Note: Descriptions are shown in the official language in which they were submitted.
WO92/16355 ~ Q ~ PCT/CA92/00111
FLEXI~ SL--LAR S~ E
The present invention relates to tubular
structures formed in part by composite materials.
A composite material can be defined as a
macroscopic combination of two or more distinct materials
having a recognizable interface between them. Composites
typically have a discontinuous fibre or particle phase
and a continuous matrix phase. The discontinuous phase
is stiffer and stronger than the continuous matrix phase
and there is generally a 10% or greater volume fraction
of the discontinuous phase.
Composites may be divided into classes in
various manners. One classification scheme is to
separate them according to the form of reinforcement used
in the discontinuous phase, i.e. particulate-reinforced,
fibre-reinforced, or laminar composites. Fibre-
reinforced composites contain reinforcements having
lengths much greater than their cross-sectional
dimensions. Fibre-reinforced composites can be further
divided into those containing discontinuous or continuous
fibres. A composite is considered to be a discontinuous
fibre or short ~ibre composite if its properties vary
with fibre length. on the other hand, when the length of
the ~ibre is such that any further increase in length
does not, for example, further increase the elastic
modulus of the composite, the composite is considered to
be continuous ~ibre reinforced. Most continuous fibre -~
30 reinforced composites contain fibres that are comparable ~
to or greater in length than the overall dimension~ of -
the composite part. -~
.; -
Glass fibre reinforced organic matrix
composites are the most familiar and widely used, and
have extensive application in industrial, consumer,
military and aerospace markets. The glass fibre most
commonly used is known as E-glass, a calcium
aluminoborosilicate glass having a useful balance of
,
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W092/16355 PCT/CA92/00ll1
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mechanical, chemical, and electrical properties, at
moderate cost. Other fibre reinforcement materials
include synthetic organic fibres (such as nylon,
polyester and aramids) and synthetic inorganic fibres
5 (such as boron, carbon and silicon carbide).
Matrix materials cover the range from polymers
to metals to ceramics. Polymers are the most commonly
used matrix materials, specifically the organic polyester
and vinyl ester resins. The polymers are characterized
by low densities, relatively low strengths, a nonlinear
stress-strain relationship, and relatively high strains-
to-failure. When property requirements justify the
additional costs, other matrixes are used, including
epoxy, butadiene, bismaleimide, polyimide and other
thermosetting resins, and thermoplastic resins.
Thermoplastic co-mingled fibre-bundles can also be used.
. . .
Composite structures that incorporate
continuous, unidirectionally-oriented fibres can be
radically ani50tropic in nature: that is, they exhibit
significantly diffsrent properties along different axes.
Strength, stiffness, and co-efficient of thermal
expansion can vary by more than ten times in different
directions. In the ~ibre direction, loads are carried
primarily by the fibres, which determine the mechanical
properties in that direction. The fibres deform very
little and constrain the matrix to small deformations.
on the other hand, the fibres do not contribute -
significantly in the direction normal to the fibres, so
that the matrix acts as a continuous load carrying
structure and the fibres move with the deforming matrix,
without signifi¢antly impeding deformation. Mechanical
properties measured transverse to the reinforcement
direction will thus be similar to those of non-reinforced
matrix materials.
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WO92/1635~ 2 1 ~ ~ ~ 9 ~3 PCT/CA92/00111
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The purpose of the composite matrix is to keep
the reinforcing fibres in the proper orientation and
position so that they can carry the intended loads,
distribute the loads more or less evenly among the
S fibres, and provide resistance to crack propagation and
damage. Th~ mechanical properties of the matrix usually
have little effect on the overall strength of the
composite, other than from the load transfer
characteristics and the strength of the interphase. The
matrix generally determines the overall service
temperature limitations of the composite, and may also
control its environmental resistance.
A tubular structure subjected to free end
closure pressure stress, such as a pressure vessel or
pressure containing pipeline, can be subjected to
internal or external pressure and so requires the tubular
wall structure to simultaneously resist longitudinal and
circumferential stresses. In addition, a tubular
structure may be simultaneously subjected to one or a
combination of external direct or shear stresses provided
by external pressure, bending, torsional or thermal
loading.
In the case of rigid tubular structures
employing isotropic materials such as steel or other
metals, the structure can simultaneously resist both ~--
longitudinal and circumferential stresses with a single
wall structure. ~
~ ~-
Since unidirectional composites typically have
exceptional properties in the direction of the
reinforcing fibres, but poor to mediocre properties
perpendicular ttransverse) to the fibres, the approach
taken with prior art continuous fibre-reinforced
composite tubular structures which may be subjected to
~ore than one-dimensional loading is to combine layers or
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WO92/16355 ~ PCT/CA92/00111
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plies with differing fibre orientations. In this way,
the lesser properties perpendicular to the fibre
direction are augmented by the superior properties in the
direction of the fibre orientation. The adjoining layers
of plies are bonded together into a laminate and oriented
at different angles with respect to each other such that
the effective properties of the laminate match some
particular loading condition. Outside loads or stresses
applied to a composite tubular structure result in
internal stresses which are different in the individual
layers. External direct stresses may result not only in
internal direct stresses but in internal shear stresses,
and external shear stresses may result in internal direct
stresses as well as internal shear stresses. Therefore,
laminate effective material properties are tailored to
meet performance requirements through the use of laminate
theory, where the stress-strain relationships for a thin
laminated plate are developed for the case of plate
membrane forces and bending moments.
Pri~r art laminated composite tubular
structures employ a variety of continuous fibre
reinforcement patterns to achieve the required effective
laminate properties. These include a pattern which
orients the reinforcing flbres at a constant helix angle
whlch resolves the various external forces into a single
resultant force in the direction of the fibre. Another ~
pattern utilized where torsional forces are absent -
combines longitudinal-oriented reinforcing fibres
(parallel to the cylinder axis) to resist axial loads
together with circumferential-oriented reinforcing fibres
(perpendicular to the cylinder axis) to resist hoop
loads.
A further pattern combines circumferential-
oriented reinforcing fibres to resist a portion of the
hoop load, together with helically-oriented reinforcing
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fibres to resist torsional and axial loads and a portion
of the hoop load. A still further pattern of continuous
fibre orientation utilized in prior art composite tubular
structures combines circumferential-oriented reinforcing
5 fibres to resist a portion of the hoop load, together
with helically-oriented reinforcing fibres to resist
torsional loads and a portion of both hoop and axial ~-
loads, together with longitudinally-oriented reinforcing
fibres to resist a portion of the axial load.
Where the structure is intended to be
relatively rigid and is not required to exhibit
significant flexibility, the laminate may employ
appropriate patterns to meet the anticipated loading ~ -
conditions. However, where a flexible structure is
required, additional considerations apply.
The flexular rigidity or bending stiffness of a
tubular structure is the measure of its stiffness or
resistance to displacement perpendicular to its length as
determined by ~oth material elastic properties and
cros6-sectional dimensions. The flexular rigidity of a
tubular structure can be eXpressed by the radius of
curvature (r) resulting from an applied bending moment
(M), and is proportional to the modulus of elasticity (E)
and moment of inertia (I) as governed by the formula 1/r
~ M/EI. The deflection in bending of a tubular structure
places one-half of the cylinder wall into compresæion and
one-half into tension, with the neutral axis unchanged in
length. Unlike simple axial compression or tension,
however, the longitudinal axial stress varies linearly -
above and below the neutral axis.
Tubular structures are limited in the extent to
which they can be deflected perpendicular to their length
in bending by the maximum tensile or compressive stress
value (whichever causes failure) to which the wall of a
.... .. . . . .
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W092/t6355 t~ ~ 3 ~ d ~ ~ - 6 - PCT/CA92/00111
cylinder at the furthest point from the neutral axis can
be loaded without failure. This relationship can be
described by the formula o- = Ec/r, where o- =
longitudinal stress in the cylinder wall at a distance
from the cylinder centre line (c), given a radius of
curvature (r)6 The longitudinal stress generated in the
wall of a cylinder deflected in bending is thus inversely
proportional to the radius of curvature and directly
proportional to the distance from the centre line of the
cylinder. Greater curvature (smaller radius) increases
axial stress in the cylinder wall and the maximum stress
i9 experienced at the perimeter of the cylinder at the
furthest distance from its neutral axis. The flexular
strength of a tubular structure is generally referred to
as the maximum stress that can be borne by a surface
element of a cylinder in bending without failure.
For composite tubular structures, the
fundamental principles governing bending are the same.
However, there are some additional factors. For
composite tubular structures comprising continuous fibre-
reinforced laminate plys oriented at various directions
relative to each other, the maximum bending stress does
not necessarily occur at the outermost perimeter o~ the
cylinder as it does with isotropic materials. Due to the
differing directional orientation of the fibre
reinforcement, each laminate layer is likely to have a
different strength and stiffness when measured in the
direction of the cylinder axis. When a bending moment
is applied to the composite tubular structure, a
longitudinal stress is produced in each of the laminate
plies proportional to the elastic modulus of that layer
and its distance from the neutral axis. The maximuim
bending stress in each layer is experienced at the
radially outer edge of each laminate ply. This
longitudinal stress generated in each laminate ply is
resisted by the longitudinal strength of each laminate,
Sl,ll~STl~UTE SHEEI
WO92/16355 ~ PCT/CA92/00
- 7 -
with failure occurring in the individual laminate ply
with the lowest ultimate strength (within its elastic
limit) relative to the induced bending stress.
Therefore, although the laminate construction of
composite tubular structures creates a potentially
different point of failure in bending other than at the
outermost perimeter of the cylinder, the maximum bending
deflection of prior art composite tubular structures is
limited to the maximum longitudinal stress that can be
borne by the earliest failing laminate ply.
The anisotropic nature of continuous fibre
reinforced composites places a severe limitation on the
ability to incréase the maximum bending deflection of
prior art composite tubular structures. Laminate plys
containing fibre-reinforcements oriented parallel to the
bending stress will exhibit the highest ultimate
strength, but also the highest elastic modulus. Fibres
oriented transverse to the bending stress will exhibit
the lowest elastic modulus, but also the lowest ultimate
strength. -
Given the high levels of strength and
predictability of continuous fibr~ reinforced composite
structures in axial tension, that portion of the prior
art cylinder wall which is placed in tension is unliXely
to experience failure prior to the portion of the
cylinder wall placed in compression. The compressed
portion behaves far less predictably. Axial compression -
of continuous fibre reinforced composite structures
produces shear components of load between the fibre and
matrix. These out-of-plane components can lead to
tension loads in the matrix that may cause premature
matrix failure. The results of analysis of composites
indicate a significant variability in axial compressive
strength as it i9 essentially a matrix-dominated
variable. Therefore, prior art composite tubular -
..
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WO92/163~ PCT/CA92/00111
- 8 -
structures exhibit minimal capacity for axial deflection
without failure due to limited and significantly variable
maximum compressive stress values which renders them
unsuitable for flexible tubular structures.
A further problem associated with prior art
composite tubular structures is that due to the low
elastic modulus of glass-reinforced composite materials
in contrast to steel, such structures exhibit significant
axial expansion when subjected to internal pressure
stress. In restrained end closure pressure-containing
pipelines, this characteristic places all or a portion of
the pipeline structure into compression and can impose
large and potentially damaging loads on fittings such as
15 elbows, and on terminal equipment such as valves and -
pumps. As composite materials exhibit limited and highly
variable maximum compressive stress values, and this
magnitude of axial expansion cannot in practice be
accomodated with conventional steel expansion devices,
significant limitations are placed on the performance of
prior art composite tubular structures when used as
pressure vessels or pressure-containing pipelines.
To provide a flexible tubular structure,
various arrangements have been proposed in which the wall
o~ the structure is formed from several different
components. In the case of flexible tubular structures
employing isotropic materials such as steel and other
metals, there is a significant reduction in structural
efficiency in contrast to rigid tubular structures since
the designer must provide a structural wall or layer to
resist each of the longitudinal and circum~erential
forces. One structural wall or layer must be oriented so
as to predominantly resist circumferential forces while
concurrently having the capacity to spread itself axially
to permit bending, thus having little or no resistance to
longitudinal forces. A second wall or layer must be
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WO92/16355 2 ~ a ~ ~ PCT/CA92/00111
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oriented so as to predominantly resist longitudinal
forces while concurrently having the capacity to spread
itself axially to permit bending, thus having little or
no resistance to circumferential forces. Both
independent layers are designed to perform their
specialized function by the use of narrow,
helically-oriented strips, which in both cases are
stressed predominantly along the strip length with little
or no stress induced across the width of the narrow
strip. For this reason, isotropic materials such as
steel and other metals are inefficient materials for such
flexible structures, since the strength of the material
in the direction transverse to the strip length is
underutilized and thus wasted in resisting stresses
placed on the tubular structure.
Typically prior art steel flexible tubular
structures utilize a mechanism of helically-oriented
interlocking metal strips which serve to limit the
maximum axial strain in flexure at any point along the
length of the cylinder. This mechanism is provided by
forming a "U" or "Z" shaped profile and subsequently post
forming it into a the helically-oriented steel strip in
such a manner as to provide interlocking of the strip as
25 it i8 Sormed around the pipe. In flexure, this ;~
interlocXing mechanism restricts the gap between ad~acent
strips to a maximum specified dimension, thus providing a
defined containment "net" through which the internal
plastic liner or bladder will not extrude.
However, as noted above, isotropic materials
such as steel and other metals are inefficient materials
for such flexible structures, since the strength of the
material in the direction transverse to the strip length
is underutilized and thus wasted in resisting stresses
placed on the tubular structure.
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WO92~16355 PCT/CA92/00111
3 ~ ~ -
-- 10 --
Although composites are recognized as
anisotropic and should therefore be more efficient than
isotropic material in such structures, interlocking
mechanisms such as those used for steel structures are
not practical with flexible tubular structures which
employ continuous fibre-reinforced composite materials.
Although a linear, "U" or "Z" shaped fibre reinforced
composite part can be fabricated using the process of - - -
pultrusion, this process is not practical for the
produation of helically-oriented components as used in
the steel structures because such part cannot be post
formed.
It is therefore an object of this invention to
provide a flexible tubular structure which permits the
use of fibre reinforced composites as a structural
component. ~-
In general te DS, the present invention
provides a tubular structure having a circumferential
wall formed from a pair of juxtaposed wall elements. One
of the wall elements comprises a plurality of juxtaposed
layers, one of which is continuous and flexible and has a
spirally wound radial pro~ection directed toward another
of the layers. The other layer includes a first spirally
wound composite strip having a radial projection directed
toward the one layer. The other layer further includes a
spirally wound elastomeric strip interposed between
adjacent passes of the composite strip. The projections
on the one layer and the other layer are staggered
relative to one another in an axial direction and overlap
one another in the radial direction. The layers are
separated by an intermediate layer having a spirally
wound composite strip located between each pair of
projections and flanked by spirally wound elastomeric
strips so as to locate an elastomeric strip between a
composite strip of said intermediate layer and an -
~ .
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W092/16355 2 ~ ~ ~ D ~ ~ PCT/C~9~/00111
adjacent one of said projections. The composite strips
of the layers overlap one another in the axial direction
to provide a continuous composite barrier in the one wall
element in the radial direction. The other wall element
s comprises a layer of alternating spirally wound composite
strips and elastomeric strips. The pitch of the spirally
wound composite strips in the radially outer of the wall
elements is greater than the pitch of the composite
strips in the radially inner of the wall elements. The
elastomeric strips in each wall element uniformly
distribute the composite strips in the respective wall
element upon flexure of the tubular structure to maintain
the structural integrity thereof.
. .: . .
lS In bending, the three layers which comprise the
one wall element act to permit and facilitate realignment .. -
of the composite strips in a manner which seeks to .;
minimize the stresses induced in such structural
components and which attempts to maintain a maximum
uniform strain throughout the cylinder length by limiting
the maximum axial distance which a~y two adjacent
spirally wound strips can separate from one another.
Bending stiffness of the cylinder is largely determined
by the radial thickness and elastic modulus of the
continuous flexible layer. The intermediate and other
layer of the one wall element provide the primary
resistance to hoop tensile stresses derived from internal
pressure, and resistance to hoop compressive stresses
derived from axial loading and external pressure. In
flexure, the deformation of elastomeric material between
adjacent spirally wound composite strips permits a
shortening of that half of the wall element placed in
compression, by the transfer of a portion of the
elastomeric material to the opposite half of the wall
element placed in tension.
.
' ~ . .
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WO92/16355 PCT/CA92/00111
J~ S3
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The other wall element provides resistance to
longitudinal tensile stresses derived from internal
pressure, torsional and axial loading, and resistance to
compressive stresses derived from external pressure.
5 When subjected to a bending force, the portions of the
wall elements which are placed in compression achieve a
shortening in their longitudinal axes by a reduction in
the distance between adjacent composite strips. The
portions of the wall element which are placed in tension
achieve a lengthening in their longitudinal axis by an
increase in the distance between adjacent composite
strips. For any given cylinder length in flexure, the
increase in area above the neutral axis is equal to the
reduction in area below the neutral axis. In flexure, a
lS portion of the elastomeric material in the reduced area
between adjacent composite strips in the half of the
cylinder that is shortened axially by compression is
redistributed to the increased area between adjacent
composite strips in the half of the cylinder in tension.
In this fashion, minimal bending stress is induced in the
fibre-reinforced composite strips, but rather the flexure
is made possible by a change in their geometry and the
deformation of elastomeric material.
The tubular structure of the preferred
embodiments minimizes the reliance upon the limited and
significantly variable maximum compressive stress value
to permit a smaller radiu- of curvature to be obtained.
-.
A tubular composite structure which may be
subjected to internal or external pressure, thermal or
torsional stress, or a combination of these loading
conditions must be designed such that the ultimate
strength of the laminate is sufficient to reslst the
combined total of all stresses, including bending stress,
without failure. Therefore, the applied stress on a
cylinder in flexure must be added to the applied stress
.
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WO92/16355 2 1 3 ~ 3~ ~ ~ PCT/CA92/00111 : .
from other loading conditions in determining required
laminate orientation and thickness. In the preferred
embodiment, because the structural components of the ~ .
tubular structure, namely the spirally wound composite
strips, are not significantly stressed in flexure, the
laminate thickness is determined principally by the other ~ :
loading conditions. :.
. Embodiments of the present invention will now
be described with reference to the accompanying drawings
in which: ~ .
Figure l is a general side view of a tubular
structure with layers thereof progressively removed;
Figure 2 is a side elevation of the structure
shown in Figure l;
Figure 3A is a sectional view of Figure 2 on
the neutral axis as indicated by section line 3A-3A; ~:
Figure 3B is a view similar to Figure 3A taken
on the line 3B-3B;
Figure 3C i8 a view similar to Figure 3A taken
on the line 3C-3C;
Figure 4 is a general perspective view of a ~.
further embodiment of tubular structure;
Figures 5-14 are schematic representations of . : :
succes6ive stages in the manu~acture of the structure
shown in FigurQ l;
Figure 15 is a representation of apparatus used
as an alternative to the procedure used in Figure 5; and
Figures 16-23 show schematically successive
steps in a procedure for joining two tubular structures
similar to that of Figure l. -
Referring therefore to Figure l, a tubular
~structure lO has a circumferential wall 12 that is formed
35 from a pair of juxtaposed wall elements 14,16. An outer :
sheath 18 comp}etes the wall 12 and provides protection
from the environment for the elements 14,16.
. ,.
SUBSTi~UTE SHEEl: ~
W 0 92/1635~ P ~ /CA92/00111
~ 14 -
As can best be seen in Figure 3A, the radially
inner wall element 14 comprises three separate layers,
namely 20, 22 and 24. The inner layer 20 consists of a
continuous flexible plastic cylinder 26 having a spirally
wound protrusion 28 projecting radially outwardly
therefrom. The layer 20 can typically be formed from a
thermoplastic polymer or elastomeric material and is
preferably impermeable to the fluids to which it may be --
exposed. In certain cases, layer 20 may include an inner
liner (not shown) of impermeable material so that the
cylinder 26 may be formed from a material having
different properties.
outer layer 24 consists of a spirally wound
composite strip 30 having a radially inward projection 32
directed towards the inner layer 20. The composite strip
30 has the same pitch and hand as the spiral projections
28. However, the projections 32 and 28 are staggered
axially and overlap in the radial direction. A second
spirally wound composite strip 34 is located between the
successive pas~es of the strip 30 and located axially so
as to be ali~ned with the projection 28. Composites
strips 30,34 each con~ist of a bundle of fibres or
roving, for example E-glass, generally orientated in the
direction of the winding with a matrix disbursed between
the fibres. The fibres in the roving may be contained by
tran5verse f ibres extending about the roving to provide a
smooth exterior surface and resist torsional loads in the
strip induced in bending of the structure. The matrix
may, for example, be polyester. Typically, the composite
strips will have 75% by weight of ~ibre and 25% by weight
of matrix although, as will be discussed more fully
below, alternative materials and ratios may be used.
Located between the composite strips 30,34 are
a pair of spirally wound elastomeric strips 36,38. These
strips may be any suitable elastomer such as neoprene.
`'' '
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W092/t635~ PCT/CA92/00111
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Strips 36 and 38 are located on opposite flanks of the
composite strip 30 and act to maintain the composite
strips 30 and 34 in spaced relationship.
.~
An intermediate layer 22 is located between the
layers 20,24 and consists of a pair of composite spirally
wound strip~ 40,42. Each of these strips 40,42 is of the
same hand and same pitch as the strips 30 and 34 and is
axially located so as to overlap in the axial direction
each of the adjacent strips 30,34 in the outer layer 24. -
Each of the strips 40 and 42 is located between adjacent
ones of the projections 32,28. A pair of elastomeric
strips 44,46 and 48,50 is associated with the composite
strips 40 and 42 respectively and located on opposites
sides thereof. Strip 44 is thus interposed between the
composite strip 40 and the projection 28 and elastomeric
strip 46 is interposed between the strip 40 and
projection 32. Similarly, the elastomeric strips 48 and ;
50 are interposed between the composite strip 42 and the
20 projection 32 and 28 respectively. -
,
A layer of friction-reducing material such as
polyethylene film 52 i8 located between the inner layer
20 and intermediate layer 22. Similarly, a layer of
friction reducing material 54 is applied between the
outer layer 24 and intermediate layer 22 so as to
minimize the resistance to relative axial movement
between the layers 22 and 24.
, :
Outer wall element 16 is separated from the
inner wall element 14 by a friction-reducing film 56. ~ -
The outer wall element 16 consists of inner and outer
layers 58,60 which in turn are separated by a friction-
reducing film 62. Each of the layers 58 and 60 consists ~;
of a~ternating composite strips 64 and elastomeric strips
66 that are spirally wound. The pitch between successive
passes of each strip 64 is greater than that of the -
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W092/163~5 PCT/CA92/00111
2~ 3 - 16 -
composite strips of the inner wall element l4 so that in
general there will be a greater number of individual
strips 64 than there are strips 30,34. For added
clarity, each separate strip 64 has been denoted with a
5 suffix a, b in Figure 3A with the corresponding
elastomeric strip 66 also denoted with suffixes a, b and
c. The pitch of the strips 64,66 in outer layer 60 is
the same as that of the inner layers 58 but is of
opposite hand as can be seen in Figure l.
A friction-reducing film 68 is located between
the outer sheath 18 and the layer 60 to minimize -'
resistance to relative movement between the sheath and
outer layer 60.
In operation, the principal bending stiffness
of the structure lO is determined by the flexible layer
20. The composite strips of the outer layer 24 and . .
intermediate layer 22 of wall element 14 essentially
constitute helical springs formed from composite material
and do not contribute significantly to the bending
stiffness of the overall structure. The overlapping of
the composite strip~ of the intermediate layer 22 and
outer layer 24 provides a continuous barrier of co~posite,
material in a radial direction in the wall element 14 and
thereby supports the layer 20 against internal pressure
to inhibit extrusion of the layer 20 through the wall
element 14. The elastomeric strips act to maintain the
composite strips uniformly distributed along the axial
30 length of the tubular structure and interact with the ,
projections 28 and 32 to maintain the composite strips
40,42 of the intermediate layer centred between the
composite strips 30,34 of the outer layer 24. As can be
seen from Figures 3B and 3C, as the tubular structure is .
35 flexed transverse to its longitudinal axis, the composite '
strips on one side of the neutral axis move apart and the
composite strips on the other side of the neutral axis
SL~BSTITUTE SHEET..
WO92/16355 PCT/CA92/00l11
21~&l)~
- 17 -
move together This is accomodated by a bodily
displacement of the elastomeric strips which however
maintain a uniform loading across the composite strip to
maintain them uniformly distributed and maintain the
continuous composite barrier in the radial direction
In flexure, the behaviour of each of the
components contained within the layers is governed by the
behaviour of the components which have greater bending
stiffnoss In flexure, that component which has the
greatQst bending stif~nQss will first seek its modified
shape tend to force the component with the next greatest -
bsnding stiffness to comply with its movement The
component with the second grQatest bending stiffness will
sQQk its modifiQd shape, within the limitations provided
by the component with the greatest bending stiffness, and
tend to forcQ tho component with the third great~st
bonding stlffno~s to comply with it~ ~ovement By
modifying the dimensions and ela8tic ~oduli of the
composito, pla~t~c and elasto~eric co~ponents which ~ake
up the lay-r~, it i~ po~ibl- to gov-rn the behaviour of
ach o~ th- co~pon-nt- in fl xure For a tubular
structur- with an inside diaueter o~ 3" and a hel~x angle
of 70 d-gr--~, th- following co~pon-nt di~-n-ion~ and
la~tic ~oduli provide th~ following r--p-ctiv- bending
stiffn-~ for ach of th compon-nt~
'
a t~ D a-~l-l ~ l-a ~
C~K~ t _ ~ ~ u~ ~ ~t~ ~ t~tt- ~-
Pl- elc- 26 ~O ln conelnuou~ 3~,000 ~-1 3,000
3 0 llnd-r _ lb.lr~
~l--eo -~ 36,~ , 0~0 ~n ~0 ln ~00 p l ~,000
Strlp 6,4~,~0 lb.lr~
cc~p~ ~e- 30,3~,~0,~ .0~0 ln. 1.~2~ ln 3.~ ~Illlon ~0
~trlp- p 1 l~ lr~ ~ -
~ .
In the above example, th- pla-tic cylindsr 26 will
dictate the behaviour of the remaining co~ponQnts by virtue
of ~ts significantly greater bending stiffna~s r~lative to
SU~STITUTE SHEEI
.
.. . .. . . .. .. ~ .. . .
W O 92/16355 PC~r/CA9t/00111
210~6 18 -
the other components. The spirall~ wound elastomer strips,
by virtue of their next highest bending stiffness, will
modify their shape within the limitations defined by the
plastic cylindrical component and in turn cause the
composite strips, with the lowest relative bending
stiffness, to conform. By reliably controlling the
behaviour of the components in this manner, and by virtue of ~ -
the minimal bending stiffness of the structural composite
components, the tubular structure can be deflected in
bending to a radius of curvature 10 times its diameter
without subjecting the composite structural components to
significant bending stresses. In flexure, the half of the
inner wall element which is placed in tension achieves a
lengthening in its longitudinal axis by an increase in the
axial distance between the protrusions extending from the
inner plastic cylinder. The opposite half of such inner
wall element which is placed in compression achieves a
shortening in its longitudinal axis by a reduction in the
distance between the protrusions extending from the inner
plastic cylinder. This adjustment in spacing between
protrusions of the high bending stiffness plastic cylinder
26 forces the deformation of elastomeric material from the -
reduced area in the half of the cylinder shortened axially
in compression, to the increased area in the half of the
cylinder lengthened axially in tension. This deformation of
elastomeric material from one h~lf of the tubular structure
to the other causes a realignment of the spirally wound
composite strips which have the lowest bending stiffness.
In flexure, the protrusions 28 and 32 co-operate with the
elastomeric s~rips of the intermediate layer 22 to ensure
that the composite elements remain overlapped and a
continuous wall of composite material ia provided.
The proviaion of the films 52, 54, 56, 62 and 68
avoids direct contact between the layers and therefore
SUBSTITUTE SHEEI :: -
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... - .: , . i. ,.i , .. ..... .. .... - .. , ~ `.... .. ...... ; ... ; .. . . ~ , . . ..
-. . . ~, ,. ~ ., . . . .. . , ..... ,.... .. , . . ... ,., , , . , ~.
W092/163~5 2 ~ PCT/CA92/OOIll
- 19 - ~
facilitates relative movement between the elements of the
layers during bending.
- The principle function of the outer wall element
16 is to resist axial loads. As the helix angle of the
strips 64 decreases, i.e. as the pitch increases, so the
axial strength of the structure increases. ~,
The relative radial thicknesses of the composite
strips 30,34, and 40,42,64 and the relative pitches of each
of the wall elements determines the maximum loading
capability available for a given stru~ture. As may be seen
from Table I appended to the description, the parameters are
to a certain extent interdependent but can be adjusted to
accomodate a wide variety of operating conditions.
As can be seen from Row A of Table I, as the
maximum internal pressure is increased, the radial thickness
of each of the layers 22, 24 and 58,60 similarly increases
in a generally linear manner. It will be noted, however,
that the bending stiffness remains substantially the same,
indicating, as noted above, that the bending stiffness is
determined essentially by the oylinder 26.
Row B o~ Table I illustrates the ef~ect of varying
the helix angle in the outer wall element 16. As might be
expected, as the helix angle increases to 50- from 40-
(pitch decrea~es), the axial strength is significantly
affected and a large increase in the thicXness of the layers
58,60 is necessary. A small reduction in the thickness of
the layers 22,24 also results but not enough to offset the
increase in elements 58,60.
: . .
Row C shows how varying the helix angle of the
components of wall element 14 does not signi~icantly affect
: ~
. :-
~: SUBSTITUTE SHEE~ , ~
~ . .
.; , ~ . , ~ ; ; ~ - , ` ` ' ` ,
WO92t16355 PCT/CA92/00111
2 1 ~ 6
- 20 -
bending stiffness but requires a large increase in radial
thickness to maintain the maximum internal pressure rating
for a change from 70 to 60: There is a corresponding
decrease in the thickness of layers 58,60 but this is
reflected in the decrease in axial strength.
Rows D & E show clearly how the helix angles of
the composite strips in wall element 14,16 have optimum
values for maintaining a maximum internal pressure rating.
In the above exampl~s, the elastomeric strips will
have an axial width of 0.25 in. and the composite strips a
width o~ 1.25 in. - ~ -
By way o~ comparison, Table 2 below shows the
configuration of components in a three-inch diameter pipe
and a six-inch diameter pipe intended to withstand the same
maxi~um internal pressure, namely 5,000 p. 8. i .
Th~o~ o T~ _ Th~cbl
l~nr L~-r~ H l~ 7 S~-r bl~ 7 ~ ne ~-~ 0 ndln~
DI~t~r Z0 22 211~n~l- Co~o~t~ ~,60 ~n~- Co~- 1~ 5~h ~rrn~
iIn.)~ln.~ (;n.) ~-) ~ (-n.) (~) (~ ~ln.) (1--.) ~ n')
3~ .~o.~670 7~ o.~ o ~9 o.~o 20,000 ~6"~
_ _. .
6.o . 2 0.013 70 t~ 0.~3 ~0 ~ 0.~0 ~,000 r~ o~
.:
'~hu~, a doubling of vall thickn-~ i8 required but
a ~igni~icant four~old incr~ase in axial 3trength is
obtained. Tho larg--incr~a~ in b-ndlng stirrn-Js is
attributablQ mainly to incr~aJ-d diametQr o~ the cylinder
26.
. .
SUBSTITUTE SHEEI
.~ .. . .. , i . , ' . .. . . . .. .. . .. .... . . . .. ~ . .
WO92/1635S 21~ PCT/CA92/00111
- 21 -
The arrangement shown in Figures 1, 2 and 3A
illustrates relatively simple wall structures suitable for
use in a wide variety of applications. Where a pipe is to
be used in an environment requiring a high level of
integrity, the wall element 14 may be replicated so that the
wall element 16 is located between a pair of wall elements
each similar to wall element 14. This provides a degree of
redundancy for the containment of the layer 20 should a
failure occur in element 14. This arrangement is shown in
Fi~ure 4 where like reference numerals will be used to
denote like elements with a prefix "1" added for clarity.
As can be seen from Figure 4, a radially inner
wall element 114 having layers 120, 122, 124 as described
above as with respect to Figures 1 and 2 is encompassed by a
wall element 116 formed from layers 158 and 160. A further
wall element 170 is located radially outwardly of the wall
element 116 and is similar in construction to the wall
element 114. However, the hand of the spiral composite and
elastomeric strips in the wall element 170 is opposite to
that o~ the wall element 114, although the pitch is similar.
A sheath 118 completes the wall structure. The wall element
170 provides further resistance to hoop tensile stresses
derived from internal pressure, resistance to hoop
compressive stresses derived from longitudinal tensile
loading and external pressure and resistance to external
impact or handling damage.
The arrangement shown in Figure 4 has the
advantage that there is a neutral torque loading due to
axial loads and internal pressure when using the pair of
similar but opposite hand wall elements 114, 170. This
reduces flexing of the wall and of course torque loads that
may be imposed upon couplings at opposite ends o~ the
tubular structure. The wall element 170 may also be used to
'.
SUBSTITUTE SHEEI
W O 92/t6355 . PC~r/CA92/00111
- 22 -
adjust the density of the tubular structure to a desired
value.
It will be appreciated that the above
configurations are exemplary only and additional wall
element thicknesses or alternative wall element pitch can be
designed to meet a particular set of loading conditions.
The relative thickness and disposition of the various layers
may be optimized to meet those parameters while maintaining
the basic structural elements shown in the drawings.
The above description has referred generically to
a plastics material for layer 20, and composite strips and
elastomeric strips in the wall elements 14 and 16. It will,
however, be appreciated that a wide variety of materials are
suitable to form the individual elements that may be chosen
to suit particular applications. For example, the plastic
layer may be a thermoset or thermoplastic polymer, such as
polyethylene, polybutylene, polypropylene, polyurethane,
fluoroplastics, polyamides or polyamide-imides.
Similarly, the composite strip may be formed from
any suitable fibre interspersed with a suitable matrix.
Typical of such fibres are gla~ ~ibre, nylon, polyester,
aramid, boron, carbon and silicon carbide. Typical of such
matrix materials are polyester, vinyl ester and epoxy. The
individual characteristics and preferences for the use of
each material are well known within the composites art and
therefore need not be elaborated further.
Elastomeric materials may also be selected from a
wide range of available materials. Elastomeric materials
include natural and synthetic thermoset rubber~ and
thermopla~tic elastomers. Synthetic rubbers include nitrile
35 rubber, EPDM, butyl rubber, silicone rubber and a variety of -
.. ...
SUBSTITUTE SHEET, ~ -
.. ,. ..... .... .~...... . ,.. . . ~ . . .... . ... ....... . . .. ~ .. . . .
WO92/1635S 2 ~ PCT/CA92/00111
- 23 -
specialized blends designed for specific service conditions.
Thermoplastic elastomers include styrenic block copolymers,
polyolefin blends, elastomeric alloys, thermoplastic
polyurethanes, thermoplastic copolyesters, and thermoplastic
polyamides.
: ..
The manner of manufacturing the tubular structure
10 is shown more fully in Figures 5 through 14. It will be
appreciated in these Figures that the components of the
manufacturing apparatus are individually well known although
their combination to produce the process described below and
the tubular structure described above is believed to be
novel. The process will be described to produce the tubular
structure shown in Figures l and 2 and similar reference
lS numerals will used for the same components.
Referring therefore to Figure 5, the tubular wall
26 of intermediate layer 20 is extruded from a die 200 and -
moved axially by mean~ of gripper wheels 202. The radial
pxojection 28 is formed on the outer surface of the wall 26
by an elongate strip of similar material that is welded or
bonded to the outer surface of the wall 26 as it is applied.
A coil 204 o~ the strip 28 i5 ~ounted on a spider 206 that
i5 rotated about the axis o~ movement o~ the wall 26 as it
is moved axially. Accordingly, the strip i6 laid down as a
continuous spiral protrusion with the requisite pitch.
A layer of film 52 is then applied between the
projections 28 from a roll 208 that is mounted on a spider
210 and rotated about the axis of movement. The protrusions
28 ~erve as a guide for the film 52 so that it is neatly and
uniformly laid down on the surface of the element 26 between
; the projections 28.
: ~
SUBSTITUTE SHEEI :
.
W092/16355 PCT/CA92/OOtlt
`2 ~
- 24 -
Referring to Figure 6, the elastomeric strips 50
are then applied from a coil 2}2 mounted on a spider 214 and
abut the projection 28 that serves as a guide for the strips
50. A slight tension is applied to the elastomeric strip 50
5 so that it grips the outside of the wall 26. The
elastomeric strip 44 to the opposite side of projection 28 -
is similarly applied in an axially spaced location from a
roll 216 that is rotated on a spider 218.
The strips 46 and 48 are applied between the
projections 2~ from a roll 220 rotated about the axis of the
tubular structure by means of a spider 222. As can be seen
from Figure 6, an additional strip 224 is applied between
the strips 46,48 to maintain them in spaced relationship.
Again, a slight tension is applied to the elastomeric strips
to maintain them in place during formation.
As can be seen in Figure 7, the composite material
forming the strips 40 is then applied in a similar manner
from coils of fibre 224 rotated on a spider 226. Although
shown schematically as a single coil, it will be appreciated ~-
that the fibre may be supplied from a number of separate
coils rotated in union about the axis of the structure. The
matrix material may be applied to the fibre as it is unwound
from the coil 224 or alternatively, pre-impregnatéd fibres
or thermoplastic co-mingled fibres could be utilized to
provide the matrix material. The previously applied
elastomeric strips 44,46,48 and 50 serve as a mould for the
composite 40,42 allowing it to be applied in a continuous
30 manner to the tubular structure prior to curing. After i-~
application, the composite material is cured by suitable
curing technigues such as infrared or heat. At this stage,
the inner layer 20 and intermediate layer 22 has been
completed.
SUBSTITUTE SHEEI
:: ,
WO92/1635~ 9 ~ PCT/CA92/00111
- 25 -
In order to produce the outer layer 24, it isnecessary to provide a mould for the projection 32 of the
composite strip 30. This is provided by removal of the
strip 2 2 4 that was appl ied between the strips 4 6 and 4 8 .
5 Once the strip 224 is removed, a spiral recess is formed on
the outer surface of the tubular structure which will
accomodate the projection 32. The film 54 is then applied
to the outer surface of the tubular structure from a coil
228 mounted on a spider 230 rotating about the axis of the
structure. This is shown in Figure 8.
As can be seen from Figure 9, the elastomeric
strips 36,38 are next applied to the outer surface from
coils 232,234 respectively that are mounted on spiders 236,
238. As shown in Figure l0, the composite strips 30,34 are
then wound onto the outer surface between the elastomeric
strips 36 and 38 in a manner similar to that of strips
40,42. It will be noted that the recess left by the strip
224 is located between the passes of strips 36,38 and during -
application of the composite, the film 54 deflects into the
recess, allowing the composite similarly to flow into the
recess and form the radial projection 32. Again, the
composite i8 effectively moulded "in situ" by virtue of the
constraints placed by the strips 36,38 and the configuration
of the radially inner wall on which the composite is placed.
The composite is then cured and a continuous film 56 applied
to the outer surface to complete the inner wall element 14.
Thereafter, outer wall element 16 is formed, as
can be seen in Figure ll. Elastomeric strips 66 are first
applied from respective rolls 240 rotated on spiders 242 to
provide a mould for the composite strips 64 which are
applied from their respective rolls 244 rotated on spiders
246 (Figure 12). The composite is cured and film 62 applied ~:
SUBSTITUTE SHEEI
-
. . ~. ~ - . -
.
~ . . .
WO 92/16355 PCI'/CA92/00111
3 ~ - :
- 26 -
from the roll 248 on spider 250. This completes the inner
layer 58 of the outer wall element 16.
It will be noted that the composite strips 64 of
inner layer 58 of outer wall element 16 are applied in
opposite hand to the composite strips 30,34,40,42 of inner
wall element 14. Subsequently as shown in Figure 13, the
outer layer 60 is formed by application of the elastomeric
strips 66 and, as shown in Figure 14, the composite strips
64 which are subse~uently cured. The strips 64,66 of layer
60 are applied in opposite hand to the strips 64,66 of layer
58. Thereafter the film 68 is applied and the outer sheath
18 extruded over the tubular element.
It will be noted that throughout the production
process, the elastomeric elements are utilized as a mould
for the application of the composite strips so that the
composite strips may be applied in a pliable form but when
cured provide the requisite spirally wound structure. -
It w~ll be appreciated that further layers may be
similarly formed utilizing the steps shown above with
resp~ect to the embodiment of Figures 1 and 2 but in view of
the repetitive nature of the process, it is believed that it
need not be descr~bed further.
The preparation of the layer 20 has been described
by the bonding or welding of a separate strip to form the
projection 28 but it will be appreciated that the same
structure may be formed by utilizing a rotating extrusion
dye 250 as shown in Figure 15 in which the projection 28 is
simultaneously extruded with the cylindrical wall 26 by
rotation of the dye as the wall 26 is axially extruded.
This avoids the need to bond or weld a separate strip to the
wall 26.
SUBSTITUTE SHEE~ -- -- -
..
' : , . . , . , . ':
WO92/16355 21 0 ~ ~ 9 ~ PCT/CA92/00111
- 27 -
The arrangement descri~ed above provides a tubular
structure that makes use of continuous fibre reinforced
composites and has particularly beneficial structure and/or
characteristics. However, a further benefit found from the
structure described above with respect to Figures l through
4 is the ability to make a structurally sound connection
between two lengths of tubular structure. Previously this
has been extremely difficult with fibre reinforced composite
pipes and has not resulted in a structurally satisfactory
arrangement.
In order to form a joint between two lengths of
the tubular structure lO shown above or of one length to a
fitting, advantage is taken of the nature of the layers that
15 form the structure and in particular the provision of the -
elastomeric strips within that structure.
As shown in Figure 16, the initial step in joining
two lengths of the structure lO is to remove a portion of
each layer that increases progressively from the radially
inner to the radially outer layer so that a portion of each
layer is exposed. The port~on exposed will depend upon the
composition of the structure and the loads to which it is to
be subjected but will typically be three times the diameter
o~ the layer. For convenience the ~ull extent o~ the
exposure of each layer has not been depicted in the figures.
With the individual layers exposed as shown in
Figure 16, a portion of the elastomeric elements in each
exposed portion is then removed as indicated by dotted
lines. Typically, one-half of the elastomeric strip exposed
will be removed so that spiral recesses are formed between
the composite strips forming each layer as indicated in
Figure 17.
.,.............................. ~
SU~STITUTE SHEEI.
.
. ` . . . .
. . . . ~ . .. .~. . .
W092/16355 PCT/CA92/OOt1t
~ 96 28 -
To establish the connection between two tubular
structures, a pair of the prepared ends as shown in Figure
17 are aligned as indicated in Figure 18 so that the exposed
ends of the inner layer 26 abut. The projections 28 will be
exposed on the layer 26 and may, if desired, be aligned so
as to form a continuous spiral projection from one body to
the other. In this position, a thermoplastic welding device
is applied to consolidate the abutting liners 26.
As shown in Figure 19, a continuous fibre
rein~orced composite material 260 is then wound about the
abutting layers 20, 22 and 24. Several layers of material
are wound across the abutting ends 26 and, as then shown in
Figure 20, a plastic film 262 is wrapped about the structure
and welded to the film 56. As indicated in Fiqure 21, a
composite material 264 is then wound about the layers 58 in
one hand and (Figure 22) about the layer 60 in an opposite
hand. As shown in Figure 23, a plastics sleeve 266 is
welded to the layer 18 to provide a continuous outer cover. ~- -
The wound fibres key into the recesses formed by the removal
of the elastomer and provide a strong mechanical structure
which inhibits relative movement between adjacent composite
strips. In this manner, as noted above, a strong structural
joint is created with the structural integrity of the
components maintained. Obviously the requisite number of
layers will be filament wound dependin~ upon the structural
makeup of the wall 12, but in each case the removal of the
elastomeric elements enables a strong connection to be made.
The procedure described above is of cour~e
particularly beneficial when used with the tubular structure
of Figures 1 to 4. Similar advantages could be obtained
when used with a rigid multilayer structure having several
helically wound composite strips in at least some of the
layers. It would then be necessary to remove selected ones
,~
.. .. . .
SU~STITUTE SHEEI :: -
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W092/t635~ 2~ 3 b PCT/CA92/00111
- 29 -
of the strips to provide the spiral recesses to which the
composite filaments would be applied. Similarly,
connections could be made between the tubular structure and
a coupling by providing appropriate layered helical recesses
on the coupling to permit winding of the overlying
filaments.
SUBSTITUTE SHEEI
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S - ; ~ ~t ~; 'a ia ia i ia ~ ia ;i ~ ia a i ~ ~t ia Ij ~ ... .. . .
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g . i 3~ 3r i ~ 3E 2t i ~ il3 i ~t i~ t i - t~ ~t t~ ~ sj -
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