[Detailed description of the invention]
According to the invention, the proposal is to use poly(etherketoneketone) (PEKK) for manufacturing
parts which have a low gas permeability, and particularly with respect to CO2 and/or H2S.
PEKK
5 “PEKK” refers to PAEK polymers which comprise units of formulae (-Ar-X-) and also units of formula (-
Ar'-Y-), in which:
– Ar and Ar’ each denote a divalent aromatic radical;
– Ar and Ar' may be selected, preferably, from optionally substituted 1,3-phenylene and 1,4-
phenylene;
10 – X denotes a carbonyl group;
– Y denotes a group selected from an oxygen atom.
The poly-ether-ketone-ketone (PEKK) comprises a succession of repeating units of type -(Ar1-O-Ar2-COAr3-CO)n-, with each Ar1, Ar2 and Ar3 representing independently a divalent aromatic radical, preferably
a phenylene.
15 In the above formula, just as in all of the formulae which follow, n represents an integer.
The bonds on either side of each unit Ar1, Ar2 and Ar3 may be of para or meta or ortho type (preferably
of para or meta type).
In certain embodiments, the PEKK comprises a succession of repeating units of formula (IA) and/or of
formula (IB) below:
20 (IA)
(IB)
The units of formula (IA) are units derived from isophthalic acid (or I units), whereas the units of
25 formula (IB) are units derived from terephthalic acid (or T units).
In the PEKK used in the invention, the proportion by mass of T units, relative to the sum of the T and I
units, may range from 0% to 5%; or from 5% to 10%; or from 10% to 15%; or from 15% to 20%; or from
15% to 20%; or from 20% to 25%; or from 25% to 30%; or from 30% to 35%; or from 35% to 40%; or
6
from 40% to 45%; or from 45% to 50%; or from 50% to 55%; or from 55% to 60%; or from 60% to 65%;
or from 65% to 70%; or from 70% to 75%; or from 75% to 80%; or from 80% to 85%; or from 85% to
90%; or from 90% to 95%; or from 95% to 100%.
Ranges of from 35% to 100%, notably from 55% to 85% and even more specifically from 60% to 80%
5 are particularly suitable. In all the ranges set out in the present patent application, the limits are
included, unless otherwise mentioned.
The PEKK preferably has an intrinsic viscosity of 0.4 to 1.5 dL/g, preferably from 0.6 to 1.4 dL/g, more
preferably from 0.8 to 1.2 dL/g, in 96% sulfuric acid.
The degree of crystallinity of a polymer may affect the gas permeability properties. Indeed, it has been
10 noted that the gas permeability of PEKK, especially with respect to CO2 and H2S, goes down as the
crystallinity increases. It is therefore preferable for the PEKK used to have a maximum degree of
crystallinity, preferably of greater than 5%, particularly of greater than 15% and very particularly of
greater than 25%. In the PEKK used in the invention, the proportion by mass of crystalline PEKK may
in particular vary from 0% to 1%; or from 1% to 5%; or from 5% to 10%; or from 10% to 15%; or from
15 15% to 20%; or from 20% to 25%; or from 25% to 30%; or from 30% to 35%; or from 35% to 40%; or
from 40% to 45%; or from 45% to 50%.
For certain applications, it may be advantageous to use amorphous PEKK. Amorphous PEKK denotes
a PEKK with an enthalpy of fusion of less than 10 J/g as measured by DSC in accordance with the
standard ISO 11357-3:1999.
20 The degree of crystallinity may be measured by WAXS. By way of example, the analysis can be carried
out by wide-angle X-ray scattering (WAXS), on a device of Nano-inXider® type, with the following
conditions:
− Wavelength: main Kα1 line of copper (1.54 angströms).
− Generator power: 50 kV – 0.6 mA.
25 − Observation mode: transmission
− Counting time: 10 minutes.
A spectrum of the scattered intensity as a function of the diffraction angle is thus obtained. This
spectrum makes it possible to identify the presence of crystals, when peaks are visible on the spectrum
in addition to the amorphous halo.
30 In the spectrum, it is possible to measure the area of the crystalline peaks (designated AC) and the area
of the amorphous halo (designated AH). The proportion by mass of crystalline PEKK in the PEKK is then
estimated using the ratio (AC)/(AC + AH).
It is usually advantageous for the content of crystalline PEKK to be relatively high, for example greater
than or equal to 5%, or greater than or equal to 10%, or even greater than or equal to 15%, to provide
35 parts having high mechanical performance. A further advantage of a high degree of crystallinity is
7
better mechanical properties, including those at high temperature, in terms, for example, of modulus
or of yield stress.
An alternative possibility is to calculate the degree of crystallinity from the enthalpy of fusion of the
PEKK, measured for example by DSC, by dividing it by the enthalpy of fusion of a PEKK having a degree
5 of crystallinity by mass of 100%.
The PEKK resin may comprise one or more additional polymers belonging or not to the class of PAEKs.
The content by mass of PEKK in the PEKK resin is preferably greater than or equal to 50%, preferably
greater than or equal to 60%, particularly greater than or equal to 70%, preferably greater than or
equal to 80%, and more preferably greater than or equal to 90%. In certain embodiments, the PEKK
10 resin consists essentially of one or more PEKKs.
The resin may comprise additives such as fillers and functional additives. Accordingly, the resin may
comprise reinforcing fillers, especially continuous fibers, particularly carbon fibers. It is also possible
to dispense with fillers and/or to dispense with functional additives.
The resin may particularly comprise one or more phosphates or phosphate salts, to improve the melt
15 stability of the PAEK.
According to the invention, the parts manufactured using PEKK have a low gas permeability, especially
with respect to CO2 and/or H2S. In certain applications, such as, especially, underwater petroleum
extraction, pipes are needed which are resistant and which maintain these properties under severe or
even extreme operating conditions, so as to limit the migration of the gaseous species and to limit
20 corrosion. These conditions typically include an operating temperature of more than 100°C, preferably
more than 110°C, particularly more than 120°C and very particularly more than 130°C and/or a
pressure of more than 10 bar, preferably more than 20 bar, particularly more than 30 bar and very
particularly more than 40 bar, or even more than 50 or even more than 100 bar.
The part advantageously has a CO2 permeability at 130°C of less than 10 ·10-8
, particularly 5 ·10-8
,
especially 1 ·10-8
, preferably 5 ·10-9 and particularly less than 1 ·10-9
cm3 25 of CO2 for a thickness of 1 cm
and a surface area of 1 cm2
, per second and per bar of CO2 pressure, the amount of CO2 being measured
by GC.
Moreover, the H2S permeability of the part at 130°C is preferably less than 10 ·10-8
, particularly 5 ·10-
8
, especially 1 ·10-8
, advantageously 5 ·10- 9
, more preferably less than 1 ·10-9
, particularly less than 5
·10-10 and very particularly less than 1 ·10-10 cm3 30 of H2S for a thickness of 1 cm and a surface area of
1 cm2
, per second and per bar of H2S pressure, the amount of H2S being measured by GC.
8
In one embodiment, the part may comprise two or more layers. It may in particular combine at least
one layer comprising PEKK with at least one layer of a different material, especially of PVDF, of
polyamide, of polyethylene, especially of PE-RT, or else of material acting as a binder for assembling
the respective layers to one another.
5 Pipes
In certain technical sectors, especially in petroleum extraction, materials are sought which combine
temperature resistance and resistance to chemical products with a low gas permeability, especially
with respect to the acidic compounds CO2 and H2S. The reason is that these compounds, present in
the petroleum, are acidic and give rise to corrosion of metallic components. The use of PEKK is
10 therefore especially advantageous for the manufacture of parts used in transporting liquid and/or
gaseous hydrocarbons, referred to hereinafter as petroleum effluents.
In a second aspect, therefore, the invention pertains to a pipe comprising a layer intended to be in
contact with the petroleum effluent, characterized in that said layer intended to be in contact with the
petroleum effluent comprises PEKK and has a CO2 permeability at 130°C of less than 10-8
cm3 of CO2
for a thickness of 1 cm and a surface area of 1 cm2 15 , per second and per bar of CO2 pressure, and/or an
H2S permeability at 130°C preferably of less than 10 ·10- 8
, particularly 5 ·10-8
, especially 1 ·10-8
,
advantageously 5 ·10- 9
, more preferably 1 ·10-9
, particularly 5 ·10-10 and very particularly 1 ·10-10 cm3
of H2S for a thickness of 1 cm and a surface area of 1 cm2
, per second and per bar of H2S pressure, the
amount of CO2 and H2S being measured by GC.
20 These pipes may be useful in extraction facilities, for transporting a petroleum effluent, or else for
transporting other mixtures comprising CO2 and/or H2S under severe pressure and/or temperature
conditions.
Provided in particular are pipes intended for transporting hydrocarbons, especially mixtures
comprising at least one gaseous acidic compound, especially a gas selected from CO2 and H2S.
25 These pipes may have various structures, according to their specific usage and the associated stresses.
Therefore, the pipes may for example be single-layer pipes or else may comprise two, three, four or,
indeed, an even greater number of layers. Multiple-layer pipes are enabled in particular to withstand
the mechanical or thermal stresses at exterior layers which are not in contact with the petroleum
effluents.
30 Generally, the layer intended to be in contact with the petroleum effluent constitutes the interior layer
of the pipe. Nevertheless, the invention also encompasses the case in which this layer is in indirect
9
contact with the petroleum effluents. In one embodiment of the invention, therefore, the pipe
comprises a leaktight or nonleaktight interior layer, for example a metal carcass, which is surrounded
by a layer comprising PEKK. In this case, the petroleum effluent passes at least partially through the
nonleaktight interior layer, and therefore enters indirectly into contact with the layer comprising PEKK.
5 In one embodiment, the carcass is surrounded by a membrane comprising PEKK. In another
embodiment, the membrane is composed of a plurality of layers, and comprises at least one additional
layer to a layer comprising PEKK, made of a different polymer, such as for example of PVDF, of
polyamide, of polyethylene, especially of PE-RT, or else of material acting as a binder for assembling
the respective layers to one another.
10 Said multilayer membrane may for example comprise a layer comprising PEKK and a layer based on
PVDF. PVDF is a material which is valued especially for its flexibility and its chemical resistance and
thermal resistance (up to 280°C), although its gas permeability means that it offers little protection
from corrosion. Advantageously, the PVDF layer may be disposed in contact with the carcass, and the
layer comprising PEKK may be disposed on the exterior of the carcass. Other layers may be disposed
15 between these two layers forming the membrane.
The layers making up the membrane may be bonded to each other for example by mechanical
fastening, in other words by engagement of roughnesses present on their respective surfaces.
Hence the pipe may be of the type referred to as “rough bore”. In this type of pipe, the layer intended
to be in contact with the petroleum effluent may constitute a sealing sheath surrounding a metal
20 carcass. The carcass is formed by a metal strip wound helicoidally, which serves to enhance the
resistance of the pipe with respect to external pressure. Pipes of this kind may further comprise a
vault, made for example of fastened metal wires, to ensure resistance to the internal pressure within
the pipe, and tensile armor plies composed of metal wires wound helically at a specified angle, allowing
the pipe in particular to possess better tensile strength.
25 The pipe may alternatively be of the type referred to as “smooth bore”. This type of pipe has no metal
carcass. The petroleum effluent may then be in direct contact with the layer comprising PEKK. In both
types of pipe, the layer intended to be in contact with the petroleum effluent may or may not contain
reinforcing fibers. In any case, as well as the low gas permeability, especially with respect to CO2 and
H2S, an advantage of the PEKK is an excellent abrasion resistance, especially if it is formulated with
30 other agents, particularly reinforcing fibers, especially carbon fibers. Accordingly, an interior layer of
PEKK provides effective resistance to abrasion caused by solid particles, which are often present in the
effluents.
10
The pipes according to the invention typically further comprise – as explained earlier on for the rough
bore pipes – at least one mechanical reinforcement layer, forming armature, in order to resist the
exterior and interior pressure. There are, however, also flexible pipes composed exclusively of
thermoplastic polymers, such as those sold by Airborne. In these pipes, the reinforcement layers and
5 optional metallic armatures are replaced by reinforcements composed of thermoplastic composites.
The at least one mechanical reinforcement layer may be made of metal. In this case, it may be a metal
tube or else, for greater flexibility, may be a winding of metal wires or of metal fabric.
The mechanical reinforcement layer may alternatively be made of composite material. The composite
material is preferably composed of a polymer reinforced with reinforcing fillers. The polymer is
10 preferably a high-performance thermoplastic polymer, for example a polymer from the class of
polyamides, polyethylene, especially PE-RT, PVDF, PAEKs, especially selected from PEKK and/or PEEK.
In the composite, the polymer is reinforced with reinforcing fillers, especially fibers, especially carbon
fibers or aramid fibers or glass fibers. A mechanical reinforcement layer of this kind comprising PEKK
may, furthermore, replace both the metal carcass and the vault, where appropriate, to give a flexible,
15 smooth bore pipe.
In one embodiment, the pipe further comprises a flexible exterior armature. In another embodiment,
the pipe further comprises a rigid exterior armature.
The layer intended to be in contact with the petroleum effluent may especially be present in the form
of a tube, a sheath or a pressure layer or else an interior coating. The interior coating may particularly
20 be a liner intended for insertion into pipes, especially metal pipes, in order to renovate them.
In a third aspect, the invention provides for a method for manufacturing pipes as described above.
Particularly, when the layer intended to be in contact with the petroleum effluent takes the form of a
tube or sheath, it may be obtained, for example, by extrusion or coextrusion. When the layer is in the
form of an interior coating, it may be obtained, for example, by powder coating.
25 A part composed of a plurality of layers, as described above, may also be obtained by sheathing
extrusion or else by winding of strips and subsequent welding. In this case, the layer intended to be in
contact with the petroleum effluent is also designated as pressure layer or sheath.
More specifically, when the pipe to be manufactured or renovated is a rigid pipe, the method of the
invention comprises the steps of:
30 (a) preparing a tube comprising PEKK of appropriate size; and
(b) inserting said tube inside a metal tube to form a liner.
11
In one embodiment, the tube comprising PEKK may further comprise one or more additional layers,
for example of PVDF, of polyamide, of PE-RT or else of material acting as a binder for assembling the
respective layers to one another.
When the pipe to be manufactured is a flexible rough bore pipe, the method of the invention comprises
5 the steps of:
(a) providing a metal carcass;
(b) extruding around said metal carcass at least one layer of a composition comprising PEKK, by
crosshead extrusion; and
(c) installing a vault around the resulting structure;
10 (d) installing one or more tensile armor plies; and
(e) extruding an external polymer sheath around the resulting assembly.
It is possible before step (b) to extrude one or more other layers on the metal carcass, especially a
layer based on PVDF, on polyamide, on polyethylene, especially on PE-RT, or else on material acting as
a binder for assembling the respective layers to one another.
15 When the pipe to be manufactured is a flexible smooth bore pipe, the method of the invention
comprises the steps of:
a) extruding at least one layer of a composition comprising PEKK, by crosshead extrusion; and
b) installing a vault around the resulting structure;
c) installing one or more tensile armor plies; and
20 d) extruding an external polymer sheath around the resulting assembly.
It is possible during step (a) to extrude one or more other layers, especially based on PVDF, on
polyamide, on polyethylene, especially on PE-RT, or else on material acting as a binder for assembling
the respective layers to one another.
The invention will be described in more detail in the nonlimiting examples below.
25
[Examples]
Example 1 PEKK permeability
12
The permeability of the PEKK to gases, and especially to CO2 and H2S, plays a particularly large role in
petroleum applications, and accordingly a plaque of PEKK (KEPSTAN® 7002, sold by ARKEMA France,
ratio T:I = 70: 30) with dimensions of 100 mm x 100 mm x 2 mm was prepared by injection molding. A
plaque of KEPSTAN® 8002 PEKK (sold by ARKEMA France, ratio T:I = 80: 20) with dimensions of
5 100 mm x 100 mm x 2 mm was also prepared, by strip extrusion followed by machining to the desired
dimensions.
The crystallinity of the PEKK in the injection-molded plaque was characterized by measuring the
enthalpy of fusion by differential scanning calorimetry (DSC). This was also carried out for the extruded
plaque. From this it is possible to obtain, by comparison with the theoretical enthalpy of 100%
10 crystallization, the degree of crystallinity of the PEKK in the injection-molded plaque and the extruded
plaque.
The CO2 permeability of the injection-molded plaque under severe conditions was then evaluated by
placing disks machined from the plaque, with a diameter of 90 mm, into a heated permeation cell
(T = 130°C). The same test was carried out for the extruded plaque, on disks 70 mm in diameter.
15 The permeation cell is supplied with a gas (presently CO2) which enters at a specified pressure and
comes into contact with one face of the plaque of the test material. The entry pressure of the gas
(presently 40 bar) can be controlled by a compressor system. On the other side of the plaque, a carrier
gas (presently nitrogen) carries the gas which is permeated through the plaque to a detector (presently
a gas chromatograph (GC)), where it is quantified. The measured amount of permeated gas is used to
20 calculate the permeability, taking account of the surface area of the plaque, the partial pressure
difference in permeating gas, the measuring time, and the thickness of the plaque.
The permeability is calculated in steady state, following the transitory state, which reflects the time
required by the permeating gas molecules to diffuse through the plaque. The steady state is
considered to have been reached when the measured flow of CO2 does not increase by more than 1%
25 between two samplings at an interval of 24 h. As an example, in the case of the plaques studied,
10 days were needed in total to carry out the permeability measurement.
The results are collated in table 1 below.
The H2S permeability of the PEKK was evaluated as described above for CO2, but using a Kepstan® 7002
plaque with a thickness of 0.5 mm (machined in the form of a disk 70 mm in diameter), instead of a
30 2 mm plaque, and under a pressure of 15 bar.
The results are collated in table 2 below.
13
Furthermore, amorphous films with a thickness of 50 µm were prepared by extrusion calendering from
KEPSTAN® 7002 PEKK (sold by ARKEMA France, ratio T:I = 70: 30. These films were crystallized by heat
treatment in an oven at 210°C for 40 minutes. Disks 50 cm2
in area were removed from these two films
(amorphous and crystalline) and used for measuring the permeability to CO2, O2, N2 and CH4 gases.
5 The measurements were carried out in a permeation cell as explained above, but at ambient
temperature and atmospheric pressure.
The results are collated in table 3 below.
Example 2 (comparative) PEEK permeability
10 To compare the properties of PEKK with those of PEEK, example 1 was repeated, this time using an
injection-molded plaque of PEEK with a thickness of 2 mm (450G, sold by VICTREX).
The H2S permeability of was evaluated as described above for CO2, but using an injection-molded
plaque of PEEK (450G, sold by VICTREX) with a thickness of 0.5 mm (machined subsequently in the
form of 70 mm disks), under a pressure of 15 bar.
15 The results are collated in tables 1 and 2 below.
Furthermore, disks 70 mm in diameter were removed from 50 µm films of 450 G PEEK implemented
by extrusion calendering (amorphous extrudates and also extrudates crystallized at 205°C for times of
greater than 1 h), and were used for measuring the permeability to CO2, O2, N2 and CH4 gases. The
measurements were carried out in a permeation cell as explained above, but at ambient temperature
20 and atmospheric pressure.
The results are collated in table 3 below.
The results show that the CO2 permeability of PEKK under severe temperature and pressure conditions
is markedly superior to that of PEEK. This observation is all the more surprising because PEEK has a
higher degree of crystallinity than PEKK. The reason is that the enthalpy of fusion of the PEEK plaque
25 is greater than that of the PEKK plaque.
14
Table 1: CO2 permeability
Polymer Enthalpy
of fusion
[J/g]
Temperat
ure [°C]
Pressure
[bar]
Permeability
[cm3
/cm·s·bar]
Diffusion
coefficient
[cm2
/s]
PEKK
KEPSTAN® 7002
32 130 40 6.1 ·10-9 3.6 ·10-8
PEKK
KEPSTAN® 8002
39 130 40 7.5 ·10-9 4.7 ·10-8
PEEK
450G
46 130 40 15 ·10-9 9.5 ·10-8
With regard to the permeability for H2S, a clear superiority is found in the same way for the PEKK by
5 comparison with the PEEK, since the permeability of the PEKK is observed to be 2.8 times less than the
permeability of the PEEK.
Table 2: H2S permeability
Polymer Temperature [°C] Pressure [bar] Permeability
[cm3
/cm·s·bar]
Diffusion
coefficient
[cm2
/s]
PEKK* 130 15 6.5 ·10-9 8.0 ·10-9
PEEK* 130 15 1.8 ·10-8 2.0 ·10-8
* measured on a plaque 0.5 mm thick
10
It is also found that the films made of crystallized PEKK are markedly better in barrier properties toward
all of the test gases, as compared with the crystallized PEEK films. Similarly, the amorphous PEKK films
are better in barrier properties as compared with the amorphous PEEK films.
Tests also reveal that PEKK, even in amorphous form, exhibits better barrier behavior toward the gases
15 CO2, O2, N2 and CH4 than does crystallized PEEK.
15
Table 3: Permeability of PEKK and PEEK films
Polymer Crystallized
/amorphou
s
Permeability [cm3
·50 µm/m2
·24 h·atm]
CO2 O2 N2 CH4
PEKK
KEPSTAN® 7002
crystallized 140 80 10 7
PEEK
450G
crystallized 840 180 30 20
PEKK
KEPSTAN® 7002
amorphous 645 170 ND 12
PEEK
450G
amorphous 1790 345 ND 40
These results show that at the same thickness, the use of PEKK in pipes for transporting petroleum
effluents allows better protection of metal components from corrosion brought about by the migration
5 of gases such as CO2 and H2S. Moreover, in order to reach a target permeability, it is possible by using
PEKK to reduce the thickness of the sheaths and so to reduce the weight of the pipe.
16
CLAIMS
1. The use of PEKK for lowering the CO2 and H2S permeability of a part intended to be in contact
5 with a petroleum effluent.
2. The use as claimed in claim 1, wherein the PEKK has a degree of crystallinity by mass of greater
than 5%.
10 3. The use as claimed in claim 1 or 2, wherein the PEKK has a ratio T:I of 35% to 100%, preferably
of 55% to 85% and more specifically of 60% to 80%.
4. The use as claimed in one of the preceding claims, wherein the CO2 permeability at 130°C is
less than 10 · 10-9
cm3 of CO2 for a thickness of 1 cm and a surface area of 1 cm2
, per second
and per bar of CO2 pressure, and/or an H2S permeability at 130°C is less than 10-8
cm3 15 for a
thickness of 1 cm and a surface area of 1 cm2
, per second and per bar of H2S pressure, the
amount of CO2 and H2S being measured by GC, respectively.
5. The use as claimed in one of the preceding claims, wherein the part is selected from a tube, a
20 sheath, a pressure layer and an interior coating, especially intended for transporting a
petroleum effluent.
6. A pipe for transporting a petroleum effluent, comprising a layer intended to be in contact with
the petroleum effluent, characterized in that said layer intended to be in contact with the
petroleum effluent comprises PEKK and has a CO2 permeability at 130°C of less than 10 ·10-9 25
cm3 of CO2 for a thickness of 1 cm and a surface area of 1 cm2
, per second and per bar of CO2
pressure, and/or an H2S permeability at 130°C of less than 10-8
cm3 for a thickness of 1 cm and
a surface area of 1 cm2
, per second and per bar of H2S pressure, the amount of CO2 and H2S
being measured by GC, respectively.
30
7. The pipe as claimed in claim 6, wherein said layer intended to be in contact with the petroleum
effluent is a sealing sheath surrounding a metal carcass.
17
8. The pipe as claimed in claims 6 or 7, wherein said layer intended to be in contact with the
petroleum effluent is devoid of reinforcing fibers.
9. The pipe as claimed in one of claims 6 to 8, wherein said layer intended to be in contact with
5 the petroleum effluent is surrounded by at least one mechanical reinforcement layer.
10. The pipe as claimed in claim 9, wherein the at least one mechanical reinforcement layer is
made of metal.
10 11. The pipe as claimed in claim 9, wherein the at least one mechanical reinforcement layer is
made of composite material.
12. The pipe as claimed in claim 11, wherein the composite material comprises PEKK and carbon
fibers.
15
13. The pipe as claimed in one of claims 6 to 12, further comprising a rigid metal armature.
14. The pipe as claimed in one of claims 6 to 13, further comprising a flexible metal armature.
20 15. A method for manufacturing or renovating a pipe as claimed in claim 13, comprising the steps
of:
a. preparing a tube comprising PEKK of appropriate size; and
b. inserting said tube inside a metal tube to form a liner.
25 16. A method for manufacturing a pipe as claimed in claim 14, comprising the steps of:
a. providing a metal carcass;
b. extruding around said metal carcass at least one layer of a composition comprising
PEKK, by crosshead extrusion; and
c. installing a vault around the resulting structure;
30 d. installing one or more tensile armor plies; and
e. extruding an external polymer sheath around the resulting assembly.
17. A method for manufacturing a pipe as claimed in claim 14, the method of the invention
comprises the steps of:
18
a. extruding at least one layer of a composition comprising PEKK by crosshead extrusion;
and
b. installing a vault around the resulting structure;
c. installing one or more tensile armor plies; and
5 d. extruding an external polymer sheath around the resulting assembly.