Abstract:
Apparatus and method are provided for connecting electrical power for heating subsea pipelines after the pipeline is deployed. Electrical connections may be made subsea using wet-mateable connectors. The electrical power may be supplied from a boat or may be supplied from a host structure. A Remotely Operated Vehicle may be used to make the subsea electrical connections. Single Heated Insulated Pipes, Pipe-in-Pipe, heat tracing and other configurations for heating may be employed. The deployment of cables and other equipment for heating may be delayed until a need or potential need for heating or the probable locations of impediments to flow are identified in the subsea pipeline.

Description:
This application is a continuation in part of Ser. No. 08/921,737, filed Aug. 27, 1999, now U.S. Pat. No. 6,142,707. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to electrical heating of subsea pipelines. More particularly the invention relates to making subsea pipelines ready for electrical heating, such that electrical power can be applied to a selected segment of a pipeline after deployment and when heating is needed. 
     2. Description of Related Art 
     Offshore hydrocarbon recovery operations are increasingly moving into deeper water and more remote locations. Often satellite wells are completed at the sea floor and are tied to remote platforms or other facilities through extended subsea pipelines. Some of these pipelines extend through water that is thousands of feet deep and where temperatures of the water near the sea floor are in the range of 40° F. The hydrocarbon fluids, usually produced along with some water, reach the sea floor at much higher temperatures, characteristic of depths thousands of feet below the sea floor. When the hydrocarbon fluids and any water present begin to cool, phenomena occur that may significantly affect flow of the fluids through the pipelines. Some crude oils become very viscous or deposit paraffin when the temperature of the oil drops, making the oil practically not flowable. Hydrocarbon gas under pressure combines with water at reduced temperatures to form a solid material, called a “hydrate.” Hydrates can plug pipelines and the plugs are very difficult to remove. In deep water, conventional methods of depressurizing the flow line to remove a hydrate plug may not be effective. Higher pressures in the line and uneven sea floor topography require excessive time and may create more operational problems and be costly in terms of lost production. 
     The problem of lower temperatures in subsea pipelines has been addressed by placing thermal insulation on the lines, but the length of some pipelines makes thermal insulation alone ineffective. Increased flow rate through the lines also helps to minimize temperature loss of the fluids, but flow rate varies and is limited by other factors. Problems of heat loss from a pipeline increase late in the life of a hydrocarbon reservoir because production rates often decline at that time. Problems become particularly acute when a pipeline must be shut-in for an extended period of time. This may occur, for example, because of work on the wells or on facilities receiving fluids from the pipeline. The cost of thermal insulation alone to prevent excessive cooling of the lines becomes prohibitive under these conditions. 
     Heating of pipelines by bundling the lines with a separate pipeline that can be heated by circulation of hot fluids has been long practiced in the industry. Also, heating by a variety of electrical methods has been known. Most of the proposals for electrical heating of pipelines have related to pipelines on land, but in recent years industry has investigated a variety of methods for electrical heating of subsea pipelines. (“Direct Impedance Heating of Deepwater Flowlines,” OTC 11037, May, 1999.) Previously developed apparatus included “Combipipe,” which employs electrical conductors in the insulation layer of a pipe, (“Heating of Pipelines, and Power Supply to Subsea Electrical Equipment,” DOT, 1995) and heat tracing, which employs a conductor inside a heat tube in the vicinity of the pipeline (“A New Method for Heat Tracing Long Pipelines,” ASME 74-Pet-35, 1974). 
     Two configurations for electrical heating have been particularly considered in recent years. In one configuration, a single flowline is electrically insulated and current flows along the flowline. This is called the “SHIP” system (Single Heated Insulated Pipe). Two SHIP systems have been considered: the fully insulated system, requiring complete electrical insulation of the flowline from the seawater, and the earthed-current system, requiring electrical connection with the seawater through anodes or other means. For both systems, current is passed through the flowline pipe. A fully insulated method of electrically heating a pipeline is disclosed in U.S. Pat. No. 6,049,657. In this method, an electrically insulated coating covers a single pipeline carrying fluids from a well. An alternating current is fed to one end of the pipeline through a first insulating joint near the source of electrical current and the current is grounded to seawater at the opposite end of the pipe through a second insulating joint. 
     In a second configuration for electrical heating, a pipe-in-pipe subsea pipeline is provided by which a flow line for transporting well fluids is the inner pipe and it is surrounded concentrically by and electrically insulated from an electrically conductive outer pipe until the two pipes are electrically connected at one end. Voltage may be applied between the inner and outer pipes at the opposite end and electrical current flows along the exterior surface of the inner pipe and along the interior surface of the outer pipe. This pipe-in-pipe method of heating is disclosed, for example, in Ser. No. 08/921,737, filed Aug. 11, 1999, which is commonly assigned and hereby incorporated by reference herein. A center-fed pipe-in-pipe configuration is disclosed in the commonly assigned application titled “Electrical Heating of Pipelines with Pipe-in-Pipe and Mid-Line Connector,” filed concurrently herewith and hereby incorporated by reference herein. 
     In all the configurations for electrical heating, it will often not be necessary to supply power to the pipeline continuously. In fact, heating may not be needed until years after a pipeline is deployed. For example, heating may only be needed with the production rate from an oil or gas field has declined, such that the fluids cool more in moving through a pipeline. A temporary interruption in flow through a pipeline may cause the need for heating, but after a plug has been removed there will be no need for heating. Also, only segments of the pipeline may require heating at any time—where plugging has occurred or where it is considered more likely. Installation of electrical cables or other facilities for heating a subsea pipeline requires significant capital expenditures. It will be advantageous to delay as many of these expenditures as long as possible. Therefore, there is a need to install subsea pipelines that can be heated only when the heating is required for optimum operation of the pipeline system. Such pipelines will be referred to as “electrically ready.” 
     SUMMARY OF THE INVENTION 
     Toward providing these and other advantages, apparatus and method are provided for enhancing the flow of fluids through a subsea pipeline by heating a segment of the pipeline using portable or fixed electrical power generation equipment that is connected after the pipeline is deployed to the seafloor. The apparatus and method may be applied to the pipe-in-pipe configuration, the Single Heated Insulated Pipe (SHIP) configuration or any other configurations. The power generation equipment may be a conventional electrical generator mounted on a ship or a fixed structure. Preferably, alternating current is used, but direct current may also be used. Multiple segments of the pipeline may be heated, either contiguous segments or discontinuous segments, or the entire pipeline may be considered a segment. 
     In one embodiment, a mid-line electrical connector is installed with the pipe-in-pipe configuration and a wet-mateable connector is attached to the mid-line connector. The wet-mateable connector may be attached directly to the mid-line connector or it may be attached through a cable. The cable may be buoyed so that is more easily accessed by a Remotely Operated Vehicle (ROV). An ROV may be used at a later time to connect electrical power to the mid-line connector. 
     In another embodiment a wet-mateable connector is connected to one or more of the electrical connectors used to pass current through a segment of a Single Heated Insulated Pipe. The wet-mateable connector may be attached directly to one or more of the connectors or it may be attached through a cable. The cable may be buoyed and connected to electrical power at a later time. There may be a midline connector in the segment to be heated and it likewise may be accessible through a wet-mateable connector. The mid-line connector may be formed on the seafloor from a connector penetrating the insulation coating on the pipeline. 
     An electrically ready heated pipe is heated by connecting a source of power to the electrical conductors used in heating after the pipeline is deployed on the seafloor. For any configuration, the source of power may be lowered to the vicinity of a wet-mateable connector and connected, which may employ an ROV. To minimize power loss in an umbilical used to supply electrical power, the voltage may be stepped up at the source of power and stepped back down in the vicinity of the connector to the pipeline. The power factor of the power supplied may be improved to increase efficiency of heating. 
     In another embodiment a toroidal transformer is used to apply power. In another embodiment sea water electrodes are used to complete an electrical circuit through a segment of pipeline to be heated. In yet another embodiment, power is supplied to a riser along with a segment of the pipeline on the sea floor. Multiple segments may be heated simultaneously or in sequence. Selection of segments to be heated at any time may be made from measurements of pressure or other physical variables indicating where heating is needed. 
     In yet another embodiment, a toroidal transformer is used to extract power from a selected location along the segment being heated. A wet-mateable connector may be used to connect with the wire of the toroidal transformer. The power extracted may be used to operate a device, heat another short segment of pipeline or for other purposes. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding of the invention and the advantages thereof, reference is now made to the following description taken in conjunction with the following drawings in which like reference numbers indicate like features and wherein: 
     FIG.  1 ( a ) is a conceptual layout of an electrical readiness system for heating of a subsea pipeline having a pipe-in-pipe configuration; 
     FIG.  1 ( b ) is a detailed view of one end of a heated segment of pipeline; 
     FIG.  1 ( c ) is a detailed view of portable electrical power equipment. 
     FIG. 2 is a cross-section view of a mid-line connector with a wet-mateable connector and a pre-installed jumper cable. 
     FIG. 3 is a cross-section view of a mid-line connector with a dry penetration connector and a pre-installed jumper cable. 
     FIG. 4 is a cross-section view of a midline connector with a wet-mateable connector with a pipe frame. 
     FIGS.  5 ( a ) and  5 ( b ) are cross-section and end views of a midline connector for a pipe-in-pipe configuration. 
     FIGS.  6 ( a ) and  6 ( b ) are cross-section and end views of a midline connector for a Single Heated Insulated Pipe (SHIP) configuration; 
     FIGS.  6 ( c ) and  6 ( d ) are cross-section and end views of a pre-deployment contactor for the SHIP configuration. 
     FIG. 7 is a cross-section view of a Single Heated Insulated Pipe deployed with a buoyed seawater electrode and a wet-mateable buoyed connector. 
     FIG. 8 is a cross-section view of a Single Heated Insulated Pipe with a mid-line connector deployed with heaters outside the heated segment and buoyed wet-mateable connectors. 
     FIGS.  9 ( a ) and  9 ( b ) are cross-section and end views of a Single Heated Insulated Pipe with a mid-line toroidal transformer deployed with seawater electrodes at ends of the heated segment. 
    
    
     DETAILED DESCRIPTION 
     Referring to FIG. 1, the concept of one embodiment of “electrical readiness” is illustrated for the pipe-in-pipe configuration of electrical heating. In FIG.  1 ( a ), pipeline  10  is shown on the sea floor. Pipeline  10  may be divided into Segments  10   a ,  10   b , and so on. The segments may be heated simultaneously or sequentially in any order. The pipe-in-pipe configuration is described more fully in the patent application entitled “Electrical Heating of Pipelines with Pipe-In-Pipe and Mid-Line Connector,” filed concurrently and commonly assigned, which has been incorporated by reference herein. FIG.  1 ( b ) shows the detail of each end of a segment having a pipe-in-pipe configuration, such as Segment  10   a . The pipeline has inner pipe  12 , which is the flowline, and outer concentric pipe  14 . These pipes are electrically isolated except at bulkheads, such as bulkhead  16 , which exist at the end of each segment to be heated (unless replaced by an insulating joint, as discussed below). A bulkhead is an electrical conductor between the inside and the outside pipe. It is normally a welded-in ring that separates the annulus between the inner and outer pipes into compartments. 
     Referring again to FIG.  1 ( a ), between the bulkheads in each segment is mid-line connector  20 . Mid-line connector  20  will be described in more detail below. Its function is to allow electrical contact to the inside and outside pipes and electrically isolate the pipes. Connector  20  is attached to cable  21 , which has wet-mateable connector  22  attached at the opposite end. (Wet-mateable connectors are available, for example from Tronic Ltd., Cumbria, England.) The cable and connector may be supported by buoyancy module  24 . Alternatively, cable  21  and module  24  may be omitted, leaving the possibility of electrical connections directly to wet-mateable connector  22 , which is attached to mid-line connector  20 . 
     The concept of electrical readiness is that the equipment to provide for electrical heating of a segment or segments of the pipeline be installed when the pipeline is installed such that electrical heating may be applied at sometime later in the life of the pipeline. In one embodiment, electrical readiness provides that the power for electrical heating be supplied by shipboard equipment. FIG.  1 ( a ) illustrates heating of segment  10   b  by equipment mounted on a ship, shown generally at  40 . FIG.  1 ( c ) illustrates in more detail ship-mounted equipment. Umbilical reel  42  is used to store and control release of an umbilical to the sea floor. Preferably, step-up transformer  44  provides that power be transported subsea at a higher voltage than applied to the pipeline, to minimize current requirements of the umbilical. Phase balance and power factor correction network  46  optimizes use of the electrical power. Switch gear  48  provides ability to control the power from electrical power generator  49 . Other power supply configurations may be used that do not require a transformer or matching network, which is well know to one of skill in the art. 
     When the need for pipeline remediation occurs due to a flowline restriction or blockage, intervention vessel  40  moves into the proper location, deploys transformer  30  (FIG.  1 ( a )) into the water and lowers it to the seabed in close proximity to the mid-line connector of the segment to be heated, such as segment  10   b . Marine umbilical  32  suspends subsea transformer  30  and also provides for the transmission of high voltage power from intervention vessel  40  to subsea transformer  30 . Once transformer  30  is lowered to the seabed, ROV  26  then retrieves the free end of cable  21  and connects it to the output receptacle of transformer  30 , using wet-mateable connector  22 . On the deck of intervention vessel  40 , power generation equipment  49  then supplies three-phase electrical power to heat the pipeline segment. The output of the generator connects through electrical switch gear  48  to phase balance and power factor correction network  46 . Switch gear  48  may provide the overriding control of the power delivery system and protection against electrical faults. It may also be linked to other equipment for safety interlocks and emergency protection. 
     Since pipeline segment  10   b  is strictly a single-phase mode and has a relatively poor electrical power factor, phase balance and power factor correction network  46  may be included to provide a means to balance and correct the power drawn from three-phase generator  49 . The output of this network is connected to the primary step-up transformer  44 . Due to the high current levels required for the pipeline segment, it is more feasible to transmit the power subsea through a marine umbilical at a higher voltage. This provides more efficient transmission through the marine umbilical and provides for a more easily achieved design of a marine umbilical. Output of subsea step-down transformer  30  is designed to be at the voltage and current levels as prescribed in the design basis for heating the pipeline. This power is transmitted through mid-line power cable  21  and connector  20  to pipeline segment  10   b  to heat the segment. 
     Inner pipe  12  (FIG.  1 ( b )) conducts the heating current away from mid-line connector  20  in both directions and outer pipe  14  is the return conductor for this current back into mid-line connector  20 . The inner and outer pipes are short-circuited at bulkheads  16  at each end of segment  10   b  to complete the circuit. Since mid-line connector  20  is normally located halfway between bulkheads  16 , the heating current is roughly divided evenly between the two halves of the heated segment. 
     Each segment such as segment  10   a  and  10   b  may be equipped with mid-line connector such as  20 . The distance between bulkheads  16  may vary along pipeline  10  or may be approximately the same. The distance between bulkheads will ordinarily be from about one mile to about 10 miles, but may be smaller or greater. The mid-line connector may be installed as the pipeline is assembled on a J-lay vessel. Mating subsea power jumper cable  21  may be connected to each mid-line connector and deployed during the deployment process. There are two possible approaches to accomplish this: (1) The cable may be mounted to mid-line connector  20  onboard the J-lay vessel and temporarily attached to the pipeline above the connection point. As pipeline  10  is deployed and once power cable  21  is sufficiently submerged, divers may remove the temporary attachments and attach buoyancy through the free end of cable  21 . Or, (2) the pipeline may be deployed from the vessel with mid-line connector  20  installed but without cable  21 . Once mid-line connector  20  is sufficiently submerged, cable  21  may be lowered from the vessel and divers may mate it with the mid-line connector using wet-mateable connector  22 . In this case, buoyancy may be pre-attached to the free end of the cable, such as by buoyancy module  24 . In either case, some cable connector components would be subject to impact, vibration and structural loads while being deployed through the J-lay equipment. 
     Buoyancy module  24  attached to cable  21  will keep the free end above the pipeline as it lands on the sea floor and allow easy access to that end by an ROV. When a need for flowline remediation occurs, submersible transformer  30  may be deployed to the sea floor in close proximity to mid-line connector  20 . ROV  26  would then mate the free end of cable  21  to a receptacle on transformer  30 , using wet-mateable connector  22 . 
     Power cable  21  and connector assembly  22  are intended to be ROV-retrievable and ROV-installable. After installation of pipeline  10 , then ROV  26  would be able to de-mate a failed power cable from the mid-line connector and install a replacement. 
     Placement of mid-line connectors on the sea floor may require consideration of pipe rotation during placement. Steps may also be taken to minimize this problem using the methods described in co-pending arid commonly assigned patent application entitled “Apparatus and Method for Connecting Cables to Subsea Flowlines” filed Aug. 1, 2000, which is hereby incorporated by reference herein. 
     In another embodiment, buoyancy may not be provided for power cable  21  when it is attached to mid-line connector  20 , but power cable  21  may be pre-attached, as shown in FIG.  2 . In this embodiment, when electrical power is to be supplied to a segment of pipeline  10 , power cable  21  may be raised by buoyancy module  24  to allow easier access by an ROV (not shown) for mating of wet-mateable connector  22  with subsea transformer  30 . Subsea transformer  30  is supported by umbilical  32 . 
     In another embodiment, shown in FIG. 3, fixed penetrator  23  is installed before the pipeline is deployed and replaces a wet-mateable connector attached to midline connector  20 . Power cable  23 A is connected to penetrator  23  and may then be attached to subsea transformer  30  by wet-mateable connector  22 . Transformer  30  is supported by umbilical  32 . The mid-line penetrator, cable assembly and wet-mate connection, if damaged, could lead to complete failure of the system due to the irreplaceable nature of the penetrator. Repair would require return of the mid-line connector to the surface. This embodiment requires that the penetrator/cable assembly be in place during the fabrication process, thereby increasing risk of damage. However, the embodiment offers the possibility of reducing costs. 
     In yet another embodiment, shown in FIG. 4, connection to mid-line connector  20  is accomplished through wet-mateable connector  22  and connector  25  to transformer  30  is dry-mateable. This connection is therefore made before transformer  30  is deployed. This reduces the expenses and risks of subsea operations. When the cable assembly is deployed with transformer  30 , there is also a reduced short-term risk during deployment and fabrication and also less long-term risk due to fouling, anchor damage, environmental and other factors. This method may employ an external pipe lifting H-frame  70 . A support vessel would be required to support H-frame  70  before it is deployed. External rotating mudmat  72  may be deployed during the pipe laying operation. This would elevate the single mid-line connector receptacle to a position which would allow ROV access regardless of pipe rotation. Mudmat  72  may be installed by divers after pipeline  10  has passed through the rollers during installation. 
     Mid-line connectors on or near the sea floor must be accessible for mating with wet-mateable connectors. Multiple mid-line connectors may be placed on a pipeline such that one connector will more likely be accessible for application of an ROV to make connection with a power cable. Mid-line connectors may be placed 180° apart on the pipeline, for example. In the worst case configuration from a rotation perspective then, both mid-line receptacles would be located parallel to the seabed, at or below the mudline. This could require jetting out a section of the pipeline in order to gain adequate access to the receptacle. This design has the advantage of providing redundancy from a connector standpoint. 
     A cross-sectional view of a wet-mateable mid-line connector for a pipe-in-pipe configuration is shown generally at  20  in FIG.  5 ( a ). Inside pipe  52  is adapted to connect to inside pipe  12  of pipeline  10  (FIG.  1 ). Outside pipe  54  is likewise adapted to connect to outside pipe  14  of a pipeline. Housing  55  contains electrical conductors  57  and  58 , which contact the outside and inside pipes, respectively. Wet-mateable connector  56  is attached to housing  55 . Referring to FIG.  5 ( b ), which is an end view, connector  56  contains contacts  59 , which are connected to conductors  57  and  58 . 
     Electrical readiness may also be applied to Single Heated Insulated Pipe (SHIP) systems. Such systems are described in co-pending and commonly assigned application Ser. No. 08/921,737, filed Aug. 11, 1999, which is hereby incorporated by reference herein, and co-pending and commonly assigned application titled “Apparatus and Method for Heating Single Insulated Flowlines,” filed Aug. 1, 2000, which is hereby incorporated by reference herein. Electrical readiness may include, but is not limited to, wet-mateable connectors to make up the umbilical subsea, mid-line electrical connectors or insulating joints, seawater electrodes or insulating joints to complete the circuit, along with electrical insulation to isolate the pipe from the seawater if the fully insulated system is used. If the “earthed current” system is used, as described in the publication “Introduction to Direct Heating of Subsea Pipelines,” overview by Statoil, Saga, et al, February 1998, provisions for connecting to seawater electrodes, for example, may be provided as a part of electrical readiness. 
     A mid-line connector that may be used in the SHIP configuration is illustrated in FIG.  6 . Such a connector is shown generally at  60  in FIGS.  6 ( a ) and  6 ( b )(end view). To prepare for later installation of the mid-line connector, through-insulation contactor  61  may be installed before pipe  11  with insulation  11 A is deployed, as indicated in FIGS.  6 ( c ) and  6 ( d ) (end view). At a later time, compartment  62  may be placed around contactor  61  and clamped in place. Alternatively, compartment  62  may be placed around contactor  61  before deployment of the pipeline. Any seawater inside compartment  62  may be the flushed from the compartment through ports  64 . Only low pressure exists across seals between the walls of compartment  62  and layer of insulation  11 A. An expansion chamber may be connected to compartment  62  to provide for thermal expansion and contraction of fluid in compartment  62 . During placement of compartment  62 , electrical contact between conductor  66  and through-insulation contactor  61  may be established. If compartment  62  is placed after deployment of the pipeline, contactor  61  may be cleaned of corrosion or other films before deployment of compartment  62 , to insure a good electrical contact between conductor  66  and contactor  61 . If compartment  62  is placed before deployment of the pipeline, contactor  61  may be connected to wet-mateable connector  68 . If compartment  62  is placed after deployment, conductor  66  may be attached to wet-mateable connector  68 . Therefore, power may be supplied through mid-line connectors to pipe  11  of a segment to be heated using the apparatus and methods described above. 
     Since the power for electrical readiness may be rarely needed, it is a significant advantage that one work boat, such as shown in FIG. 1, may support a large number of flowlines, spreading the cost of the umbilical, the generator and other ancillary equipment over many flowlines instead of requiring installation of this equipment for each flowline. 
     FIG. 7 illustrates application of electrical readiness to heating a segment of a Single Heated Insulated Pipe with electrical current flow from the first end of the segment to the second end. Pipe  11  is covered with insulation  11 A between electrical connectors  74  and  76 . Connectors  22 A are attached to pipeline connector  74  and  76 . Connectors  22 A may be either dry-mateable or wet-mateable. If dry-mateable, they must be installed before pipeline  11  is deployed subsea. Power cable  21  connects to wet-mateable connectors  22 . Buoyancy module  24  may be used to support power cable  21 . Seawater electrode  77  is shown attached to one of the wet-mateable connectors  22 . In one mode of operation of the SHIP, return current from the pipeline is carried by seawater through seawater electrodes. Seawater electrode  77  may be installed along with power cable  77 A and a mating part of wet-mateable connector  22 . A second wet-mateable connector  22  is attached to electrical connector  76 . For electrical heating of pipeline  11  in the segment between electrical connector  74  and  76 , electrical power may be applied through wet-mateable connector  22  that is attached to connector  76 . This power may be supplied by shipboard equipment as shown in FIG.  1 ( c ). Boat  40  may be moved into place to supply power to connector  76  when heating of the segment between  74  and  76  is desired. Return current through seawater electrode  77  may be collected through a second seawater electrode that may be in the vicinity of boat  40  or at a suitable location. The apparatus and method of electrical readiness illustrated in FIG. 7 may be applied to any single pipe configuration employing electrical current entering or leaving a segment to be heated between two electrical connectors. For example, they may be applied to the earthed-current system referenced above. 
     FIG. 8 illustrates an alternate heating method in which there is provided a center feed into a SHIP. In this configuration, as more fully explained in co-pending and commonly assigned patent application entitled “Apparatus and Method for Heating Single Insulated Flowlines,” filed Aug. 1, 2000, which is incorporated by reference herein, electrical power may be fed to center connector  82  and return current may be conducted from connectors  84  and  86  at each end of a segment of pipe  11  that is to be heated. Alternatively, electrical current may be withdrawn from electrical connectors  84  and  86  at the end of the primary segment to be heated and passed through electrical heaters  87  and  88  that are outside the primary segment to be heated. These heaters may be used to heat buffer zones or jumpers, as more fully explained in the referenced application. Connectors  22 A may be either dry-mateable or wet-mateable. If dry-mateable they must be attached before the connector is deployed subsea. If wet-mateable, one portion of the connector will be attached on land and the mating portion, attached to cable  21 , will be joined after deployment of pipeline  11 . Power cable  21  extends to a second wet-mateable connector  22 . All connectors  22  may be supported by buoyancy module  24 . If power cables  21  are attached to pipeline  11  before it is placed subsea, buoyancy module  24  may be used or may be omitted. Wet-mateable connectors  22  are intended to be operated by ROV. The power umbilical and transformer such as shown at  32  and  30  in FIG. 1 may be connected to electrical connector  82  in the center of the segment to be heated. Return cables or seawater electrodes may be connected either at electrical connectors  84  and  86  or at the end of either heater  87  or  88  or at the end of both heaters  87  and  88 , such that electrical current passes through the heaters. Alternatively, power cables  21 , wet-mateable connectors  22  and buoyancy module  24  may be omitted and power from ship  40  and return cables to ship  40  may be connected directly into connectors  22 A, in which instance connectors  22 A will be wet-mateable connectors. In another alternative, power cables may be attached between connectors on each end of heater  87  or heater  88 , illustrating how the apparatus and method of electrical readiness may be applied to any type of electrical heater. 
     An alternative apparatus and method for introducing electrical power to a segment of pipeline to be heated is illustrated in FIG.  9 . Using this apparatus and method a mid-line connector, such as shown at  82  in FIG. 8, is eliminated, while the benefits of the midline concept are retained. A toroidal transformer, shown generally at  90  in FIG.  9 ( a ), is used. Transformer  90  may be permanently installed, with a buoyed pigtail such as shown connected to connector  82  in FIG.  8 . Pipe  11  and surrounding seawater form the secondary circuit of a transformer formed by looping cable  86  around core  88 . Alternatively, seawater electrodes  77  may be eliminated and a cable may be attached from one end of the pipe to the other to complete the secondary. The ends of cable  86  may terminate in a wet-mateable connector such as connector  56 , shown in FIG.  5 . Core  88 , preferably steel, is laminated in the radial direction to prevent excessive eddy current losses. Laminations must be thin to allow for the skin effect. The preferred thickness depends on choice of core material and frequency, but in some cases would be in the range of conventional lamination thicknesses for power applications, which are in the range of 9-14 mils. Alternatively a ferrite core may be used, which will allow higher frequency operation and may be clampable, but would generally need to be larger than steel for the same power rating. This may reduce the needed size of the apparatus subsea transformer, or eliminate it altogether, as well as reduce the current that must be carried by an umbilical, such as umbilical  32  of FIG.  1 . Given the proper current, thermal insulation value and temperature target, the cross-sectional area and therefore the volume of the transformer needed is proportional to the voltage required in the pipe, and therefore the length of pipe to be heated. Cable  86  may be installed with multiple loops around core  88 . This allows generation of the desired current in pipe  11  by using a higher voltage and lower current to excite the primary winding. The lower current could reduce the size and cost of the cable used to connect power to the pipe. FIG.  9 ( b ) shows a cross-section (b—b) through transformer  90 . Only one loop of cable  86  is illustrated here, although multiple loops may be used. Multiple transformers with parallel excitation may be used to increase the length of pipeline to be heated, rather than making bigger transformers. The pipe may be equipped with electrical insulation and seawater electrodes such as seawater electrode  77 , which may be connected by cable  77 A. 
     The use of a midline transformer as illustrated in FIG. 9 requires no penetration of insulation layer  11 A on the pipeline, which may reduce cost of pipe construction and risk of failure as compared with a mid-line connector. Also, primary excitation current through an umbilical can be lower current and higher voltage, which may reduce umbilical costs. It is only necessary to introduce seawater electrodes, which may be pre-installed, at each end of a segment of the pipeline to be heated. The toroidal transformer size depends on frequency, amount of insulation and desired temperature of the pipeline segment. As an example of size, for a SHIP the transformer may be 1 inch thick and 30 inches long for every 500 feet of pipe length to be heated. This size becomes large for a pipe several miles long. 
     As another example, assume a thickness of 1 inch for a toroidal transformer. The magnetic permeability of steel used in laminations is chosen to run the core at about the saturation flux. Otherwise the desired current may not be developed if the core is being used to apply power to the pipe. A permeability of approximately 1500 times the permeability of free space is compatible with a current of about 270 amperes in a pipe of 6.625 inches diameter. Assume a core length of 0.5 meter, one turn of cable and 4 volts applied to the cable (or wire). This would produce about 270 amperes in the pipe. The current to the cable would be 270/number of turns. The voltage is proportional to the core length and number of turns. The length of the core required is as follows: if the length of pipe to be heated has impedance z, the voltage V required on the pipe is (z)×(current). The length of core required to power this length of pipe is then (0.5 meter)×(V/4). 
     The voltage developed is proportional to core cross-sectional area, so the core length may be shortened in approximately the same proportion as core thickness is increased, as long as the core is not saturated. A somewhat longer core than 0.5 meter may be used because the magnetic field falls off in proportion to distance from the center of the pipe. 
     A toroidal transformer may also be used to extract power for small electrical loads such as heating of pipeline jumpers, operating equipment or other purposes. This may be combined with an electrically ready mid-line connector on the main pipeline segment to speed up the heating process by not requiring a separate heating operation for a pipeline jumper. The same configuration as shown in FIGS.  9 ( a ) and  9 ( b ) may be used to extract power. The toroidal transformer may be placed on the pipeline when the pipeline is deployed and placed at a selected location in the segment to be heated. 
     The apparatus and methods of electrical readiness have been particularly described herein with respect to configurations for heating using pipe-in-pipe and Single Heated Insulated Pipe. It should be understood that the methods of installing wet-mateable connectors subsea and later connecting cables, saltwater electrodes or other types of apparatus for supplying electrical power to a segment of a pipeline, either from a portable power source such as may be mounted on a boat, or from a fixed power source that may be available on a structure such as a platform, as described herein, may be applied to any type of electrical heating method. For example, the method may be applied to “Combipipe,” heat tracing or other forms of electrical heating known in the art. 
     While particular preferred embodiments of the present invention have been described, it is not intended that these details should be regarded as limitations on the present invention, except to the extent that they are included in the following claims.