Patent Publication Number: US-2015063919-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. 
         FIG. 3  depicts an exploded view of different components of the packer of  FIG. 2 . 
         FIG. 4A  depicts a section view of the example packer of  FIG. 2  in an unengaged state within a pipeline. 
         FIG. 4B  depicts a section view of the example packer of  FIG. 2  in an engaged state within a pipeline. 
         FIG. 5  depicts a detail view of a locking mechanism of the example packer of  FIG. 2 . 
         FIG. 6  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 apparatus includes first and second mandrels coupled in selectively axial moveable relation to one another, and an elastomeric expansion boot circumferentially disposed around a portion of the second mandrel. The first mandrel is responsive to fluid flow in the pipeline to move axially toward the second mandrel from a first position to a second position. In the second position, the expansion boot is compressed axially between the first and second mandrels and 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. The packer seals the inner diameter of the pipeline to prevent or significantly inhibit water from flooding the submerged pipeline. 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 inner diameter 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. However, deploying supply lines from the surface downpipe to the packer will add cost and complexity to the system. 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. However, the inclusion of a battery or other power source to actuate the packer will add cost and complexity to the device. In some cases, therefore, wet buckle packers are believed to be better configured to automatically actuate without the use of a power source or external actuation generator like a supply line run downpipe from the surface. As a result, while power sources or external actuation may be used in association with wet buckle packers as described herein, the examples of this disclosure are in accordance with what is believed to be the better configuration, where no such power or external source is necessary for actuation. 
     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 top of the main pipeline  14  in which the piggy-back lines are received. 
       FIG. 2  depicts example wet buckle packer  100 . Packer  100  includes a hoist ring  102 , first and second end caps  104  and  106 , first and second mandrels  108  and  110 , and elastomeric expansion boot  112 . Packer  100  also includes end plate  114 , which is connected to second end cap  106 . Packer  100  is coupled to hoist line  113  by hoist ring  102 , which is connected to first end cap  104 . 
     Packer  100  is configured to be deployed from a pipelay vessel down a submerged pipeline via hoist line  113 . 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. The generally cylindrical shape of packer  100  defined by the outer peripheries of end caps  104  and  106 , first and second mandrels  108  and  110 , and expansion boot  112  are configured to slide within the pipeline as packer  100  is deployed downpipe from the pipeline vessel. Additionally, first end cap  104  and second end cap  106  each include a number of freely rotating wheels  116  and  118 , respectively, which are distributed around the outer circumference of each of the components. Wheels  116  and  118  facilitate travel of packer  100  through the submerged pipeline as packer  100  is lowered from the pipelay vessel and as otherwise may be needed during the pipe laying process. First mandrel  108  also includes a number of axially spaced, circumferential ribs  120 . Ribs  120  can provide a number of functions including centralizing packer  100  within and guiding packer  100  through a pipeline during deployment or use. 
     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 and pipeline above packer  32  from being flooded with sea water, which is described in more detail with reference to  FIGS. 4A and 4B . 
     Hoist line  113  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. In  FIG. 3 , packer  100  includes an additional hoist ring connected to end plate  114 , which is connected to second end cap  106 . Packer  100  is configured to be arranged within the pipeline such that the end including first end cap  104  faces the region of the pipeline that is at risk of a wet buckle (or other failure). 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 likely wet buckle location, e.g., somewhere along sea floor  26 . 
     In this example, the packer deployed closer to the surface would be arranged within suspended pipe span  28  such that first end cap  104  faces down toward the likely location of the wet buckle in the sagbend. This upper packer could include a hoist line running from the end of the device including second end cap  106  and another line running from perforated cap  104  to the lower packer. The lower packer closer to sea floor  26  would be arranged within the pipeline such that first end cap  104  faces up toward the likely location of the wet buckle in the sagbend and the lower packer would be connected to the upper packer by the line coupled to the first end caps of each device. 
       FIG. 3  depicts some components of packer  100  in an exploded view to illustrate the components in greater detail. First end cap  104  includes rim portion  130 , hub portion  132 , and spokes  134 . Hub  132  is arranged at the center of first end cap  104  and spokes  134  extend radially outward from hub  132  to rim  130 . Spokes  134  are offset from one another by approximately 90 degrees. Hub  132  includes central bore  136  and the spaces between spokes  134  define apertures  138 . 
     Second end cap  106  includes cylindrical base  140  and shaft  142  extending radially from base  140 . Wheels  118  are distributed around the circumference of base  140  of second end cap  106 . End plate  114  is configured to be connected to base  140  of second end cap  106 , e.g., by fasteners, welding, or another mechanism. End plate  114  includes rim portion  144 , hub portion  146 , and spokes  152 . Hub  146  is arranged at the center of end plate  114  and spokes  152  extend radially outward from hub  146  to rim  144 . Spokes  152  are offset from one another by approximately 90 degrees. Hub  146  includes central hole  150  and the spaces between spokes  134  define apertures  148 . Central hole  150  in end plate  116  may receive a hoist ring for connecting a hoist line to the end of packer  100  including end plate  114  and second end cap  106 . 
     First mandrel  108  is a generally cylindrical component with one end open and the other end partially closed and including rim  154  with central thru hole  156 . Extending from the end of first mandrel  108  that is opposite rim  154  is central bore  158 . Bore  158  extends from the end of first mandrel  108  and terminates at rim  154 . The inner surface of central thru hole  156  can include groove  160 , which can be configured to receive an O-ring or other appropriate sealing element. The surface of bore  158  also includes grooves, which can receive sealing elements such as, e.g., O-ring  162  configured to provide a seal between bore  158  of first mandrel  108  and a portion of second mandrel  110 . 
     Second mandrel  110  includes a number of differently sized cylindrical portions. As illustrated in  FIG. 3 , second mandrel  110  includes a base  164 , a middle  166 , and an end  168  portion. Base  164  includes a generally “V” shaped groove  170 . Middle portion  166  includes a number of grooves, one or more of which can be configured to receive sealing elements such as, e.g., O-ring  172  configured to provide a seal between middle portion  166  of second mandrel  110  and bore  158  of first mandrel  108 . Second mandrel  110  also includes thru bore  174 . 
     Expansion boot  112  includes two annular elastomeric boots separated by a spacer  176 , about which boot  112  is substantially symmetrical. Expansion boot  112  includes central hole  178 , through which middle portion  166  of second mandrel  110  is configured to be received. 
     Packer  100  also includes lock ring  180 . Lock ring  180  is configured to lock packer  100  in an engaged state, as described in more detail below. Lock ring  180  includes ring  182  and tines  184 . Ratchet teeth  186  are inscribed in the radially outer surface of each of tines  184 . 
       FIGS. 4A and 4B  depict section views of wet buckle packer  100  within pipeline  200 . In  FIG. 4A , packer  100  is unengaged with pipeline  200 . In  FIG. 4B , packer  100  is engaged with pipeline  200  to substantially seal the inner diameter of pipeline  200  from water invasion. As illustrated in the section views of  FIGS. 4A and 4B , the components of packer  100  are axially aligned along longitudinal axis  202  of packer  100 . 
     Second mandrel  110  is arranged between first end cap  104  and second end cap  106 . Hub  132  of first end cap  104  is received in bore  204  through end portion  168  of second mandrel  110 . Shaft  142  of second end cap  106  is received in bore  174  through base and end portions  164  and  166  of second mandrel  110 . As illustrated in  FIG. 4A , second end cap  106  is a hollow component that defines cavity  206  within base  140  and shaft  142 . 
     First and second end caps  104  and  106  can be coupled to second mandrel  110  with a variety of mechanisms. In one example, hub  132  of first end cap  104  is press or interference fit with bore  204  of end portion  168  of second mandrel  110 . Similarly, shaft  142  of second end cap  106  can be press or interference fit with bore  174  of second mandrel. In another example, hub  132  and shaft  142  can be threaded into bore  204  and bore  174 , respectively. 
     First mandrel  108  is circumferentially disposed about and in axially moveable relation with second mandrel  110 . Hole  156  in rim  154  of first mandrel  108  receives end portion  168  of second mandrel  110 . Bore  158  of first mandrel  108  receives middle portion  166  of second mandrel  110 . The space between rim  154 , bore  158 , and middle portion  166  forms cavity  208 . 
     Expansion boot  112  includes two annular elastomeric boots separated by a spacer  176 . Expansion boot  112  includes central hole  178 , which receives middle portion  166  of second mandrel such that boot  112  is circumferentially disposed about middle portion  166 . Expansion boot  112  is arranged between one end of first mandrel  108  and base portion  164  of second mandrel  110 . First mandrel  108  is configured to move axially toward second mandrel  110  from a first position to a second position. As first mandrel  108  moves toward second mandrel  110 , first mandrel  108  compresses expansion boot  112  axially. As expansion boot  112  is compressed axially, boot  112  also radially expands into engagement with an inner surface of pipeline  200 . 
     Packer  100  is configured to be automatically actuated in the event of a wet buckle of pipeline  200 . In such an event, water invades pipeline  200  and flows through the pipe toward first end cap  104 . As noted, first mandrel  108  is configured to move axially toward second mandrel to engage packer  100 . Without the application of an external force like the pressure produced by water in pipeline  200 , first mandrel  108  is positioned closer to first end cap  104  to which hoist ring  102  is connected, as illustrated in  FIG. 4A . When the wet buckle occurs, water invading pipeline  200  passes through apertures  138  (see  FIG. 3 ) in first end cap  104  and strikes rim  154  of first mandrel  108 . (The section view of  FIGS. 4A and 4B  are cut through spokes  134  of first mandrel  108  and, as such, apertures  138  are not visible in these figures.) The surface of rim  154  presents a relatively large surface area against which the water invading pipeline  200  can strike. The force of the water on rim  154  causes first mandrel  108  to move axially toward second mandrel  110 . As first mandrel  108  moves toward second mandrel  110 , hole  156  slides along end portion  168  and bore  158  slides along middle portion  166 . The end of first mandrel  108  pushes expansion boot  112  against base portion  164  of second mandrel  110  to axially compress and radially expand boot  112  into engagement with the inner surface of pipeline  200 , as illustrated in  FIG. 4B . 
     As noted above, expansion boot  112  includes two annular elastomeric boots separated by a spacer  176 . However, in other examples, expansion boot  112  can include 1 or more than two elastomeric elements. Spacer  176  can be a Teflon, brass, rubber, or other appropriate type of spacer element or elements interposed between the elastomeric boots of expansion boot  112 . Employing multiple elastomeric boots allows each boot of expansion boot  112  to be formed of different durometer material. Employing multiple boots with multiple, different durometer elastomers can allow packer  100  to be used in a range of different depths and different temperatures. 
     The two elastomeric elements of expansion boot  112  include a non-linear edge profile on the edge of each boot opposite spacer  176 . The shape of the edge of expansion boot  112 , which is engaged by base portion  164  of second mandrel  110  and the end of first mandrel  108  may be configured to increase or assist the radial expansion of expansion boot  112 . In particular, tapers  212  can function to improve the radial expansion of expansion boot  112 , when boot  112  is compressed axially between first mandrel  108  and second mandrel  110 . 
     Expansion boot  112  serves to both substantially seal pipeline  200  and to inhibit movement of packer  100  once the device has been engaged within the pipeline. In other words, packer apparatus in accordance with this disclosure include an elastomeric expansion boot that can be automatically actuated in response to and as a result of water invasion into a pipeline to both substantially seal and to inhibit the apparatus from moving within the pipeline. Although it may be included to augment the function of the boot, no additional or separate brake or slip mechanism is required to properly engage packer  100  (or another device in accordance with this disclosure) within pipeline  200 . 
     In some cases, a principle of differential area can be employed to cause first mandrel  108  to move axially engage expansion boot  112 . Ribs  120  can be designed to impede the flow of water but not to seal on the inner surface of pipeline  200 . In some cases, therefore, it is assumed that water pressure will act on surfaces not protected by seals, including, e.g., the two ends of first mandrel  108 . Water pressure is therefore assumed to be acting on the surface area of the end of first mandrel  108  that engages expansion boot  112  in addition to acting on the end of first mandrel  108  including rim  154 . However, the surface area of the end of first mandrel  108  that engages expansion boot  112  is smaller than the surface area of the opposite end including rim  154 . As such, even though the pressure may be balanced on both ends of first mandrel  108 , the differential area causes the net force on first mandrel  108  to move first mandrel  108  toward the base portion  164  of second mandrel  110 . This net force causes the first mandrel  108  to move towards second mandrel  110  to compress expansion boot  112  axially and expand boot  112  radially into engagement with pipeline  200 . 
     In one example, the air in cavity  208  is at atmospheric pressure when packer  100  is in the unengaged state. The pressure in cavity  208  will increase when the packer is in the engaged state. However, packer  100  can be configured such that the increase in pressure in cavity  208  does not adversely affect engagement of the device. 
     The amount of force generated during actuation of packer  100  is a function of the water pressure inside pipeline  200  and also the surface areas of the end of first mandrel  108  that engages expansion boot  112  and the opposite end of first mandrel  108  including rim  154 . To design packer  100  to withstand sufficient force to actuate the device without needing to withstand significant excess force during actuation, in some examples, rim  154  and the rest of the structure of first mandrel  108  can be fabricated as separate components that are configured to be connected when assembled into packer  100 . Fabricating the rim separately can enable different rims with different amounts of surface area to be employed in the same or similar packer apparatus. In this manner, one or a small number of base packer apparatus can be configured to be deployed at different depths that will subject the devices to different water pressure levels by selecting the appropriate rim for each particular depth and expected water pressure. 
     In some examples, packer  100  can include an actuator that either augments the effect of the water pressure on rim  154  of first mandrel  108  or is employed in lieu of automatic actuation by the water pressure. For example, in the event the water pressure fails to actuate the device, packer  100  could include an actuator that drives first mandrel  108  to cause expansion boot  112  to engage pipeline  200 . Example actuators that could be employed with packer  100  include a variety of mechanical and electromechanical devices that are configured to be actuated to drive first mandrel  108 . For example, the actuator can include a pneumatically or hydraulically actuated piston that drives first mandrel  108  with air or a hydraulic fluid supplied by a supply line connected to packer  100 . In another example, the actuator includes an electrically activated solenoid that drives first mandrel  108 . In another example, the actuator includes an electromagnetic piston that drives first mandrel  108  based on controlled electricity transmitted to packer  100  via the supply line. 
     In another example, a plurality of springs can be arranged between first end cap  104  and first mandrel  108 . A plurality of shear pins can be arranged through radially aligned apertures (not shown here) in first mandrel  108  disposed at different angularly disposed, circumferential positions around a longitudinal axis of packer  100 . The shear pins can engage grooves in middle portion  166  of second mandrel  110  between O-ring  162  and lock ring  180 . In such an example, the force generated by the water pressure will shear the pins and the spring force will augment the force generated by the water pressure to engage packer  100  within pipeline  200 . 
     In some examples, packer  100  can include a sensor system that detects the invasion of water into the inner diameter of pipeline  200 . 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  200  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 an actuator of packer  100  or can transmit signals to a surface system, which, in turn, transmits control signals to an actuator via a supply line. Wet buckle detection via such a sensor system could be employed to test or verify whether packer  100  is actuated and, in some examples, could be used as a trigger to activate an actuator included in packer  100 . 
     Packer  100  is configured such that in the unengaged state illustrated in  FIG. 4A  at least some portions of the outer boundaries of packer  100  are offset from the inner surface of pipeline  200 . The offset distance between packer  100  and the inner surface of pipeline  200  may differ at different points along the axial length of packer  100 . For example, offset  214  between expansion boot  112  and the inner surface of the pipeline  200  is different than the offset between other components of packer  100  and the inner surface of pipeline  200 . In one example, packer  100  is designed such that offset  214  is less than or equal to ⅛ inch, while the offset between unengaged components of packer  100  and pipeline  200  is greater than ⅛ inch. However, in other examples, offset  214  can be larger or smaller depending on the clearance between packer  100  and pipeline  200  necessary to allow packer  100  to be deployed through pipeline  200  and the amount of radial expansion of expansion boot  112  and brake pads  168  that is provided when spindle  106  moves axially toward base cap  108 . 
     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 less than or approximately equal to ⅛ inch will separate the sealing and braking elements of the packer and the pipeline inner surface and a radial clearance of less than or approximately equal to ¼ inch will separate unengaged components 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 configure packer  100  such that offset  214  between expansion boot  112  and the inner surface of the pipeline  200  is as small as possible while still allowing packer  100  to be deployed downpipe within pipeline  200 . In one example, the outer periphery of expansion boot  112  is configured to abut or nearly abut the inner surface of pipeline  200  even in the unengaged state of packer  100 , as illustrated in  FIG. 4A . In practice, there may be a delay between the occurrence of a wet buckle to pipeline  200  and water striking rim  154  of first mandrel  108  to cause packer  100  to become engaged with the inner surface of pipeline  200 . During the delay in actuation of packer  100  some water may pass through packer  100 . Reducing offset  214  between expansion boot  112  and the inner surface of the pipeline  200  will reduce the amount of water that floods pipeline  200  before packer  100  is engaged and expansion boot  112  substantially seals the inner diameter of the pipeline. Additionally, to further reduce water flow by packer  100 , the outer periphery of first and second end caps  104  and  106  and first and second mandrels  108  and  110  may also be configured to fit closely with the inner surface of pipeline  200 . 
     As noted above, first mandrel  108  includes ribs  120 . In addition to centralizing and guiding packer  100  within pipeline  200 , ribs  120  may also serve to reduce the amount of water that passes packer  100  within pipeline  200  as packer  100  is engaged in response to a wet buckle. As such, the offset between ribs  120  and pipeline  200  can be equal to, or, in some cases, less than offset  214  between expansion boot  112  and pipeline  200 . 
     As is illustrated in  FIGS. 4A and 4B , first and second end caps  104  and  106 , and first and second mandrels  108  and  110  are hollow, relatively thin-walled components. It may be desirable to design the components of packer  100  and other wet buckle packers in accordance with this disclosure in order to reduce the weight of the device. Packer  100  may be employed in relatively large pipelines. In one example, pipeline  200  has an inner diameter that is approximately equal to 40 inches. The large size of pipeline  200  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 thousands of pounds. In such situations, removing as much material from first and second end caps  104  and  106 , and first and second mandrels  108  and  110  can have a significant impact on the weight of packer  100 . 
     The overall weight of packer  100  also affects the amount of load on hoist line  113  and, as a result, the amount of work required by the hoist machine operating hoist line  113 . As such, reducing the weight of packer  100  can also reduce the cost and complexity of deploying packer  100  via hoist line  113 . 
     The forces encountered by packer  100  in the event of a wet buckle of pipeline  200  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. 
     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  200  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 water pressure is balanced on either side of a wall of one or more of first and second end caps  104  and  106 , and first and second mandrels  108  and  110 . For example, in the event of a wet buckle, packer  100  can be configured to allow some water flow past the device within pipeline  200 . Water may pass through apertures  116  in first end cap  104  and enter bores  208  and  174  in second mandrel. Additionally, water may flow through apertures  148  in end plate  114  into cavity  206  in second end cap  108 . Cavity  208 , on the other hand, can be configured to remain substantially sealed against water invasion to maintain the cavity with atmospheric air, as described above. 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 first and second end caps  104  and  106 , and first and second mandrels  108  and  110  of packer  100  may differ significantly depending on the amount of pressure/force encountered in the event of a wet buckle. 
     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 end caps  104  and  106 , and first and second mandrels  108  and  110  can be fabricated from a variety of different types of steel or aluminum. Expansion boot  112 , however, can be fabricated from a variety of elastomeric materials including rubber. Additionally, in one example, ribs  120  are fabricated from a different material than the rest of first mandrel  108 . For example, first mandrel  108  may be fabricated from a rigid material such as steel or aluminum, while ribs  120  are fabricated from an elastomer such as polyurethane. In one example, expansion boot  112  and/or ribs  120  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, expansion boot  112  and/or ribs  120  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 boot  112  may need to be fabricated from elastomers that can withstand relatively low temperatures without causing boot  112  to become too hard, stiff and/or brittle such that the disks are incapable of sufficiently sealing the inner diameter of pipeline  200 . 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. 
     Packer  100  also includes a locking mechanism including lock ring  180  and ratchet teeth  222  inscribed in a portion of the inner surface of bore  158  of first mandrel  108 .  FIG. 5  depicts a detail view of locking mechanism  220  including lock ring  180  and ratchet teeth  222 . Locking mechanism  220  is configured to lock packer  100  in engagement with the inner surface of pipeline  170 . 
     Locking mechanism  200  includes lock ring  180  and ratchet teeth  222 . Lock ring  180  is circumferentially disposed around middle portion  166  of second mandrel  110  within bore  158  of first mandrel  108 . Lock ring includes axially extending tines  184 , each of which includes ratchet teeth  186 . As first mandrel  108  moves axially toward second mandrel  110 , the tapered surfaces of ratchet teeth  222  in first mandrel  108  cause teeth  186  on lock ring  180  to be pushed outward to allow first mandrel  108  to move in one direction one row of teeth  186  at a time. When expansion boot  112  has been radially expanded into engagement with pipeline  200  by the movement of first mandrel  108 , the blocking surfaces of teeth  186  of lock ring  180  and teeth  222  of first mandrel prevent first mandrel  108  from moving away from second mandrel  110 . In this manner, locking mechanism  220  locks packer  100  into engagement against the inner surface of pipeline  200 . 
       FIG. 6  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 ( 300 ) and actuating the packer apparatus in response to water ingress into the pipeline ( 302 ). The packer apparatus can be deployed into the pipeline via a hoist line connected to a hoist machine on a pipelay vessel. In one example, the packer apparatus that is employed in conjunction with the example method of  FIG. 6  is similar to packer  100  described above. As such, in one example, packer  100  employed to carry out the method of  FIG. 6  includes first and second mandrels  108  and  110  coupled in selectively axial moveable relation to one another, and elastomeric expansion boot  112  circumferentially disposed around a portion of second mandrel  110 . First mandrel  108  is responsive to fluid flow in the pipeline to move axially toward second mandrel  110  from a first position to a second position. In the second position, expansion boot  112  is compressed axially between first and second mandrels  108  and  110  and expanded radially into engagement with an inner surface of the pipeline. 
     Packer  100  is actuated in response to and as a result of water ingress into the pipeline. For example, actuating packer  100  can include moving first mandrel  108  axially toward second mandrel  110  from a first position to a second position. First mandrel  108  is moved from the first to the second position as a result of fluid pressure generated by the water in the pipeline. The fluid pressure of the water in the pipeline acts to push rim  154  of first mandrel  108 , which drives first mandrel  108  axially toward second mandrel  110 . In the second position, one end of first mandrel  108  engages one side of expansion boot  112  and base portion  164  of second mandrel  110  engages the opposite side of expansion boot  112  to axially compress and radially expand expansion boot  112  into engagement with the 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 likely 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. 
     The method of  FIG. 6  includes actuation of a packer apparatus in response to and as a result of water ingress into a pipeline. As illustrated by the examples of packer  100 , the packer can not only be actuated in response to but also as a result of the water the water in the pipeline. In other words, the packer actuation is automatically caused by fluid pressure generated by the water invading the pipeline. Thus, the example method of  FIG. 6  can be carried out with any packer apparatus that is configured to be automatically actuated by fluid pressure within a pipeline. Additional examples of such apparatus are disclosed and described in U.S. application Ser. No. ______ (Atty. Docket No. 1880.517US1), filed on July ______, 2013, U.S. application Ser. No. ______ (Atty. Docket No. 1880.519US1), filed on July ______, 2013, and U.S. application Ser. No. ______ (Atty. Docket No. 1880.523US1), filed on July ______, 2013, all of which are entitled “METHODS AND APPARATUS FOR ARRESTING FAILURES IN SUBMERGED PIPELINES,” and the entire contents of all of which are incorporated herein by reference. 
     Various examples have been described. These and other examples are within the scope of the following claims.