U.S. patent application number 13/676547 was filed with the patent office on 2013-05-16 for component for drilling and operating hydrocarbon wells.
This patent application is currently assigned to VAM DRILLING FRANCE. The applicant listed for this patent is VAM DRILLING FRANCE. Invention is credited to Didier DAVID.
Application Number | 20130118728 13/676547 |
Document ID | / |
Family ID | 45688559 |
Filed Date | 2013-05-16 |
United States Patent
Application |
20130118728 |
Kind Code |
A1 |
DAVID; Didier |
May 16, 2013 |
COMPONENT FOR DRILLING AND OPERATING HYDROCARBON WELLS
Abstract
The tubular component (30) comprises a main body (32) of
rotation about a longitudinal axis (X) of the component (30)
provided, at least at one of its ends (34B), with a first connector
(36B) for attaching the component (30) to another tubular component
(30). The component (30) is moreover intended to be at least
temporarily gripped in a peripheral zone (Z, Z1, Z2) by means for
retaining the component (30) on the operating facility (10). The
component (30) comprises inside the zone (Z, Z1, Z2) a coating (58)
for protecting the component (30) against mechanical damage likely
to be caused by the retaining means. In particular, the coating
(58) being produced from a material with a hardness greater than
the hardness of the material forming the component but less than a
value of 70 HRC.
Inventors: |
DAVID; Didier; (Ruesnes,
FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
VAM DRILLING FRANCE; |
Cosne-Cours-sur-Loire |
|
FR |
|
|
Assignee: |
VAM DRILLING FRANCE
Cosne-Cours-sur-Loire
FR
|
Family ID: |
45688559 |
Appl. No.: |
13/676547 |
Filed: |
November 14, 2012 |
Current U.S.
Class: |
166/85.1 |
Current CPC
Class: |
E21B 17/1085 20130101;
E21B 17/00 20130101 |
Class at
Publication: |
166/85.1 |
International
Class: |
E21B 17/00 20060101
E21B017/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 16, 2011 |
FR |
11 03484 |
Claims
1. Tubular component (30) of a landing string for oil or gas
exploitation from an operating facility (10), comprising a main
body (32) of rotation about a longitudinal axis (X) of the
component (30) provided, at least at one of its ends (34A, 34B),
with a first connector (36B) for attaching the component (30) to
another tubular component (30), the component (30) moreover being
intended to be at least temporarily gripped in a peripheral zone
(Z) by means (40) for retaining the component (30) on the facility
(10), characterized in that the component (30) comprises, inside
the clamping zone (Z), a coating (58) for protecting the component
(30) against mechanical damage likely to be caused by the retaining
means, the coating being produced from a material with a hardness
greater than the hardness of the material forming the component
(30) but less than a value of 70 HRC.
2. Component (30) according to the previous claim, in which the
coating (58) is a sacrificial coating.
3. Component (30) according to one or other of the previous claims,
in which the hardness of the coating (58) increases progressively
in the direction from the component (30) to the coating (58).
4. Component (30) according to any one of the previous claims, in
which the coating (58) is formed by a plurality of layers.
5. Component (30) according to any one of the previous claims, in
which the clamping zone (Z) extends between an end face of the
first connector (36B) as far as at most one-third of the body
(32).
6. Component (30) according to one or other of the previous claims,
in which the first connector (36B) is of the type having a female
thread.
7. Component (30) according to the previous claim, being provided,
at the other (34A) of its ends (34A, 34B), with a second connector
(36A) with a male thread.
8. Component (30) according to any one of the previous claims, in
which, the connector or connectors (36A, 36B) being connected to
the body (32) by welding, forming a support (38) for joining the
connector (36A, 36B) to the body (32), the coating (58) leaves the
joint support (38) exposed.
9. Component (30) according to any one of the previous claims, in
which the thickness of the body (32) is greater than 12.7 mm.
10. Component (30) according to any one of the previous claims, in
which the coating (58) has a roughness greater than the surface
roughness of the tubular component (30) in order to facilitate the
adherence of the retaining means (42) to the body (32) of the
component (30).
11. Component (30) according to any one of the previous claims, in
which the thickness of the coating (58) is greater than 1 mm and
preferably greater than 2 mm.
12. Component (30) according to any one of the previous claims, in
which the coating (58) is formed by a layer obtained by thermal
spraying, for example of the electric arc type, or by
electroplating.
13. Component (30) according to any one of the previous claims, the
coating (58) is formed by a metal alloy comprising at least one or
more main elements chosen from nickel, chromium, molybdenum,
tungsten, boron.
14. Component (30) according to the previous claim, in which the
metal alloy comprises at least one or more secondary elements
chosen from silicon, carbon, chromium, boron, vanadium, titanium,
iron and aluminium.
15. Component (30) according to any one of the previous claims, in
which the zone (Z) starts at the end of the body and extends for
example over approximately 1.5 metres.
Description
[0001] The present invention relates to the technical field of the
exploitation of oil and gas deposits. It applies more particularly,
but not exclusively, to the exploitation of offshore deposits, for
example from platforms known more generally as "offshore"
platforms.
[0002] The invention applies in particular to the components used
in landing strings, for positioning tubes for casing, tubing or
also various tools such as for example wellheads.
[0003] A landing string is formed principally by a series of
tubular components, hereafter called landing tubes, and is attached
to the string to be positioned. This landing string is thus
generally intended to remain outside of the well, the main
functions of this string being in particular to route the casing
string to its final position in the well or also to cement the
casing in the well, etc.
[0004] Conventionally, a landing tube differs from other
operational tubes or casings by specific dimensional
characteristics. In fact, the landing tubes must have a large
tensile capacity. To this end, a landing tube generally has a
diameter greater than 127 mm (or 5 inches) and a thickness greater
than 12.7 mm (or 0.5 inches). However, the landing tube can be
formed by a standard drilling tube used for a landing
application.
[0005] In general, in order to form a landing string, landing tubes
are placed end to end. Thus, a landing tube generally comprises a
body rotating about a longitudinal axis of the component and two
connectors, also called "tool-joints", connected respectively to
the ends of the body for attaching the tube to another tube. The
connectors comprise for example male and female threaded elements
that allow the tubes to be attached to each other by make up.
[0006] For positioning tubes, in the case of offshore operations, a
certain length of string is extended from the platform to the
seabed, from which the well is sunk, this length depending on the
depth of the sea beneath the platform, which can sometimes reach
several hundred metres, or even several kilometres.
[0007] The casing string is suspended from the landing string being
formed, itself held on the platform by the last tube connected,
hereafter called "surface tube", the latter being held temporarily
on the platform for the time it takes to add one or more tubes to
the string being formed, increasing as much as the length of the
latter.
[0008] The surface tube is secured to the platform using retaining
means, themselves integral with a rotary table of the platform,
which grip the tube like a vice. The retaining means generally
comprise a plurality of slips having gripping elements on the
surface, such as for example jaws, capable of being secured to the
tube in order to retain it.
[0009] As a result, because of its function, the surface tube is
subjected to very high axial tensile forces associated in
particular with the mass of the string in the course of formation.
This mass increases as the landing string forming operation
progresses. This mass is of course greatest at the end of the
operation and corresponds to the mass of the string extended
between the surface and the bottom of the well and, in the case of
the landing string, to the mass of the string extended between the
surface and the seabed added to the mass of the tube string to be
positioned in the well. The mass can then reach several thousand
tonnes.
[0010] The clamping of the surface tube increases as the mass of
the string increases. Thus, under the effect of very high tensile
forces, the gripping elements leave an impression around the
surface tube, promoting the appearance of cracks and other
mechanical damage which embrittle the tube and reduce its period of
use.
[0011] It has already been proposed in the state of the art, in
particular in the document U.S. Pat. No. RE37,167 E filed by Grant
Prideco, to solve the problem of the resistance of drilling tubes
to the force exerted by the slips. This document teaches remedying
this problem by manufacturing the tubes from a martensitic steel in
order to limit the penetration of the slips into the material.
[0012] It has also been proposed in the state of the art, in
particular in the document U.S. Pat. No. 3,080,179 filed by C. F.
Huntsinger, to insert a portion of protective tube with an
increased thickness between the connector and the main body of the
component, at the level of a zone for clamping the component.
However, the creation of an additional weld at the junction between
this additional portion of tube and the body of the component
presents an increased risk of the component breaking.
[0013] The purpose of the invention is in particular to propose a
solution for best protecting the tubes of the landing strings
against the mechanical damage to which the means of retaining on
the platform are subjected without the drawbacks of the prior
art.
[0014] To this end, a subject of the invention is a tubular
component of a landing string for oil or gas extraction from an
operating facility comprising a main body of rotation about a
longitudinal axis of the component provided, at least at one of its
ends, with a first connector for attaching the component to another
tubular component, the component moreover being intended to be at
least temporarily gripped in a peripheral zone by means for
retaining the component on the facility, characterized in that the
component comprises, inside the clamping zone, a coating for
protecting the component against mechanical damage likely to be
caused by the retaining means, the coating being produced from a
material with a hardness greater than the hardness of the material
forming the component but less than a value of 70 HRC.
[0015] Thanks to the invention, the coating, arranged as an
interface between the tubular component and the retaining means,
makes it possible to reduce the depth of the grooves likely to be
formed by the retaining means on the component and thus to preserve
the integrity of the component. This thus makes it possible to
mitigate any defect that has begun to appear, but also to reduce
any risk of crack initiation in the component clamping area.
[0016] Thanks to the physical hardness properties of the coating,
the latter is ductile enough to deform, substantially following the
profile of the galling surface of the retaining means, while being
hard enough to ensure an effective protection of the tubular
component. The relative ductility ensures a more homogeneous
distribution of the stresses and thus a reduction in the stress
concentration factor. The length of the coating is adapted for
example as a function of the needs and dimensional constraints
associated in particular with the retaining means and the practices
of the user.
[0017] A component according to the invention can moreover comprise
one or more of the following features: [0018] the coating is a
sacrificial coating; [0019] the hardness of the coating increases
progressively in the direction from the component to the coating;
[0020] the coating is formed by a plurality of layers; [0021] the
peripheral clamping zone extends from an end face of the first
connector as far as at most one-third of the body; [0022] the first
connector has a female thread; [0023] the component is provided, at
the other of its ends, with a second connector with a male thread;
[0024] the connector or connectors are connected to the body by
welding, forming a support joining the connector to the body;
[0025] the coating leaves the joint support exposed; [0026] the
thickness of the body is greater than 12.7 mm; [0027] the coating
has a roughness greater than the roughness on the surface of the
tubular component in order to facilitate the adherence of the
retaining means to the body of the component; [0028] the thickness
of the coating is greater than 1 mm and preferably greater than 2
mm; [0029] the coating is formed by a layer obtained by thermal
spraying for example of the electric arc type or by electroplating;
[0030] the main element or elements are selected from nickel,
chromium, molybdenum, tungsten and boron; [0031] the secondary
element or elements are selected from silicon, carbon, chromium,
boron, vanadium, titanium, iron, manganese and aluminium; [0032]
the zone starts at the end of the body and extends for example over
approximately 1.5 metres.
[0033] Other characteristics and advantages of the invention will
become apparent in the light of the following description, made
with reference to the attached drawings, in which:
[0034] FIG. 1 represents an oil platform illustrating an assembly
stage of a string of tubular components according to the
invention;
[0035] FIG. 2 represents a detailed view of the oil platform of
FIG. 1;
[0036] FIG. 3 represents a perspective view of a set of three
tubular components according to the invention, dismantled;
[0037] FIG. 4 represents a partial section view of a tubular
component according to the invention gripped in retaining means on
the platform of FIG. 1;
[0038] FIG. 5 represents a diagrammatic view of a slip forming a
part of the retaining means;
[0039] FIG. 6 represents a cross-section along a longitudinal axis
of a tubular component of the set of FIG. 3;
[0040] FIG. 7 is a diagrammatic top view of a cross-section along
the line 7-7 in FIG. 4.
[0041] A drilling facility denoted by the general reference 10 and
in which the present invention can be used advantageously is shown
in FIG. 1. In the described example, the facility 10 comprises an
offshore platform 12, located on the surface of the sea or
ocean.
[0042] This platform 12 is conventionally equipped with a certain
number of accessories used for the drilling of the well and
subsequent operation of the well. In the described example and as
illustrated in detail in FIG. 2, the platform 12 comprises in
particular a derrick 14 equipped with a rotary table 16 as well as
numerous accessories that allow the handling and gripping of the
various elements used to manufacture the well and exploit it. In a
manner known per se, the rotary table 16 is capable of being
actuated by means, not shown, which make it possible in particular
to set in rotation, for example, a drill string of a well.
[0043] As illustrated in FIG. 1, the platform 12 comprises a
floating support 18 in order to keep it substantially at the level
of the surface S of the water. The platform 12 is thus located in
line with an offshore well 20 drilled into the seabed F. The
offshore well 20 may or may not have a casing. Moreover, as a
variant, the platform 12 can optionally rest directly on the bed
when the sea is less deep.
[0044] For the operation, the drilling, or also the manufacture of
the well, the facility 10 also comprises a set of tubular
components connected to one another in order to form strings with
varying functions. Thus, for example, the strings can be intended
for drilling the well. In this case, the term "drill string" is
more accurately used. They can also be intended to produce a casing
of the drilled well, or also to actually exploit the well or also
to route such strings inside the well (landing strings). All of
these strings are generally produced by placing tubular components
end to end from the drilling platform 12.
[0045] As illustrated in FIG. 2, the facility 10 can also comprise
a riser 22 which forms a pipe between the floating or semi-floating
platform 12 and the well 20, and inside which one or other of the
above-listed strings is extended. Its main function is in
particular to protect the strings extending inside the pipe against
the external environment. The riser 22 can for example be suspended
from the platform 12.
[0046] In the example illustrated in the figures, the string being
formed shown in FIG. 1 is a landing string 24. The production or
casing tubes are generally positioned in two stages: a first stage
of forming the string to be positioned and a second stage of
forming the landing string which is carried out following the
string to be positioned. Thus, in the example illustrated, this
landing string 24 in the course of production is attached by its
lower end 24A to another string 26 of tubular components, such as
for example a casing string, and is attached by its upper end 24B
to the platform 12. For example, the two strings 24 and 26 are
attached to one another by means of a specific connection piece
28.
[0047] Thus, a portion of the landing string 24, in dismantled
state, comprising three tubular components 30 is shown in FIG. 3.
Preferably, each tubular component 30 comprises a main body 32
rotating about a longitudinal axis X and is provided, at least at
one of its ends 34B, with a first connector 36B for attaching the
tubular component 30 to another tubular component. For example,
this first connector 36B has a female thread.
[0048] In this example, the tubular component 30 is also provided,
at the other of its ends, with a second connector 36A with a male
thread. As illustrated in FIG. 3, the tubular components 30 are
capable of cooperating with one another by make up. The connectors
36 are connected to the body 32 by welding, forming a support 38
joining the connector 36 to the main body 32.
[0049] Generally, the tubular components 30 used to form the
landing string 24 have a diameter greater than the diameter of the
standard tubular components. For example, a diameter usual for this
type of tube is greater than 127 mm (5 inches). Moreover, such a
component generally has an increased thickness, for example greater
than 12.7 mm (0.5 inches). Moreover, the tubular components are
preferably produced from a material of a grade higher than 105 KSI
(725 MPa) and more commonly higher than 135 KSI (931 MPa). Such
properties allow them to withstand the very high tensile forces
associated with the mass of the string that they are supporting.
However, as a variant, the landing tube can be formed by a drilling
tube.
[0050] As illustrated in FIG. 2, in order to produce such
assemblies and to hold them on the platform 12, the facility 10 is
equipped with means 40 for retaining tubular components 30. As can
be seen in this figure, the retaining means 40 comprise for example
a lower head 42 for securing the tubular component 30, and
therefore the string in the course of production, to the platform
12. This lower head 42 makes it possible to retain the string on
the platform 12, by gripping the last tubular component connected
30, i.e. by the upper end 24B of the string being formed 24. As can
also be seen in FIG. 2, the retaining means 40 also comprise an
upper head 44 for suspending and raising a tubular component 30 (or
several components) in order to connect it to the last component of
the portion of string 24 already formed. It can thus be seen in
FIG. 2 that a first tubular component 30 is suspended by the upper
head 44 while a second tubular component 30, at the upper end of
the string 24, is secured to the platform 12 by the lower head
42.
[0051] The lower 42 and upper 44 heads of the retaining means 40
are shown in detail in FIG. 4. Preferably, the lower head 42
comprises at least one slip 46. In the described example, the lower
head 42 comprises a plurality of slips 46, for example three (FIG.
7), capable of substantially following the shape of the body 32 of
the tubular component 30 and gripping it in a vice-like manner. The
lower head 42 moreover preferably comprises a main body 48 formed
in this example by the rotary table 16. The rotary table 16 thus
comprises a housing 50 for receiving the slips 46. In the described
example, the lower head 42 also comprises adaptation parts 52
positioned between the slips 46 and the rotary table 16 making it
possible to facilitate the positioning of the slips 46 inside the
body.
[0052] A detailed view of a slip 46 is shown in FIG. 5. The slip 46
thus in this example has the general shape of a cone portion and
has a gripping surface 54 for retaining the component. For example,
the lower head 42 comprises a plurality of gripping elements 56,
for example of the jaw type, capable of grasping the tubular
component 30. Each gripping element 56 is formed for example by a
strip produced from treated steel. Moreover, the upper suspension
head 44 comprises, as illustrated in detail in FIG. 4, a main body
provided with an orifice for guiding the tubular component and is
connected to a lifting device 47 shown diagrammatically in FIG.
2.
[0053] As can be seen in FIGS. 4 and 6, the tubular component is
intended to be at least temporarily gripped inside a peripheral
zone Z for clamping the component by the retaining means 40. In
this example, this zone Z extends from one end edge of the first
connector 36B as far as at most one-third of the body 32. In this
example, the zone Z comprises first Z1 and second Z2 zones: [0054]
a first zone Z1 for gripping the component 30 by the lower head 42,
[0055] a second zone Z2 for gripping the component 30 by the upper
head 44.
[0056] Generally, a tubular component 30 has a length comprised
between eight and fourteen metres (i.e. approximately 25 to 45
feet). In the example illustrated, the tubular component 30 has a
standard length of ten metres (approximately thirty feet). In this
case, the zone Z extends for example as far as two metres (eighty
inches), i.e. less than one-third of the standard length of the
component 30. Preferably, the zone Z starts at 0.5 metres (nineteen
inches) from the end edge of the female connector 36B, which
corresponds approximately to the standard length of the female
connector 36B of such a tube. The zone Z extends in this case over
a length of 1.5 metres (sixty inches) along the axis X of the
tubular component 30. Moreover, the first zone Z1 extends for
example over 0.5 metres (approximately 20 inches) and the same
applies to the second zone Z2. These two zones Z1 and Z2 are
distinct in the described example. However, optionally, in a
variant not illustrated, the two zones Z1 and Z2 can overlap at
least partially. The delimitation of this zone Z or of these two
zones Z1 and Z2 depends on different parameters, such as the
dimension of the tubular components, the retaining surface of the
retaining head, the connector length 36B, etc.
[0057] According to the invention, in order to protect the
component 30 against mechanical damage likely to be caused by the
retaining means 40, and in particular by the jaws of the lower head
42, the component 30 comprises a protective coating 58. More
particularly, the coating 58 is produced from a material with a
hardness greater than the hardness of the material forming the
component 30 but less than a value of seventy Rockwell, on the C
scale (unit known by the acronym HRC), preferably less than a value
of fifty HRC.
[0058] In this example, the jaws are produced from a material with
a hardness substantially equal to 55 HRC and preferably, the
coating 58 is produced from a material with a hardness less than
the hardness of the material of the jaws, therefore less than 55
HRC. During the clamping of the component by the jaws the relative
ductility of the coating 58 compared with the jaws causes a
deformation of the coating 58 according to the surface profile of
the jaws and thus a homogeneous distribution of the stresses.
Moreover, the relative hardness of the coating 58 compared with the
tubular component 30 ensures an effective protection of the
component 30. Thus, for example, the tubular component 30 has a
hardness value substantially equal to twenty-eight HRC.
[0059] The coating 58 is for example produced from a metal alloy in
which: [0060] the main element or elements are selected from
nickel, chromium, molybdenum, tungsten and boron, [0061] the
secondary element or elements are selected from silicon, carbon,
chromium, boron, vanadium, titanium, iron, manganese and aluminium.
The quantities of the different elements of the alloy are chosen so
as to obtain the hardness characteristics required by the
invention.
[0062] For example, an alloy composition suitable for the invention
comprises 45% chromium, 6% boron as main elements and silicon (2%),
carbon, iron and sulphur (less than 0.1%) as secondary elements. A
hardness of 58 HRC is measured.
[0063] Another suitable composition comprises 20% chromium, 15%
molybdenum, 10% tungsten as main elements and carbon (<2%),
manganese (<5%), silicon (<2%), boron (<5%) and iron as
secondary elements. A hardness of 54 HRC is measured.
[0064] Preferably, the coating 58 is produced by thermal spraying.
This is a method consisting of spraying heated particles of the
material to be applied to a surface of the tubular component, for
example prepared beforehand by sanding or shot-blasting. The
accumulation of the particles on the component 30 forms the coating
58. This method has in particular the advantage of preventing the
tubular component 30 from being exposed to temperatures that are
too high and may damage its mechanical integrity. In fact, the
particles are heated and cooled again when sprayed onto the surface
of the tubular component 30.
[0065] For example, the coating 58 can be produced by means of an
electric arc thermal spraying method. This method is based on
melting one or more wires formed by the material to be sprayed, by
means of an electric arc. Preferably, the molten material is
atomized by a compressed gas, for example air, and is thus sprayed
onto the part to be hard-surfaced. This method makes it possible to
obtain a coating with a high adherence and low porosity thanks in
particular to the combination of a high spraying speed and a high
temperature.
[0066] As a variant, the coating 58 can be produced by
electroplating. In this case, the product used is generally a
composition based on nickel sulphamate. The coating 58 obtained
then in this example has a Rockwell hardness of fifty HRC.
[0067] Preferably, the hardness of the coating 58 increases
progressively in the direction from the component 30 to the coating
58. This property of the coating 58 makes it possible in particular
to ensure better adhesion of the coating to the body of the tube.
In order to produce this hardness progression, it is desirable to
form a coating 58 comprising a plurality of layers, each of the
layers being produced from a material with a predefined hardness
and a value that increases in the direction from the component 30
to the coating 58.
[0068] Moreover, in the described example, the coating 58 has a
thickness greater than 1 mm and preferably greater than 2 mm. This
minimum thickness makes it possible to ensure a sufficient
protection of the component with regard to the depth of the
imprints likely to be produced for example by the jaws of the lower
head 42.
[0069] According to the invention, the coating 58 extends inside
the peripheral clamping zone Z. In this example, the coating 58
very largely, or even completely, covers the first zone Z1 and
preferably also the second zone Z2. It may be envisaged to cover
all of the zone Z or only the first zone Z1 or also only the first
Z1 and second Z2 zones. A person skilled in the art knows how to
suitably adjust the dimensions of the coating 58 in order to reap
the benefits provided by the invention as a function of the
different constraints of the facility. The delimitation of the
zones Z1 and Z2 and thus of the zone Z depends on the dimensional
constraints of the retaining means and/or on the practices of the
users.
[0070] Moreover, the coating 58 preferably leaves the joint support
38 exposed. For example, the coating 58 extends below the joint
support 38 of the female connector 36B and the body 30 as
illustrated in FIG. 6. The joint support 38 remaining uncovered
thus forms a visual marker in order, during the positioning of the
lower 42 and upper 44 heads for gripping the component, to prevent
the latter from accidentally gripping the component 30 around the
joint support 38 which forms a relatively fragile region of the
component 30. In this figure, the body 32 has a general cylindrical
shape. Of course, this representation is diagrammatic. In a
variant, the body 32 can thus have a profile with variable
thickness. For example, the body can locally have a thin section
formed by a reduction in its external diameter and/or an increase
in its internal diameter. In this case, the coating can extend at
least partially around the thinned zone of the tube body.
[0071] Preferably, the coating 58 is a sacrificial coating. It can
thus optionally be replaced in the event of its significant
degradation.
[0072] In order to facilitate the adherence or securing of the
lower head 42 to the component 30, the coating 58 preferably has a
roughness greater than the surface roughness of the tubular
component 30. For example, in order to achieve the desired
roughness, various technical means can be implemented, such as
machining, localized or wide-spread grinding, etc.
[0073] The main aspects of operation of a tubular component 30
according to the invention will now be described. Initially, the
landing string 24, as illustrated in FIG. 2, is in the course of
formation and is suspended from the platform by a tubular surface
component. This component is gripped by the lower head 42. Once the
tubular component or components suspended from the surface
component have been connected, the string of components in the
course of production is lowered a distance substantially equivalent
to the length of the tubular components added. This handling
operation is accomplished, on the one hand, for example, by means
of the upper suspension head which is supported by an elevator link
connected to the lifting system of the platform (not shown) and, on
the other hand, by means of the lower gripping head which is
capable of releasing the surface component in order to allow the
string being formed to be lowered to the last newly connected
component. The further the operation of forming the string
progresses, the greater the tensile forces generated by the weight
of the string on the gripped surface component.
[0074] Thanks to the invention, the last temporarily-gripped
surface component is protected by the coating 58 against mechanical
damage likely to be caused in particular by the gripping elements
of the retaining head. Moreover, when this coating 58 is too
damaged and its efficacy is consequently reduced, it can
advantageously be replaced without damaging the component 30
itself. This makes it possible to prolong the life of such tubular
components 30.
[0075] Of course, other embodiments can be envisaged without
exceeding the scope of the invention. Thus, various modifications
can be made by a person skilled in the art to the invention which
has just been described by way of example.
* * * * *