U.S. patent application number 12/595376 was filed with the patent office on 2010-06-17 for method of making an udersea pipe, the method including peening assembly welds inside the pipe.
This patent application is currently assigned to SAIPEM S.A.. Invention is credited to Patrick Cheppe, Jean-Michel Duchazeaubeneix, Philippe Jacob, Eric Kerdiles.
Application Number | 20100147047 12/595376 |
Document ID | / |
Family ID | 38667096 |
Filed Date | 2010-06-17 |
United States Patent
Application |
20100147047 |
Kind Code |
A1 |
Kerdiles; Eric ; et
al. |
June 17, 2010 |
Method of Making an Udersea Pipe, the Method Including Peening
Assembly Welds Inside the Pipe
Abstract
A method of making undersea steel pipes, by assembling unit pipe
elements together end-to-end by welding, the steel or metal alloy
weld beads of said welds being disposed on the outside of the pipe,
wherein localized peening is performed on the inside of the pipe to
increase the compression of the steel or metal in the vicinity of
the welds and over the adjacent peripheral inside surface of the
pipe on either side of the weld so as to create a swath of surface
that has been peened over a limited distance L in the axial
longitudinal direction of said pipe. The peening is preferably
performed using a wheeled carriage fitted with a peening tool.
Inventors: |
Kerdiles; Eric; (Marcq,
FR) ; Duchazeaubeneix; Jean-Michel; (Les Sorinieres,
FR) ; Jacob; Philippe; (Orvault, FR) ; Cheppe;
Patrick; (Basse Goulaine, FR) |
Correspondence
Address: |
COHEN, PONTANI, LIEBERMAN & PAVANE LLP
551 FIFTH AVENUE, SUITE 1210
NEW YORK
NY
10176
US
|
Assignee: |
SAIPEM S.A.
MONTIGNY LE BRETONNEUX
FR
|
Family ID: |
38667096 |
Appl. No.: |
12/595376 |
Filed: |
April 9, 2008 |
PCT Filed: |
April 9, 2008 |
PCT NO: |
PCT/FR08/50625 |
371 Date: |
November 17, 2009 |
Current U.S.
Class: |
72/367.1 |
Current CPC
Class: |
B25D 2250/311 20130101;
F16L 55/26 20130101; B25D 2250/285 20130101; F16L 1/26 20130101;
C21D 9/08 20130101; F16L 13/02 20130101; E21B 17/01 20130101; B23K
2101/10 20180801; C21D 9/50 20130101; B25D 11/06 20130101; B23K
9/282 20130101; C21D 7/06 20130101; B25D 2250/291 20130101; B24B
39/026 20130101 |
Class at
Publication: |
72/367.1 |
International
Class: |
B21D 3/00 20060101
B21D003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 12, 2007 |
FR |
07 54425 |
Claims
1-21. (canceled)
22. A method of making steel undersea pipes, the method comprising
end-to-end assembly by welding of unit pipe elements with welds
having steel or metal alloy weld beads, the steel or metal alloy
weld beads of said welds being located on the outside of the pipe,
wherein localized peening is performed inside the pipe to increase
the compression of the steel or metal in said welds and over the
adjacent peripheral inside surface of the pipe on either side of
the weld so as to create a surface swath that is peened over a
limited distance L in the axial longitudinal direction XX of said
pipe, preferably over a distance L that is not less than the width
of the weld, on the inside of the pipe, plus a width of 1 mm to 10
mm on either side thereof.
23. The method according to claim 22, wherein the weld comprises a
main weld bead at the outside of the pipe and an inside projection
or seam of smaller thickness standing proud of the inside of the
pipe.
24. The method according to claim 22, wherein said ends of unit
pipe elements for welding together present, in longitudinal axial
section, a straight end on the inside of the pipe forming a root
face preferably occupying at least one-fourth of the thickness of
the main portion of the pipe, and extended towards the outside of
the pipe by a sloping chamfer.
25. The method according to claim 22, wherein material is removed
by machining, preferably by grinding or by milling, from the inside
surface of the pipe and from the weld bead over the surface that is
to be peened, prior to said peening.
26. The method according to claim 22, wherein said peening is
performed at least in the transition region between the inside
surface of the weld bead and the adjacent inside surface of the
pipe.
27. The method according to claim 22, wherein said peening is
performed in such a manner as to establish compression or to
increase compression over a thickness of 0.2 mm to 2 mm of said
inside surface of the pipe and of said weld.
28. The method according to claim 22, wherein the limited distance
L represents one to three times the thickness of the pipe.
29. The method according to claim 22, wherein peening is performed
in such a manner as to obtain compression stress that is greater
than 5 MPa, preferably greater than 50 MPa, over the entire peened
surface.
30. The method according to claim 22, wherein said peening is
performed with a peening device that is moved inside said pipe in
translation and in rotation in the vicinity of said weld, the
peening device comprising: at least one peening tool mounted on a
first motor-driven carriage; said first carriage being suitable for
moving inside said pipe in translation in the axial longitudinal
direction XX of said pipe; said first carriage supporting means for
moving said peening tool in radial translation YY relative to said
first carriage, enabling said peening tool to be applied against
the inside surface of the pipe, or enabling the peening tool to be
set back away from said inside surface of the pipe; and means for
moving said peening tool in rotation about said axial longitudinal
axis XX of the pipe, enabling said peening to be performed over the
entire circumference of the inside surface of said pipe one said
rotation of the peening tool.
31. The method according to claim 30, wherein said peening tool
comprises a vibratory surface that preferably extends over said
limited distance L in the axial longitudinal direction XX, and a
plurality of projectiles of rounded or pointed type suitable for
being projected towards the inside surface for treatment by said
vibrating surface in order to create a plurality of impacts.
32. The method according to claim 30, wherein said first carriage
includes means for moving said peening tool in translation relative
to said first carriage in said longitudinal axial direction XX.
33. The method according to claim 30, wherein: said first carriage
is moved in translation inside said pipe in said axial direction
XX, such that said peening tool is substantially positioned so that
it can perform peening in said weld region and on either side
thereof over a said distance L for peening, in said longitudinal
axial direction XX and astride said weld; then said peening tool is
moved against or close to the inside surface of the pipe by moving
said peening tool in radial translation YY; then said peening tool
is then moved in rotation about said axial longitudinal axis XX
over the circumference of the inside surface of the pipe; and then
where appropriate, the peening tool is moved in translation in the
axial longitudinal direction XX relative to said first carriage so
as to perform the peening and compression over the entire peened
surface, in particular for a peening tool including a plurality of
said projectiles of pointed or rounded type that are spaced about
from one another.
34. The method according to claim 30, wherein: said first
motor-driven carriage supports a first shaft placed in said axial
longitudinal direction XX; and said first shaft supports a
transverse guide support suitable for guiding the movement of a
second carriage in radial translation in a transverse direction
perpendicular to said axial longitudinal direction XX, and
comprising means suitable for keeping said peening tool in position
facing the inside surface of said pipe; and said first shaft
comprises means for driving it in controlled rotation about its
said axial longitudinal axis XX, so as to enable said peening tool
to be moved over the circumference of the inside surface of the
pipe in controlled rotation about its axis; and said first shaft is
preferably suitable for being driven in translation relative to
said first carriage in said axial longitudinal direction XX, over
at least a said limited distance L.
35. The method according to claim 30, wherein said peening tool
comprises a plurality of projectiles that are projected against
said surface for peening from a vibrating surface of said peening
tool.
36. The method according to claim 35, wherein said peening tool is
mounted to pivot relative to said second carriage thus enabling the
angle of inclination .beta. of the projection direction
Y.sub.1Y.sub.1 of said projectiles to be varied relative to said
direction YY of movement in radial translation of said second
carriage.
37. The method according to claim 30, wherein prior grinding is
performed of the surface for peening with a grinder tool having a
rotary grindwheel mounted in the place of or together with a said
peening tool on a said first carriage.
38. The method according to claim 22, wherein said welding is
performed using carbon steel, stainless steel, or a
corrosion-resisting alloy of the Inconel type having high
elasticity, and good fatigue resistance, and preferably Inconel of
grade 625 or 825.
39. The method according to claim 22, comprising the following
successive steps: 1) in a workshop on land, assembling the
respective ends of at least two unit pipe elements together
end-to-end by said welding in order to form pipe strings; and 2) at
sea, on board a laying ship fitted with a J-lay tower, assembling
respective ends of said strings together by said welding to form a
pipe.
40. An undersea bottom-surface connection pipe including at least a
portion having regions of said welds assembling together unit pipe
elements, the welds being put into uniform compression by the
method according to claim 22.
41. An undersea bottom-surface connection pipe according to claim
19, wherein it acts as an SCR catenary pipe having at least a
portion that includes a region in contact with the bottom that
extends above the bottom over at least 100 m, and preferably 200 m,
said portion being assembled using a method according to claim
22.
42. A peening device suitable for use in a method according to
claim 30, the device including at least one said peening tool
mounted on a said first carriage suitable for moving in translation
inside a pipe, the device comprising a said peening tool suitable
for moving in longitudinal translation XX relative to said first
carriage and in rotation about said axial longitudinal axis XX of
the pipe in the vicinity of said welds, as defined in claim 30.
Description
[0001] The present invention relates to a method of making undersea
pipes for conveying corrosive fluids, and in particular water, the
method comprising assembling unit pipe elements together by
welding.
[0002] The present invention relates more particularly to a
subsurface connection installation between a floating support and
an oil loading buoy.
[0003] The present invention relates more particularly to a
bottom-surface connection installation comprising at least one
undersea pipe providing a connection between a floating support and
the bottom of the sea, in particular at great depth. Such undersea
pipes are referred to as "risers" and they are made up of unit
tubular elements made of steel that are welded together
end-to-end.
[0004] More particularly, the present invention provides a riser
type undersea pipe for making a connection between a floating
support and the bottom of the sea, said riser being constituted by
a rigid, catenary-type pipe that extends from said floating support
to a point of contact with the sea bottom.
[0005] The technical field of the invention is thus the field of
fabricating and installing undersea pipes and more particularly
production bottom-surface connections for offshore extraction of
oil, gas, or other soluble or phase-change material, or a
suspension of mineral material, from an undersea well head in order
to develop production fields located at sea or off-shore. The main
and immediate application of the invention lies in the field of oil
production, and also in reinjecting water and producing or
reinjecting gas.
[0006] In general, a floating support includes anchor means
enabling it to remain in position in spite of the effects of
currents, winds, and swell. It also generally includes means for
drilling, storing, and processing oil, and means for off-loading to
off-loading tankers that call at regular intervals to remove
production. Such floating supports are referred to as floating
production storage off-loading (FPSO) vessels or as "floating
drilling and production units" (FPDU) when the floating support is
also used for performing drilling operations with wells being
deflected in the depth of the water.
[0007] An undersea pipe or "riser" of the invention may constitute
either a "production pipe" for crude oil or gas, or a water
injection pipe providing a connection with an undersea well head at
the sea bottom, or indeed a "drilling riser" providing the
connection between the floating support and a well head located on
the sea bottom.
[0008] A multiplicity of lines are generally installed on FPSOs and
it is necessary to implement either hybrid-tower type
bottom-surface connections or else catenary type connections, i.e.
connections that follow a catenary curve.
[0009] When the bottom-surface connection pipe is of the catenary
type, it provides a direct connection between a floating support
and a point of contact with the sea bottom that is offset from the
axis of said support, said pipe taking up a so-called "catenary"
configuration under the effect of its own weight, i.e. a curve
having a radius of curvature that decreases from the surface down
to the point of contact with the sea bottom, with the axis of said
pipe forming an angle .alpha. relative to the vertical that varies
in general from 10.degree. to 20.degree. at the level of the
floating support up to, theoretically, 90.degree. at the sea bottom
corresponding to a theoretical position that is substantially
tangential to the horizontal, as explained below.
[0010] Catenary type connections are generally made with the help
of flexible pipes, however they are extremely expensive because of
the complex structure of the pipe.
[0011] As a result, substantially vertical risers have been
developed so as to bring the catenary-configuration flexible
connection closer to the surface near the floating support, thus
making it possible to minimize the length of said flexible pipe,
and also to minimize the forces that are applied thereto, thereby
considerably reducing its cost.
[0012] Once the depth of water reaches or exceeds 800 meters (m) to
1000 m, it becomes possible to make said bottom-surface connection
with the help of a thick-walled rigid pipe since the considerable
length of the pipe presents sufficient flexibility to obtain a
satisfactory catenary configuration while remaining within
acceptable stress limits.
[0013] Such rigid risers of thick strong materials in a catenary
configuration are commonly referred to as steel catenary risers
(SCRs) regardless of whether they are made of steel or of some
other material such as a composite material.
[0014] Such "SCRs" are much simpler to make than flexible pipes and
therefore much less expensive.
[0015] The geometrical curve formed by a pipe of uniform weight in
suspension and subjected to gravity, known as a "catenary", is a
mathematical function of the hyperbolic cosine type (Cos
h(x)=(e.sup.x+e.sup.-x)/2), relating the abscissa and the ordinate
of an arbitrary point on the curve in application of the following
formulae:
y=R.sub.0(cos h(x/R.sub.0)-1)
R=R.sub.0(Y/R.sub.0+1).sup.2
in which: [0016] x is the distance in the horizontal direction
between the point of contact and a point M on the curve; [0017] y
represents the altitude of point M (x and y are thus the abscissa
and the ordinate of a point M on the curve relative to an
orthogonal frame of reference having its origin at said point of
contact); [0018] R.sub.0 is the radius of curvature at said point
of contact, i.e. the point where the tangent is horizontal; and
[0019] R is the radius of curvature at the point M (x,y).
[0020] Thus, curvature varies along the catenary from the surface
where its radius of curvature has a maximum value R.sub.max down to
the point of contact where its radius of curvature has a minimum
value R.sub.min (or R.sub.0 in the above formula). Under the effect
of waves, wind, and current, the surface support moves laterally
and vertically, thereby having the effect of raising and lowering
the catenary-shaped pipe in the vicinity of the sea bottom.
[0021] Thus, the pipe presents a radius of curvature that is
greatest at the top of the catenary, and in generally at least 1500
m, and in particular lies in the range 1500 m to 5000 m, i.e. at
the point where it suspended from the FPSO, with said radius of
curvature decreasing down to the point of contact with the bottom.
At that location, the radius of curvature is at a minimum in the
portion that is suspended. However, in the adjacent portion that is
resting on the sea bottom, said pipe is theoretically in a straight
line so its radius of curvature is theoretically infinite. In fact,
since some residual curvature remains, said radius is not infinite,
but it is extremely large.
[0022] Thus, as the floating support moves on the surface, the
point of contact moves forwards and backwards, and in the region
that is lifted from or lowered onto the bottom, the radius of
curvature passes in succession from a minimum value R.sub.min to a
value that is extremely large, or even infinite in a theoretical
configuration where the undersea pipe rests on the sea bottom
substantially in a straight line.
[0023] This alternating flexing gives rise to fatigue phenomena
that are concentrated throughout the foot region of the catenary,
and as a result the lifetime of such a pipe is greatly reduced and
in general not compatible with the lifetimes desired for
bottom-surface connections, i.e. 20 to 25 years, or even more.
[0024] In addition, during these alternating movements of the point
of contact, it is observed that the stiffness of the pipe
associated with the above-mentioned residual curvature acts over
time to dig a furrow over the entire length that is raised and then
lowered back down again, so as to create a transition region in
which there exists a point of inflection where the radius of
curvature, which is at a minimum at the foot of the catenary,
changes direction in said transition region and increases finally
to reach an infinite value in a portion of undersea pipe that is
resting in a straight line on the sea bottom.
[0025] These repeated movements over long periods dig a furrow of
considerable depth in bottoms that are poorly consolidated, as are
commonly to be found at great depths, thereby having the effects of
modifying the curvature of the catenary and, if the phenomenon
becomes amplified, of leading to risks of damage to the pipes, or
to other undersea pipes lying on the sea bottom, or to the SCRs
that provide connections between said undersea pipes resting on the
sea bottom and the surface.
[0026] These pipes are made by welding unit pipe elements together
end-to-end. The unit pipe elements are themselves assembled to form
strings, in general strings of two to four unit elements welded
end-to-end, which strings are then taken to sea. In known manner,
these strings are assembled by being welded to one another at sea
from a pipe-laying ship, in particular in a J-lay tower. The
assembly welds are made preferably and for the most part from the
outside of the pipe.
[0027] The most critical portion of a riser is situated at the
assembly welds between unit pipe elements, in particular in the
portion of the riser that is closest to the point of contact, and
the major fraction of the forces in this low portion of the
catenary are generated by the movements of the floating support and
by the excitations that are applied to the top portion of the
catenary, which is subjected to current and swell, with all of
these excitations then propagating mechanically along the entire
length of the pipe to the foot of the catenary.
[0028] The steels from which pipes are made are selected to
withstand fatigue throughout the lifetime of installations,
however, the welds between pipe elements, in this catenary foot
region constitute weak points when said pipe conveys water or fluid
that includes water, and more particularly salt water. In the
presence of water, said welds are subjected to fatigue and
corrosion phenomena that give rise over time, and under varying
bending stresses, to cracks that lead to said pipes being
destroyed.
[0029] To mitigate that problem, welds are made between pipe
elements using a stainless steel or an alloy that withstands
corrosion. Anti-corrosion alloys are well known to the person
skilled in the art, and are constituted mainly by nickel-based
alloys, in particular of the Inconel type, preferably of a specific
grade, and in particular Inconel 625 or 825. Such Inconels also
present excellent resistance to fatigue as a result of their high
elastic limits, thereby making it possible to achieve lifetimes of
20 to 30 years.
[0030] In order to enable the welds to be strong and to be made
under good conditions, proposals have been made to line the insides
of two pipe elements for welding together with the same stainless
steel or corrosion-resistant alloy over a length of a few
centimeters in the vicinity of each end of the pipe elements for
welding together, so that the penetration pass of the weld that
constitutes the future wall in contact with the fluid is of the
same metal as the welding filler metal, and in particular Inconel.
Such a lining of stainless steel or anti-corrosion alloy, in
particular of the Inconel type, is provided using an expensive arc
method referred to as "cladding", and generally performed using a
tungsten inert gas (TIG) method or a plasma method, associated with
a filler wire or with a powder of stainless steel or of
corrosion-resistant alloy.
[0031] The object of the present invention is to provide a novel
method of fabricating and installing undersea pipes for conveying
corrosive fluids and in particular water, the method comprising
welding together undersea pipe strings at sea on board a ship for
laying undersea pipes, which method should: [0032] be reliable in
terms of resistance to fatigue at each of the welds, and in
particular avoid cracks appearing over time; [0033] have as little
effect as possible on the mechanical strength of the pipe and/or
increase as little as possible head losses in the fluid conveyed
inside the pipe when in operation; and [0034] be as simple and as
inexpensive as possible to implement, in particular with the
assembly steps and in particular the welding, being performed as
little as possible on board the laying ship.
[0035] In the present invention, the inventors have discovered that
incipient cracks are located on the inside of the pipe in the
vicinity of the small projection of the weld bead that extends
towards the inside of the pipe, and not on the outside face
comprising the main bulk of the weld bead on the outside of the
pipe. More precisely, and as explained in the detailed description
below given with reference to FIGS. 3E and 3F, the inventors have
discovered that the origin of weld destruction lies in the
transition region between the welds and the inside surface made of
the base steel of the adjacent pipe, in which region traction
stresses associated with thermal shocks during welding can give
rise to physical defects, and in particular to incipient cracks
located in said zone.
[0036] During welding, uncontrollable localized quenching or
shrinkage occurs, leading to contraction stress states of the metal
that are localized in and close to the weld region, even though the
remainder of the adjacent surface of the pipe is either at rest or
in compression.
[0037] In general, these problems of localized contraction stress
in welds are solved by annealing to relax the stress. Other means
are known for treating such problems in welds in order to relax
traction stress, but they are not compatible with the time
constraints and the desired rates of laying at sea. However, in
present circumstances, annealing treatments are not possible for
the welds made between undersea pipe elements while laying the pipe
at sea.
[0038] The present invention provides a method of making steel
undersea pipes for conveying corrosive fluids and in particular
water, the method comprising assembling unit pipe elements together
end-to-end, the weld beads of steel or metal alloy of said welds
being located on the outside of the pipe, the method being
characterized in that localized peening is performed inside the
pipe to increase the level of compression stress in the steel or
the metal in the vicinity of said welds and in the adjacent
peripheral inside surface of the pipe on either side of the welds
so as to create a peened surface swath that is peened over a
distance L that is limited in the axial longitudinal direction XX
of said pipe, i.e. over a fraction only of the length of each of
the two pipe elements that are assembled together by said welds,
and as measured from their respective abutting ends.
[0039] More particularly, said peened swath extends over a distance
L that is not less than half the thickness of the pipe wall, and
more preferably over a distance L that is less than twice the
thickness of the pipe.
[0040] More particularly, the weld comprises a main weld bead on
the outside of the pipe and a projection or seam on the inside that
is of smaller thickness and that projects into the inside of the
pipe.
[0041] This internal projection or seam results from the partial
melting of the ends of the unit elements that are assembled
together by welding, said melting taking place during the welding
heat treatment.
[0042] More particularly, said peened swath extends over a distance
L corresponding to the width of the weld on the inside of the pipe,
in particular the width of said internal seam, which seam presents
a width lying in practice in the range 3 millimeters (mm) to 5 mm,
plus a width on either side lying in the range 1 mm to 10 mm, so as
to give a distance L lying in the range 5 mm to 25 mm.
[0043] The term "peening" is used herein to mean surface treatment
by multiple impacts using one or more projectiles so as to increase
the level of compression stress in a region of the surface under
treatment.
[0044] According to the present invention, it is the entire surface
of said swath, i.e. the cylindrical inside surface section on
either side of the weld, overlapping the weld, that is subjected to
these impacts, with no region of the surface outside said swath
being subjected to such an impact.
[0045] The projectiles may be in the form of balls or the tips of
pointed spindles, the projectiles striking the surface for
treatment at their ends and, during impacts, the kinetic energy of
the projectiles is transformed into plastic and elastic deformation
energy in the surface being treated, thereby having the effect of
increasing the compression stress in the material where it is
treated, and as a result eliminating residual regions of traction
stress.
[0046] Peening tools that can be used in the present invention are
described in FR 2 791 293 in the name of one of the Applicants,
however more rudimentary peening tools as described for example in
U.S. Pat. No. 3,937,055 could also be used.
[0047] Peening in the present invention consists, so to speak, in
cold forging to eliminate residual traction stresses by deforming
the material in the peened surface. It should be observed that it
is not desired to eliminate any extra thickness associated with an
inside seam or projection of the weld bead, but only to apply
compression in substantially uniform manner to the surface of the
welding region and of the adjacent regions, using sufficient energy
to plasticize and deform the metal so as to eliminate any residual
traction stresses due to the welding operation.
[0048] Still more particularly, said ends of the unit pipe elements
for welding together comprise, in longitudinal axial section, a
straight end beside the inside of the pipe forming a root face that
preferably occupies at least one-fourth of the thickness of the
main portion of the pipe and that is extended towards the outside
of the pipe by a sloping chamfer.
[0049] Under such circumstances, the inside projection or seam of
the weld that stands proud is a made up molten metal from said root
face and of the filler metal.
[0050] It will be understood that said chamfer faces towards the
outside of the pipe so that it can receive a weld bead deposited
between the two chamfers at the ends of two abutting pipe elements,
thereby substantially forming a V-shape at the end of the two pipe
elements for butt welding together.
[0051] In an advantageous implementation, material is removed by
prior machining, preferably by grinding or by milling, from the
inside surface of the pipe and from the weld bead over the surface
that is to be peened, prior to said peening.
[0052] Also advantageously, said peening is performed at least in
the transition region between the inside surface of the weld bead
and the adjacent inside surface of the pipe.
[0053] More particularly, said peening is performed in such a
manner as to establish compression or to increase compression over
a thickness of 0.2 mm to 2 mm of said inside surface of the pipe
and of said weld.
[0054] In one implementation, the limited distance L represents one
to three times the thickness of the pipe.
[0055] Still more particularly, peening is performed in such a
manner as to obtain compression stress that is greater than 5
megapascals (MPa), preferably greater than 50 MPa, in particular
lying in the range 50 MPa to 1000 MPa, over the entire peened
surface.
[0056] In a preferred implementation, said peening is performed
with a peening device that is moved inside said pipe in translation
and in rotation in the vicinity of said weld, the peening device
comprising: [0057] at least one peening tool mounted on a first
motor-driven carriage; [0058] said first carriage being suitable
for moving inside said pipe in translation in the axial
longitudinal direction XX of said pipe; [0059] said first carriage
supporting means for moving said peening tool in radial translation
YY relative to said first carriage, enabling said peening tool to
be applied against the inside surface of the pipe, or enabling the
peening tool to be set back away from said inside surface of the
pipe; and [0060] means for moving said peening tool in rotation
about said axial longitudinal axis XX of the pipe, enabling said
peening to be performed over the entire circumference of the inside
surface of said pipe one said rotation of the peening tool.
[0061] In a particular implementation, said peening tool comprises
a vibratory surface that preferably extends over said limited
distance L in the axial longitudinal direction XX, and a plurality
of projectiles of rounded or pointed type suitable for being
projected towards the inside surface for treatment by said
vibrating surface in order to create a plurality of impacts.
[0062] In a preferred implementation, the method of the invention
is characterized in that said first carriage includes means for
moving said peening tool in translation relative to said first
carriage in said longitudinal axial direction XX.
[0063] In particular, when the peening tool has a plurality of
projectiles that are projected radially from a vibration surface,
itself extending over at least some distance in the longitudinal
direction, said means for imparting relative movement in
longitudinal translation to the peening tool are suitable for
moving said projectiles over at least a distance corresponding to
the spacing between two successive projectiles so that the entire
treated surface can be peened completely in substantially uniform
manner.
[0064] Still more particularly, the method of the invention is
characterized in that it includes the following steps: [0065] said
first carriage is moved in translation inside said pipe in said
axial direction XX, such that said peening tool is substantially
positioned so that it can perform peening in said weld region and
on either side thereof over a said distance L for peening, in said
longitudinal axial direction XX and astride said weld; then [0066]
said peening tool is moved against or close to the inside surface
of the pipe by moving said peening tool in radial translation YY;
then [0067] said peening tool is then moved in rotation about said
axial longitudinal axis XX over the circumference of the inside
surface of the pipe; and then where appropriate, the peening tool
is moved in translation in the axial longitudinal direction XX
relative to said first carriage so as to perform the peening and
compression over the entire peened surface, in particular for a
peening tool including a plurality of said projectiles of pointed
or rounded type that are spaced about from one another.
[0068] It will be understood that the longitudinal movement of the
peening tool in translation relative to said first carriage may be
performed either continuously, or else essentially between two of
said rotations of said peening tool. This makes it possible to
avoid leaving any non-peened area between two impact regions of
said successive projectiles, and thus to reach the most critical
regions that are situated at the interface between the seam of the
weld bead and the base metal of the pipe.
[0069] According to other characteristics that are advantageous:
[0070] said first motor-driven carriage supports a first shaft
placed in said axial longitudinal direction XX; and [0071] said
first shaft supports a transverse guide support suitable for
guiding the movement of a second carriage in radial translation in
a transverse direction perpendicular to said axial longitudinal
direction XX, and comprising means suitable for keeping said
peening tool in position facing the inside surface of said pipe;
and [0072] said first shaft comprises means for driving it in
controlled rotation about its said axial longitudinal axis XX, so
as to enable said peening tool to be moved over the circumference
of the inside surface of the pipe in controlled rotation about its
axis; and [0073] said first shaft is preferably suitable for being
driven in translation relative to said first carriage in said axial
longitudinal direction XX, in particular over at least a short
distance .delta.x corresponding to a fraction of the distance
between two successive projectiles if any, or over a distance lying
in the range 0.1 mm to 10 mm when using a peening tool having a
single row of projectiles.
[0074] In a particular embodiment, said peening tool has a
plurality of projectiles, in particular of the rounded or pointed
type that are projected from a vibrating surface of said peening
tool against said surface for peening, in particular in a radial
direction, where appropriate.
[0075] Nevertheless, in a particular embodiment, said peening tool
is mounted to pivot relative to said second carriage, thus enabling
the angle of inclination 3 of the projection direction
Y.sub.1Y.sub.1 of said projectiles to be varied relative to said
direction YY of movement in radial translation of said second
carriage.
[0076] This embodiment makes it possible to optimize peening of the
transition regions between the inside weld seam and the adjacent
pipe wall, in particular when there is no prior machining of said
inside weld seam.
[0077] In the method in which prior grinding is performed, the
prior grinding of the surface for peening is performed with a
grinder tool having a rotary grindwheel mounted in the place of or
together with a said peening tool on a said first carriage.
[0078] More particularly, said welding is performed using carbon
steel, stainless steel, or a corrosion-resisting alloy of the
Inconel type having high elasticity, and good fatigue resistance,
and preferably Inconel of grade 625 or 825.
[0079] Still more particularly, the method of the invention
comprises the following successive steps:
[0080] 1) in a workshop on land, assembling the respective ends of
at least two unit pipe elements together end-to-end by said welding
in order to form pipe strings; and
[0081] 2) at sea, on board a laying ship fitted with a J-lay tower,
assembling respective ends of said strings together by said welding
to form a pipe.
[0082] The present invention also provides a bottom-surface
connection undersea pipe having at least a portion including
regions of said assembly welds between unit pipe elements that have
been put into compression by a method of the invention.
[0083] More particularly, the present invention provides a
bottom-surface connection undersea pipe of the invention that is
characterized in that it is a catenary pipe of the SCR type with at
least a portion thereof, including the region that comes into
contact with the bottom and extending from the bottom over at least
100 m, and preferably 200 m, being assembled by a pipe-making
method of the invention.
[0084] Finally, the present invention provides a peening device
comprising at least a said peening tool mounted on a said first
carriage suitable for moving in translation inside a pipe, the
device comprising a said peening tool suitable for moving in
longitudinal translation XX relative to said first carriage and in
rotation about said axial longitudinal axis XX of the pipe in the
vicinity of said welds, as defined above.
[0085] Other characteristics and advantages of the present
invention appear in the detailed light of embodiments described
below with reference to the accompanying figures, in which:
[0086] FIG. 1 is a side view of a pipe in a simple catenary
configuration 1, suspended from a floating support 10 of the FPSO
type, having its bottom end resting on the sea bottom 13, and shown
in three different positions 1a, 1b, and 1c;
[0087] FIG. 1A is a side view in section showing in detail the
trench 12 that is dug by the foot 11 of the catenary during
movements in which the pipe is lifted off and rested on the sea
bottom;
[0088] FIG. 2 is a longitudinal section of a pipe and a side view
of a peening robot 3 inside the pipe while it is being assembled,
shown during peening treatment of the weld 6 between the ends of
two pipe elements 2a and 2b, the weld being shown in the bottom
half only of the section;
[0089] FIG. 2A is a section view of the pipe showing the peening
robot 3 inside the pipe;
[0090] FIG. 3 is a longitudinal section view of one end of a pipe
element showing a straight portion (root face) and an inclined
portion (chamfer);
[0091] FIGS. 3A, 3B, 3C, and 3D are side views in section showing
all or part of the respective ends of two pipe elements to be
assembled together, respectively during an approach and positioning
stage (3A), a welding stage (3B), an internal grinding stage (3C),
and a peening stage (3D). FIGS. 3C and 3D show only a bottom
portion of the weld so as to show more clearly the inside surface
6.sub.3 of the weld bead 6 after it has been ground;
[0092] FIG. 3A' shows a variant of FIG. 3A in the event of a small
offset between the end root faces of two pipe elements for
assembling together;
[0093] FIGS. 3B' and 3C' are fragmentary longitudinal sections
corresponding to FIGS. 3B and 3C and showing only the bottom
portion of the weld and of the pipe;
[0094] FIGS. 3E and 3F show variants of FIGS. 3B' in the event that
the pipe ends are offset, as in FIG. 3A', with a incipient crack
from the inside being shown at 2k in FIG. 3F;
[0095] FIG. 4A shows a pipe-laying ship fitted with a J-lay
tower;
[0096] FIG. 4B is a side view of a pipe 2P being lowered down to
the sea bottom and held under tension within said J-lay tower, and
a string 2N held in the top portion of said J--lay tower, said
string being approached to said suspended pipe 2P for the purpose
of being assembled thereto by welding;
[0097] FIG. 4C is a side view in section showing the two ends of
the pipe elements, in the bottom portion of the figure peening has
not yet been performed at 7.sub.2, while said peening is taking
place in the top half-portion at 7.sub.1;
[0098] FIG. 4D is a side view showing a string 2 made up of four
pipe elements 2a-2d assembled to one another and ready for
transferring to the J-lay ship of FIG. 4A;
[0099] FIG. 5 is a detail view of the peening tool 5;
[0100] FIG. 5A is a side view of a tiltable peening tool having a
single row of projectiles; and
[0101] FIG. 6 is a detail view of a grinder tool 19 mounted on a
said second carriage 4c, taking the place of the peening tool
5.
[0102] In FIG. 1, there can be seen a side view of a bottom-surface
connection 1, 1a, 1b, and 1c of the SCR type, that is suspended
from a floating support 10 of the FPSO type anchored at 15, the
pipe resting on the sea bottom 13 at its point of contact 14a, 14b,
14c.
[0103] Curvature varies along the catenary from the surface, where
the radius of curvature has a maximum value, to the point of
contact where the radius of curvature has a minimum value R.sub.0,
R.sub.1, R.sub.2. Under the effect of waves, wind, and current, the
floating support 10 moves, e.g. from left to right as shown in the
figure, thereby having the effect of lifting or lowering the
catenary-shaped pipe off or onto the sea bottom. In position 10c,
the floating support is away from its normal position 10a, thereby
having the effect of tensioning the catenary 1c and raising it,
thereby moving the point of contact 14 towards the right from 14a
to 14c; the radius of curvature at the foot of the catenary
increases from R.sub.0 to R.sub.2, and the horizontal tension in
the pipe generated at said point of contact also increases, and
consequently the tension increases in the pipe and said floating
support. In similar manner, when in position 10b, the movement to
the right of the floating support has the effect of relaxing the
catenary 1b and of resting a portion of pipe on the sea bottom. The
radius R.sub.0 at the point of contact 14a decreases to a value
R.sub.1, and similarly the horizontal tension in the pipe at the
same time also decreases, as does the tension in the pipe at said
floating support. This reduction in the radius of curvature at 14b
gives rise to considerable internal stresses with the structure of
the pipe, thereby generating fatigue phenomena that are cumulative
and that can lead to the bottom-surface connection being
destroyed.
[0104] Thus, the pipe presents a radius of curvature that is at its
greatest at the top of the catenary, i.e. the point where it is
suspended from the FPSO, and that decreases down to the point of
contact 14 with the bottom 13. At this location, the radius of
curvature at the suspended portion is at its smallest, however in
the adjacent portion that is resting on the sea bottom, and
assuming that said pipe is extending in a straight line, its radius
of curvature becomes theoretically infinite. In fact said radius of
curvature is not infinite but is very large, since, as a general
rule, some residual curvature persists.
[0105] Thus, as explained above, as the floating support 10 moves
on the surface, the point of contact 14 moves from right to left
and in the region that is lifted off or rested on the bottom, the
radius of curvature passes successively from a minimum value
R.sub.min to a value that is extremely large, or even infinite, in
a configuration that extends substantially in a straight line.
[0106] This alternating flexing gives rise to fatigue phenomena
that are concentrated within the foot region of the catenary, and
the lifetime of such pipes is greatly reduced, and in general is
not compatible with the lifetimes that are desired for
bottom-surface connections, i.e. 20 to 25 years, or even more.
[0107] Furthermore, as shown in FIG. 1A, during these alternating
movements of the point of contact, it is observed that the
stiffness of the pipe, associated with the above-mentioned residual
curvature, will over time dig a furrow 12 over the entire length
that is raised and lowered, thereby creating a transition region in
which a point of inflection 11 will exist, where the curvature
changes direction in the transition regions, so as finally to reach
an infinite value in the portion of the undersea pipe that rests in
a straight line on the sea bottom, said portion being raised only
exceptionally, e.g. in the event of the disturbing elements (swell,
wind, current) acting on the floating support and on the catenary
all accumulating maximally in the same direction, or else in the
event of resonant phenomena appearing in the catenary itself. When
the pipe rises, the point of inflection disappears and fibers that
were previously in traction are put under compression, thereby
creating a considerable amount of fatigue in this portion of pipe.
Said fatigue is then one or two orders greater than the fatigue in
the main section where no change of curvature occurs, and is
incompatible with the looked-for lifetime of 25 to 30 years, or
even more.
[0108] FIG. 4D shows a string 2 comprising four unit pipe elements
2a-2d that are assembled together by welds 2.sub.2, 2.sub.3, and
2.sub.4 made in a workshop. The first end 2.sub.1 of said string is
for welding to the end 2.sub.5 of already-assembled pipe that is
being laid, with the end 2.sub.5 of the string then constituting
the new end 2.sub.5 of the pipe being laid and being ready for
assembly with the end 2.sub.1 of the next string, assembly taking
place on board the laying ship 8 shown in FIG. 4A, which ship is
fitted with a J-lay tower 9. On board the ship, the strings are
stored horizontally on deck, and then they are raised one after
another by a pivoting ramp 18 from a horizontal position to a
position in which they can be inserted in the J-lay tower 9. The
already-laid portion of pipe 2P (not shown in FIG. 4A but visible
in FIG. 43) is held under tension within the tower by means of a
clamp. Thereafter, a new string 2N is lowered towards said pipe 2P
that is held under tension, as shown in detail in FIG. 4B, and is
finally welded thereto, and then subjected to the peening treatment
of the invention, as shown in detail in FIG. 4C.
[0109] FIG. 2 is a section in side view showing two pipe elements
2a and 2b assembled end-to-end by welding 6 in a workshop, the top
half-portion being shown in the approach stage prior to welding.
Once the welding process has terminated and the weld has been
subjected to quality control, a remotely-controlled device or robot
3 is inserted from the right-hand end of the right pipe 2b, said
robot carrying a peening tool 5 of the invention and serving to
position said peening tool astride said weld 6, substantially on
the axis thereof. The robot 3 serves to enable the inside wall and
the weld to be subjected automatically to peening treatment over a
swath 7 of width L, e.g. having a total width of 2 centimeters (cm)
to 6 cm, i.e. substantially 1 cm to 3 cm on either side of the weld
bead 6.
[0110] FIG. 3 is a section showing the face of a pipe element that
has machined in order to enable it to be assembled to the following
element by welding. The face is machined in the plane perpendicular
to the axis XX of the pipe and, towards the inside of the pipe, it
presents a root face 16 occupying a few millimeters, generally 2 mm
to 4 mm, followed by a chamber 17, e.g. a straight and conical
chamfer as shown, or a curved and parabolic chamfer (not
shown).
[0111] In FIG. 3A, two pipe elements have been positioned face to
face, ready for welding. When the pipe elements present an
extremely high level of quality, or when they have been made so as
to present a diameter that is perfectly circular, the inside wall
surfaces of said pipe element are substantially continuous. During
welding (FIG. 3A, FIGS. 3B-3B'), this gives rise to a small
internal projection 6.sub.2 that is substantially uniform to the
right (2k) and to the left (2h) and all around the periphery, as
shown in detail in FIG. 3B'.
[0112] FIGS. 3E and 3F show the above-described unwanted phenomenon
for this type of pipe that is to be subjected to fatigue over a
period that may exceed 25 to 30 years. During welding performed
from the outside by multi-head orbital welding robots, the first
pass needs to merge perfectly with the respective root faces 16 of
the two ends of the two pipe elements 2a and 2b. For this purpose,
the chamfers 17 are prepared as shown in FIGS. 3 and 3A. It is the
melting of said root faces that gives rise to a small amount of
extra thickness in the form of a narrow seam or projection 6.sub.2
(FIG. 3B) towards the inside of the pipe, said extra thickness
being substantially rounded but presenting an irregular shape
around the periphery of the inside wall of said pipe, and sometimes
presenting an angular junction at the interface between the welding
and the base metal of the inside surfaces 2i of the pipe
elements.
[0113] In general, the pipe elements do not have an internal
cross-section that is perfectly circular, with the section being
slightly ovalized. Furthermore, wall thickness may vary around the
periphery. Thus, when the ends of the two pipe elements for
assembling together are placed face to face, although the alignment
of FIG. 3A will be found at certain locations of the periphery,
there will be other regions where there is an offset, as shown in
FIG. 3A'. During the welding process, the projection 6.sub.2, which
is substantially symmetrical in FIG. 3B', then presents unbalance,
as shown in FIG. 3E. Thus, at 2h and 2k respectively identifying
the transition region between the welding itself and the base metal
of the pipe elements 2a and 2b, there exist respective angles
.alpha..sub.1, .alpha..sub.2 between the tangents to the projection
and the inside surface 2i of the pipe, which angles are open to a
greater or lesser extent, as shown in FIG. 3E. In general, on the
side set back inwards, on the left pipe element 2a in the drawing,
the connection angle .alpha..sub.1 is small, whereas on the other
element 2b, the connection angle .alpha..sub.2 is larger and may
result in a sharp angle.
[0114] It is then in this region presenting sharp angles
.alpha..sub.2 that there is a risk of generally-localized incipient
cracks appearing under the effect of fatigue, which cracks
initially propagate in the direction FF as shown in FIG. 3F, and
finally propagate around the entire periphery of the pipe, thus
leading to destruction of the weld and to destruction of the
bottom-surface connection.
[0115] The welding process involves the use of heating and melting
powers, and thus of considerable amounts of energy, since it is
desirable to minimize cycle time, particularly for the welding that
is performed on board the laying ship 8, as explained above with
reference to FIG. 4A to 4D. Such pipe-installing ships have
extremely high hourly operating costs, with welding and preparation
operations constituting critical busy times. It is desirable to
have welding process cycle times of the order of 10 minutes (min)
to 12 min for pipes having a diameter of 300 mm and a thickness of
20 mm. The localized thermal shocks created by the power of the
welding equipment are considerable and they give rise to residual
regions of stress concentration that cannot be treated in
conventional manner, in particular by thermal annealing, in order
to obtain acceptable relaxation of stresses within a lapse of time
that is compatible with the desired rates of laying. Said residual
stresses may be compression stresses or traction stresses with
traction stresses being more dangerous in terms of fatigue behavior
over the lifetime of installations that may exceed 25 to 30 years
or more.
[0116] During fatigue testing performed on lengths of pipe
subjected to fatigue simulations corresponding to that which might
be expected over a lifetime of 25 to 50 years, but actually carried
out on a fatigue test bench, together with automated frequency
spectrum and amplitude for the alternating stress cycles, the
inventors have observed localized cracking phenomena at the
interface between the base metal of a pipe element and the weld
region, mainly where the root faces 16 melt and at the internal
seam 6.sub.2 of the weld bead 6. Because of localized quenching
phenomena, combined with irregularities in local melting, weak
points appear in which the material is in a residual traction
stress state to significant level, generally in combination with
the presence of a localized physical defect, such as angle. During
movement of the pipe, it is specifically at such a location that
incipient cracks will appear at 2.sub.k, as shown in FIG. 3F, said
cracks then propagating rapidly in radial and peripheral manner, in
general in a direction FF through the thickness of the wall,
thereby leading rapidly to destruction of the pipe and to
unacceptable risks of pollution.
[0117] The device of the invention is constituted by a first
carriage 3 having wheels 3e driven by a motor 3a and powered by an
umbilical cord 3d. The wheels are connected to an axial main body
3.sub.1 of the first carriage via a system of arms 3b mounted as a
hinged parallelogram, preferably three parallelogram structures 3b,
each carrying two wheels in alignment on the direction XX. The
three parallelogram structures 3b are preferably uniformly
distributed at 120.degree. from one another, as shown in the
cross-section of FIG. 2A, and they are actuated synchronously by
springs or actuators 3c so that the main body 3.sub.1 of the robot
remains substantially on the axis XX of said pipe. The first
carriage or robot 3 carries at its front end an axial shaft 4 that
is movable in translation along the axis XX in a guide barrel 4a
that is secured to the main body 3.sub.1, passing axially
therethrough, and movable in translation along said axis XX by an
actuator (not shown) that may be a hydraulic cylinder or an
electric motor, and that is preferably servo-controlled and
operated by a computer via the umbilical cord 3d. Furthermore, said
shaft 4 is capable of rotating about the same axis XX within said
guide barrel 4a. Said rotation of the shaft 4 is actuated by an
electric motor (not shown) incorporated in the main body 3.sub.1,
and preferably controlled and operated by said computer. At the
front of the shaft 4, a guide support 4b secured to said shaft
serves to support a second carriage 4c and guided in a direction
perpendicular to the axis XX and to the inside wall 2i of the pipe
2. Said second carriage 4c carries a peening tool 5 that is secured
thereto. Said peening tool is held in intimate contact with the
inside wall 2i of the pipe 2, preferably with a constant bearing
force, e.g. by means of a pneumatic actuator 4d, with said second
carriage 4c being moved in a transverse direction. Thus, after the
weld has been made and inspected, said robot 3 is inserted from the
right-hand end of the pipe 2b, carrying the second carriage 4c that
in turn carries the peening tool 5 in a retracted position, thus
ensuring that the peening tool does not interfere with the inside
surface of the pipe wall. Under drive from the motor 3a, the robot
is moved to the weld 6 for treatment, under monitoring via a video
camera 4e carried by the carriage 4c. The carriage is then locked
in longitudinal position by locking its motor drive 3a and by
increasing the pressure in the actuators 3c so as to cause the
hinged arm 3b to pivot and jam the wheels 3a against the inside
surface 2i of the wall of the pipes. The main body is then
substantially on the axis XX of the pipe, and the position of the
peening tool 5 is adjusted by acting on the position of the shaft 4
that is movable in translation along the axis XX, still under
monitoring via the video camera 4e. The actuator 4d is then
actuated so as to deploy the peening tool in a transverse direction
in order to press it against the surface 2i of the wall of said
pipe. The peening tool is then actuated while also driving the
shaft 4 in rotation about its axis XX in order to apply said
peening tool to the entire periphery of the inner weld bead
together with the adjacent internal surfaces 2i of each of the pipe
elements so as to form a peened swath 7 of width corresponding to
the active width of said peening tool. The peening process is
advantageously improved by performing successive circular passes of
the peening tool that are slightly offset in longitudinal
translation towards the left or towards the right, by modifying the
longitudinal position of the shaft 4 that is movable in translation
along the axis XX in the guide barrel 4a secured to the carriage
3.
[0118] A peening tool 5 is used that is of the kind described in
FIGS. 6 and 7 of FR 2 791 293. More particularly, its vibratory
surface is constituted by the end of a sonotrode. The metallic
sonotrode is secured to a piezoelectric emitter via one or more
acoustic amplifiers that, in known manner, present a profile that
is adapted to amplify the amplitude of the oscillations of the
sonotrode. The projectiles may be in the form of balls or in the
form of spindles, or in the form of spikes. The ends of the
projectiles strike the surface for treatment, and on impact their
kinetic energy is transformed into plastic and elastic deformation
energy, thereby creating or increasing the level of compression
stress in the material at the point of impact.
[0119] FIG. 5 shows in greater detail a carriage 4c fitted with its
peening tool 5 that is remotely controlled via an umbilical
connection 5.sub.3, the tool having a surface that vibrates under
the effect of an ultrasound wave 5.sub.2 in a transverse direction
YY perpendicular to the longitudinal direction XX, thereby
projecting the elongate projectiles 5.sub.1 from a retracted
position 5.sub.1a to a deployed position 5.sub.1b, with two
successive such projectiles being spaced apart by a distance e
lying in the range 2 mm to 5 mm.
[0120] Shifting the peening tool 5 in translation along the
direction XX through a distance .delta.x=e/5, for example, enables
the surface for treatment to be peened between the point of impact
of the various projectiles 5.sub.1 when the peening tool is in a
given longitudinal position, with this serving to peen the entire
surface for treatment, and also to peen with insistence on some
particular region, and/or to make peening uniform.
[0121] FIG. 5A shows a peening tool 5 having a single row of
projectiles 5.sub.1 in the direction XX. Said peening tool pivots
about the axis 4f of the support 4g that is secured to the carriage
4c. The axis Y.sub.1Y.sub.1 of the projectiles 5.sub.1, which also
corresponds to the direction in which said projectiles 5.sub.1 are
projected against the surface for peening, is inclined at an angle
.beta. relative to said direction (YY) of radial movement in
translation of the carriage 4c so as to arrive under the best
conditions in the transition region 2h-2k as described above with
reference to FIGS. 3B' and 3F, i.e. substantially as close as
possible to the direction perpendicular to the surface of the
projection in said region. This makes it possible to peen with
insistence on said transition regions 2h-2k in which unwanted
cracking is liable to appear. Thus, a first peening tool as
described with reference to FIG. 5 is used advantageously to
perform general peening. Thereafter, peening is performed with
insistence on each of the transition regions 2h-2k by means of said
peening tool having a single row of projectiles, with both peening
tools advantageously being installed on a common carriage 4c or on
carriages that are independent and both secured to the same axial
shaft 4.
[0122] This peening serves to provide local deformation over a
controlled thickness as a function of the energy transmitted by the
sonotrode to said needles, the metal of the weld, and the base
metal at the end of each of the pipe elements. This plastic
deformation of the metal makes it possible to establish a
generalized and substantially uniform compression stress state
throughout the treated region 7, thereby having the effect of
absorbing any residual localized traction stress state that might
result from the welding process and the above-described undesirable
localized quenching phenomena.
[0123] Achieving compression depends on the power and the accuracy
of the peening process, and it is generally performed over a
thickness lying in the range 0.2 mm to 2 mm, thereby advantageously
preventing unwanted incipient cracks from appearing.
[0124] The quality of the pipe in the welding region is
advantageously improved by internally grinding 6.sub.3 the weld
prior to peening so as to eliminate geometrical surface defects,
thereby enabling peening to be performed over an inside surface of
the pipe and the welding that is substantially cylindrical where it
is peened. Grinding is advantageously performed using a grinder
tool 19 as shown in FIG. 6, which tool is mounted on a device
similar to said above-described peening tool, but in which the
peening tool is replaced with a grinder tool 19. The grinder tool
19 comprises a rotary grindwheel 19.sub.1 that is mounted an a said
second carriage 4c and that can therefore be moved in translation
in the transverse direction YY such that the rotary grindwheel
19.sub.1 comes to bear against the inside surface of the pipe and
of the weld for grinding. At least one guide wheel 20 is securely
mounted to the grinder tool 19 on one side thereof to serve as a
guide to ensure that the rotary grindwheel 19.sub.1 is held in
position when it comes to bear against said inside surface of the
pipe, i.e. so as to ensure that said rotary grindwheel 19.sub.1
does indeed remain tangential to the bore of the pipe, and thus
removes only the necessary quantity of the projection 6.sub.2 of
the weld bead 6, as shown in FIGS. 3C-3C'.
[0125] FIG. 6 shows a rotary grindwheel 19.sub.1 of cylindrical
shape and having an axis of rotation X.sub.1X.sub.1, which axis
extends in a longitudinal direction parallel to the axial
longitudinal direction XX of the pipe, the abrasive surface of the
grindwheel corresponding to its cylindrical outer surface. In one
embodiment, the cylindrical rotary grindwheel may extend in the
direction X.sub.1X.sub.1 over a said distance L. Similarly, the
guide wheel 20 presents an axis of rotation X.sub.2X.sub.2 in the
longitudinal direction parallel to the axes XX and X.sub.1X.sub.1,
such that the guide wheel 20 and the rotary grindwheel 19.sub.1
present a common tangent X.sub.3X.sub.3 beside the inside surface
2i of the pipe, thus enabling the guide wheel 20 to guide the
grinder tool by maintaining its axis X.sub.1X.sub.1 tangential to
the bore 2i of the pipe, as described above.
[0126] FIG. 3D shows the state of the inside surface of the pipe in
the peened region 7 of the inside surface of the weld over a width
L that corresponds substantially to the width of the vibrating
surface of the peening tool 5.
[0127] During prefabrication on land of the strings 2 as shown in
FIG. 4D, the length of the unit elements 2a to 2d lies in the range
about 6 m to 12 m, thereby making it necessary to insert the
peening robot from the end that is closest to the weld for
treatment, i.e. at a distance of about 6 m to 12 m depending on
circumstances, and then cause the robot to travel along said
distance in order to take up an accurate position astride said weld
for treatment.
[0128] During on-site installation, the prefabricated strings
generally have a length of about 50 m, as shown in FIG. 4D, or
under certain circumstances of 25 m or of 100 m, and it is then
necessary to make the robot travel over that distance in order to
reach the welding region for treatment.
[0129] FIGS. 4A to 4C show two strings being assembled together
together with the welding region being treated by peening, during
on-site installation as performed on board a laying ship 8 that is
fitted with a J-lay tower 9, as shown in FIG. 4A. For this purpose,
the already-laid pipe element 2P is held securely in suspension
from the foot of the tower, and a new pipe element 2N is
transferred by means of a pivoting ramp 18 and in known manner from
the horizontal position to the oblique position that corresponds to
the inclination of the tower, after which it is positioned on the
axis of the terminal suspended pipe element. Said pipe element 2N
that is to be assembled is subsequently moved axially along the
direction XX towards the suspended terminal pipe element 2P, as
shown in FIG. 4B, and is then welded thereto in known manner. From
the top end of the tower, the peening robot 3 is inserted into the
pipe and lowered to the welding region that is situated 50 m below
when using 50 m string, as shown in FIG. 4C, after which a swath 7
is peened in a manner similar to the treatment performed in a
workshop and as described in detail with reference to FIGS. 2-2A.
At the end of treatment, the peening robot is raised back to the
top of the tower 9 and then the top end of the pipe is grasped and
lowered towards the bottom of the tower so as to be ready to
perform a new cycle of assembling and treating a new pipe
string.
[0130] In the workshop, and on board the installation ship, at the
end of the peening treatment of the welding region, it is
advantageous to monitor the state of stresses in the treated region
so as to ensure that traction stress states have been eliminated
and replaced by compression stress states. The most appropriate
inspection technique is the X-ray method that makes it possible to
measure the inter-atomic distances within the surface of the
material, and thus to characterize very accurately the stress state
and level, regardless of whether stress is in traction, at rest, or
in compression. Such means are available from the Applicant and are
implemented using a robot similar to that described above, the
peening tool 5 being replaced by the X-ray source and the
associated sensors that are available from the supplier Stresstech
(Finland). The signals recovered by the sensors are then sent to a
signal processor unit, e.g. a computer, which deduces therefrom the
real stress level that exists after and possibly also before the
peening treatment of said welding region.
[0131] The present invention is described mainly for solving the
problem associated with bottom-surface connections and more
particularly in the region of the point of contact with the sea
bottom in an SCR type connection. Nevertheless, the invention
applies to any type of undersea pipe, whether it rests on the sea
bottom, whether it is incorporated in a vertical tower, or indeed
whether it constitutes a subsurface connection between two FPSOs,
or between an FPSO and an unloading buoy.
[0132] The various types of subsurface connection are described in
patent FR 05/04848 in the name of one of the Applicants, and more
particularly in FIGS. 1A-1D and 2A. Said subsurface connections are
particularly subject to fatigue phenomena when they are subjected
to swell and to currents and above all to the movements of the
floating supports, FPSO or loading buoy, which generates
alternating stresses, particularly in the regions close to said
floating supports.
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