Pipeline plugging apparatus

Apparatus for plugging a pipeline may comprise: a tubular body; seal assemblies carried by the body for moving the body through the pipeline in response to fluid flow therethrough and for sealing between the body and pipeline; an internal valve carried by the body for establishing fluid communication between downstream and upstream portions of the pipeline; and a stop device extendable into the pipeline for arresting movement of the body and for operating the internal valve. A method is disclosed for utilizing the apparatus.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention pertains to pipelines and apparatus for use 
therewith. In particular, it pertains to apparatus for closing or plugging 
a section of pipeline in order to repair or work on such. In particular, 
the present invention pertains to apparatus suitable for isolating a 
section of pipeline under pressure without the necessity of draining the 
entire pipeline. 
2. Description of the Prior Art 
Occasionally it is necessary to work on sections of pipelines for various 
purposes, e.g., repairing leaks, replacing sections of pipe, installing or 
replacing valves, connecting branch lines, etc. In the past, it has been 
necessary to drain the pipeline or a substantial portion thereof in order 
to repair or perform any other maintenance on the line. This of course 
resulted in the time-consuming operation of draining the line and 
transporting the drain fluid to storage facilities. This also results in 
pump or compressor stations of the pipeline being completely shut down. 
Within the past few years devices have been developed to isolate short 
sections of pipeline, eliminating the necessity for draining substantial 
lengths thereof. One such device comprises a plug member which is inserted 
through a lateral opening which has been previously cut in the pipeline by 
"hot tap" methods. The plug is inserted through the lateral opening and 
rotated so as to be in axial alignment with the pipeline and is then 
caused to expand into sealing engagement with the inner walls thereof. The 
lateral opening which is cut in the pipe for these type devices is 
substantially the same dimension as the inside diameter of the pipe. While 
offering certain advantages, this method introduces disadvantages such as 
the removal of a substantial amount of the pipe by cutting the lateral 
entry hole, thereby weakening the structural continuity of the pipe 
itself. Further, these devices are sometimes difficult to insert and 
remove from the pipeline, creating a possible hazard of permanently 
blocking the pipeline. Examples of such prior art may be seen in U.S. Pat. 
Nos. 2,929,410 and 3,285,290. 
In other prior art, plugging devices have been provided for traveling 
inside the pipeline to a predetermined point, propelled by fluid flow 
within the pipeline. These devices, commonly referred to as "plugging 
pigs" are launched at some convenient point upstream and travel to a 
preselected downstream location where small diameter pins, relative to the 
pipe diameter, are extended into the pipe through valves connected to the 
pipe and through holes of approximately the same diameter as the pin which 
have been cut under pressure by "hot tapping" methods. Upon contact with 
the pin, the plugging pig will stop, at which time a seal or packer 
element thereon will be expanded sufficiently to establish sealing contact 
with the inner pipe wall. Various means are used to expand the seal, 
including the inflation of the seal by fluid connection with an external 
fluid pressure source through the pin. Examples of such prior art may be 
seen in U.S. Pat. Nos. 2,929,410 and 3,285,290. 
When such prior art plugging pigs are used in pairs to isolate a section of 
pipeline, it is necessary to establish external fluid bypasses around the 
first pig, upon arrival at a predetermined pin location, in order to 
enable the second pig to approach. Such bypasses require at least three 
hot taps to be made, in addition to the pin device hot taps, in order to 
establish the desired fluid communication for operation of the two pigs. 
In addition, as previously stated, a rather complex design may be required 
to inflate the packer or sealing element from an external pressure source. 
In a more recent development a plugging pig has been designed which 
incorporates an integral fluid bypass valve. Such a valve eliminates the 
necessity of the external bypasses previously required in the prior art to 
bring the second pig into position. This also reduces the number of holes 
in the pipeline and requires less welding. Furthermore, the integral 
bypass valve may be automatically actuated as the pig approaches its stop 
pin or restraining device, preventing undue hydraulic shock created by 
sudden stoppage of the pig. The ingtegral bypass valve is also designed 
for selective operation externally of the pipeline allowing much 
flexibility, including the automatic refilling of a newly repaired pipe 
section. Such a plugging pig and its method of use may be seen in U.S. 
Pat. No. 3,503,424. 
SUMMARY OF THE INVENTION 
The present invention pertains to improvements in the above described 
plugging pig of the integral fluid bypass valve type. Such a pig may 
comprises a central tubular body; seal means carried by the body for 
moving the plugging pig though the pipeline in response to fluid flow 
therethrough and for sealing between the pig and the pipeline; and 
integral bypass valve means carried by the body having an open position in 
which fluid communication is established between downstream and upstream 
portions of the pipeline, and a closed position in which the fluid 
communication is prevented. Stop means are provided for extension into the 
pipeline and operable externally thereof to arrest movement of the 
plugging pig through the piepline. 
Like in the aforementioned U.S. Pat. No. 3,503,424, the plugging pig of the 
present invention incorporates an integral fluid bypass valve which may be 
automatically actuated as the pig approaches a stop pin, thereby 
preventing undue hydraulic shock created by sudden stoppage of the pig. 
Furthermore, no external bypass is required to bring the second pig into 
position. As earlier stated, this permits fewer holes in the pipe and less 
welding is required. However, in the improved version of the present 
invention, the integral bypass valve is pressure balanced and is much 
simplified in construction and operation. The valve is of the sliding 
sleeve type and is easily operated by a unique stop apparatus. Ports are 
provided in the central tubular body of the pig through which the internal 
bypass may be established. These ports, or port as it may be called, are 
provided by a circumferential slog completely surrounding the tubular body 
member. Thus, a considerably larger flow area is permitted in the present 
invention than in prior devices. The sleeve of the valve is normally 
biased toward a first position, in which the ports are blocked. 
The stop means comprises at least one stop pin radially movable from a 
retracted position, in which the flow area of the pipeline is 
uninterrupted, to an extended position for engagement with a portion of 
the pig to arrest its movement through the pipeline. Further extension of 
the stop pin engages a locking flange around the tubular body, preventing 
movement of the pig in either direction. In addition, the stop pin is 
provided with a plunger means, which may be operated hydraulically or 
mechanically from a point outside of the pipeline, to open or close the 
valve. The plunger means may comprise a rod connected to a piston member 
which is disposed for reciprocating movement within a chamber in the stop 
pin. The plunger is movable from a retracted position, in which the valve 
is maintained in the closed position, to an extended position in which the 
sleeve member of the valve is moved to the second position, opening the 
valve and establishing fluid communication through the tubular body 
member. The plunger can be placed in the extended position before the pig 
reaches the stop pin, causing the valve to be automatically opened upon 
contact, preventing undue hydraulic shock created by a sudden stoppage of 
pigs. 
In addition to the improved and simplified bypass valve design, the pig of 
the present invention utilizes a unique, self-energizing seal which may be 
actuated for expansion without requiring external inflation means. Cup 
type seal assemblies are mounted on the tubular body of the pig for 
propelling the pig through the line in response to fluid flow 
therethrough. The cup type seals may be slidably mounted on the body for 
limited axial movement relative thereto so as to axially compress and 
radially expand an intermediate expansible seal or packer when a suitable 
differential pressure exists across the pig with the bypass valve closed. 
The expansible seal may be of the spherical type and its interior may be 
in fluid communication with upstream fluid pressure by means of ports in 
the tubular body. Thus, the seal may be partially collapsible to enable 
the pig to traverse sharp bends. It is relatively inexpensive to produce 
and may be molded from high wear resistant materials. It is 
bidirectionally actuated with no external pressurizing source required. In 
addition, the expansible seal assists in propelling the pig and also 
assists in supporting the pig weight within the pipeline. 
Many other objects and advantages of the present invention will be apparent 
from the description which follows in conjunction with the accompanying 
drawings.

DESCRIPTION OF PREFERRED EMBODIMENTS 
Referring first to FIGS. 1-3, a pipeline pig 10, according to a preferred 
embodiment of the invention, is shown traveling through a pipeline 1, 
through the walls of which project stop means 20, to be more fully 
described hereafter. The plugging pig 10 comprises in general, a central 
tubular body 11 closed at the forward end by a head member 12, a bypass 
valve 13, a pair of seal assemblies 14 and 15 and an intermediate 
expansible seal 16. 
The head member 12 provides an annular locking surface 9, the purpose of 
which will be seen hereafter. The walls 17 of the head member 12 may be 
considered a part of the tubular body member 11 and could be integrally 
formed therewith. However, for assembly purposes these two tubular members 
may be attached by a threaded connection 18. A circumferential slot 19 may 
be cut through the walls 17 and serves as the ports or flow passage for 
the internal bypass valve 13. The head member 12 may also comprise a 
central core portion 12a from which a plurality of support vanes or 
members 21 radially project to the walls 17. Thus, except where 
interrupted by vanes 21, the port 19 completely surrounds the pig and 
provides a large flow area, which helps reduce hydraulic shock when 
movement of the pig is arrested within the pipeline, as will be seen 
hereafter. 
Projecting radially from the tubular body means 11 is a bumper means which 
may comprise a radial flange portion 22 and a cylindrical skirt portion 25 
surrounding an annular recess 26. The purpose of the bumper means will be 
more fully understood hereafter. 
The valve 13 is of the sleeve type and comprises a sleeve 27 movable from a 
first position, as shown in FIG. 1, in which the ports 19 are blocked to a 
second position (see FIG. 2) in which the ports are unblocked permitting 
fluid communication between the downstream and upstream ends of the pig. 
The sleeve 27 is provided with a radial extension 28, the forward face of 
which will provide a bearing surface for operating the valve, as will be 
seen hereafter. The valve is biased toward the first or closed position by 
a spring member 29 which is disposed within the annular recess 26 and one 
end of which bears against the flange portion 22 of the bumper. If a 
sufficient force is applied to the flange portion 28 of the sleeve 27, the 
bias of the spring 29 may be overcome allowing the sleeve valve to open. 
Appropriate annular seals 30 and 31 may be provided to prevent leakage of 
the valve 13 in its closed position. Since the only sealing against the 
sleeve member 27 is at seals 30 and 31, it will be noted that the sleeve 
member 27 is completely pressure balanced. There are no sealing areas at 
the ends of the sleeve 27, and the same pressure exists at the opposite 
ends of the sleeve 27 whether the valve is closed, as in FIG. 1, or open, 
as in FIG. 2. Since the lateral area at the opposite ends of sleeve 27 are 
equal, the forces acting thereon are equal and in opposite axial 
directions. Thus, only the biasing force of spring 29 need be overcome in 
opening the valve. Prior devices require overcoming force created by 
differential line pressure. 
The annular seal assemblies 14 and 15 are substantially the same and will 
now be described with reference to the assembly 14. The primary seal 
element 32 of the assembly 14 is of the cup type having a lip portion 32a 
which points in an upstream direction, preventing flow of fluid by the 
seal assembly in a downstream direction. Thus, the pig 10 will be caused 
to flow in a downstream direction, with the fluid flow of the pipeline. 
The sealing element 32 may be sandwiched between a pair of retainer rings 
33 and 34 connected by suitable means such as screws 35. The seal element 
and retainer rings 33 and 34 are mounted around and carried on a 
cylindrical member 36. The internal diameter of cylindrical member 36 is 
slightly greater than the external diameter of tubular body member 11 and 
may slidingly reciprocate thereon within certain limits. This movement is 
limited toward the forward end by annular stop shoulder 37. An O-ring seal 
38 may be provided to prevent leakage past seal assembly 14. 
The second seal assembly 15 is almost identical to the seal assembly 14. 
All elements are reversed except the seal element 39 which is identical to 
seal element 32. A retainer ring 40 may be threadedly connected at 41 to 
the tubular body member 11. Thus, an annular stop surface 42 is also 
provided to limit axial movement of the seal assembly 15. In addition, 
removal of the retainer ring 40 permits assembly and replacement of the 
seal assemblies of the pig 10. 
Also carried on the tubular body member 11 between the annular seal 
assemblies 14 and 15 is the expansible seal assembly 16. The expansible 
seal assembly 16 shown in the drawings is of the spherical type. However, 
it should be understood that a cylindrically shaped type could also be 
used. The expansible seal 16 may comprise a core 43 of relatively soft 
material, such as polyurethane foam, surrounded by an outer layer 44. The 
outer layer 44 is preferably of a harder polyurethane or any other 
suitable material, e.g. neoprene. It will be noted that the inner retainer 
rings, such as 34, of the seal assemblies 14 and 15 are provided with 
spherical surfaces 46 for bearing against a portion of the outer layer 44 
of the expansible seal 16. It can easily be seen that if sufficient 
oppositely directed forces are acting on seal assemblies 14 and 15, the 
axial dimension of spherical seal 16 will be contracted, causing the 
assembly to expand against the inner walls of the pipeline 1 creating a 
fluidtight seal therebetween. In addition, the interior of the seal 
assembly 16 is in fluid communication with the interior of tubular body 11 
through ports 47, allowing the pressure within tubular body 11 to assist 
in expanding the seal assembly 16. 
Thus, the seal of the pig of the present invention is self-energizing and 
requires no external inflation means as in the prior art. The cup type 
seal assemblies 14, 15 propel the pig through the line and when the pig 
movement is arrested applies mechanical force to axially compress and 
radially expand the expansible seal 16 when a suitable differential in 
pressure exists across the pig. During travel through the pipeline, the 
seal 16 is partially collapsed, enabling the pig to traverse sharper 
bends. In addition, the seal assembly 16 assists the other seal assemblies 
14 and 15 in propelling the pig through the pipeline and also assists in 
supporting the pig weight. Seal 16 may be spherical, cylindrical, or a 
combination of both, in shape and may be inexpensively molded from high 
wear resistant materials. 
A necessary part of the invention is the stop means 20. When a point is 
selected at which the pig 10 is to be stoped, one or more holes 50 may be 
cut in the walls of the pipeline 1 by hot tapping methods. In such 
methods, a nozzle and flange assembly 51 may be welded to the pipeline. 
Then a valve is attached thereto through which a drilling device may be 
inserted for cutting through the pipeline wall. Pressure protection is 
maintained throughout this procedure. This procedure is well known in the 
prior art and will not be further discussed herein. 
As mentioned, a valve 52 is attached to the nozzle and flange assembly 51. 
Attached to the valve 52 may be a mechanical or hydraulically operable 
unit (not shown) for manipulating the pin member 53. Such units are known 
in the prior art and may be seen, for example, in the aforementioned U.S. 
Pat. No. 3,503,424. For present purposes, it is sufficient to note that 
the pin member 53 may be moved with such a unit from a retracted position, 
in which the flow area of the pipeline 1 is uninterrupted, to an extended 
position, as shown in FIG. 1. As will be seen hereafter, it may also be 
moved to a further extended position. 
The stop means 20 also comprises a plunger member 55 which may comprise a 
rod portion 56 at one end of which is a piston portion 57. The piston 57 
may be mounted in a chamber 58 within pin member 53 for reciprocating 
movement along an axis which is substantially parallel to the axis of the 
pipeline 1 and tubular body member 11. When the piston member 57 is at one 
end of the chamber the rod member 56 extends toward pig 10 (see FIG. 1). 
When the piston member 57 is at the opposite end of the chamber 58, the 
rod 56 is retracted within the pin member 53 (see FIG. 3). Ports 59 and 60 
may be provided for supplying operating fluid to the plunger 55. These 
ports may be connected by suitable conduits 61, 62, schematically shown in 
FIG. 1, connected to a suitable control valve 63. The valve 63 is in turn 
connected to a fluid pressure source (not shown). When pressure is applied 
through port 59, the plunger is extended as shown in FIG. 1. When pressure 
is applied through the port 60, the plunger would be retracted as shown in 
FIG. 3. Although the plunger 55 has been shown for hydraulic operation, it 
could be adapted for mechanical or even electrical operation. 
STATEMENT OF OPERATION 
Referring now to FIGS. 4-9, in conjunction with FIGS. 1-3, the operation 
and method of the present invention will be described. As shown in FIG. 4, 
a section of pipe is to be replaced. 
Stop pin units 70, 71 and 72, similar to the units 20 described with 
reference to FIG. 1, are first installed at required locations. The units 
70 are installed at a location slightly downstream of the pipe section to 
be replaced. The units 72 are installed at a position slightly upstream of 
the section to be replaced. The units 71 are installed at some 
intermediate position, preferably fairly close to upstream station units 
72. A vent connection 73 may also be installed at a point between the 
upstream and intermediate pin stations. The pin and plunger members of the 
intermediate station pin units 71 are positioned in the extended position, 
such as 53 and 55 respectively in FIG. 1. 
Two pigs 10 and 10', of the design shown in FIGS. 1-3, are then inserted 
into the pipeline at any convenient upstream pig launching site. The pigs 
are normally launched fifteen to thirty minutes apart. The distance 
upstream may be anywhere from a few hundred feet to many miles. The bypass 
valves of each of the pigs 10 and 10' are closed allowing the pipeline 
flow and seal units to propel the pigs through the pipeline. 
As the first pig 10 arrives at the intermediate station 71, its internal 
bypass valve is automatically opened. As can best be seen in FIG. 2, this 
is due to the fact that the plunger 55, which is in the extended position, 
contacts the bearing plate 28 of the sleeve valve 27 moving the valve from 
the closed to the open position shown in FIG. 2. This accomplishes two 
things. First, it acts as a shock reducing device to reduce the hydraulic 
shock that would otherwise occur upon arresting travel of the pig 10 
through the pipeline. Secondly, it allows flow of fluid through the 
tubular body 11 and ports 19 as the second pig 10' approaches the first 
pig. Thus, fluid may be displaced between the pigs without the external 
bypass arrangements of the prior art. As the sleeve valve is opened, 
cushioning hydraulic shock, the pig 10 continues for a slight distance 
until the bumper skirt 25 engages stop pin 53, finally arresting further 
downstream movement of the pig. 
After movement of the first pig 10 has been arrested and its internal 
bypass valve opened, the pin members of the upstream station pin units 72 
are extended to arrest movement of the second pig 10'. The plungers of the 
pin units 72 may also be extended to cushion hydraulic shock caused by the 
arriving pig 10'. As previously mentioned, fluid between the pigs 10 and 
10' is displaced through the internal bypass valve of the first pig. After 
movement of the second pig has been arrested, its valve may be closed and 
the pig locked against movement in either direction by futher extension of 
the pin units to the positions shown in FIG. 1. Since the internal bypass 
valve is closed and since movement of the pig is arrested, axial forces 
will be applied to the annular seal assemblies, such as 14 and 15, causing 
the intermediate spherical seal 16 to sealingly engage the pipeline walls. 
As previously pointed out, this sealing is also aided by communication 
between upstream pressure and the interior of the seal assembly 16 through 
ports 47. 
After the second pig 10' has been locked in place, the internal bypass 
valve of the first pig 10 may be closed, by retracting the plungers 55, 
and the pin unit 71 may be retracted. Then an inert gas, such as nitrogen, 
may be introduced through connection 73 to propel the first pig 10 toward 
the downstream station 70 whose pin members have been extended, as in FIG. 
1, to arrest movement of the pig 10. In this case, however, the plungers 
may be retracted to prevent opening of the bypass valves and intermingling 
of the inert gas with pipeline fluids downstream. Since the introduction 
of inert gas may be easily regulated, very little shock will be 
experienced upon arresting movement of the first pig at the downstream 
station 70. See FIG. 6. Displacing of the first pig with the inert gas 
also automatically evacuates the line contents from the section of 
pipeline to be replaced. Although one is not needed, an external bypass 75 
can be installed as shown in FIG. 6 if it is desired to maintain flow 
through the pipeline while work is being done. 
Once the movement of the first pig is arrested at the downstream station 
70, the pin units are further extended, as in FIG. 3, locking the first 
pin in position with its internal bypass valve closed. The differential 
pressures across the pig causes the first pig expansible seal to sealingly 
engage the pipeline in a fluidtight connection. One desirable feature of 
the seal of the pig of the present invention is that it is bidirectional 
in operation. Thus, a seal can be maintained whether pressure is greater 
on one side of the pig or the other. 
With both pigs locked in position and with their bypass valves closed, the 
pipe section to be replaced can be cut out of the line, as shown in FIG. 
7. A new section may be safely welded into place and the welds tested 
while holding high test pressures. 
After the new section has been welded in place, the internal bypass valve 
of the second pig 10' is opened by actuation of the plungers of the pin 
unit 72. This allows the new pipeline section to be filled with line fluid 
and equalizes the pressure across the pigs. As the line fluid fills the 
new section, any air or other gas may be vented through the vent 
connection 73. 
When the new section is completely filled, the bypass valve of the second 
pig is again closed, by retracting the plungers of pin units 72 and the 
pins of all pin units are retracted, releasing the pigs for pumping to 
downstream receiving traps. All pin units may then be removed and the 
nozzle fittings to which they were attached may be blinded over. 
It should here be noted that the intermediate pin station 71 could be 
eliminated if desired. In such a case the first pig would be sent directly 
to the downstream station 70. However, in such a method it would be 
necessary to remove pipeline fluids trapped between the pigs by pumping 
out the section to be repaired. 
From the foregoing description, it can be seen that the method of replacing 
a section of pipeline as described herein is much superior to the prior 
art. No external bypass arrangements are required. Fewer strength reducing 
holes are required in the pipe. Less welding is required. Automatic 
evacuation and refilling of the pipe section is accomplished. 
This method is made possible by the use of the unique and improved plugging 
pig of the present invention. The novel sleeve type, pressure-balanced, 
internal bypass valve and the novel bidirectional, self-energizable seal 
of this pig is superior to any of those of the prior art. In addition to 
replacing sections of pipeline, a pair of the pigs of the present 
invention may be used to replace or repair valves, install lateral 
connections or special fittings, tie-in booster stations, install 
detectors or other special equipment, etc. The pigs may be used in pairs 
with either two or three stop pin stations. If only two stop pin stations 
are employed, it will ususally be necessary to pump out the line fluid 
trapped between pigs. A single pig may be used for replacement of scraper 
trap assemblies, replacement of block valves, installation of lateral 
lines and tie-ins, and hydrostatic testing. In fact, the pig of the 
present invention is extremely versatile and flexible. 
Although only one embodiment and method of use of the invention have been 
described herein, many modifications and uses can be made without 
departing from the spirit of the invention. It is therefore intended that 
the scope of the invention be limited only by the claims which follow.