Note: Descriptions are shown in the official language in which they were submitted.
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A seafastening apparatus for a tensioner assembly
Field of the invention
The invention concerns devices for retraining and supporting equipment on a
movable platform, such as a vessel floating in water. More specifically, the
invention concerns a seafastening apparatus specified in the introduction to
claim 1.
Background of the invention
In the offshore petroleum industry it is well known to use tensioner systems
on
floating drilling rigs and other vessels, in order to maintain a pre-selected
vertical
tension in a marine riser extending from the rig and down to a subsea
wellhead. When
the vessel is heaving and rolling due to waves, currents and winds, the
tensioner system
will try to keep constant tension in the riser.
One type of tensioner system which is known in the art, is termed a "direct
acting
tensioner" (DAT) system. In a typical arrangement on a drilling vessel, a DAT
system
basically comprises a number of hydraulic-pneumatic cylinders suspended
underneath
the drill floor in a circle-symmetrical configuration above the lower deck.
The cylinders'
free (lower) ends are connected to a so-called tensioner ring, which may be
connected to
the riser.
When the DAT system is not in use, i.e. not being connected to the riser, the
assembly is
"parked" in a location away from the well centre, where it does not interfere
with other
operation taking place above or through the moonpool. However, as the drilling
rig may
be moving considerably in waves and swell, the cylinders (and thus the
tensioner ring) of
a parked DAT system is susceptible of swinging uncontrolled back and forth,
with the
risk of damaging adjacent equipment ¨ as well as the cylinders themselves ¨
and causing
harm to personnel.
Methods and means of DAT system seafastening exist, commonly employing an
arrangement of wires and winches. The known systems are, however, cumbersome
and
time consuming to connect and activate. In addition, the prior art
seafastening systems
induce large, undesired, forces on the cylinders and/or packing boxes. The
uncontrolled
movement of the DAT system also makes connecting the tensioner ring to the
riser
difficult and potentially dangerous.
Another problem with DAT systems arises when the tensioner ring is connected
to the
riser and the DAT system is in operation: Due to the rig motions, the
hydraulic and/or
pneumatic hoses extending from the pressure source and to each of the
tensioner
cylinders are swinging about in the moonpool in an uncontrolled manner, and
are often
damaged.
The state of the art includes US 2010/0047024 Al (Curtiss), which describes an
apparatus to restrain a riser tensioner of an offshore drilling rig when the
tensioner
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is not connected to a riser. The apparatus includes a restraint cone
configured to fit
within hydraulic cylinders of the riser tensioner, a hoist configured to
extend and
retract the restraint cone, and a tension member extending from a lower end of
the
restraint cone, the tension member configured to engage a lower end of the
riser
tensioner and maintain a wedging action between the restraint cone and the
hydraulic cylinders.
The present inventor has devised and embodied this invention to overcome these
shortcomings and to obtain further advantages.
Summary of the invention
The invention is set forth and characterized in the main claims, while the
dependent
claims describe other characteristics of the invention.
The purpose of the invention is to achieve a seafastening device for a DAT
system
or similar equipment which is safe and reliable, easy to assemble and
disassemble,
and does not subject the system to unwanted loads.
Another purpose of the invention is to provide a guiding device for aiding in
the
connection of the tensioner ring to the riser, and contribute to closing the
hinged
tension ring.
Another purpose of the invention is to provide a support element for DAT
hoses,
when the DAT system is in use in the moonpool.
It is thus provided a seafastening apparatus, characterized by a movable frame
having an opening configured for receiving and at least partially supporting
an
equipment unit, and by locking means configured for selective locking an
releasing
of the equipment unit and hence controlling lateral movements of the equipment
unit relative to the apparatus.
In one embodiment, the locking means comprise a pair of locking arms which by
means of actuators are rotatable about respective joints on the frame and
configured
for extending at least partially around a circumference of the equipment unit
in a
region between the upper end and a lower end.
In one embodiment, the locking means comprise abutment portions for contact
with
corresponding abutment elements on the equipment unit. The abutment portions
advantageously comprise an elastic, shock absorbing and abrasion reducing
material.
In one embodiment, the locking means are arranged to rotate in a plane which
is
substantially perpendicular with respect to the equipment unit longitudinal
axis.
The apparatus comprises in one embodiment one or more support devices for
supporting hoses, cables and similar components extending from the equipment
unit. The support device is advantageously rotatably connected to the frame at
a
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first end and is height adjustable with respect to the frame via actuation
means. In
one embodiment, the support device comprises an arc-shaped support tray.
In one embodiment, the apparatus comprises locking elements for fixing the
locking
means in position when they are in engagement with the equipment unit.
In one embodiment, the locking means comprise wires configured for connection
to
the equipment unit and tensioners configured for controlling the tension in
each
wire. A pair of extendible and retractable arms is arranged on the frame, each
arm
configured for conveying and guiding at least one of the wires.
In one embodiment, the opening is defined by support regions in the frame,
said
regions being shaped complementary with a corresponding portion of the
equipment
unit. The apparatus comprising in one embodiment fastening lugs for connection
between the frame and selected portions of the equipment unit.
The apparatus advantageously comprises frame motion means and fixing means,
whereby the apparatus is movable on a supporting surface and is releasably
lockable
with respect to the supporting surface. The motion means advantageously
comprises
wheels for interaction with rails and drive units. The apparatus and the
equipment
unit are in one embodiment arranged on a movable platform, such as a vessel
floating in a body of water.
In one embodiment, the equipment unit comprises a Direct Acting Tensioner
(DAT)
unit, having a plurality of cylinders, each one suspended via a respective
upper end
to the structure above the apparatus, and each one connected at a respective
lower
end to a ring element for connection to a riser or similar.
Brief description of the drawings
These and other characteristics of the invention will be clear from the
following
description of a preferential form of embodiment, given as a non-restrictive
example, with reference to the attached drawings wherein:
Figure 1 is an elevation view of the device according to the invention next to
a DAT system on a drilling rig, the DAT system being connected to a riser;
Figures 2 and 3 are perspective views of a first embodiment of the device
according to the invention;
Figure 4 is an elevation view of the device illustrated in figures 2 and 3;
Figure 5 is a perspective view of the device illustrated in figures 2 and 3,
with the locking arms in an open position;
Figure 6 is a plan view of the device illustrated in figures 2 and 3, with the
locking arms in a closed position, enclosing the DAT tensioner cylinders;
Figures 7, 8 and 9 are a perspective view, front view, and top view,
respectively, of a second embodiment of the device according to the invention;
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Figures 10, 11 and 12 are a perspective view, side view, and top view,
respectively, of the second embodiment of the device according to the
invention
connected to DAT cylinders via stabilizing wires, and the wires are not
tightened;
Figures 13 and 14 are a top view and a side view, respectively, of the second
embodiment of the device according to the invention connected to DAT cylinders
via stabilizing wires, and the wires have been tightened;
Figures 15, 16 and 17 are a side view, top view, and perspective view,
respectively, of the second embodiment of the device according to the
invention
connected to DAT cylinders, showing a state where the telescopic arms have
been
retracted and the DAT cylinders are locked to the device;
Figure 18 is an elevation view of the device according to the invention, in a
closed position, enclosing the tensioner cylinders, and in parked
(seafastened)
position to one side of the moonpool, and
Figure 19 is an elevation view similar to figure 18, illustrating a parked
(seafastened) position to the other side of the moonpool.
Detailed description of preferential embodiments
Figure 1 shows part of a drilling vessel, which per se is known in the art
(only parts
which are relevant for the elucidation of this invention are illustrated). A
DAT
system 70, comprising a plurality of tensioner cylinders 73, is suspended
underneath
a drill floor 8, above a moonpool 7 in a lower deck 6. The cylinders 73 are
suspended by a trip-saver 10, by means of which the DAT system (package of
cylinders) may be moved back and forth above the lower deck and moonpool. The
cylinders 73 are connected to a riser 1 via a tensioner ring 72, in a manner
which is
known in the art. In this configuration, the DAT system is operating to
provide the
required tension in the riser while drilling is taking place (rotary table 9
schematically illustrated on drill floor 8). Reference number 4 indicates a
BOP
crane.
Arranged on the lower deck 6 and resting on rails 5, adjacent to the moonpool
7, is
a so-called DAT seafastening trolley 20; 40, i.e. the motion control and
restraining
device according to the invention. Hydraulic hoses 71, extending from on-board
supply and control systems (not shown) to each of the tensioner cylinders 73,
are
supported by a support element on the DAT seafastening trolley, in a manner
which
is explained below.
Description of a first embodiment
Referring now to figures 2 - 6, illustrating a second embodiment, the support
device
20 according to the invention comprises a u-shaped frame (or undercarriage) 23
supported via wheels 21 on tracks 5 (indicated in figure 3). The tracks are
advantageously the BOP/x-mas tree tracks. The DAT seafastening trolley 20 is
self-
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propelled, via motors 22 and cogwheels 22' which interact with corresponding
pinions (not shown) in the lower deck. Movable dowels 31 are provided for
locking
the trolley in a desired position against a corresponding interface
(receptacle, etc.,
not shown) on the deck.
Locking arms 25a, 25b are arranged on respective sides of the opening "A"
defined
by the u-shaped frame, defining a gripping, or locking, jaw. Each locking arm
is
pivotally connected to the frame 23 via respective pivotal joints 27 and is
operative
to move (rotate) about its respective joint between an open position of the
jaw
(figure 5) and a closed position of the jaw (figures 2, 3, 5). Movements of
the
locking arms 24a, 25b are effected by actuators 28 (e.g. hydraulic actuators).
Hydraulic lines, cables, control systems, etc., which are required in order to
operate
the DAT seafastening trolley are not disclosed, as such items are well known
in the
art.
Each locking arm is provided with a protective fender 26 of an elastic and
shock
absorbing material, in order not to damage the tensioner cylinders.
Each locking arm is preferably provided with a mechanical locking device (not
shown), whereby the arm may be fixed with respect to the frame when in the
seafastening position.
Support trays 29 for cables, hoses, etc., are arranged on both sides of the
jaw. Each
support tray 29 is connected to the frame via respective hinges 32 and is
height
adjustable by means of actuators 28. Arrow denoted "R" on figure 4 indicates
direction of tray movement.
Figure 6 illustrates the DAT seafastening trolley in position around the
tensioner
cylinders 73. Both locking arms 25a, 25b are in a closed position, abutting
against
the cylinders 73. Each cylinder is preferably furnished with one or more
fenders 74,
extending along a portion of the cylinder. In this position, the locking arms
provide
lateral support for the tensioner cylinders, and thus an effective
seafastening for the
DAT system.
Description of a second embodiment
Referring now to figures 7 ¨ 17, illustrating a second embodiment, the support
device 40 according to the invention comprises a u-shaped frame (or
undercarriage)
49 supported via wheels on tracks as described above. The DAT seafastening
trolley
is self-propelled, via motors 22 and cogwheels 22' which interact with
corresponding pinions (not shown) in the lower deck. Movable dowels (not
shown)
35 may advantageously be provided for locking the trolley in a desired
position,
similar to the first embodiment. Support trays 29 for cables, hoses, etc., are
arranged on both sides of the jaw. Each support tray 29 is connected to the
frame in
a manner similar to that of the first embodiment, described above.
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The u-shaped frame 49 has a rear support region 50a and two side support
regions
50b,c, together defining an opening "A" Each support region may be provided
with
protective fenders (not shown).
Arranged on each side of the u-shaped opening A are two arms 46, 47, each of
which is telescopically movable between an extended position (see e.g. figure
12)
and a retracted position (see e.g. figure 16). Each arm comprises a sheave 51
in the
tip region and a rearward sheave 52. A first wire 44 runs from a first linear
tensioner 54, via a rearward sheave 52, through the right-hand arm 46 and over
the
forward sheave 51. Similarly, a second wire 45 runs from a second linear
tensioner
55, via a rearward sheave 52, through the left-hand arm 47 and over the
forward
sheave 51. A third wire 43 runs from a third linear tensioner 53, via a
rearward
sheave 52' and into the opening A near the rear support region 50a.
A number of seafastening lugs 48 are arranged on the frame 49, around the
opening,
each of which is configured for connection the DAT cylinders.
Figures 10 ¨ 12 show the DAT seafastening trolley 40 arranged on a pair of
rails 5
and being connected to DAT cylinders 73. The DAT cylinders are typically
suspended by a trip saver 10, having pinions 11 which ride on a rack 12 which
is
connected to the underside of the drill floor 8. This trip-saver arrangement
is
illustrated schematically on figures 1, 11, 14, 15, 18 and 19, but has been
omitted
from the other figures. The rails 5 for the trolley are arranged on the lower
deck 6,
as shown in figure 1. However, the deck structures have been omitted from
figures 7
¨ 17. In the state illustrated in figures 10 ¨ 12, the first wire 44 and the
second wire
45 are connected to respective DAT cylinders, and the third, central, wire 43
is
connect to the two rearmost DAT cylinders via a crow foot or yoke 56. Each DAT
cylinder is furnished with a protective collar 77, to which the wires also may
be
connected. The wires are slack, allowing DAT movement. In this state, the DAT
system is typically connected to the riser (not shown) via the tensioner ring
72, and
the DAT cylinders move with the riser (in fact, the rig is moving, and the
riser and
cylinders are connected to the seabed and are not moving). This configuration
of the
DAT seafastening trolley is typically used when preparing to open the
tensioner
ring and disconnect the DAT cylinders from the riser.
Figures 13 and 14 show a state where the wires 43, 44, 45 have been tightened
(by
the linear tensioners) in order to hold the DAT cylinders still. The tensioner
ring 72
is open, allowing the trolley and DAT system to move away from the riser 1.
The
linear tensioner (compensators) are active in this state. The tensioner ring
is
subsequently closed and the DAT cylinders are pulled into the opening A by
retraction of the arms 46, 47 and a further tightening of the wires.
Figure 15, 16 and 17 show the DAT cylinders fully retracted into the DAT
seafastening trolley, bearing against the complementary shaped support regions
50a-
c and locked to the frame by the lugs 48. Turnbuckles 42 on the frame,
connectable
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to the seafastening lugs, prevent rotation of the lugs. The arms 46, 47 are
fully
retracted. . In this position, the locking DAT seafastening trolley 40
provides lateral
support for the tensioner cylinders, and thus an effective seafastening for
the DAT
system.
Hydraulic lines, cables, control systems, etc., which are required in order to
operate
the DAT seafastening trolley are not disclosed, as such items are well known
in the
art.
Alternative seafastening positions are illustrated by figures 18 and 19, i.e.
showing
the DAT system and DAT seafastening trolley 20; 40 in "parked" positions on
respective sides of the moonpool. The tensioner cylinders are retracted. In
the
position illustrated by figure 18, the DAT hoses 71 are supported by the
support
trays 29. This hose support feature is also shown in figure 1, where the trays
29
provide support for the hoses 71 even when the DAT is connected to and
providing
tension on the riser 1.
The DAT seafastening trolley may also be used when the DAT system is to be
moved (by means of the trip-saver) from a "parked" position (figures 18 or 19)
to an
operative position over the moonpool 7 (figure 1). Having the DAT seafastening
trolley thus connected to the DAT system during this procedure ensures that
the
relocation of the DAT system and connecting the tensioner ring to the riser
may be
performed in a controlled and safe manner.
