A fluid-swivel with a first member having a first face, a second member having a second face adjoining and mating with the first face of the first member, the first face and the second face being positioned to rotate relative to each other about a common axis, a fluid conduit defined by a first raceway in the first face and a second raceway in the second face opposite the first raceway when the first and second raceways are at a predetermined index point relative to each other, said fluid conduit at the indexed condition defining a path in one revolution about the common axis which advances the conduit a distance of at least one width of the conduit, an inlet conduit communicating with the fluid conduit, and an outlet conduit communicating with the fluid conduit.

This invention relates to a rotary or swivel joint for fluid flow. More 
particularly, the invention is concerned with a fluid-swivel which is 
piggable for use in loading and unloading a tanker offshore. 
The loading and unloading of ocean-going tankers moored at offshore 
locations has become common. Many such moorings comprise a fixed or 
buoyant offshore terminal to which the tanker is secured by a suitable bow 
attachment which permits the vessel to swing in a complete circle about 
the terminal in response to the forces of wind, sea currents and tide. See 
U.S. Pat. Nos. 3,074,082; 3,077,615; 3,817,355 and 3,614,869. One or more 
conduits leading from the terminal to the tanker permit the tanker to be 
loaded or unloaded with a variety of liquids, including crude oil. 
In order to permit the tanker to swing around the terminal, each conduit 
must be equipped with a swivel joint. Swivel joints of various types are 
known in the art. See U.S. Pat. Nos. 4,052,090; 3,698,433; 3,614,869; 
3,430,670; 3,351,360; 3,082,440 and 2,894,268. 
Crude oils are widely loaded and unloaded through fluid-swivels on offshore 
terminals. Many of the crude oils contain solid materials, such as wax or 
asphalt, which stick to the walls of the pipes feeding oil to and from the 
fluid-swivel, as well as in the conduits in the fluid swivel itself. 
Unless these solid deposits are removed, the effective internal diameter 
of the pipes and fluid-swivel will be reduced so much that fluid flow is 
seriously impeded, even to the point of total blockage. It is customary in 
the oil industry to force a pig through pipelines to remove solids 
deposited in them. However, present fluid-swivels and associated piping 
are not designed to be piggable, and will not permit a pig to travel 
through, so that cleaning them of deposits involves a costly and time 
consuming disassembly and reassembly operation. There is thus a need for a 
piggable fluid-swivel which can be used on an offshore tanker mooring 
terminal. 
According to the invention, there is provided a piggable fluid-swivel 
comprising a first member having a first face, a second member having a 
second face adjoining and mating with the first face of the first member, 
the first face and the second face being positioned to rotate relative to 
each other about a common axis, a spiral conduit defined by a first 
raceway in the first face and a second raceway in the second face opposite 
the first raceway when the first and second raceways are at a 
predetermined index point relative to each other, said fluid conduit at 
the indexed condition defining a path in one revolution about the common 
axis which advances the conduit a distance of at least one width of the 
conduit, an inlet conduit communicating with the fluid conduit, and an 
outlet conduit communicating with the fluid conduit. 
Regardless of whether the first member or the second member is stationary 
and the other is rotated, there is continuous communication between the 
raceways on the drum first and second members so that fluid can flow from 
the inlet conduit, through the fluid-swivel, and to the outlet conduit, at 
all positions through 360.degree. rotation of the first member or second 
member relative to the other. The fluid-swivel, however, is only piggable 
when the first and second members are located in or about in the indexed 
condition or position which provides a smooth bore fluid conduit, such as 
one circular in cross-section. When the first and second members are 
properly indexed, a pig can readily enter the fluid-swivel, continue 
through the fluid conduit, and exit through the outlet conduit. The 
construction of the fluid-swivel prevents the pig from going in an endless 
circle in it and avoids ports which could bind the pig in place or direct 
it back to the inlet conduit. 
The fluid-swivel can take several forms which are related structurally. 
Thus, the first member can be a drum and the second member can be a ring 
which surrounds the drum. The fluid conduit can be partially in the ring 
and partially in the drum. The fluid-swivel can also be formed of two 
plates, one on top of the other with the fluid conduit partially in each 
plate. Structurally intermediate to these two embodiments is a third 
embodiment in which the first and second faces of the members are matching 
conical surfaces which contain raceways defining the fluid conduit. 
Regardless of the shape of the faces, a seal is generally located on each 
side of the liquid conduit to restrain liquid flow between the mating or 
matching faces. 
The fluid conduit formed by the first and second faces is advisably a 
spiral or helix with a uniform pitch or curve from inlet to outlet. 
However, the fluid conduit can have a non-uniform pitch from inlet to 
outlet. Thus, the fluid conduit can have a stepped portion which displaces 
the path of the fluid conduit from a smooth curve or arc. 
To facilitate movement of a pig into and out of the fluid-swivel, the inlet 
and outlet conduits are made circular and with a diameter substantially 
the same as the diameter of the fluid conduit. 
The flow of fluid through the fluid-swivel is sometimes further facilitated 
by providing a second outlet located about 180.degree. from the first 
outlet and with the second outlet about normal to the fluid conduit at 
that location. By having the second outlet normal to the fluid conduit a 
pig is unlikely to become stuck in it. However, when the fluid-swivel is 
to be pigged, this second outlet can be plugged and the fluid conduit 
thereby made smooth for uninterrupted passage of the pig. 
It is further desired to have the inlet conduit, and outlet conduit, 
communicate tangentially with the fluid conduit. 
A preferred embodiment of piggable fluid-swivel provided by the invention 
comprises a drum having a peripheral circular wall, a raceway in, and 
extending completely around, the circumference of the drum wall, a ring 
coaxially positioned around the drum and having an internal circular wall 
in mating contact around the drum wall, the drum or the ring being in 
stationary position during fluid flow and the other being rotatable 
relative to it, a raceway in, and extending completely around, the ring 
internal wall, the raceways in the drum and the ring being opposite and 
matching each other when the drum and ring are at a predetermined index 
point relative to each other thereby forming a fluid conduit circular in 
radial vertical section through the drum and ring, said fluid conduit at 
the indexed condition defining a path in one revolution which advances the 
conduit a distance of at least one conduit diameter in a direction axial 
to the drum and ring, an inlet conduit communicating with the fluid 
conduit, and an outlet conduit communicating with the fluid conduit. 
The fluid conduit formed by the drum and ring raceways is advisably a 
spiral or helix with a uniform pitch from inlet to outlet. However, the 
fluid conduit can have a non-uniform pitch from inlet to outlet. Thus, the 
fluid conduit can have a stepped-up portion which displaces the path of 
the fluid conduit about one diameter about the drum and swivel coaxis. 
Except for the stepped-up portion, the remainder of the fluid conduit 
would lie in two spaced apart planes, perpendicular to the coaxis of the 
drum and ring. The stepped-up portion is desirably located in an angle of 
about 270.degree., and advisably about 180.degree., defined by radii of 
the drum and ring coaxis. 
Although the drum and ring mating walls may be sloped or conical sections, 
it is preferable to have the mating walls parallel to the drum and ring 
axis as circular cylindrical surfaces.

The fluid-swivel 10 embodiment of FIGS. 1 to 4 is mounted on a support base 
11 which can be located on an offshore tanker loading or unloading 
terminal which permits a tanker moored to it to rotate 360.degree.. The 
fluid swivel 10 has a stationary drum 12 fixedly joined to support base 
11. Drum 12 has parallel top and bottom surfaces 13 and 14, an outer 
peripheral vertical circular wall 15 and an inner vertical circular wall 
16. 
Raceway 17 in the form of a helix is located in, and extends completely 
around, the circumference of drum wall 15. The raceway 17 is semi-circular 
in radial vertical section through the drum with the diameter of the 
raceway located in the surface of drum wall 15. The slope of helical 
raceway 17 is slightly more than one raceway diameter per revolution of 
the drum, thereby providing a landing 18 (FIG. 2) between the beginning 
and the end of the raceway. 
Ring 21 is coaxially positioned around drum 12. Ring 21 has top and bottom 
spaced-apart horizontal surfaces 22 and 23, an internal vertical circular 
wall 24 and an external vertical circular wall 25. Ring 21 is rotatably 
supported by rollers 26 mounted at the top of support base 11. The ring 
internal wall 24 fits in mating contact with drum external wall 15. 
Helical raceway 27 is located in, and extends completely around, the ring 
internal wall 24. Raceway 27 is semi-circular in radial vertical section 
through ring 21 with the diameter of the raceway located in the surface of 
ring wall 24. The pitch of raceway 27 is the same as the pitch of raceway 
17. When the fluid-swivel is in indexed position, as shown in FIGS. 1 to 
4, the ring raceway 27 of the drum raceway 17 will be precisely opposite 
each other and together they form a fluid conduit 28 circular in 
cross-section through which a pig can travel unobstructed. 
Packing glands 29, shown schematically in FIG. 2, hold sealing material in 
place to prevent or restrain fluid flow between the mating drum and ring 
walls and out of the fluid-swivel. 
The fluid-swivel 10 of FIGS. 1 to 4 has an inlet conduit 30 which 
communicates tangentially with the fluid conduit 28. In addition, the 
fluid-swivel 10 has an outlet conduit 40 communicating tangentially with 
the fluid conduit 28 but in an opposite direction to the inlet conduit 30, 
at the index point or position. This tangential arrangement of the inlet 
and outlet conduits permits a pig to readily go in the fluid conduit 28 as 
well as out of it. 
FIG. 5 shows schematically the relationship of the profile of the ring 
raceway 27 taken at the outlet conduit to the drum raceway 17 as the ring 
21 is rotated counter-clockwise when viewed in plan as shown in FIG. 1. 
FIG. 5 also shows the relationship of the raceways when the outlet conduit 
profile of the ring raceway is located at various angles of rotation away 
from the index position, thus establishing that there can be fluid flow 
along the raceways no matter where the ring is positioned around the drum. 
There will be, as shown in FIG. 5, a cross-over of fluid between the upper 
and lower parts of the ring raceway 27 where it spans the drum raceway 17. 
This may lead to turbulent fluid flow which can be reduced by including a 
second fluid outlet 50 in normal communication to the fluid conduit 28. 
The second outlet 50 is desirably located about 180.degree. from the first 
outlet 40. When the fluid-swivel is to be pigged, second outlet 50 is 
advisably plugged so that the pig cannot be deflected into that outlet 
instead of continuing on its route to the first outlet. 
It will be apparent that if reverse fluid flow and pigging in the 
fluid-swivel 10 is desired that outlet 40 may be made an inlet, and inlet 
30 may be made an outlet. 
FIG. 6 illustrates a second embodiment of the invention which differs from 
the embodiment shown in FIGS. 1 to 4 only in the path of the fluid conduit 
60. The fluid conduit 60 has two portions 61 and 62 which lie in two 
spaced-apart planes perpendicular to the coaxis of the drum 12 and ring 21 
and these portions are joined by a smoothly curved stepped-up portion 63 
which can be readily traversed by a pig. The stepped-up portion extends 
less than 180.degree. around the swivel. The complementary mirror-image 
raceways in the drum and ring form a fluid conduit which is circular in 
vertical section when the ring and drum are in index position as shown in 
FIG. 6. This embodiment also permits continuous fluid flow at all 
positions of rotation of the ring around the drum. 
In order to have fluid flow through the swivel of this invention, 
regardless of the position of the ring on the drum, the fluid conduit 
should rise for a distance at least the diameter of the fluid conduit per 
each revolution but it should not rise close to or more than two diameters 
because then there will be very limited or no fluid flow at some portions 
during rotation of the ring on the drum. 
FIGS. 7 to 10 illustrate another embodiment of the invention. In this 
embodiment, the first member is plate 70 and the second member is plate 
71. Each of plates 70 and 71 is shaped like a circular disc with 
horizontal top and bottom parallel surfaces and a hole 72 in the center. 
Spiral fluid conduit 73 is defined by two matching but opposing spiral 
raceways. One raceway 74 is in the top of plate 70 and the other raceway 
75 is in the bottom of plate 71. Seals 76 are positioned on each side of 
fluid conduit 73 to prevent leakage. Clamp means, not shown, is used to 
hold plates 70 and 71 rotatably together. 
Inlet conduit 77 communicates smoothly with one end of fluid conduit 73 and 
outlet conduit 78 communicates smoothly with the other end of fluid 
conduit 73. As a result, when the two plates are indexed as shown in FIGS. 
7 to 9, the fluid conduit 73 has a smooth bore, circular in lateral 
cross-section, through which a pig can move unobstructively. A second 
outlet conduit 79 can be placed in plate 71 to communicate with the fluid 
conduit 73 to thereby facilitate removal of fluid when the swivel rotates 
substantially out of the index position. 
FIG. 10 illustrates the various cross-sectional shapes of the fluid conduit 
73 as the top plate 71 is rotated while the lower plate 70 is stationary. 
The angle degrees adjacent to the top plate indicate the degrees of 
clockwise rotation of the top plate from the index point or position as 
shown in FIG. 7. It can be readily seen from FIG. 10 that a continuous 
fluid conduit is maintained during complete rotation of plate 71 relative 
to plate 70 so that fluid can flow into the swivel and out at all swivel 
angle positions. 
The third embodiment of the invention illustrated by FIG. 11 has a lower 
plate 90 with a central hole 91 and a top plate 92 with a central hole 93. 
Lower plate 90 has in its top a conical face 94 which mates with conical 
face 95 in the bottom of top plate 92. 
Spiral fluid conduit 96 is formed by opposing matching raceways 97 and 98 
in conical faces 94 and 95 respectively. The spiral fluid conduit is thus 
similar to fluid conduit 73 in the second embodiment. Seals 99 are placed 
on each side of fluid conduit 96 to prevent leakage of fluid between 
conical faces 94 and 95. Clamp means, not shown, is used to rotatably 
secure plates 90 and 92 together. Inlet conduit 100 communicates with one 
end of fluid conduit 96 and outlet conduit 101 communicates with the other 
end of the fluid conduit 96. In this embodiment it is generally preferred 
to have plate 90 stationary and to rotate plate 92. During such rotation a 
continuous fluid conduit 96 is maintained since the fluid conduit will 
take forms very similar to those illustrated by FIG. 10. 
FIGS. 12 and 13 illustrate a further embodiment of the invention which 
substantially employs the fluid-swivel arrangement already illustrated by 
FIGS. 1 and 2. The embodiment of FIGS. 12 and 13, however, not only 
permits the ring 21 to rotate but also the drum 12 to a limited extent. 
Thus, the inlet conduit 30 is connected to a swivel 105 from which conduit 
106 extends to swivel 107. Conduit 108 then leads away from swivel 107 to 
be connected to a suitable joint. FIG. 13 illustrates in phantom how drum 
12 can be rotated due to the swivels 105 and 107 positioned in the inlet 
feed line. By providing the drum 12 with a capability to be rotated it is 
much easier to index the drum and ring for a pigging operation rather than 
to move the ship or vessel to reach the desired index point. It should be 
understood that the ring 12 of the embodiment shown in FIGS. 12 and 13 can 
rotate 360.degree.. The vertical center pipe 115 passing through the 
center of the fluid-swivel can be used as an independent fluid flow line 
for loading or unloading a ship or vessel. 
The system shown in FIGS. 12 and 13 can also be used on the ring instead of 
the drum when the drum is the primary rotating member, and it does not 
make any difference whether the inlet or outlet is on the drum or the 
ring. The system can also be used in the embodiments of the invention 
illustrated by FIGS. 7 to 11. 
The described fluid-swivel embodiments can be used to convey liquids, gases 
and liquefied gases such as crude oil, fuel oil, natural gas and liquefied 
natural gas. 
It should be understood with respect to the invention that all of the 
piggable fluid-swivel embodiments shown herein can be used in conjunction 
with an axially positioned fluid line having its own conventional swivel, 
thereby providing a multi-line fluid loading or unloading system. 
Furthermore, the fluid-swivels of this invention can be mounted one above 
or around the other to obtain a multi-line fluid handling system. 
The foregoing detailed description has been given for clearness of 
understanding only, and no unnecessary limitations should be understood 
therefrom as modifications will be obvious to those skilled in the art.