U.S. patent application number 10/666468 was filed with the patent office on 2004-03-25 for lower turret bearing system for fpso.
This patent application is currently assigned to FMC Technologies, Inc.. Invention is credited to Boatman, L. Terry, Garnero, Charles L..
Application Number | 20040055522 10/666468 |
Document ID | / |
Family ID | 31998107 |
Filed Date | 2004-03-25 |
United States Patent
Application |
20040055522 |
Kind Code |
A1 |
Boatman, L. Terry ; et
al. |
March 25, 2004 |
Lower turret bearing system for FPSO
Abstract
A radial bearing assembly for a turret mooring system. The
radial bearing has a radial clearance sufficient to allow the
turret to have minor deflection without bearing contact against the
turret's sliding surface. As a result, sliding wear on the lower
bearing is reduced, and the upper bearing is allowed to rotate
without incurring unnecessary bending moments caused by unavoidable
structural tolerances in misalignment of the lower bearing with
respect to the upper bearing's axis of rotation. In a storm
environment, the lower bearing is capable of radially supporting
the turret while allowing relative rotation of the vessel around
the geostationary turret when larger mooring loads occur on the
turret. A mounting arrangement for pads on radial bearing
assemblies and the radial clearance allow replacement of the
bearing elements while the vessel is moored by the turret in
offshore waters.
Inventors: |
Boatman, L. Terry; (Houston,
TX) ; Garnero, Charles L.; (Cypress, TX) |
Correspondence
Address: |
GARY L. BUSH
ANDREWS & KURTH L.L.P.
600 TRAVIS, SUITE 4200
HOUSTON
TX
77002
US
|
Assignee: |
FMC Technologies, Inc.
|
Family ID: |
31998107 |
Appl. No.: |
10/666468 |
Filed: |
September 19, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60412413 |
Sep 19, 2002 |
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Current U.S.
Class: |
114/230.12 |
Current CPC
Class: |
B63B 21/507
20130101 |
Class at
Publication: |
114/230.12 |
International
Class: |
B63B 021/00 |
Claims
What is claimed is:
1. In a turret mooring arrangement in which a turret (16) is
disposed in a moonpool tube (13) of a vessel (1) and the turret is
rotationally supported on said vessel by an axial bearing, (15) a
radial bearing arrangement comprising, a cylindrical bearing
surface ring (4) disposed about an exterior portion of said turret
(16), said ring characterized by an outer surface with an outer
diameter, a plurality of radial bearing assemblies (14), with each
assembly secured in a ring inwardly of said moonpool tube (13),
with each radial bearing assembly (14) having a pad (5) with a
surface which faces radially inwardly, the inward facing surfaces
of said pads (5) collectively defining a segmented substantially
cylindrically shaped surface having an inner diameter, said inner
diameter of said pads of said radial bearing assemblies being
greater than said outer diameter of said bearing surface ring such
that when said turret (16) is substantially axially aligned with
said moonpool tube (13), a radial gap (7) exists between each
inward facing low friction material surface of said pads (5) and
said bearing surface ring (4).
2. The arrangement of claim 1 wherein, said outer surface (19) of
said cylindrical surface ring (4) is corrosion resistant.
3. The radial bearing arrangement of claim 1 wherein, each of said
plurality of radial bearing assemblies (14) is mounted on a bearing
support ring (11) which is secured inwardly of said moonpool tube
(13).
4. The radial bearing arrangement of claim 1 wherein, said surface
of said pads (5) of each radial bearing assembly (14) is of a low
friction material.
5. The radial bearing arrangement of claim 3 wherein, each radial
bearing assembly (14) includes a bearing bracket (9) with a
releasable attachment device (10) which releasably attaches said
bracket (9) to said bearing surface ring (1), and said pad (5) is
constructed of a low friction material and is secured to said
bracket (9), whereby said bracket (9) and said pad (5) can be
removed and said pad 5 can be replaced while said vessel (1)
remains moored at an offshore location, wherein said radial gap (7)
and said releasable attachment device (10) enables removing of a
selected pad (5) and replacing same while said vessel remains
moored at an offshore location.
6. A radial bearing arrangement for rotatably supporting a turret
with respect to a vessel, comprising, a ring disposed around a
surface of the turret, a plurality of radial bearing assemblies
mounted on each vessel with each assembly including a low friction
pad (5) surface which is radially spaced from said ring.
7. The arrangement of claim 6 wherein, said low friction pads (5)
are characterized by a radial thickness in the range of from about
25 to about 50 millimeters.
8. In a radial bearing arrangement for rotatably supporting a
turret with respect to a vessel, the arrangement including a ring
(4) disposed around a surface of the turret and a plurality of
radial bearing assemblies (14), each assembly including a bracket
(9) which is removably secured to the vessel, with a low friction
pad (5) removably secured to each corresponding bracket, with each
pad having an inner surface that is juxtaposed but radially spaced
form said ring, a method for replacing said pad while said vessel
is moored by anchor legs from the sea floor to the turret
comprising the steps of, removing said bracket (9) and said pad (5)
from securement to said vessel, moving said bracket (9) and said
pad (5) vertically away from said ring so that said pad is not
juxtaposed with said ring, then replacing said pad (5) on said
bracket, and then securing said bracket (9) with replaced pad to
said vessel with said replaced pad radially spaced from and
juxtaposed with said ring.
Description
CROSS REFERENCE RELATED TO APPLICATION
[0001] This application is based upon and claims the priority of
U.S. Provisional Application No. 60/412, 413 filed Sep. 19,
2002.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention relates generally to Floating Production
Storage and Offloading vessels (FSO's and FPSO's). In particular,
this invention relates to large diameter mooring turrets requiring
a lower bearing system that will have high reliability and can be
constructed at lower cost as a result of a new configuration of the
bearing arrangement.
[0004] 2. Description of the Prior Art
[0005] Numerous references to turret lower bearings are known in
the prior art. Two of the more recent patents are Braud, U.S. Pat.
No. 5,913,279, and Boatman, U.S. Pat. No. 5,306,186. Both of these
patents illustrate versions of adjustable and self-aligning lower
bearings.
[0006] 3. Identification of Objects of the Invention
[0007] A primary object of this invention is to provide an improved
lower bearing arrangement that is highly reliable and of lower cost
than that of prior lower bearing arrangements.
[0008] Another object is to provide a lower bearing arrangement
that operates in combination with an upper bearing where the upper
bearing is not supported by elastomeric or metal springs.
[0009] Another object of the invention is to provide an improved
lower bearing arrangement that operates in combination with an
upper bearing wherein the upper bearing is supported by elastomeric
or metal springs.
[0010] Another object of the invention is to provide a lower,
radial bearing arrangement that operates in combination with a rail
and wheel type upper bearing.
[0011] Another object of the invention is to provide a lower
bearing arrangement where the low friction material of the sliding
surface of the bearings units can be replaced while the vessel
remains moored at its offshore location.
[0012] Another object of the invention is to provide a lower
bearing arrangement where a radial clearance is provided for the
purpose of reducing sliding wear of the low friction material of
the surface of the bearing unit.
[0013] Another object of the invention is to provide a lower
bearing arrangement where the low friction material is thick enough
such that the thickness provides sufficient wear life even if the
bearing support foundation is installed with inherent
out-of-roundness as a result of unavoidable shipyard manufacturing
dimensional tolerances.
[0014] Another object of the invention is to provide a lower
bearing arrangement that can be constructed within a turret
moonpool without costly machining of the lower bearing support
structure attached to the vessel hull structure.
SUMMARY OF THE INVENTION
[0015] The objects identified above along with other features and
advantages of the invention are embodied in an improved radial
bearing arrangement for a turret mooring arrangement in which a
turret is rotationally supported on a vessel. The turret is placed
within a moonpool tube with rotational support between the turret
and the vessel provided by an axial support bearing and the
improved radial bearing arrangement of the invention.
[0016] The improved radial bearing arrangement utilizes an inner
ring with a cylindrical bearing surface secured about an exterior
portion of the turret. The inner ring has an outer surface with an
outer diameter. A plurality of separate radial bearing assemblies
are arranged in an outer ring inwardly of the moonpool tube. Each
of the assemblies has a pad of low friction material with an
inwardly facing surface such that the inwardly facing surfaces
collectively define a segmented substantially cylindrically shaped
surface having an inner diameter.
[0017] The inner diameter of the cylindrically shaped surface
defined by the pads of the radial bearing assemblies of the
moonpool tube is greater than the outer diameter of the inner ring
of the turret, such that when the turret is substantially axially
aligned with the moonpool tube, a radial gap exists between each of
the inward facing low friction material surfaces of the pads and
the inner bearing surface ring of the turret.
[0018] A mounting arrangement for the radial bearing arrangements
and the radial gap allows replacement of the bearing elements when
the vessel is moored by the turret in offshore waters.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] The invention is illustrated by the attached drawings of
which:
[0020] FIG. 1 is a cross-sectional elevation view through an
internal turret and vessel;
[0021] FIG. 2 is an enlarged view of the chain table area at the
bottom end of the turret; and
[0022] FIG. 3 is an enlarged elevation view of the area at the
lower bearing.
DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION
[0023] The invention is embodied in a lower bearing arrangement for
a turret transfer system of a FPSO as illustrated in the figures
where reference numbers are assigned to the following elements:
[0024] 1 FPSO vessel hull
[0025] 2 Chain table
[0026] 3 Chain support
[0027] 4 Bearing surface ring
[0028] 5 Low friction material
[0029] 6 Fastener
[0030] 7 Radial gap
[0031] 8 Lifting eye
[0032] 9 Bearing bracket
[0033] 10 Attachment device
[0034] 11 Bearing support ring
[0035] 12 Hull bracing
[0036] 13 Moonpool tube
[0037] 14 Lower bearing unit
[0038] 15 Upper bearing
[0039] 16 Mooring turret
[0040] 17 Risers
[0041] 18 Riser guide tube
[0042] 19 Corrosion resistant surface
[0043] 20 Inside diameter
[0044] 21 Anchor leg
DETAILED DESCRIPTION
[0045] FIG. 1 illustrates a cross sectional elevation view through
an internal turret wherein mooring turret 16 is rotatably supported
by upper bearing 15 within vessel hull 1. Multiple lower bearing
units 14 spread about the inner surface of the moonpool tube 13
provide radial support of turret 16 at the outside diameter of
chain table 2. The turret 16 is of the arrangement as illustrated
in FIG. 1 and as shown in more detail in corresponding U.S.
application Ser. No. 10/325,122 filed on Dec. 19, 2002 and
incorporated by reference herein. The shape of the turret is not
limited to that of FIG. 1, but may be a typical tube shape turret
or a turret of other shapes.
[0046] The preferred embodiment of the upper bearing 15 comprises a
rail and wheel type upper bearing such as manufactured by Hydralift
Amclyde Incorporated, but the present invention may also be used in
combination with an upper bearing of the multiple row slewing ring
bearing type. The upper axial bearing arrangement is also shown in
the above mentioned U.S. application Ser. No. 10/325,122. Anchor
legs 21 attach to chain table 2 by means of chain supports 3.
Fluids and gases are transferred to and from the FPSO vessel
through risers 17 that pass through chain table 2 by means of riser
guide tubes 18.
[0047] FIG. 2 shows an enlarged view of chain table 2 at the bottom
end of mooring turret 16. Bearing surface ring 4 is a continuous
ring encircling and rigidly attached to chain table 2. A plurality
of lower bearing units 14 are secured in a ring secured to the
inside of moonpool tube 3 with each of the units 14 facing the
bearing surface ring 4.
[0048] FIG. 3 is an enlarged elevation view of the area at lower
bearing unit 14 that shows a section detail of the preferred
embodiment of a lower bearing unit 14. Each lower bearing unit 14
includes low friction material pad 5, bearing bracket 9, and
attachment device 10. Corrosion resistant surface 19, preferably of
INCONEL.TM., or stainless steel, is attached to bearing surface
ring 4 to provide a surface on which the pads 5 of low friction
material, such as ORKOT.TM. or similar non-metallic material, may
slide with low friction and minimal wear. The trademark ORKOT is a
mark of ORKOT Marine Bearings that are manufactured by impregnating
cloths of fibers with thermosetting resines. Such materials have
exceptional wear resistant properties with or without lubrication.
Radial gap 7 provides a predetermined clearance between a low
friction material pad 5 and surface 19 under normal operation and
rotation of the FPSO around geostationary turret 16. Flexure of
turret 16 in addition to unavoidable misalignment of upper bearing
15 with lower bearing units 14 causes clearance gap 7 to increase
and decrease during operations with only occasional contact between
surface 19 and low friction material pad 5. Only when sea
conditions become more severe does contact and heavy sliding action
take place between surface 19 and low friction material 5.
[0049] Low friction material 5 is attached to bearing bracket 9 by
fasteners 6. Bearing brackets 9 are arc segments disposed outwardly
and spaced around bearing surface ring 4. Attachment device 10
locks each bearing bracket 9 to bearing support ring 11. Lifting
eyes 8 are provided for lifting each attachment 10 and bearing
support ring 11. Bearing support ring 11 is rigidly attached,
preferably by welding, to hull bracing 12 outside of moonpool tube
13. Inside radius 20 is gas flame cut and hand trimmed within a
suitable radial accuracy of about .+-.3 to 5 millimeters deviation
from a true circle.
[0050] A sufficient thickness, such as from 25 to 60 millimeters,
of low friction material 5 provides a wear allowance to compensate
for small variances in radial position of lower bearing units 14 in
addition to normal wear incurred over the service life of mooring
turret 16.
[0051] Each bearing low friction material pad 5 and bearing bracket
9 can be removed from bearing support ring 11 while the turret is
secured to a sea bottom by anchor legs 21. The procedure is enabled
because of the presence of gap 7. The attachment device 10 is
released from bearing support ring 11, and the pad and bearing
bracket 9 is lifted with lifting eyes 8 such that attached pad 5
and bearing bracket 9 are lifted together above ring 11. A worn pad
5 can be removed at that point by removing fasteners 9. A new pad 5
can be substituted for a worn pad. The bracket 9 and new pad 5 are
then lowered by lifting eye 8, and the attachment device 10 secures
the bearing members 5 and 9 again to bearing support ring 11.
* * * * *