A piggable fluid swivel comprising a first element on which a second element is rotatably mounted. Grooves in both the first and second elements align to form a continuous flow passage between the elements. Openings are provided through the first and second elements and into the flow passage whereby fluid can enter through one element, flow through at least a portion of the flow passage, and then exit through the other element. A flow barrier means similar to a gate valve is provided on one of the elements and includes a baffle plate that is extendable between an open position and a closed position. In an open position, the elements can be easily assembled and disassembled. In a closed position, the baffle plate blocks backflow in the fluid passage which allows pressure to build behind any pig that may become stuck in the flow passage to free the pig and carry it from the swivel. The swivel may be coaxially stacked to provide a multiline piggable fluid swivel.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a fluid swivel and more particularly 
relates to a multiline piggable fluid swivel which allows a pig used for 
the removal of deposits from the inner walls of the fluid lines connected 
to the swivel to readily pass therethrough. 
2. Description of the Prior Art 
In the marine production and/or transportation of hydrocarbons and related 
products, it is common to use an offshore terminal to load/offload the 
hydrocarbons onto or off sea-going tanker vessels. Such offshore terminals 
are well known and are collectively referred to as single point moors. In 
carrying out such loading/offloading operations, a vessel is moored to the 
terminal and flowlines from the vessel are attached to corresponding 
flowlines on the terminal. Since it is well known that the wind and waves 
will normally cause a vessel to move (i.e. weathervane) about its mooring 
point, the flowlines need to be connected through a swivel mounted on the 
terminal so that the vessel may weathervane during the loading/offloading 
operations without snarling or damaging the flowlines. Further, since 
several fluids may be simultaneously loaded/offloaded, the swivel needs to 
accommodate a multitude of flowlines. 
Multiline swivels of the type mentioned above are well known in the art, 
see, for example, U.S. Pat. Nos. 2,894,268; 3,082,440; 3,351,360; 
3,698,433; 4,052,090; 4,111,467 and 4,126,336. However, many of the 
hydrocarbons (e.g. crude oil) loaded/offloaded through such swivels 
contain components such as wax or asphalt which can deposit and build up 
in the flow conduits of the swivel and on the interior walls of the 
flowlines connected to the swivel. Unless these deposits are routinely 
removed at desired intervals, flow through the flowlines and swivel may 
become severely impeded or blocked altogether. 
It is common in the petroleum art to remove such deposits from ordinary 
flowlines by pumping a through-flowline-tool or "pig" through the lines 
which scrapes or dislodges the deposits from the flowlines so that the 
deposits are carried out of the lines by the fluids flowing therethrough. 
However, most multiline swivels of the types disclosed in the above cited 
patents are not designed to be piggable and will not permit a pig to be 
pumped therethrough without the risk of sticking the pig in the swivel. 
When such swivels are used in terminals through which deposit-forming 
fluids are loaded/offloaded, operations have to be suspended at determined 
intervals so the flowlines can be pigged and the swivel can be 
disassembled and cleaned. 
To avoid such timely and costly delays, swivels which are piggable, 
commonly referred to as piggable swivels, have recently been designed and 
proposed for use in such environments. For example, in U.S. Pat. No. 
4,174,127 a piggable swivel is disclosed wherein a guide means is 
assembled through the outlet conduit of the swivel and projects into the 
flow path of the swivel to physically catch and direct the pig out of the 
swivel as it passes therethrough. Further, in U.S. Pat. No. 4,183,559, a 
piggable swivel is disclosed wherein the fluid path through the swivel is 
designed so that when the swivel is properly and precisely indexed, the 
pig can smoothly pass through the swivel. 
SUMMARY OF THE INVENTION 
The present invention provides a multiline piggable swivel which allows a 
pig to pass therethrough even when the swivel is in any of a wide range of 
different positions. Basically, each flow passage through the multiline 
swivel is provided with a flow barrier means which is movable back and 
forth between an open position and a closed position. When the barrier 
means is in its open position, the swivel can be easily assembled and/or 
disassembled. When the barrier means is in its closed position, fluid flow 
through the flow passage is blocked at that point thereby preventing 
backflow through the passage when and if a pig becomes stuck in the 
passage. 
More specifically, the piggable fluid swivel is comprised of at least one 
first element such as a cylindrical core having an outer cylindrical 
surface thereon. A second element such as a cylindrical ring having an 
inner cylindrical surface is rotatably mounted onto the core so that the 
inner surface of the ring rotatably mates with the outer surface of the 
core. Both the outer surface of the core and the inner surface of the ring 
have respective circumferentially-extending grooves thereon which align to 
form a flow passage through the swivel. 
An opening into the groove on the core and an opening into the groove on 
the ring provide for ingress and egress of fluid to and from the swivel. 
These openings enter the flow path at as smooth of angles, e.g. tangential 
to flow passage, as is possible. A fluid barrier means is provided on 
either the ring or the core and has structure similar to a gate valve in 
that a baffle plate is movable into and out of the flow passage of the 
swivel. When the barrier means is in an open position, the baffle plate is 
retracted sufficiently so that the ring can be positioned onto or removed 
from the core. When the barrier means is in a closed position, the baffle 
plate will fully extend into the flow passage to substantially block flow 
through the flow passage at that point. 
To carry out a pigging operation, barrier means will be in its closed 
position. A pig enters either the opening in the core or the ring, flows 
through at least a portion of the flow passage, and exits through the 
other of the openings. If a pig gets stuck in the flow passage, the fluid 
can only backflow within the flow passage to the closed baffle plate. This 
permits pressure within the flow passage to build behind the stuck pig to 
free same. The barrier means may be left in its closed position even when 
pigging is not being carried out since the closed baffle plate will not 
interfere with normal flow through the swivel. The barrier means is 
normally opened only when the swivel is to be assembled or disassembled. 
In the preferred embodiment, the present piggable swivels, as described 
above, can be coaxially stacked to provide a multiline piggable swivel. In 
another embodiment, a multiline piggable swivel is provided in accordance 
with the present invention which has a core element on which a plurality 
of spaced ring elements are rotatably mounted, each ring element 
constructed substantially as described above and each having a separate 
barrier means thereon which operates as previously described. Further, in 
still another embodiment of the present invention, the swivel is comprised 
of first and second cylindrical elements which rotate one on top the other 
.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring more particularly to the drawings, FIGS. 1-3 disclose fluid 
piggable swivel 10 which is comprised of a first or core element 12 having 
an outer surface 13. Core element 12 is mounted on support 11 which may be 
any structure on which a swivel of this type is employed, e.g. an offshore 
loading/offloading terminal such as a single point mooring facility. A 
second or ring element 14 having an inner surface 15 is concentrically 
mounted on core element 12 by means of bearings 16 (FIG. 3) or the like so 
that elements 12 and 14 are free to rotate relative to each other. 
Circumferential grooves 17 and 18 both having semi-circular cross-sections 
are provided on surfaces 13, 15, respectively, and are positioned so that 
when ring element 14 is assembled on core element 12, grooves 17 and 18 
cooperate to form substantially circular, continuous fluid passage 20 in 
swivel 10. Seals 21, e.g. O-rings or, preferably, lip type seals, are 
provided (FIG. 3) between surfaces 13, 15, to prevent leakage from passage 
20 as is understood in the art. 
A first opening 22, normally functioning as the inlet for swivel 10, is 
provided through core element 12 into groove 17 and is adapted to be 
connected to an external source, e.g. fluid conduit 23 (FIG. 1). A second 
opening 24, normally functioning as the outlet for swivel 10, is provided 
through ring element 14 into groove 18 and is adapted to be connected to a 
second external source, e.g. a flowline (not shown). As shown in FIG. 2, 
both inlet 22 and outlet 24 are constructed so that each will enter or 
exit passage 20 at as flat of angle with respect thereto as is possible 
(i.e. as close to tangential as practical) so that pig 30 (described 
below) may easily and smoothly enter and exit passage 20. 
As illustrated, swivel 10 also has a pipe 25 (FIG. 1) extending upward 
along the center axis of swivel 10 and out top plate 26. Pipe 25 is 
connected to conduit 28 through a conventional swivel 27 and normally 
provides a second fluid path through swivel 10. However, as understood in 
the art, pipe 25 could also be representative of an electric line, 
electric swivel, a cable, or similar element normally associated with 
swivels of this type. 
The present description to this point describes the basic structure of a 
typical concentric fluid swivel of the type known in the art. However, it 
is considered impractical to attempt to pig such swivels, even those 
modified to have tangential inlets and outlets, since tests have shown 
that it is necessary to be able to build up pressure behind a pig to 
insure that it will pass completely through the swivel and will not become 
stuck in the flow passage of the swivel. As understood in the art, pigs 
used for this type of pigging operation are normally spherical or 
cylindrical in shape and are formed from an elastic material, e.g. 
neoprene rubber, etc. with a diamater slightly greater than the diameter 
of the flowlines to be pigged. The pigs are slightly compressed as they 
pass through the lines which insures that the pigs will remain in good 
contact with the flowline walls thereby dislodging the unwanted deposits. 
However, if the deposits are thick enough to substantially reduce the 
diameter of the flowline, there is a real possibility that a pig may 
become stuck. In a regular flowline, the pressure behind the stuck pig 
continues to build up until it is sufficient to free the pig. 
However, as can be seen in FIG. 2, if pig 30 becomes stuck in flow passage 
20 of a conventional concentric fluid swivel of the type described, the 
normal path for fluid flow (clockwise in FIG. 2) becomes blocked whereupon 
the fluid will merely backflow (counterclockwise in FIG. 2) to equalize 
the pressure across pig 30 before it flows out swivel 10 through outlet 
24. Therefore, the pressure in passage 20 cannot build up sufficiently 
behind pig 30 to unstick pig 30 and the swivel must be disassembled to 
free the pig. 
In accordance with the present invention, swivel 10 includes a fluid 
barrier means 31 which is movable between a retracted or open position, in 
which it permits easy assembly and disassembly of the swivel, and an 
extended or closed position in which it substantially blocks backflow of 
fluid in the fluid passage of the swivel. In its closed position, the 
barrier means 31 provides a means by which sufficient pressure may be 
built up to free a stuck pig. 
More particularly, fluid barrier means 31, which is basically a gate valve, 
is comprised of baffle plate 32 having a semi-circular forward edge 33 
which substantially conforms to the cross-sectional configuration of 
groove 17 (FIG. 3). Operating rod 34 is rotatably attached to the rear end 
of plate 32 by any suitable means, such as flange or shoulder 35 on rod 34 
which is rotatably received in a slightly oversized, complementary recess 
in plate 32. Rod 34 is threaded at its other end and extends through 
housing 36 which, in turn, is preferably formed as an integral part of 
ring element 14. Housing 36 has a recess 37 which is adapted to receive 
baffle plate 32 when plate 32 is in its open position (shown by dotted 
lines in FIG. 3). The threaded end of rod 34 cooperates with threaded 
portion 38 of housing 36 whereby baffle plate 32 is moved back and forth 
between its open and closed positions by rotation of rod 34. Seal 39, e.g. 
O-ring, is positioned in housing 36 around rod 34 to prevent leakage from 
housing 36. 
Although threaded rod 34 is the preferred means for operating baffle plate 
32, it should be understood that other means may also be used to move 
baffle plate 32 between its open and closed positions. For example, FIG. 4 
discloses a modified operating means for baffle plate 32 which comprises 
housing 36a having hydraulic chamber 40 therein. Rod 34a has piston 41 and 
seal 44 attached on the rear end thereof and positioned for slidable 
movement in chamber 40. Ports 42, 43 are provided into chamber 40 and are 
adapted to be connected to hydraulic source (not shown) to operate piston 
41 as is understood in the art. 
Still other actuating means, e.g. rack and pinion, ratchet mechanisms, 
etc., may be used to operate rod 34 and move baffle plate 32 between its 
open and closed positions without departing from the present invention. 
In operation, ring element 14 is assembled and/or disassembled onto core 
element 12 with baffle plate 32 in its open or retracted position within 
recess 37 of housing 36. This allows ring element 14 to easily slip over 
core element 12 since the inner end 33 of plate 32 does not protrude 
beyond ring element 14 and does not interfere with the assembly or 
disassembly of swivel 10. Once swivel 10 is assembled, baffle plate 32 is 
moved to its closed position by actuating rod 34. Preferably, baffle plate 
32 is bottomed in groove 17 and then backed off until it just clears 
groove 17. A minimal clearance is thus achieved between edge 33 of plate 
32 and groove 17 which allows elements 12 and 14 to smoothly rotate 
relatively to each other but at the same time the clearance is small 
enough so as to provide any substantial bypass for fluid flow around plate 
32. Barrier means 31, once closed, may be left closed even during normal 
loading/offloading operations since the closed position of means 31 will 
not interfere in any way with the normal flow of fluid through passage 20 
of swivel 10 and will serve in some degree as a scraper to remove deposits 
from passage 20 whenever elements 12 and 14 rotate relative to each other. 
When a pigging operation is to be carried out, barrier means 31 is in its 
closed position. The pigging operation can be carried out in all of the 
relative indexed positions between ring element 14 and core element 12 
except that position where barrier means 31 is positioned directly 
adjacent inlet 22. In such an event, ring element 14 is rotated slightly 
to move baffle plate 32 to one side or the other of inlet 22. Pig 30 is 
then flowed into swivel 10 through inlet 22, through passage 20, and out 
outlet 24. If pig 30 becomes stuck, fluid can only backflow within passage 
20 until it encounters baffle plate 32 which physically prevents it from 
flowing into outlet 24. This blockage of backflow allows fluid pressure to 
build behind stuck pig 30 to free same and carry it out of swivel 10 along 
its normal path through outlet 24. Further, if the need arises, swivel 10 
may also be pigged in a reverse direction wherein pig 30 enters through 
outlet 24 (now the inlet) and exits through inlet 22 (now the outlet). 
Housing 36 is shown as preferably being positioned on second or ring 
element 14 adjacent outlet 24 and constructed so that baffle plate 32 
moves between its open and closed positions along a path which is 
substantially parallel to the outlet. This positioning and construction of 
housing 36 is considered to be most practical in allowing ease of 
operation in the majority of applications where swivel 10 is likely to be 
used. However, it should be recognized that housing 36 can be positioned 
at other points on ring element 14 or can be positioned on core element 12 
without departing from the present invention. It is only necessary that 
baffle plate 32 be movable to an open position to allow assembly and 
disassembly of swivel 10 and be movable to a closed position to 
substantially block fluid flow through passage 20. Likewise, housing 36 
can be constructed so that its axis lies on lines other than that parallel 
to outlet 24, e.g. on a radius of concentric elements 12, 14, whereby 
baffle plate 32 would move between its open and closed positions along a 
path different than that shown. Again, it is only necessary that baffle 
plate 32 be capable of being retracted sufficiently in recess 37 of 
housing 36 to completely clear groove 17 and be capable of being 
extendable to substantially block flow through flow passage 20. 
Although it will be recognized that a plurality of piggable fluid swivels 
10 can be coaxially stacked one on another to provide a multiline piggable 
swivel, a preferred multiline piggable swivel 100 in accordance with the 
present invention is shown in FIG. 5. Swivel 100 is comprised of a 
plurality of modules (six shown) 101a-f which are vertically stacked and 
mounted together. Each module, e.g. 101a, is comprised of a first or core 
element 112a and a second or ring element 114a rotatably mounted thereon. 
Each core element and ring element combination, e.g. 112f, 114f, has 
circumferentially extending grooves, e.g. 117f, 118f, respectively, 
therein which form a flow passage, e.g. 120f, through their respective 
module. A plurality of flowlines 123a-f extend upward through respective 
core elements 112 and are connected to their respective inlets 122a-f. In 
accordance with the present invention, each ring element 114a-f has a 
tangential outlet 124a-f, respectively. For a more detailed description of 
the structure of swivel 100 and its normal operation, reference is made to 
U.S. Pat. No. 4,126,336 which is incorporated herein by reference. 
Each module 101a-f of swivel 100 has a fluid barrier means 131 (only three 
shown; 131b, 131d, 131e) on its respective ring element 114a-f. Each fluid 
barrier means 131 is identical in structure and operation as that of fluid 
barrier means 31 described in detail above. It can be seen that a separate 
pigging operation can be carried out through each flowline 123a-f through 
its respective swivel module 101a-f in the same manner as fully described 
above. 
A further embodiment of the present invention is disclosed in FIGS. 6 and 7 
wherein piggable swivel 50 is comprised of a first or lower element 51 
having a first surface 52 thereon. Second or upper element 53 a second 
surface 54 is rotatably mounted onto lower element 51 by means of bearings 
(not shown) or the like. Surface 52 has a circularly extending groove 55 
of semi-circular cross-section provided therein which aligns with an 
identical groove 56 in surface 54 to define fluid passage 57 through 
swivel 50. Seal means (not shown), e.g. O-rings or lip type seals, are 
properly positioned between elements 51, 53 to prevent leakage from 
passage 57. A first opening 58, normally the inlet, is provided through 
lower element 51 into passage 57 and a second opening 59, normally the 
outlet, is provided through upper element 53 into passage 57. Both 
openings enter passage 57 at a smooth angle and are preferably flared to 
allow smooth entry and exit of a pig during pigging operations. 
Fluid barrier means 31a is shown as being positioned on upper element 53 
but it should be understood that means 31a can equally as well be 
positioned on bottom element 51. The construction and operation of flow 
barrier means 31a is identical to that of flow barrier means 31 (see FIG. 
3) as fully described above. It is understood that the baffle plate (not 
shown) of means 31a will be received into a recess within housing 36a when 
in open position so that it completely clears groove 55 and will extend 
into groove 55 when in a closed position to substantially block flow 
through passage 57. With means 31a in a closed position during a pigging 
operation, if pig 30 (FIG. 6) becomes stuck, backflow from inlet 58 will 
be blocked by means 31a allowing pressure to build behind pig 30 to free 
same and carry it out of swivel 50 through outlet 59. Where conditions 
allow swivel 50 to be assembled and/or disassembled by merely moving 
elements 51, 53 directly toward or away from each other, there will be no 
need to move means 31a to an open position. However, if swivel 50 must be 
assembled and/or disassembled by sliding elements 51, 53 one onto the 
other, then means 31a will have to be moved to an open position. 
Various modifications and alterations of this invention will become 
apparent to those skilled in the art without departing from the scope and 
spirit of this invention, and it should be understood that this invention 
is not to be unduly limited to that set forth herein for illustrative 
purposes.