Note: Descriptions are shown in the official language in which they were submitted.
CA 02307488 2000-OS-04
1 "CORRUGATED THICK-WALLED PIPE
2 FOR USE IN WELLBORES"
3 FIELD OF THE INVENTION
4 The present invention relates to corrugated pipe and its use in tubular
strings conveying fluid through earth material, for example as part of a
buried
6 pipeline or casing in a well.
7
8 BACKGROUND OF THE INVENTION
9 The invention was initially developed as a means to reduce thermally
induced axial load in the production casing string of a well undergoing cyclic
11 steam stimulation. The production casing strings in such wells are normally
12 cemented in place and are therefore largely constrained from expanding or
13 contracting axially during heating and cooling cycles. This constrained
14 thermal strain is manifested as axial load which becomes more compressive
during heating and more tensile during cooling. Depending on the thermo-
16 mechanical material properties of the casing and the magnitude of
17 temperature cycling, the axial stress may exceed the axial yield strength
of
18 the pipe in compression during heating and may exceed the axial yield
19 strength in tension during cooling. Among other consequences, the high
stresses place severe demands on the structural and sealing capacity of the
21 tubular connections between casing joints and significantly reduce the
ability
22 of the pipe body to withstand collapse, bending and shear loads which may
23 arise from various hydraulic and geomechanical factors. The incidence of
24 leakage, fracture and access impairment'failures' is therefore relatively
high in
connection with the casing of thermal process wells.
1
CA 02307488 2002-07-23
1 Approaches taken by the industry to address this problem have
2 typically included improving the strength and leakage resistance of the
3 connections by utilizing mare complex designs, for example substituting
4 premium connections for the standard 8-round or buttress threadform
connections, or increasing the grade of steel used. These approaches, while
6 potentially providing significantly better seepage control and modest
7 incremental structural performance, tend to increase cost and do not
8 substantially reduce the risk of fracture or deformation induced failure.
9 Therefore there remains a need to address the primary confounding
variable, namely the high axial stress induced by confined thermal expansion
11 and contraction.
12 While thermal well design has been the primary motivator for the
13 present invention, it is not to be limited to this application. The
invention finds
14 use in situations where there is interaction of loads between tubulars,
surrounding earth material and contained or excluded pressure fluids, and
16 where it would be desirable to increase axial or flexural compliance,
decrease
17 effective axial yield load and increase collapse resistance. One such
situation
18 involves buried pipelines. Here axial and flexural strain due to tubular-
soil
19 interaction must be absorbed without loss of pressure integrity. It would
be
desirable to provide tubulars of reduced axial and therefore flexural
stiffness
21 because these properties result in lower axial and bending loads than
straight
22 pipe for the same temperature variations and deformation magnitude.
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1 SUMMARY OF THE INVENTION
2 The phrase "string of joints" as used herein is intended to encompass a
3 plurality of joints of metal pipe, usually steel, connected end to end
either by
4 welding or threaded connections and to further encompass a sand exclusion
liner if such is part of the string. The phrase "thick-walled pipe" is
intended to
6 mean substantially rigid high pressure pipe useful as oil country tubulars,
such
7 as casing and in high pressure pipelines, said pipe having a diameter to
wall
8 thickness ratio ("D/t") less than 100, preferably less than 50. The word
9 "formed" is intended to mean that a cylindrical metal pipe wall has been
plastically deformed by hydroforming, rolling or hydrofolding preferably
triaxial
11 plane strain hydroforming.
12 The present invention applies a well known mechanical design
13 concept, corrugations, to thick-walled metal pipe which is to be used in
earth-
14 restrained applications, such as in a string of joints used as casing in a
well or
as part of a pipeline. The corrugations are incorporated for the purpose of
16 managing changes in axial load subsequent to installation.
17 More specifically, the invention involves forming thick-walled pipe to
18 convert at least part of its cylindrical side wall into a sinusoidally
corrugated
19 configuration. The corrugations are formed so as to have a corrugation
radius
of curvature to thickness ratio ("R/t") less than 10, preferably less than 5.
21 Preferably the corrugation webs have a maximum angle equal to or greater
22 than 20° with respect to the pipe axis. More preferably the
corrugations have
23 thinned webs and flattened peaks. Preferably, the pipe is hydroformed,
24 without substantially changing its original length, to create the
corrugations.
By selecting the geometry defined by these limitations we have balanced axial
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CA 02307488 2002-07-23
1 compliance (i.e. reduced axial stiffness) with diametral limitations arising
from
2 the cost of increasing annular space consumed in a wellbore and material
3 strain capacity.
4 Broadly stated then, in one embodiment the invention is concerned
with a string of joints of thick-walled pipe extending through and being
6 restrained by earth material, the string being subject to a change in axial
load
7 subsequent to installation, the side wall of at least one such joint having
been
8 formed into corrugations along at least part of its length, the corrugations
9 having an R/t ratio less than 10. Preferably, one or more of the following
conditions apply:
11 ~ the string is used in a well and is subject to changes in axial load
12 arising from thermal expansion or contraction (for example where
13 the well is involved in cyclic steam stimulation) or from earth
14 movement;
~ the string forms part of a buried pipeline;
16 ~ the R/t ratio is less than 5;
17 ~ a plurality of corrugated joints are distributed in spaced apart
18 alignment along the string;
19 ~ the corrugation webs have a maximum angle equal to or greater
than 20° relative to the pipe axis;
21 ~ the wall thickness of the webs of the corrugations are thinner than
22 the peaks;
23 ~ the corrugations having been formed by hydroforming, more
24 preferably while maintaining the length of the joint substantially
constant;
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CA 02307488 2003-10-30
1 ~ the corrugations varying in wall thickness along their length, as a
2 result of having been formed.
3 In another embodiment, the invention is concerned with a thick-walled
4 steel pipe having threaded ends, the body of the pipe between the ends
having been hydroformed to produce corrugations along at least part of its
6 length, the corrugations having an R/t ratio less than 10. Any of the
7 previously mentioned preferred conditions also may be incorporated.
8
9 DESCRIPTION OF THE DRAWINGS
Figure 1 is a partially cut-away side view of a corrugated casing joint
11 having threaded ends;
12 Figure 2 is a schematic side view showing a corrugated casing joint
13 incorporated into a casing string having a slotted liner, such as would be
used
14 in a thermal horizontal well;
Figure 3 is a side view showing an arrangement of corrugated joints
16 incorporated into a slotted liner;
17 Figure 4 is a partially sectional side view of a joint of straight-walled
18 pipe installed in tri-axial plane strain hydroforming apparatus, prior to
19 application of forming pressure;
Figure 5 is similar to Figure 4 after the joint has been formed to provide
21 corrugations;
22 Figure 6 is a longitudinal sectional side view of the corrugated joint as
23 formed under plane strain conditions, showing thickness variations; and
24 Figure 7 is a side view of part of Figure 6, showing corrugation and
pipe geometry parameters.
26
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1 DESCRIPTION OF THE PREFERRED EMBODIMENT
2 While recognizing the likely benefits of corrugated earth restrained
3 tubulars used for pipeline and well bore casing applications, the present
4 invention also required a means to place corrugations in the metal tubular
materials typically employed for these purposes. It was therefore desirable to
6 devise a manufacturing or forming process capable of creating suitably
7 shaped corrugations in the wall of standard casing and high pressure
pipeline
8 materials of more or less full standard joint length. Such tubulars have a
D/t
9 ratio less than 100, preferably less than 50. It was particularly desirable
to
discover a process suited to casing tubulars for use in well bores in a manner
11 providing a geometry yielding suitable stress and strain behaviour under
12 installation and operational loads within the allowable annular space.
13 Machining and forming are two techniques well known as means
14 capable of producing corrugation geometries in metal tubulars. Machining
provides a means to produce corrugation geometries of almost any desired
16 shape, but it is difficult to implement on the internal surfaces of casing
17 intervals beyond a few diameters of the tube ends. This technical
difficulty,
18 combined with the relatively high cost of machining compared to forming,
19 makes forming or forming combined with only external machining the
preferred alternative.
21 Existing methods for forming corrugated pipe or bellows from straight
22 tube may generally be divided into rolling and hydroforming or hydrofolding
23 processes. Rolling methods are used on thin-wailed material having smaller
24 diameter than that employed for casing or high pressure pipeline tubulars.
While other variations of rolling are applicable to larger thicknesses, where
for
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1 example an internal spiral grooved mandrel is placed on the inside of the
pipe
2 and external rollers are used to deform the pipe into the mandrel grooves,
3 such localized forming methods do not enjoy the simplicity of the global
4 forming accomplished with hydroforming.
It should be pointed out that forming corrugations in spiral welded pipe
6 by placing corrugations in the strip prior to or during the welding process
7 offers another realistic forming process for larger diameter high pressure
8 pipeline tubulars. Of course this method cannot be applied to tubes and is
not
9 suitable for smaller diameter pipeline and casing sizes.
The manufacture of corrugated pipe or bellows for applications such as
11 pipeline expansion joints, by hydroforming or hydrofolding, is a technique
well
12 known in the art. As described in US patent 4,193,280, "In a process of
this
13 kind, the operation starts with a sheet-metal sleeve of a length greater
than
14 that of the bellows to be obtained, the said length being, in fact, equal
to the
developed length of the cylindrical ends of the said bellows and of the
16 deformable corrugations therebetween. A series of suitably spaced rings is
17 applied to the outer wall of the sleeve, which is preferably provided with
end-
18 flanges, and it is then placed upon the fixed platen of a press. The
interior of
19 the sleeve is filled with a liquid which escapes at a controlled rate and
the
press is operated in such a manner that the mobile platen is applied to one
21 end of the assembly. The partially confined liquid inside the sleeve
develops
22 an internal pressure and, assisted by the axial load, causes the metal to
23 deform outwardly between the forming rings, so that the bellows is
eventually
24 shaped."
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1 As described, this technique does not contemplate application to
2 casing and high pressure pipeline tubulars which have relatively smaller
3 diameter to thickness (D/t) ratios than the pipe materials to which it is
usually
4 applied, described as a "sheet metal sleeve". Further, this description
shows
that the method as presently practiced does nat contemplate changing the arc
6 length of the shaped pipe, in that "the developed length" is expected to be
the
7 same as the initial "sheet metal sleeve" length. While the method does
8 provide for direct control of corrugation period through selection of ring
9 spacing and amount of axial compression, these parameters simultaneously
control amplitude to a large extent. Little additional control of corrugation
11 shape is possible beyond contouring of the confining rings and the natural
12 unrestrained toroidal bulge formed between the rings. Control of wall
13 thickness distribution is not considered as indicated for example by the
use of
14 the term "hydrofolding" and by the expectation that "the developed length"
remains unchanged which can not in general be the case if thickness is to be
16 varied. However for application to casing and high pressure pipeline
tubular
17 corrugation, it is desirable to obtain corrugations without dramatic
changes in
18 original tubular length, to more independently control period and amplitude
19 and to control aspects of the local corrugation geometry variables such as
shape and thickness.
21 Before considering how the modified hydroforming process of the
22 present invention may be used to overcome these difficulties and
limitations
23 and provide other advantages, it is desirable to consider the relationship
24 between these corrugation geometry variables and corrugated casing
performance. It is thus also desirable to consider how the corrugations to be
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CA 02307488 2002-07-23
1 introduced into casing materials differ from the accepted understanding of
2 corrugation geometry.
3 As a term well accepted in the art, a pipe corrugation is generally
4 meant to describe a wrinkle or wave in the wall of otherwise cylindrical
tubes.
Such corrugations commonly go from peak to valley to peak to valley etc.
6 along all or some portion of the pipe length and, even when helical, are
largely
7 circumferential in orientation. This understanding also carries the
assumption
8 that the material thickness does not vary substantially along the wave and
that
9 these pipes may be treated as shells for stress analysis purposes. Such
corrugations or bellows may be treated as shells, and design characteristics
11 such as stress and displacement response to load obtained using standard
12 treatments, such as given, for example, by W.C. Young, "Roark's Formulas
13 for Stress and Strain", Sixth Edition, McGraw Hill Inc., 1989, pg 570.
However
14 such treatments break down where the ratio of corrugation radius of
curvature
to thickness becomes small. In the given reference, this occurs for R/t ratios
16 less than 10.
17 While the term corrugation is applied herein to convey the general
18 sense of the modified casing wall geometry intended to provide the benefits
of
19 the present invention, the pecuNar requirements of the well bore casing
application require corrugation geometries substantially outside the
21 understandings of corrugations usual to the art. To provide corrugations
with a
22 significant reduction in axial compliance and yield load as needed for the
23 intended applications, it is generally desirable to create corrugations
with a
24 maximum web angle greater than about 20° with respect to the pipe
axis. To
stay within reasonable amplitudes, and to further optimize the stress and
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1 strain distributions by varying the wall thickness over the corrugation
interval
2 or wavelength, this implies a radius of curvature to thickness ratio
3 substantially less than 10, preferably less than 5, is needed. It is
therefore
4 necessary to consider the corrugations to be placed in casing or pipeline
tubular walls as thickwall corrugations and to obtain estimates of performance
6 determining stress and strain variables accordingly.
7 As will be evident to one skilled in the art, the corrugation amplitude is
8 constrained to occur within the annular clearances allowable by both outer
9 and inner confining surfaces, typically the well bore wall and production
tubing
respectively, plus additional running and cementing clearances. Within this
11 constraint, the corrugation geometry produced to obtain the desired
reduction
12 in axial stiffness must still provide for sufficient strength to run the
tubular, and
13 perhaps react pressure end load. While meeting these basic requirements it
is
14 further desirable to obtain a geometry which will produce an axial load
significantly lower than occurs with cylindrical pipe when heated, but not at
the
16 expense of high cyclic plastic strain, a parameter that strongly controls
the
17 corrosion fatigue failure response. To obtain significant stiffness
reduction, the
18 angle of the pipe wall portion falling between the peaks and valleys of the
19 corrugation, referred to here as the corrugation web, should be increased
substantially, typically above ~5° with respect to the axis. This
necessitates
21 relatively sharp curvatures in the peak and valley regions to prevent
22 amplitudes exceeding the available annular space. For casing and high
23 pressure pipeline tubulars these curvatures result in R/t ratios nearer 1
than
24 10, placing such corrugations well beyond the limits of standard membrane
stress analysis treatments. Particularly at the peak locations, this tends to
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CA 02307488 2002-07-23
1 result in severe flexural stress or strain concentrations under axial
loading if
2 typical toroidal geometries are employed. It is therefore beneficial to
provide a
3 geometry where the peaks are somewhat flattened to distribute the flexural
4 strain over a longer interval. It is further beneficial to provide a
geometry
where the web portions of the wall are somewhat thinner, providing a further
6 improvement of stress distribution and lower axial stiffness within the same
7 annular space constraint. Because the flexural wall stiffness is a very
strong
8 function of thickness (proportional to the third power of thickness for
elastic
9 deformations) apparently small variations in thickness appear to have a
disproportionately large effect on stress distribution.
11 Control of such geometry considerations, arising as they do from the
12 thick wall nature of casing corrugations, are not generally contemplated in
13 existing hydroforming processes. As already discussed, the corrugations to
be
14 formed by these existing processes are largely constant thickness, toroidal
at
peaks and valleys and thin wall in nature. The term 'triaxial hydroforming'
has
16 therefore been adopted herein to describe the more specialized process
17 needed to produce casing containing thick wall corrugations better suited
to
18 earth-restrained tubular design requirements. This process typically
requires
19 higher pressures, greater control of the axial load and is more sensitive
to
friction behaviour between the tubular and confining mold than hydrofolding
21 where compressive load is primarily used to cause internally pressured pipe
22 to buckle between confining rings.
{ET045194.DOC;1 ) 1 1
CA 02307488 2002-07-23
1 It has been found that triaxial hydroforming conducted under global
2 plane strain conditions, where the corrugations are formed by application of
3 high internal fluid pressure while the overall pipe length is kept constant,
4 produces a corrugation geometry well suited to thermal strain absorption. In
this case the axial force is in fact tensile during forming, and the resulting
6 plastic material flow which is further controlled by contact and friction
induced
7 stress between the pipe and form, produce an advantageous thinning in the
8 web region of the corrugation during forming of the corrugation 'bulge'
ander
9 pressure.
But this is just one combination of axial load or displacement and
11 pressure or fluid volume control. Other combinations are possible as for
12 example would occur if no axial load were applied (plane stress) and
forming
13 was completely accomplished by the application of internal pressure causing
14 bulges to form between rings as commonly used for hydroforming. Such
variants of the pressure axial load relationship may be manipulated to
16 produce geometries having characteristics suitable for particular
applications
17 and to simultaneously control the change in overall tubular length caused
by
18 the forming process.
19 The simplicity of the triaxial plane strain forming process used to
produce this corrugation geometry of the preferred embodiment, lends itself
21 particularly well to modest manufacturing cost and small annular space
22 requirements. The resulting tubular architecture is well suited for use in
wells
23 using the cyclic steam stimulation production method, as well as other
24 applications benefiting from tubulars with reduced axial load or greater
strain
absorption to prevent the instabilities associated with global plastic
{ET045194. DOC;1 } 12
CA 02307488 2002-07-23
1 deformation. The plane strain condition enjoys the further advantage of
2 maintaining the original joint length which facilitates interchangeability
3 between corrugated and straight tubulars.
4 From the foregoing, it should be apparent to one skilled in the art, that
the fundamental triaxial process variables of confining mold shape, axial load
6 or strain, internal pressure and contact friction, enables a pipe
corrugation to
7 be configured with significant control over both the corrugation amplitude
as a
8 function of axial length and its thickness distribution to help control
stress and
9 strain response to meet a large spectrum of design requirements for earth
restrained tubular systems. However corrugation shape obtained by plane
11 strain hydroforming provides a particularly well conditioned corrugation
shape
12 for application to cyclic steam stimulation well completion applications as
13 anticipated in the preferred embodiment.
14 The placement of suitable corrugations in the tubular wall is supported
through provision of a specialized hydroforming process providing a means of
16 creating axially compliant corrugation geometries without substantial
internal
17 machining which process employs control of axial length during hydroforming
18 and is therefore capable of controlling the change in the length of the
tubular
19 being formed. The hydroforming process comprises the steps of:
~ placing a length of cylindrical tube inside a confining surface comprised
21 of elements spaced and shaped to control the joint geometry to
22 generally have corrugations in the mid-section and cylindrical end
23 sections and contained within a confining tube supporting or guiding
24 the elements creating the confining surface;
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CA 02307488 2002-07-23
1 . applying sufficient internal pressure to force the tubular wall radially
2 outward against the confining surface while simultaneously controlling
3 the axial length of the tubular during and after application of internal
4 pressure and thus plastically form the tubular article where such axial
length control is preferably such that the original tubular length is
6 substantially preserved or unchanged;
7 removing the formed corrugated tubular jointfromthe forming
8 apparatus which removal may be facilitated the application
by of
9 external pressure sufficient to free the articlefromthe confining
surface; and
11 ~ additionally finishing the formed joint, if required, by external
machining
12 of the corrugations to further control the final geometry or machining of
13 the cylindrical ends to provide for joining by threaded connections,
14 welding or other joining method.
In its preferred embodiment, corrugated joints 1 are provided, forming part
16 of a string 50 of non-corrugated pipe joints. The joint has a side wall 52
17 comprising a corrugated mid-section 55 and cylindrical non-corrugated end
18 sections 2. The end sections 2 facilitate joining, using industry standard
19 methods such as welding for pipelines or threaded connections for well bore
casing. Such a joint of corrugated casing is shown in Figure 1 with threaded
21 pin ends 3. The diameter and wall thickness of the cylindrical end sections
2
22 are chosen to ensure compatibility with industry sizing standards. The
23 cylindrical end length would typically be chosen to allow for gripping with
24 standard connection make up and handling equipment. In certain cases other
operational or completion requirements such as packer setting locations may
{ET045194.DOC;1 } 14
CA 02307488 2003-10-30
1 dictate longer cylindrical intervals at the ends or additional cylindrical
sections
2 elsewhere along the joint length. Also, as shown in Figure 1, the
corrugation
3 valleys are arranged to coincide with the nominal pipe internal diameter so
4 that the corrugation amplitude has the effect of increasing the effective
pipe
body diameter. While it is expected this configuration will be desirable for
6 most applications, a corrugation valley diameter less than the nominal pipe
7 diameter may also be provided.
8 The triaxial plane strain hydroforming process preferred to provide such an
9 article of corrugated casing requires an apparatus 4 such as shown in Figure
4. In this apparatus 4, a confining tube 5 is provided with sealing annular
end
11 closures 6 and a contoured form 7. The form 7 comprises elements providing
12 cylindrical end sections 8 and a centre corrugating section 9 closely
fitting
13 inside said confining tube 5. The tube 5, end closures 6 and contoured form
7
14 together comprise a forming vessel 30. A forming fluid access port 10 is
provided in one annular end closure 6. A mandrel 11 with external end seals
16 12 and a forming fluid access port 13 is also provided.
17 The centre corrugating section 9 is constructed of various axisymmetric
18 ring and sleeve elements 14, 15 as shown in Figures 2 and 3. To facilitate
19 removal after forming, some or all of these elements 14, 15 are split.
Element
shapes comprising the forming profile are selected to provide a distribution
of
21 void space into which the tubular material is caused to flow under the
22 application of internal pressure. Friction forces activated by contact
stress
23 between the confining surface and casing joint 16 also contribute to
24 controlling plastic flow during forming. For a given tubular, the final
corrugation shape is thus controlled by void space distribution, lubrication
or
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CA 02307488 2002-07-23
1 friction coefficient in the interfacial region between the casing joint 16
and
2 form 7 and forming pressure.
3 The cylindrical end sections 8 have an internal diameter only slightly
larger
4 than the outside diameter of the casing joint 16 to be formed to provide
casing
joint end sections 2 of standard dimensions suitable for threading and
6 handling. The end sections 8 need not be split to allow removal. If desired,
the
7 ring and sleeve elements 14, 15 of the centre corrugating section 9, and
8 indeed the cylindrical end sections 8 as well, may all be provided as a
single
9 split half form. This configuration of the form or mold permits more rapid
assembly and disassembly where repeated forming is required.
11 As shown in Figure 4, the casing joint 16 is placed inside the forming
12 vessel 30 and the mandrel 11 is placed inside the casing joint. The mandrel
13 11 is provided with seals 32 for sealing against the inside surface 31 of
the
14 casing joint 16 at two locations, typically near the joint ends. The seals
32 are
spaced to provide an interval of the casing joint, inside the forming vessel
30,
16 that may be internally fluid loaded to a pressure causing the casing
material to
17 plastically expand outward. Similarly the annular end closures are provided
18 with seals 33 to seal between the casing joint exterior and confining tube
end
i 9 closures 6 at nearly the same axial position as the mandrel seals 32, so
that
the casing joint may be externally pressured over the same interval.
21 Thus arranged, the apparatus 4 is used to form the casing joint 16 by first
22 applying internal pressure, beyond the pipe body yield, to expand the
casing
23 material outward against the inside surface 38 of the corrugating section
9.
24 The inner contoured form of the forming vessel 30 is provided to control
the
shape of the external expansion of the casing material so that as internal
{ET045194.DOC;1 } 16
CA 02307488 2002-07-23
1 pressure is increased the casing material will be progressively forced into
2 contact with the profiled surface 38 as shown in Figure 3.
3 As shown in Figure 5, the casing joint length is not substantially reduced
4 by this process as in typical hydroforming or hydrofolding processes used to
provide corrugated pipe. It will be clear that the plane strain forming
condition
6 requires the development of axial tensile stress as the corrugations 34 are
7 formed. The apparatus 4 reacts the resulting force through friction forces
8 developed along the cylindrical end sleeves. The friction forces are enabled
9 by contact stress between the internally pressured casing material and the
confining form end sections 8 as pressure is initially increased beyond that
11 required to initiate yield and close the relatively small installation gap
provided
12 between the casing joint and form end sections 8. Further increases of
13 pressure are used to cause flow into the corrugation voids to the extent
14 required to form corrugation geometries providing substantial reductions in
tubular axial compliance, where the pressure required to cause such
16 deformation magnitudes will typically exceed the casing material yield
17 pressure by several times.
18 Following forming under these high pressures, the residual contact stress
19 between the casing joint 16 and contoured form surface 38 tends to preclude
straightforward removal of the casing joint 16 from the forming vessel 30.
21 Therefore the forming process is completed by applying sufficient external
22 pressure through port 10 to plastically yield the casing joint and cause
inward
23 radial deformation to form a gap between the joint and contoured form
surface
24 38 and thus substantially eliminate the residual contact stress inhibiting
removal. The pressure and sealing capacity of the annular end closures 6 and
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CA 02307488 2002-07-23
1 seals 33 need only provide sufficient containment to cause global pipe body
2 yield.
3 Following application and removal of external pressure, the mandrel and at
4 least one end cap are removed, The casing and contoured form are then
removed and finally the elements of the form removed from the casing. The
6 process may be repeated to form additional joints of formed pipe.
7 In certain applications, the utility of the corrugated pipe formed by this
8 process may be further enhanced by heat treatment, such as annealing for
9 steel, after forming. This may be needed because the amount of plastic
deformation imposed by the forming process may affect performance
11 properties such as corrosion sensitivity, fatigue life or simply remaining
plastic
12 capacity.
13 A typical thickwall corrugation geometry of the casing joint shown in
Figure
14 1, and formed by the plane strain tri-axial hydroforming process, is shown
in
Figure 6. This figure shows a cross section through several corrugations 34.
16 Each corrugation 34 comprises webs 53 and a peak 54. Preferably the webs
17 54 are disposed at a web angle of about 20°. The relatively subtle
variations
18 in thickness obtained using the triaxial forming process are evident.
Stress
19 analysis of this geometry using the finite element method was used to
calculate a reduction in axial stiffness of approximately 5 times that of the
21 original non-corrugated straight pipe.
22 Example
23 To illustrate the utility of the present invention in reducing thermally
24 induced axial load, consider a well where cylindrical steel casing with
yield
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CA 02307488 2002-07-23
1 strength of 550 MPa is cemented at 20° C with negligible axial load
and is
2 subsequently heated to 250° C. Typical properties for the thermal
expansion
3 coefficient and elastic modulus of casing steel are i 2 microstrain/C and
200
4 GPa respectively. For such a material, provided its elastic limit is not
exceeded, the axial stress increase upon heating is calculated from the
6 relation,
7 Axial stress = temperature change X expansion coefficient X elastic
8 modulus = 552 Mpa.
9 The casing will thus be just at its yield load with consequent deleterious
impact on connection and pipe body resistance to failure. However in this
11 same application, casing with corrugations such as shown in Figure 6 over
12 most of its length would reduce this load by a factor of nearly 5, reducing
the
13 axial stress to 110 MPa, placing the casing and connections in a much more
14 favorable load operating regime.
As an alternative to hydroforming by application of internal pressure to
16 expand a tubular against an external form as described in the preferred
17 embodiment, this process may be inverted to apply external pressure to the
18 tubular and providing a form internal to the tubular. In this case the form
would
19 typically be configured to provide spiral corrugations to facilitate
removal.
In another aspect, we believe the properties of corrugations provided
21 by the tri-axial hydroforming process may be further improved for certain
22 applications through selectively removing material by external machining
23 either before or after hydroforming. For example such machining can be used
{ET045184.DOC:1 ) 19
CA 02307488 2002-07-23
1 to further thin the web thickness and extend the range of available elastic
2 deformation.
3 In another aspect, a cylindrical liner with a first and second end is
4 provided on the interior of a corrugated tubular joint with first and second
ends
where the first end of the liner is joined/fastened to the first end of the
6 corrugated tubular joint and said liner extends to cover all or a portion of
the
7 corrugated interval. This configuration permits telescopic sliding of the
straight
8 liner relative to the corrugated tubular to provide a system retaining the
axial
9 compliance of the corrugated tubular but having increased flexural stiffness
and therefore buckling stability, reduced flow losses, simpler cleaning with
11 pigs or wiper plugs and a smooth surface for sealing of devices such as
12 packers. In a further aspect of such a corrugated tubular with internal
liner the
13 second end of the liner and second end of the tubular may be provided with
14 interlocking stop rings or similar devices permitting the telescopic
relative axial
i 5 movement only over a certain range where this range can be arranged to
limit
16 the stretch or compression of the corrugated tubular to prevent excess
strain.
17 In another aspect, a cylindrical liner with a first and second end is
18 provided on the exterior of a corrugated tubular joint with first and
second
19 ends where the first end of the liner is joinedlfastened to the first end
of the
corrugated tubular joint and said liner extends to cover all or a portion of
the
21 corrugated interval. This configuration permits telescopic sliding of the
straight
22 liner relative to the corrugated tubular to provide a system retaining the
axial
23 compliance of the corrugated tubular but having increased flexural
stiffness
24 and therefore buckling stability. In a further aspect of such a corrugated
tubular with external liner the second end of the liner and second end of the
{ET045194. DOC;1 )20
CA 02307488 2002-07-23
1 tubular may be provided with interlocking stop rings or similar devices
2 permitting the telescopic relative axial movement only over a certain range
3 where this range can be arranged to limit the stretch or compression of the
4 corrugated tubular to prevent excess strain.
In another aspect, the end sections of the forms may be configured to
6 form expanded tubular intervals suitable for internal threading and thus
7 simultaneously form a tubular article with corrugations and an integral box
8 connection on one or both ends.
9 In another aspect, the forming vessel may be arranged as a split form.
In another aspect, the forming elements may be arranged to provide
11 helical corrugations.
12 As an alternative embodiment, we believe an axially compliant tubular
13 may be formed by providing forming elements arranged to create a double
14 helix corrugation using left and right helixes. Such a geometry is similar
to that
occurring in diamond wall buckling of thin cylinders.
16 As an alternative embodiment, we believe the corrugation geometry
17 may be further controlled by application of axial load subsequent to
18 hydroforming where such load would typically be compressive.
19 As a further alternative embodiment to control corrugation geometry,
we believe the forming process may be conducted with independent control of
21 axial displacement as a function of forming fluid pressure or volume
control.
22 This embodiment requires the form to be arranged with the corrugating
23 section having floating restraint rings confining the profiled split rings
and at
24 one of the end cylindrical sections arranged to telescope within the
confining
{ET045194.~OC;1 }21
CA 02307488 2002-07-23
1 tube and on the mandrel. Control of the axial displacement of this
telescoping
2 end section with respect to the confining tube by means of a hydraulic ram
or
3 other suitable load application device then permits the desired independence
4 of axial and pressure loads or displacements.
In another aspect, material may be placed in the space between some
6 or all of the corrugations, either on the outside or inside, as a means to
control
7 or limit the compressive load displacement response of individual
8 corrugations. Materials suitable for this purpose include plastic, cement,
split
9 sleeves, rings or springs which may be used separately or in combination
with
each other.
11 In another aspect, the corrugation amplitude at the ends of a
12 corrugated interval may be ramped down over the last few corrugations to
13 provide a more gradual axial stiffness contrast between cylindrical and
14 corrugated tubular wall intervals.
{ET045194. DOC;1 }22
