PERSCHKE MALCOLM J
| US4629221A | 1986-12-16 |
| 1. | An improved product swivel which includes a cylindrical internal housing having a longitudinal axis and a rotatable swivel housing which is rotatively coupled about the outer perimeter of said internal housing, with an internal flow path provided from said internal housing to said swivel housing, said internal housing being coupled to a second cylindrical housing wherein the improvement comprises, a connector having mating box and pin end portions with one portion secured to an end of said internal housing of said product swivel and the other portion secured to an end of said second cylindrical housing, said mating box and pin end portions having nonhelical, interlocking circumferential teeth which are arranged and designed to which only when fully made up and with said box end portion being shrunk onto said pin to end portion, wherein said circumferential teeth are wedged together, thereby producing a high axial preload between said box and pin end portions that maintains stiffness and enhances fatigue characteristics of said connector. |
| 2. | The improved product swivel of claim 1, wherein, said second cylindrical housing is a mounting base member. |
| 3. | The improved product swivel of claim 1, wherein, said second cylindrical housing is an internal housing of a second product swivel stacked on top of said improved product swivel. |
| 4. | The improved product swivel of claim 1 wherein, said box portion is shrunk onto said pin end portion by injecting hydraulic fluid pressure between said pin and box end portion thereby radially expanding said box end portion onto said pin end portion while wedging said circumferential teeth together and converting radial preload to said high axial preload. |
Field of the Invention This invention relates in general to a stack of rotative couplings or swivels which are capable of transferring fluids between the sea bed and ships, tankers, and other sea-going vessels. In particular, the invention relates to structural connection arrangements for connecting swivels together in a stack.
Description of the Prior Art A swivel stack for a floating, production, storage and offloading (FPSO) vessel normally has a plurality of generally vertical product risers or pipes extending to the central body of the swivel stack from the sea floor. A swivel on the stack is normally provided for each fluid pipe which may be a manifold outlet pipe where several risers are applied to one manifold. Generally horizontal outlet pipes or conduits extend from the swivels to storage
areas of the FPSO vessel. The vessel weathervanes about a turret to which the stack body and risers are connected, and the swivels move with the vessel relative to the swivel stack body and risers or manifold outlet pipes extending within the body. The stack body or core which receives the vertical risers is of a generally cylindrical shape. It is desirable to minimize the dimensions of the stack body.
Hubs and bolted flanges have commonly been employed to connect the interior housing of one swivel in the stack to another interior housing below or to a base for the case of the lower-most swivel in the stack. Such hubs or flanges require space within the cylindrical body of the swivel stack.
A primary objective of the invention is to provide an effective structural connector for connecting interior housings of swivels together to form a swivel stack while minimizing the height of the connection between swivels thereby minimizing the total height of the swivel stack.
SUMMARY OF THE INVENTION This invention is for a swivel stack comprising a plurality of rotative fluid couplings (called swivels) which are structurally connected together in a stack. The invention provides a structural connector between the top of an inner housing of one swivel and the bottom of an inner housing of a second swivel stacked on top of the first connector for each of the swivels in the stack. Such a structural connector also connects the bottom-most swivel to a cylindrical base which in turn is secured to the top of a turret in a turret mooring system. The preferred connector for connection of the swivels together in a swivel stack is a MERLIN TAM connector of Oil States Industries (UK) Ltd.
The connector includes mating female (box) and male (pin) end portions welded to the cylindrical housing bottom of a top swivel and the cylindrical housing top of a bottom swivel. The mating female and male end portions have non-helical, interlocking circumferential teeth and are assembled with a hydraulic tool which is placed inside the connector male and female end portions. After stabbing of the male and female end portions of the swivels, hydraulic pressure is injected between the mating end portions thereby creating relative radial expansion between the male and female end portions, with equipment for pulling the two end portions into mating relationship. The hydraulic pressure is relieved and the box end shrinks about the pin end resulting in a wedging action of the teeth. The wedging action of the teeth converts radial preload into a high axial preload to maintain connector stiffness. The connector of this invention has advantages of (1) reduced size in outside diameter as well as height as compared to prior connection arrangements for swivels in a swivel stack, (2) a minimum number of connector parts (two) providing simplicity of design, and (3) significant time savings for make-up of each connection as compared to flanges or clamp style connections.
Other features and advantages of this invention will be apparent from the following specification and drawings.
BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic of a swivel stack showing a plurality of swivels connected together in a stack where each swivel is structurally connected to another swivel or to a cylindrical base with a MERLINTM non-rotational connector; and
Figures 2A, 2B, and 2C illustrate steps for installing a MERLIN type connector as a structural connector between swivel cylindrical housings or a swivel housing and a base.
DESCRIPTION OF THE INVENTION Figure 1 shows a plurality of swivels stacked together to form a swivel stack 10. The inner housing of each swivel 1 is connected to the inner housing of a stacked swivel, or to the cylindrical housing of a base 2 by means of a connector pair 3 which is preferably a MERLIN connector available commercially from Oil States Industries (UK) Ltd. of Aberdeen, Scotland. Each connector pair includes a male (pin) connector half 5 and a female (box) half 6 which have non-helical, interlocking circumferential teeth and are assembled with a hydraulic tool 7 and other equipment for installing MERLIN connectors.
Figure 1 illustrates the assembly and the method for connecting the male 5 and female 6 parts of the connector pair 3 together. With the swivel base 2 in place, a lower-most swivel assembly 1 with the male portion 5 of the MERLINS connector is lowered into the female portion 6 on top of the base 2. The swivel 1 is allowed to come to rest with the MERLIN connector halves engaged but not connected. Hoisting equipment is removed.
Next, the connector tool 7 is lowered into the swivel stack 10. Annular grooves 4 are provided in the interior of the swivel housings for engagement of the internal connector tool 7. Hydraulic pressure is injected between the teeth of the connector halves at 11 thereby creating radial elastic expansion between the male and female portions while allowing full axial insertion of the male portion into the female portion by connector tool 7. Hydraulic pressure is bled at 11 allowing the connector halves to radially contract or"shrink"elastically thereby providing radial wedging action of the teeth of the male and female portions. After
the connection is made, the connection tool 7 is retrieved upwardly from inside the swivel, and the procedure is repeated to install successive swivels in the stack.
Figures 2A, 2B and 2C illustrate the steps in assembling female end portion 6 and male end portion 5. The connector pair 3 is not fully made up in this illustration of Figure 2A, but pin end 5 is stabbed into box end 6. The interlocking teeth 20 are non-helical interlocking teeth which, because of design geometry, can mesh only in the fully made-up position. Figure 2B shows the connection after a tool 7 is placed inside the connection with dogs 10 removably secured in grooves 4 of pin end 5 and box end 6. Hydraulic pressure is applied externally via port 11 for application of hydraulic pressure between the pin 5 and the box 6. The tool 7 pulls the pin 5 and box 6 together as illustrated by arrows A-A into a fully made-up relationship as the hydraulic pressure expands the box 6 and constricts the pin 5.
When pressure is released, the box 6"shrinks"onto the pin 5. Figure 2C illustrates the connection after the hydraulic tool 7 has been removed.
Structural connection of the inner housing swivels to form a swivel stack with a MERLIN connector provides a structural connection that is simple and yet very strong. A great advantage of the use of the MERLINTM connector is that it reduces the height of the connection between swivels as compared to prior flanged type connections. Reduced height between each swivel translates into a reduced height of the entire swivel stack, resulting in a lower center of gravity of the swivel stack secured to the top of a turret in a turret mooring system of a vessel. A lower center of gravity reduces torque loads applied to the turret caused by rolling and other motions of the vessel. Lower torque loads on the turret results in less forces applied between the turret bearings and the vessel.
Another advantage in the connection of swivels together with a MERLINS connector is that an absolute minimum of parts are used: a female half is welded to the top of the
swivel (or base) and a male half is welded to the bottom of the swivel. Furthermore, significant time savings per connection are realized as compared to flange or clamp style connection of cylindrical members. Still another advantage is that the MERLIN connector has an absolute minimum cross-section thereby reducing the weight of each connection to a minimum.