force will need to be 500 lbs./0.3=1,666 lbs. So the individual required normal force is 1,666 lbs./8=208 lbs. As the conical springs  85  as seen on  FIG. 4  are designed to output 625 lbs. in each of the slip assemblies  36 , 625−208 or 417 lbs. need to be relieved from the slip assemblies  36 . As the piston area is 4.00 sq. in and the rig air supply is 120 p.s.i., 4.00 sq. in. times 120 p.s.i.=480 lbs. is available and so is sufficient. The computer will calculate 417 lbs./4.00 sq. in.=104.25 p.s.i. as required and direct pressure increase valve  106  to increase to that pressure or vent valve  110  to vent until the pressure is reduced to that level. 
     The reel is shown with 9 wraps presently on the outer layer. It will start with zero pressure in port  88  and  90 , and then after 9 revolutions of the reel it will increase the pressure in port  88  slightly to compensate for the slight smaller radius on the second layer of umbilical wraps. Twenty one wraps later, it will adjust again as it goes to the next layer. 
     A similar process happens on the motor torque controller  43 , except that it must sense the rotation of the spool  32  from its stationary position on the frame. Based on its determination of the current level of the umbilical on the spool  32 , it will adjust the pressure supplied to the motor to give a constant tension on the cable at a lower value than the slip tension, i.e. 750 lbs. 
     In this way the slip tension and motor tension can be at a desired constant value which are relatively close to one another for maximum equipment and personnel safety. 
     Referring now to  FIG. 7 , motor torque controller  43  is shown with computer  130 , revolution counter  132 , pressure increasing valve  134 , pressure reducing valve  136  and pressure transmitter  138 . Air is supplied to motor torque controller  43  through line  140  and an output signal  142  is sent to the dome regulator  144  to control the pressure sent to the main control valve  146  which in turn sends the signals to motor  38 . Manual valve  148  is used to shift the main control valve to change the direction of the motor. 
     The particular embodiments disclosed above are illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the invention. Accordingly, the protection sought herein is as set forth in the claims below.