Patent Publication Number: US-2015063920-A1

Title: Methods and apparatus for arresting failures in submerged pipelines

Description:
BACKGROUND 
     This disclosure relates generally to offshore pipelines, and more specifically to methods and apparatus for responding to failures in offshore submerged pipelines. 
     In offshore pipeline installations, as the pipeline is laid on the sea floor the pipeline is subjected to significant forces and moments that can compromise the integrity of the pipeline and, in some cases, cause failures. In the event the submerged pipeline is compromised to the point of failure, water rushes into the pipeline. Such failures are commonly referred to as wet buckles. Once a wet buckle occurs the flooded pipeline is too heavy to retrieve for repair and re-installation. 
     Companies that lay the pipeline keep a fleet of compressor ships on standby while the pipeline is being laid on the sea floor in case of a failure like a wet buckle. The compressor ships are present to pump the water out of the pipeline to facilitate repair of the buckled section, by allowing the pipeline to be pulled back to the surface, to the pipelay vessel, for removal of the damaged section. After the water has been removed, sections of the damaged pipeline can be retrieved and brought to the surface and the pipelay vessel can continue laying pipe onto the sea floor. 
     Pipeline failures like wet buckles are relatively rare. As such, during installation, the fleet of compressor ships hired by the pipeline installation company is generally inactive and serves no function for the installation process unless the rare failure occurs. The cost of the compressor ships and the associated service the ships and crew provide can reach the millions of dollars. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  schematically depicts a submerged pipeline installation system including wet buckle packers in accordance with this disclosure. 
         FIG. 2  depicts an elevation view of an example wet buckle packer in accordance with this disclosure. 
         FIG. 3A  depicts a section view of the example packer of  FIG. 2  in an unengaged state within a pipeline. 
         FIG. 3B  depicts a section view of the example packer of  FIG. 2  in an engaged state within a pipeline. 
         FIG. 4  depicts an example method of arresting a failure in a submerged pipeline. 
     
    
    
     DETAILED DESCRIPTION 
     In view of the foregoing costs and other inefficiencies associated with recovering from an offshore pipeline failure, examples according to this disclosure are directed to methods and apparatus for automatically responding to water invasion into the inner diameter of pipe in an offshore pipeline and rapidly deploying a sealing system that will prevent or inhibit the laid pipeline from being flooded with water. 
     A packer apparatus in accordance with this disclosure is configured to be arranged within and arrest a failure of a submerged pipeline. In one example, the packer includes a first disk and a second disk offset from and axially aligned with the first disk. A mandrel, elastomeric expansion boot, and brake are disposed between and axially aligned with the first and second disks. The mandrel includes a tapered outer surface and the brake includes a tapered inner surface abutting the tapered inner surface of the mandrel. The first disk is configured to move axially toward the second disk from a first position to a second position. In the second position, the first disk causes: the expansion boot to compress axially and expand radially into engagement with an inner surface of the pipeline; and the tapered inner surface of the brake to move axially along the tapered outer surface of the stationary mandrel to cause the brake to move radially outward into engagement with the inner surface of the pipeline. 
     The expansion boot of the packer apparatus can be a first elastomeric expansion boot disposed between the first disk and a first end of the brake. The packer apparatus can also include a second elastomeric expansion boot disposed between the second disk and a second end of the brake. In the second position, the second expansion boot is compressed axially between the second end of the brake and the second disk and is expanded radially into engagement with an inner surface of the pipeline. 
     In the following examples, the apparatus for arresting pipeline wet buckles (and other pipeline failures) is referred to as a wet buckle packer. However, the apparatus could also be referred to as a plug, a shutoff pig, a baffle, or other terms connoting a device that restricts, and ideally prevents fluid flow through an annular pipeline. 
     Wet buckle packers in accordance with this disclosure provide a number of functions once actuated. Packer apparatus in accordance with this disclosure are sometimes referred to as configured to arrest a failure like a wet buckle in a submerged pipeline. Arresting a failure in a pipeline includes a number of different functions. In both dry and wet buckles, for example, the pipeline failure can include a structural failure including a buckle that causes the pipeline to at least partially collapse on itself. The structural buckle can run along the length of the pipeline unless it is arrested. In wet buckles, water also invades the inner diameter of the pipe causing the pipeline to become flooded. Packer apparatus in accordance with this disclosure can function to arrest both a structural buckle in a submerged pipeline, whether from a dry or wet buckle, and deploy a sealing system that will prevent or inhibit the laid pipeline from being flooded with water in the event of a wet buckle. Additionally, the packer deploys a braking mechanism to prevent or inhibit the packer from moving within the pipeline under the significant pressures introduced by the sea (or fresh) water entering the pipe from the wet buckle. 
     As noted above, wet buckle packers in accordance with this disclosure are configured to be automatically actuated to seal the pipeline from ingress of water. The mechanisms for sealing and braking employed in a wet buckle packer can be actuated in a variety of ways. For example, electrical, hydraulic, or pneumatic supply lines can be run from the pipelay vessel on the surface to the packer. The wet buckle packer could also include a power source, e.g., a battery that could be used to actuate the seal and brake mechanisms. The packers or the systems in which they are employed can be configured to be actuated automatically using a variety of different sensors configured to detect water invasion into the pipeline. 
     Wet buckle packers in accordance with this disclosure provide a new approach to seal and anchor a packer-type plug in place within a pipeline in the event of a wet buckle. The packers are designed to provide increased durability and to include component parts that protect against external variances. Example wet buckle packers can provide a number of advantages including, e.g., removing the high cost of air compressor standby in submerged pipeline installations and providing a simple and cost effective device for arresting failures in the pipeline. 
       FIG. 1  depicts a submerged pipeline installation system  10 . Offshore submerged pipelines can be installed in a number of ways. In general, individual pipes are transported by a cargo ship to a pipelay vessel at the pipeline installation location. The individual pipes are processed and connected to one another on the pipelay vessel and laid onto the sea floor. The pipelay vessel progressively welds individual pipes or welded pipe sections to one another to assemble the pipeline. As the pipeline is assembled the pipelay vessel moves across the surface of the water and the assembled pipeline is pulled off of the ship by the weight of the pipeline. As the pipeline is progressively pulled off of the back of the pipelay vessel it descends to the sea floor. 
     Two methods that are employed to install submerged pipelines are the “J” lay and the “S” lay. The moniker of each method represents the shape of the pipeline as it is pulled off of the pipelay vessel onto the sea floor. In a “J” lay, the pipeline is pulled off of the pipelay vessel substantially vertically to near the sea floor, where the pipeline bends to run horizontally along the floor. In an “S” lay, the pipeline is pulled off of the pipelay vessel substantially horizontally, bends vertically down toward the sea floor and then bends back horizontally away from the vessel to run along the sea floor. Although the following examples are described in the context of an “S” lay installation, wet buckle packers in accordance with this disclosure can also be employed in a “J” lay installation system or other pipeline installation methods not covered here. 
       FIG. 1  depicts a submerged pipeline installation system  10  for an “S” lay installation. In  FIG. 1 , system  10  includes pipelay vessel  12  and pipeline  14 . Pipelay vessel  12  includes production factory  16 , tensioners  18 , crane  20 , and stinger  22 . As described in more detail below, after individual pipes are transported to and loaded on pipelay vessel  12 , the pipes are conveyed into production factory  16 . Production factory  16  includes a variety of processing stations for preparing pipes and coupling individual pipes into pipe sections and ultimately assembling pipeline  14 , as will be known to persons skilled in the art. 
     Pipelay vessel  12  is shown floating in a body of water  24 . Pipelay vessel  12  utilizes crane  20  to perform heavy lifting operations, including loading pipes from a cargo ship onto the vessel. In general, individual pipes on board pipelay vessel  12  are placed on an assembly line within production factory  16  and joints of the pipes are welded into pipeline  14 . Pipeline  14  is held in tension between sea floor  26  and pipelay vessel  12  by pipeline tensioners  18  as the pipeline is lowered. As pipelay vessel  12  moves forward by pulling on a mooring system off of the bow, pipeline  14  is lowered from pipelay vessel  12  over stinger  22 . Stinger  22  is attached to and extends from the stern of pipelay vessel  12 , and provides support for pipeline  14  as it leaves pipelay vessel  12 . 
     In practice, a cargo ship transports pipe sections (sometimes referred to as stands) to pipelay vessel  12 . Crane  20  moves pipe sections from the cargo ship to pipelay vessel  12  onto cradles that form a conveyor system for moving pipe into production factory  16 . Within production factory  16 , a number of different operations are carried out to prepare and join pipe sections. For example, the pipe ends are beveled (and bevels are deburred). The pipe ends are preheated within production factory  16  and moved through a number of welding stations to join different sections with weld beads applied both to the outer and inner diameters of the sections at the joints. In some cases, a final welding station within production factory  16  applies a welded cap to the joints of pipe sections. 
     The joints of the welded pipe sections can also be tested within production factory  16 . For example, the welded joints can pass through ultrasonic testing stations that apply water to the joints as the medium to transmit the ultrasonic signals. The ultrasonic signals can be processed by a computing system and graphically displayed for inspection by an operator. 
     After testing, the joints of the welded pipe sections can be grit blasted and a field joint coating can be applied. In some installation systems, each individual pipe is subjected to this process as it is welded to pipeline  14 . In other cases, multiple pipes, e.g. two pipes in a double stand facility, are first welded together and then welded to the pipeline in the firing line onboard pipelay vessel  12 . At any rate, the assembled pipeline  14  is ultimately conveyed through tensioners  18  and over stinger  22  to be dropped off of the stern of pipelay vessel  12  to sea floor  26 . 
     As pipeline  14  is laid on sea floor  26 , suspended pipe span  28  forms a shallow “S” shape between sea floor  26  and pipelay vessel  12 . The “S” shape of suspended pipe  28  is sometimes referred to as the S-curve. Second curve  30  or the tail of the S-curve just before suspended pipe span  28  meets sea floor  26  is sometimes referred as the “sagbend.” The S-curve of pipeline  14  is controlled by stinger  22  and pipeline tensioners  18 . Increases in the curvature of pipeline  14  cause increases in the bending moment on the pipeline, and, as a result, higher stresses. High stresses on pipeline  14  and, in particular, on suspended pipe span  28  can result in buckling of the pipeline  14 . For example, a loss of tension in pipeline  14  during the pipe lay will normally cause pipeline  14  to buckle at a point along the suspended pipe span  28 . A buckle in pipeline  14  is called a wet buckle if pipeline  14  has cracked or becomes damaged in a manner such that water is allowed to enter the inner diameter of the pipeline. The influx of water into the pipeline  14  greatly increases the weight of suspended pipe span  28  such that the pipe can become over stressed at a location along suspended pipe span  28 , generally near stinger  22 . In such circumstances, flooded pipeline  14  can break and drop from pipelay vessel  12  to sea floor  26 . Regardless of whether pipeline  14  breaks in the event of a wet buckle, the increased weight can prevent recovery of and repair to pipeline  14  before the water is pumped out of the pipeline. 
     Examples according to this disclosure are directed to a wet buckle packer that can be deployed within the inner diameter of pipeline  14  as it is laid on sea floor  26 . In  FIG. 1 , installation system  10  includes two wet buckle packers  32  and  34  deployed within pipeline  14 . Packer  32  is deployed along suspended pipe span  28 , while packer  34  is deployed downpipe where pipeline  14  meets sea floor  26 . Wet buckle packers  32  and  34  are deployed within pipeline  14  with a hoist line or cable (not shown). In cases where multiple wet buckle packers are deployed in series, a hoist line may be coupled between the packers. In the example of  FIG. 1 , a hoist line may be coupled to a hoist on pipelay vessel  12  to packer  32  and another line can be coupled between packers  32  and  34 . As will be apparent to persons skilled in the art, substantial benefits can be realized through an alternative configuration using only a single wet buckle packer, located generally in the position of depicted packer  34 , positioned to prevent substantial inflow of water into the already-laid portion of pipeline  14  on sea floor  26 . 
     Wet buckle packers  32  and  34  are configured to automatically respond to water invasion into the inner diameter of pipeline  14  and rapidly deploy a sealing system that will prevent the laid pipeline and pipeline above packer  32  from being flooded with sea water. For example, wet buckle packers  32  and  34  seal the inner diameter of pipeline  14  to prevent or significantly inhibit water from flooding the submerged pipeline. Additionally, wet buckle packers  32  and  34  deploy a braking mechanism to prevent or inhibit the packers from moving within pipeline  14  as a result of the pressures introduced by the sea water entering the pipe from the wet buckle. 
     In some cases one or more “piggy-back” lines may be laid from pipelay vessel  12  along with main pipeline  14 . Piggy-back lines are generally constructed from smaller diameter pipes that are assembled in a similar manner as described above with reference to pipeline  14 . The piggy-back lines are assembled in parallel with and are then coupled to pipeline  14 , e.g., with a sleeve connected to the top of the main pipeline in which the piggy-back lines are received. 
       FIG. 2  depicts example wet buckle packer  100 . Packer  100  includes a hoist ring  102 , end caps  104  and  106 , bearings  108  and  110 , first and second disks  112  and  114 , expansion boots  116  and  118 , a mandrel  120 , and brake assembly  122 . Packer  100  is configured such that generally the same components are arranged axially on either end of mandrel  120  and brake assembly  122 , which are disposed generally in the middle of packer  100 . End caps  104  and  106  generally define either end of packer  100 . Caps  104  and  106 , bearings  108  and  110 , and first and second disks  112  and  114  can be connected to one another via fasteners (not shown) received within apertures  124 , or another appropriate mechanism. Second disk  114  and mandrel  120  can also be connected via fasteners. In another example, second disk  114  and mandrel  120  are welded or otherwise adhered to one another. In another example, second disk  114  and mandrel  120  are fabricated as a single, integral component. Expansion boot  116  is disposed between first disk  112  and one end of brake assembly  122 . Expansion boot  118  is disposed between second disk  114  and the opposite end of brake assembly  122 . Packer is coupled to hoist line  112  by hoist ring  102 , which is connected to cap  104 . 
     Packer  100  is configured to be connected to hoist line  112  and deployed from a pipelay vessel within pipeline. Packer  100  can be lowered into an already submerged pipeline or can be lowered along with a particular section of the pipeline as it is dropped to the sea floor. Bearings  108  and  110  each include a number of freely rotating wheels  126  distributed around the outer circumference of the bearings. Wheels  126  facilitate travel of packer  100  within the pipeline as packer  100  is lowered from the pipelay vessel and as otherwise may be needed during the pipe laying process. 
     Packer  100  can be deployed at a number of locations within the submerged pipeline to arrest pipeline failures like wet buckles. For example, packer  100  can be deployed along a suspended pipe span of the pipeline or further downpipe where the pipeline meets the sea floor. Wet buckle packer  100  is configured to automatically respond to water invasion into the inner diameter of the pipeline and rapidly deploy a sealing system that will prevent the laid pipeline from being flooded with sea water, which is described in more detail with reference to  FIGS. 3A and 3B . 
     Hoist line  112  extends from hoist ring  102  up to, for example, a hoist machine on a pipelay vessel. In some examples, packer  100  can include hoist rings on both ends of the device to deploy multiple packers within a pipeline in spaced, series relation within the pipeline. Thus, in the example of  FIG. 1 , one packer could be deployed within suspended pipe span  28  closer to the surface than the likely location of the wet buckle in the sagbend of the “S” curve and another packer could be deployed within pipeline  14  on the other side of the possible wet buckle location, e.g., somewhere along sea floor  26 . 
       FIGS. 3A and 3B  depict section views of wet buckle packer  100  within pipeline  128 . In  FIG. 3A , packer  100  is unengaged with pipeline  128 . In  FIG. 3B , packer  100  is engaged with pipeline  128  to substantially seal pipeline  128  from water invasion. As illustrated in the section views of  FIGS. 3A and 3B , packer  100  includes an actuator  129  in addition to hoist ring  102 , end caps  104  and  106 , bearings  108  and  110 , first and second disks  112  and  114 , expansion boots  116  and  118 , mandrel  120 , and brake assembly  122 . Actuator  129  is connected to first disk  112  and mandrel  120 . Supply line  131  is coupled to actuator  129 . Supply line  131  is schematically illustrated in  FIGS. 3A and 3B  in a dashed line format. 
     Caps  104  and  106 , bearings  108  and  110 , and first and second disks  112  and  114  can be connected to one another in a variety of ways. In the example of  FIGS. 3A and 3B , caps  104  and  106 , bearings  108  and  110 , and first and second disks  112  and  114  are connected to one another via fasteners (not shown) received within apertures  124  (see  FIG. 2 ). In another example, however, caps  104  and  106 , bearings  108  and  110 , and first and second disks  112  and  114  could be welded to one another. 
     First disk  112  is configured to move axially toward second disk  114 . As first disk  112  moves axially, disk  112  pushes expansion boot  116  and brake assembly  122 , which eventually engages expansion boot  118 . Brake assembly  122  includes a number of brake mechanisms  130  that are distributed at different angularly disposed, circumferential positions around a longitudinal axis of packer  100 . In the example of  FIGS. 2-3B , brake assembly  122  includes six brake mechanisms  130 . However, in other examples, brake assembly  122  could include more or fewer individual mechanisms. 
     Each brake mechanism  130  includes a linkage  132  and a pad  134 . All of the linkages  132  of brake mechanisms  130  are pivotally connected to brake plate  136  at one end of the linkage. Each linkage  132  is pivotally connected to a respective pad  134  at the other end of the linkage. 
     Mandrel  120  includes a conical portion  138  and a cylindrical portion  140 . Brake plate  136  includes a central bore  142  in which cylindrical portion  140  of mandrel  120  is received. Brake plate  136  is configured to move axially relative to mandrel  120  guided by bore  142  sliding along cylindrical portion  140 . 
     Actuator  129  is connected to first disk  112  and mandrel  120  and is disposed within a bore  144  of cylindrical portion  140  mandrel  120 . Actuator  129  is depicted schematically in  FIGS. 3A and 3B , but generally includes housing  146  and shaft  148  movably connected to housing  146 . Shaft  148  is configured to slide in and out of housing  146 . Housing  146  of actuator  129  is arranged within bore  144  of mandrel  120 . Shaft  148  extends axially from housing  146  through a hole in first disk  112 . The distal end of shaft  148  is connected to first disk  112 . In one example, a nut and two washers are employed to fix the distal end of shaft  148  to first disk  112 . However, shaft  148  could also be attached by other mechanisms, e.g., welded to first disk  112 . In another example, first disk  112  could be fabricated with an integral shaft protruding axially toward mandrel  120  and housing  146  of actuator  129 . 
     Actuator  129  can be a variety of mechanical and electromechanical devices that are configured to be actuated to cause shaft  148  to move axially relative to housing  146 . For example, actuator  129  can include a pneumatically or hydraulically actuated piston that drives shaft  148  with air or a hydraulic fluid supplied by supply line  131 . In another example, actuator  129  includes an electrically activated solenoid that drives shaft  148 . In another example, actuator  129  includes an electromagnetic piston that drives shaft  148  based on controlled electricity transmitted to packer  100  via supply line  131 . In another example, actuator  129  includes an electric motor and screwjack, which can drive shaft  148  using electricity transmitted to packer  100  via supply line  131 . In some cases, actuator  129  can be powered by a power source like a battery deployed with packer  100 . 
     Actuator  129  is configured to cause the end of shaft  148  coupled to first disk  112  to move axially relative to housing  146 . As the distal end of shaft  148  changes axial position with respect to housing  146 , first disk  112  is drawn toward second disk  114 , which, in turn, causes first disk  112  to drive expansion boot  116 , brake plate  136 , and pads  134  toward second disk  114 . 
     In the example of packer  100 , expansion boots  116  and  118  are annular elastomeric boots. Expansion boot  116  is arranged between first disk  112  and brake plate  136 . Expansion boot  118  is arranged between second disk  114  and one end of brake pads  134 . As first disk  112  moves axially toward second disk  114 , brake pads  134  move closer to and eventually engage expansion boot  118 . Once brake pads  134  engage expansion boot  118 , both expansion boots  116  and  118  are compressed axially. Expansion boot  116  is compressed axially between first disk  112  and brake plate  136  and expansion boot  118  is compressed between brake pads  134  and second disk  114 . As expansion boot  116  is compressed axially, boot  116  also radially expands into engagement with an inner surface of pipeline  128 . Similarly, as expansion boot  118  is compressed axially, boot  118  also radially expands into engagement with the inner surface of pipeline  128 . 
     Each brake pad  134  of each mechanism  130  includes a tapered inner surface  150 . Tapered inner surface  150  is configured to match and slide along a tapered outer surface  152  formed by conical portion  138  of mandrel  120 . Axial and radial translation of brake pads  134  are guided by tapered inner surface  150  of pads  134  and tapered outer surface  152  of mandrel  120 . As illustrated in  FIGS. 3A and 3B , pads  134  may also be fixed in the circumferential direction by a number of tongues  154  configured to cooperate with corresponding grooves (not shown) in pads  134 . Tongues  154  protrude radially outward from tapered outer surface of mandrel  120  and are distributed at different angularly disposed, circumferential positions around a longitudinal axis of packer  100 . The angularly disposed, circumferential positions of tongues  154  are in general alignment with the corresponding positions of brake mechanisms  130 . 
     For each brake mechanism  130 , as first disk  112  moves axially toward second disk  114 , expansion boot  116  drives brake plate  136  axially toward second disk  114 . Brake plate  136  and linkage  132  drive brake pad  134  toward expansion boot  118 . As brake pad  134  moves axially toward expansion boot  118 , pad  134  is also drive radially outward by the interaction between tapered inner surface  150  of pad  134  and tapered outer surface  152  of conical portion  138  of mandrel  120 . To accommodate the radially changing position of brake pad  134  and the radially fixed position of brake plate  136 , linkage  132  pivots relative to pad  134  and brake plate  136  as brake mechanism  130  is driven axially toward expansion boot  118 . 
     As tapered inner surface  150  of pad  134  slides along tapered outer surface  152  of mandrel  120  to drive pad  134  radially outward, brake pad  134  is pushed radially outward into engagement with the inner surface of pipeline  128 . The outer surface of brake pad  134  includes a saw-tooth profile defined by a series of circumferentially extending ridges, which are configured to engage the inner surface of pipeline  128  without slipping. In many examples, the ridges will not be symmetrical, but will be configured particularly to prevent movement in the direction toward end cap  106  (i.e., away from the likely location of water influx due to a wet buckle). In one example, pad  134  is manufactured from steel and, in some cases, can include carbide buttons that form the saw-tooth profile of pad  134 . 
     Packer  100  can be actuated from the pipelay vessel on the surface of the sea in the event of a wet buckle in a submerged portion of pipeline  128 , e.g., in the sag bend of the “S” curve formed by the suspended span of pipeline  128  as it descends to the sea floor. Packer  100  can include a sensor system that detects the invasion of water into the inner diameter of pipeline  128 . In another example, the sensor system can be associated with a separate component and be communicatively coupled to packer  100 . In one example, the sensor system includes a water sensor including two spaced electrodes arranged within pipeline  128  such that water invading the pipeline would complete an electrical circuit of the sensor. In another example, a pressure sensor could be used to detect the invasion of water into the inner diameter of pipeline  118 . 
     The sensor system communicatively coupled to packer  100  can provide a signal directly to control electronics included in actuator  129  or can transmit signals to a surface system, which, in turn, transmits control signals to actuator  129  via supply line  131 . In the event water invasion is detected, actuator  129  causes the distal end of shaft  148  to move axially closer to housing  146 . As the distal end of shaft  148  changes axial position with respect to housing  146 , first disk  112  is drawn axially toward second disk  114 , which functions to axially compress and radially expand expansion boots  116  and  118 . In the radially expanded state illustrated in  FIG. 3B , expansion boots  116  and  118  are configured to substantially seal pipeline  128  and thereby arrest or mitigate the wet buckle in pipeline  128 . 
     Actuator  129  also deploys brake assembly  122  to prevent or substantially inhibit movement of packer  100  within pipeline  128 . For example, actuator  129  causes the distal end of shaft  148  to move axially closer to housing  146 . As the distal end of shaft  148  changes axial position with respect to housing  146 , first disk  112  drives brake mechanisms  130  toward expansion boot  118  and second disk  114 . Brake plate  136  and linkages  132  drive tapered inner surface  150  of pads  134  along tapered outer surface  152  of mandrel  120 , which pushes brake pads  134  radially outward into engagement with the inner surface of pipeline  128  to prevent or inhibit packer  100  from moving within the pipeline. 
     Although it is not illustrated in  FIGS. 3A and 3B , packer  100  can include a locking mechanism that is configured to lock brake assembly  122  once it has been engaged. In one example, the locking mechanism includes a ratchet mechanism including one or more spring loaded pawls connected to brake plate  136  and ratchet teeth inscribed in the outer surface of cylindrical portion  140  of mandrel  120 . The ratchet mechanism can be configured to allow first disk  112 , expansion boot  116 , and brake assembly  122  to move toward second disk  114 , while preventing the components from moving axially away from second disk  114  after brake assembly  122  has been engaged. An example ratchet mechanism that could be configured for use with packer  100  is disclosed and described in described in U.S. application Ser. No. ______ (Atty. Docket No. 1880.517US1), filed Jul. ______, 2013 and entitled “METHODS AND APPARATUS FOR ARRESTING FAILURES IN SUBMERGED PIPELINES,” the entire contents of which are incorporated herein by reference. 
     Packer  100  is configured such that in the unengaged state illustrated in  FIG. 3A  the outer boundaries of packer  100  are offset from the inner surface of pipeline  128 . The offset distance between packer  100  and the inner surface of pipeline  128  may differ at different points along the axial length of packer  100 . For example, offset  162  between expansion boots  116  and  118  and the inner surface of the pipeline  128  is different than offset  164  between brake pads  134  and the inner surface of pipeline  128 . In the example of packer  100  illustrated in  FIG. 3A , offset  162  and offset  164  are approximately equal. In one example, packer  100  is designed such that offset  162  and/or offset  164  are less than or equal to approximately ⅛ inch. However, in other examples, offsets  162  and  164  can be larger or smaller depending on the clearance between packer  100  and pipeline  128  necessary to allow packer  100  to be deployed through pipeline  128  and the amount of radial expansion of expansion boots  116  and  118  and brake pads  134  that is provided when actuator  129  moves moving mandrels  112  and  114  relative to stationary mandrel  120 . 
     Although particular offset distances are described with reference to example packer  100 , a packer in accordance with this disclosure will be constructed with a desired dimensional relationship with the dimensions of the pipeline in which the device is to be used. In one example configuration, a radial clearance of approximately ⅛ inch will separate the sealing element of the packer and the pipeline inner surface and a radial clearance of approximately ¼ inch will separate the braking element of the packer and the pipeline inner surface. However, as will be apparent to persons skilled in the art, difference radial dimensions may be used for any size pipe, and in some cases such dimensions may be determined by other factors, such as the designed radius of bends the pipeline will experience while being installed on the sea floor, and/or the intended characteristic of the internal welds used to join the pipeline sections. 
     In some cases, it may be desirable to configured packer  100  such that offset  162  between expansion boots  116  and  118  and the inner surface of the pipeline  128  is as small as possible while still allowing packer  100  to be deployed downpipe within pipeline  128 . In the example of  FIG. 3A , the outer peripheries of end caps  104  and  106 , bearings  108  and  110 , first and second disks  112  and  114 , and expansion boots  116  and  118  are configured to fit closely with the inner surface of pipeline  128  even when packer  100  is in an unengaged state. In practice, there may be a delay between the occurrence of a wet buckle to pipeline  128  and the resulting detection of the invasion of water caused by the wet buckle (depending in part on the location of a water sensor, if used), and activation of actuator  129  to cause expansion boots  116  and  118  and brake assembly  122  to engage the inner surface of pipeline  128 . During the delay in actuation of packer  100  some water may pass through packer  100 . Reducing offset  162  between expansion boots  116  and  118  (as well as reducing the offset between other components of packer  100 ) and the inner surface of the pipeline  128  will reduce the amount of water that floods pipeline  128  before packer  100  is engaged and the boots substantially seal the pipeline. 
     As is illustrated in  FIG. 3A , end caps  104  and  106 , bearings  108  and  110 , and mandrel  120  are hollow components. It may be desirable to design the components of packer  100  and other wet buckle packers in accordance with this disclosure as such in order to reduce the weight of the device. Packer  100  may be employed in relatively large pipelines. In one example, pipeline  128  has an inner diameter that is approximately equal to 40 inches. The large size of pipeline  128  necessitates a relatively large packer to seal the inner diameter of the pipeline. As such, in one example, packer  100  may weigh on the order of approximately 10,000 pounds. In such situations, removing as much material from end caps  104  and  106 , bearings  108  and  110 , and mandrel  120 , and other components of packer  100  can have a significant impact on the weight of the device. 
     The overall weight of packer  100  also affects the amount of load on hoist line  112  and, as such, the amount of work required by the hoist machine operating hoist line  112 . As such, reducing the weight of packer  100  can also reduce the cost and complexity of deploying packer  100  via hoist line  112 . 
     The forces encountered by packer  100  in the event of a wet buckle of pipeline  128  may be significant. For example, at a relatively shallow depth of approximately 1500 feet below sea level, the pressures generated by a wet buckle can reach approximately 660 pounds per square inch (psi). At a depth of approximately 12,000 feet, the pressures generated by a wet buckle can reach approximately 5280 psi. In view of the range of forces potentially encountered by wet buckle packer  100 , the wall thicknesses of the components of packer  100  may need to be adjusted to withstand large forces/pressures. 
     It is also noted that the forces encountered by different portions of packer  100  may differ significantly. For example, portions of packer  100  may be partially or substantially pressure balanced because water introduced into pipeline  128  is allowed to enter parts of packer  100 . In such situations, the pressure of the water is balanced on particular portions of packer  100 . For example, water may be allowed to enter portions of packer  100  such that the pressure is balanced on either side of a wall of one or more of end caps  104  and  106 , bearings  108  and  110 , and mandrel  120 . For example, a seal between shaft  148  and first disk  112  and sealing the fastener apertures in first disk  112  may allow pressure balance of all components of packer  100  except first disk  112 . Additionally, flow ports can be manufactured into end cap  104  and bearing  108  to allow rapid pressure balancing. Pressure balancing can be achieved via atmospheric air pressure, as well as water pressure. In some examples, therefore, packer  100  may be designed to allow pressure balancing of some portions of the device such that the wall thicknesses of different portions of end caps  104  and  106 , bearings  108  and  110 , and mandrel  120 , and other components of packer  100  may differ significantly depending on the amount of pressure/force encountered in the event of a wet buckle. 
     In order to engage packer  100  including radially expanding expansion boots  116  and  118  and setting brake assembly  122 , actuator  129  is configured to generate a range of setting forces. In one example, actuator  129  is configured to generate a setting force approximately equal to 60,000 pounds to substantially seal pipeline  128  with expansion boots  116  and  118  and prevent or inhibit movement of packer  100  with brake assembly  122 . In other examples, actuator  129  is configured to generate a setting force that is less or greater than 60,000 pounds. For example, in a smaller diameter pipe approximately equal to 7 inches, actuator  129  is configured to generate a setting force approximately equal to 12,000 pounds. 
     A variety of materials can be used to fabricate the components of packer  100  including, e.g., metals, plastics, elastomers, and composites. For example, first and second disks  112  and  114 , bearings  108  and  110 , brake pads  134  and mandrel  120  can be fabricated from a variety of different types of steel or aluminum. Expansion boots  116  and  118  can be fabricated from a variety of elastomeric materials including rubber. Additionally, end caps  104  and  106  can be fabricated from a variety of elastomers. In the example of  FIGS. 3A and 3B , end caps  104  and  106  are illustrated as fabricated from an elastomer. In such cases, end cap  104  may need to be structurally reinforced to withstand the pressures caused by the invasion of water into pipeline  118 . As such, packer  100  includes scaffold cone  156 , which is configured to limit the amount end cap  104  can collapse inward in the event of a wet buckle. Scaffold cone  156  can be fabricated from a strong, rigid material such as steel or aluminum. 
     In one example, end caps  104  and  106 , expansion boots  116  and  118 , and/or brake pads  134  are fabricated from a nitrile rubber. At the sea floor, packer  100  may encounter temperatures as low as 32 degrees Fahrenheit (0 degrees Celsius). As such, end caps  104  and  106 , expansion boots  116  and  118 , and/or brake pads  134  may need to be fabricated from elastomers that can withstand relatively low temperatures without significantly affecting the material properties of the components. For example, expansion boots  116  and  118  may need to be fabricated from elastomers that can withstand relatively low temperatures without causing the expansion boots to become too hard, stiff and/or brittle such that the boots are incapable of sufficiently sealing the inner diameter of pipeline  128 . The components of packer  100  can be fabricated using a variety of techniques including, e.g., machining, injection molding, casting, and other appropriate techniques for manufacturing such parts. 
       FIG. 4  is a flowchart depicting an example method of arresting a failure of a submerged pipeline. The method includes deploying a packer apparatus within the pipeline ( 200 ), detecting water ingress into the pipeline ( 202 ), and actuating the packer apparatus in response to the detection of the water ingress into the pipeline ( 204 ). In one example, the packer includes a first disk and a second disk offset from and axially aligned with the first disk. A mandrel, elastomeric expansion boot, and brake are disposed between and axially aligned with the first and second disks. The mandrel includes a tapered outer surface and the brake includes a tapered inner surface abutting the tapered inner surface of the mandrel. The first disk is configured to move axially toward the second disk from a first position to a second position. In the second position, the first disk causes: the expansion boot to compress axially and expand radially into engagement with an inner surface of the pipeline; and the tapered inner surface of the brake to move axially along the tapered outer surface of the stationary mandrel to cause the brake to move radially outward into engagement with the inner surface of the pipeline. 
     The packer apparatus can be deployed into the pipeline via a hoist line connected to a hoist machine on a pipelay vessel. Detection of water ingress into the pipeline can include sensing water invasion into the inner diameter of the pipeline with a sensor included in or separate from the packer apparatus. In one example, the packer can include a sensor system that detects the invasion of water into the inner diameter of the pipeline. The sensor system communicatively coupled to the packer can provide a signal directly to control electronics included in an actuator of the packer or can transmit signals to a surface system, which, in turn, transmits control signals to the actuator via a supply line. In the event water invasion is detected, the actuator of the packer can trigger actuation of the device. 
     Actuating the packer apparatus can include transmitting signals from the pipelay vessel on the surface to the packer via the supply line connected to the actuator of the packer. The actuator can be configured to move the first disk axially toward the second disk from a first position to a second position. In the second position, the first disk causes: the expansion boot to compress axially and expand radially into engagement with an inner surface of the pipeline; and the tapered inner surface of the brake to move axially along the tapered outer surface of the stationary mandrel to cause the brake to move radially outward into engagement with the inner surface of the pipeline. 
     The expansion boot of the packer apparatus can be a first elastomeric expansion boot disposed between the first disk and a first end of the brake. The packer apparatus can also include a second elastomeric expansion boot disposed between the second disk and a second end of the brake. In the second position, the second expansion boot is compressed axially between the second end of the brake and the second disk and is expanded radially into engagement with an inner surface of the pipeline. 
     As described above, methods of arresting failures of a submerged pipeline can include deploying multiple packers within the submerged pipeline. In one example, the packers are deployed on either side (e.g. one closer to the surface and one farther from the surface and closer to the sea floor) of the location of the wet buckle (or other failure). In such examples, both packers can be actuated to seal the region of the pipeline between the packers and including the location of the failure. 
     Various examples have been described. These and other examples are within the scope of the following claims.