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1 Copyright 2008 by ASME
Proceedings of the 3rd International Offshore Pipeline Forum
IOPF 2008
October 29-30, 2008, Houston, Texas, USA
IOPF2008-922
DEEPWATER PIPE-IN-PIPE (PIP) QUALIFICATION TESTING FOR 350F
SERVICE
Paul Jukes, PhD CEng. J P Kenny, Inc.
Houston, Texas, USA.
Francois Delille J P Kenny, Inc.
Houston, Texas, USA.
Gary Harrison BP America, Inc.
Houston, Texas, USA.
ABSTRACT Development of future deep water oil reservoirs in the
Gulf of
Mexico (GoM), where the flowline product temperatures are
approaching 350F (177C), water depths approaching 10,000ft (3050m),
and tie-backs in the order of 40 miles (64.4km), requires the
appropriate material selection for key pipe-in-pipe (PIP)
components. These extreme flowline temperatures, water depths and
distances, restrict the choices in PIP component materials, and
present real challenges to the design of centralizers, waterstops
seals, thermal insulation and loadshares. These challenging
conditions warrant qualification testing to be undertaken on PIP
components to ensure structural integrity and long-term thermal and
structural performance.
This paper describes a qualification testing programme for the
testing of PIP components for 350F (177C) service, and includes the
testing of centralizers, waterstop seals, thermal insulation and
loadshares. The following qualification tests are proposed: (i)
Centralizers tests: Slippage tests, creep tests, abrasion tests,
bolt relaxation and aging tests are undertaken. Structural
integrity testing under installation loads and in-service
conditions is undertaken to ensure no long-term creep or
degradation of the material due to temperature. (ii) Waterstop seal
tests: Load test, hydrostatic pressure test, elevated temperature
tests and material aging tests are undertaken. The material
selection for the waterstop seals are undertaken to examine the
integrity of the seal at temperature. (iii) Thermal insulations
tests: A number of tests undertaken on aerogel materials to
evaluate the effect of prolonged exposure to temperature on thermal
conductivity and mechanical integrity. Tests include checking
thermal conductivity, compressive strain recovery, long-term
exposure to high-temperature and aging effects on thermal
conductivity and mechanical integrity. (iv) Load-share tests: A
mechanical radial clamp load-share is tested to ensure performance
under sustained installation loads.
Each test planned and performed, testing rationale and results
are presented within the paper. Conclusions are drawn on the
suitability of these qualification tests for high-temperature
applications. The successful qualification testing of the
components extends the
boundaries of what is possible with PIP designs and opens up the
possibility of XHPHT field developments in the GOM.
KEY WORDS Aerogel, Annulus, Centralizer, Deep Water, Extra
High-Pressure
High-Temperature (XHPHT), Flowlines, Load-share, Nanogel,
Overall Heat Transfer Coefficient (OHTC), Pipe-in-Pipe (PIP),
Pipelines, Spacers, Thermal Insulation, Waterstop.
INTRODUCTION Pipe-in-pipe (PIP) is increasingly being used for
the transportation of hydrocarbons. Pipe-in-pipe flowline systems
are frequently used in the GoM for subsea tie-backs where there is
a requirement for high thermal performance. A PIP system consists
of the inner pipe carrying the fluid encased within a larger
diameter outer pipe. Figure 1 shows a typical PIP system
configuration.
Fig. 1: A typical PipeinPipe configuration
The outer pipe seals the annulus between the two pipes and the
annulus can be filled with a wide range of thermal insulating
materials incompatible with water exposure and hydrostatic
pressure. A PIP flowline has the advantage over traditional wet
insulated pipelines of
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2 Copyright 2008 by ASME
allowing a lower overall heat-transfer coefficient (OHTC) or U
value for the system. PIP is a common method of achieving low U
values of 0.176 BTU/hr.ft2.F (1.0 W/m2K) or less, and has been used
on a number of projects in both the North Sea and in the GoM. For
longer subsea tie-backs, a lower OHTC allows the production
temperatures of the internal contents to remain above the wax
allowable temperature (WAT) and hydrate formation temperature. Low
OHTC facilitates longer cool-down times during a shut-down, to
prevent hydrate conditions. A shut-down time of at least 8 to 10
hours is considered to be the minimum requirement, which can be a
large challenge for long tie-back distances.
Today, it is not uncommon for PIP designs to be considered in
water depths up to 10,000ft (3,050 meters) and flowline
temperatures up to 350F (177C) (1).
This paper is part of significant analysis works related to
extra high-pressure and high-temperature PIP designs sponsored by a
major operator (2, 3). The study targets the Gulf of Mexico (GoM),
where subsea production wells may be drilled at water depths (WD)
to 10,000 feet (3,050m), with a flowing product temperature to 350F
(177C), and system shut-in pressure of 65ksi (64.8MPa). These
temperatures can present real challenges in the design, and failure
modes have to be addressed (4). Also high axial loads can lead to
lateral buckling, and mitigation methods are necessary, such as
thermal expansion management with the use of sleepers, which is
integrated into the design philosophy (5, 6).
As a result of the relatively high temperatures, it is important
to determine the effect of these temperatures on the components
that make up the PIP system. A PIP system consists of a number of
additional components, such as centralizers, waterstop seals and
loadshares. It is important to gain an understanding of the effects
of temperature on the material strength and durability, and to
ensure that there is no long-term degradation of the structural
performance. These issues are addressed within this paper.
PIP COMPONENTS Centralizers, waterstops, thermal insulation and
loadshares
make up a PIP system. The function of each component is briefly
described, and issues associated with high temperatures are
addressed.
Centralizers
Depending on the thermal insulation type, centralizers are
placed between the inner and outer pipes at regular intervals. The
function of the centralizers in a PIP system are to support the
inner pipe centralized within the outer pipe, prevent possible
damage to the PIP thermal insulation between the inner and outer
pipes, and to transfer loads between the inner and outer pipes.
The distance between the spacers will depend on the loading to
which the section of the PIP will be subjected. This spacing may be
two meters for reeled pipelines, and four to six meters for S-lay
and J-lay installation methods. The presence of centralizers
provides heat loss paths and can present cold spots, reducing the
overall thermal performance of the PIP system. For high-temperature
flowlines, the temperature can reduce the structural integrity of
the centralizers, and lead to deformations that could crush the
thermal insulation.
Ability to undertake the functions of the centralizers
successfully at high temperatures requires the spacer material to
tolerate high temperatures without excessive deflections and
maintain structural integrity. Compression loads on centralizers
are a key aspect in their design.
Traditional lower temperature service centralizers are made of a
nylon material that exhibits good resistance to abrasive wear.
Other materials, such as injection-molded thermoplastic
polypropylene, have a temperature limitation of about 266F
(130C).
The selection of an appropriate material for high-temperature
applications is difficult. Tests during this project on a proposed
centralizer material resulted in cracks in the centralizer due to
the material being too brittle. Other materials are presently being
sourced. Waterstops The fundamental driver for waterstops is to
avoid flooding the entire annulus of a PIP due to a single defect
in the outer pipe of the system. To avoid this unlikely result,
most designers have opted to include waterstops capable of
preventing flooding of the entire annulus by isolating the breach
in the outer pipe between adjacent waterstops. The waterstops must
reliably seal the annulus against the maximum water pressure
expected on the seabed.
The spacing of the waterstops can be arbitrary, but there are
some practical considerations to provide guidance. The first
constraint is the maximum tolerable temperature loss from a flooded
section or sections. It may be acceptable to tolerate one or two
flooded segments with a predicted temperature loss during steady
state production of perhaps 5-20F. Burial of the pipeline will
mitigate temperature loss over the flooded section, and may
constrain waterstop spacing to the amount of spare pipeline repair
materials available. The acceptable temperature loss is determined
by a flow assurance specialist.
Waterstop spacing is also constrained by the amount of spare
materials (pipe, insulation, centralizers, etc) available for a
single repair. Assuming an accidental flooding of one segment
during construction, there should be enough spare material
available for repairs. It may be unacceptable to lose any
reasonable length of insulation, and in that case the spacing would
be solely governed by material constraint. The above waterstop
spacing constraints should be considered and evaluated in a project
during the final design work to determine final spacing. A spacing
of 3,000 feet (914 m) is a representative value.
Waterstops must be able to sustain the temperature effects from
the inner pipe for the life of the project. There is a waterstop
seal on the market that fits between the pipes and is activated by
the tightening of screws. High-temperature waterstop seals are
presently being developed and tested. The material of the seals is
a high-performance plastic and has been demonstrated to tolerance
temperatures to 350F (177C), although the long-term service life
could not be guaranteed. Thermal Insulation
The thermal insulation placed in the annulus of the PIP system
is a key component, and allows a low OHTC if the thermal
performance (k-factor) is good. There are various types of thermal
insulation on the market, such as polyurethane, rock-wool,
fiberglass, and aerogel.
The short-term loading during installation and the long-term
loading due to startup / shut down loading are important factors to
consider when choosing thermal insulation for the life of the
project. Also, no long-term thermal degradation of the insulation
can occur during the life of the project.
It is important that the thermal insulation demonstrate
acceptable performance for high temperatures, without degradation
of the thermal or structural performance due to aging. The k-factor
for
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3 Copyright 2008 by ASME
each proposed material should be checked, and aging of the
materials at elevated temperatures, should be investigated to
ensure performance and structural integrity.
Aerogel is a nanoporous solid, originally developed during the
1930s. This insulation is suitable for PIP applications, and is
classed as a high-tech material with excellent thermal properties
compared to PU foam.
Aerogel is a high-performance thermal insulation used in a
variety of forms and conditions, and is one of the worlds best
insulating solids. It has many advantages: it is lightweight, water
repellant, highly porous, has a unique microstructure, high surface
area, translucent or IR-opacified, and is available in a number of
grades. It achieves high levels of thermal insulation due to the
entrapped air in its micropore structure. It has extremely low
thermal conductivity, 0.008-0.013 BTU/hr.ft.F (14 - 22 mW/m.K) and
is stable from -321 to 662F (-196 to 350C). It is water resistant
and can be dried if there is water ingress.
Aerogel allows the design of pipelines with overall system 'U'
values significantly less than 0.176 BTU/hr.ft2.F (1.0 W/m2K)
without compromising the overall external dimensions of the PIP
system. Loadshares
Load shares are necessary to redistribute gravity loads between
the inner and outer pipes of an un-bonded PIP. Without load shares,
the accumulated in-situ compression load in the inner pipe can
reach 30% to 50% of yield strength (4). Upon startup, the added
thermal expansion compression can result in failure (axial
collapse-rupture) of the inner pipe due to combined axial
compression and internal pressure loads. Load shares combined with
pre-tensioning of the inner pipe prior to establishing the load
share coupling redistributes the PIP gravity loads to realize a
much lower in situ axial compression load in the inner pipe.
To be effective the pre-tension must be performed before
excessive friction between the inner and outer pipes prevent the
desired distribution of the pre-tension load. Practically, this
implies that the load share spacing should be something less than
the water depth, although it might approach or equal the water
depth. Detailed FEA is performed to validate the load
re-distribution achieved for a selected spacing by load shares and
pre-tensioning (7, 8).
Mechanical loadshares seem to be the preferred method of choice.
This method employs a bi-radial clamp which mechanically locks the
inner and outer pipes together. Although these clamps are
relatively expensive, it is presently the only viable method. As
these components are steel, there are no long-term degradation
issues. Finite Element Analysis (FEA) should be undertaken to avoid
a global collapse-rupture in a PIP flowline. TESTING OF PIP
COMPONENTS
J P Kenny recently undertook a series of tests for a major
operator in the Gulf of Mexico region. The objectives of the tests
were to qualify PIP components for extra high-temperature and extra
high-pressure conditions. In the following section, the different
components tested are described, and results from the tests are
presented.
The tests were undertaken for the base case of an 8 inner pipe,
12 outer pipe, with a maximum operating temperature of 350F
(177C).
Centralizer Tests Centralizers are used to avoid the loading
that could crush the
thermal insulation. Installation loads can be particularly large
during reeling, and the centralizers are tested in compression for
the maximum loads seen during the reeling process.
Operational conditions need to be considered, and degradation of
the material due to temperature, long-term creep, and structural
integrity are all issues related to the performance of the
centralizer. These high temperatures severely restrict the material
selection available for pipe-in-pipe centralizers. Based on the
temperature, a modified Polyphenylenesulphide (PPS) material was
selected for testing, based on its characteristics of having high
thermal mechanical strength, high hardness and rigidity, high creep
strength and excellent wear characteristics.
The type of tests undertaken when testing centralizers are as
follows:
Slippage Tests; Abrasion Test; Creep Tests; Bolt Relaxation
Test; Aging Test.
The test program that J P Kenny is presently undertaking is
still ongoing, however some of the preliminary findings are
presented (9). Slippage Tests. The aim of the slippage test is to
ensure the centralizer does not slip on the flowline under
installation and in-service loads. A typical test set-up for the
slippage test is shown in Figure 2.
Fig. 2: Centralizer slippage test setup Both sets of
centralizers tested suffered brittle failures prior to reaching the
weld bead, which meant that the test was abandoned and the
centralizer could not pass over the weld bead. Figure 3 shows a
failed centralizer from the slippage test.
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4 Copyright 2008 by ASME
Fig. 3: A failed specimen from slippage test
Abrasion Tests. The abrasion test consists of passing a
centralizer over a number of weld roots. A winch is used to pull
the flowline assembly along the length of an 80 ft (24m) trough. A
total of 17 runs were intended, equating to 119 weld beads passed.
However, after five complete passes (35 welds), the centralizer
suffered brittle failure.
As a result of the brittle failures, for both the slippage and
abrasion tests, the other tests were abandoned, and a search is
still continuing for an appropriate material suitable to 350F
(177C) with acceptable ductility.
Conclusions following the tests are that there is no single
thermoplastic capable of meeting the stringent demands covering
both insertion case and service conditions for a centralizer, and
the solution relies on a substrate, possibly such as a pultrusion
being overlaid with a cast polyamide material. Such configurations
could offer the temperature requirement local to the inner
pipeline, and the necessary creep and abrasion resistance to cater
for insertion. Waterstop Seal Tests
Testing of the waterstop seals is necessary to ensure the seal
can undertake the hydrostatic loads in the event of flooding. Due
to the high-temperature of the inner pipe, sealing tests at
temperature are also undertaken to ensure that material degradation
of the seal does not impact the integrity of the seal. A test is
performed to examine the integrity of the seal at temperatures of
350F (177C) and a water-depth pressure equivalent to 4500ft. Figure
4 shows a typical arrangement of the waterstop seal and clamp
arrangement to be used in a PIP. The following tests are undertaken
for the testing of PIP waterstop seals (10):
Load Tests Hydrostatic Pressure Test Elevated Temperature Test
Material Aging Test
Load Tests. Assuming a breach of the outer pipe, the hydrostatic
pressure will create an axial load on the waterstop seal and clamp.
A force based on water-depth pressure of 4500ft (1372m) was used.
The test load was 90.2Te (885kN), and this included a load factor
of 1.1. The load was applied for 5 minutes, and no slippage
occurred. The test was deemed successful.
Fig. 4: Field proven waterstop seal
Pressure Tests. A further requirement of the seal is to provide
leak-free sealing of the large pressures that occur in the PIP
annulus if the outer pipe is breached. The purpose of this test is
to verify the pressure and sealing capacity of the waterstop seal.
The seal was enclosed in a special pressure test rig consisting of
bolted end flanges. The seal was tested to 375bar (37.5MPa), which
includes a safety factor of 1.25. A pressure based on water-depth
of 10,000ft (3050m) was applied. The seal was examined after the
test, and no permanent seal damage was observed. Below is a picture
of the pressure test apparatus and setup.
Fig. 5: Waterstop seal pressure test in progress
Elevated Temperature Test. In the event that an outer pipe
breach occurs, the water in the annulus will be heated due to the
temperature of the inner pipe. Hence it was important to verify the
temperature resistance capacity of the waterstop seal. The seal was
tested at 383F (195C) with a test factor of 1.1. The applied
pressure was 375 bar (37.5MPa), and represents 10,000ft (3050m)
water depth with a test factor of 1.25. A range of different seal
materials was investigated.
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5 Copyright 2008 by ASME
The final seal type used a hydrogenated nitrile butadiene rubber
(HNBR) lip, and a thermoplastic body, as shown in Figure 6.
Fig. 6: A typical HNBR / plastic seal (10)
Hydrogenated nitrile butadiene rubber (HNBR) has an
intriguing combination of properties. Like other elastomers, the
HNBR material has high tensile strength, low permanent set, very
good abrasion resistance and high elasticity. But in HNBR, these
are complemented by good stability from thermal ageing and better
properties at low temperatures compared to other heat- and
oil-resistant elastomers. This combination of properties makes it
particularly suitable for a high-temperature waterstop seal.
Fig. 7: Pressure / temperature versus time
Temperature and pressure was held at 375 bar (37.5MPa) and
383F (195C) respectively for 24 hours. Upon inspection of the
seal following removal from the rig, it was clear that the
thermoplastic body had tolerated the pressure and temperature
combination loading. There were no leaks past the seal during the
test. The sealing lip showed no visible signs of damage or
deterioration.
Material Aging Tests. The purpose of these tests was to
investigate the integrity of the seal due to thermal aging. The
method of testing is based on the Arrhenius principle, which
artificially ages the material by applying a temperature greater
than its service condition to accelerate the deterioration. A
temperature of 554F (290C) for 6 days, which is equivalent to 30
years service at 350F (177C), was applied.
As the inner pipe will be operating at 350F (177C) continuous
service there will be a considerable temperature drop to the outer
pipe wall at seabed ambient temperature (typically 37-41F (3-5C))
in the actual service condition. It was assumed for test purposes
that the average temperature across the whole seal is approximately
194F (90C) during its working life. Based on this, age testing was
carried out at and based against the actual 194F (90C) average. It
was decided that this would give a more accurate conclusion
regarding the actual material service life.
Tests undertaken at 554F (290C), and using the Arrhenius
principle, showed that the material would still be serviceable at
350F (177C) for up to 30 years. For the test at 350F (177C) the
material was unaffected over a 42 day test period. Thermal
Insulation Testing
The primary objectives of these tests are to evaluate the effect
of exposure to extreme operating temperatures of 350F (177C) and
compressive stresses (due to pipe laying and lateral buckles). The
compressive stresses are applied for prolonged periods of time to
determine the insulation performance and mechanical integrity of
the aerogel material. Two different types of material tests were
undertaken to examine this effect.
The first test evaluates the thermal conductivity of the
material after aging at the maximum operating temperature, and the
second evaluates the mechanical integrity of the material after
thermal aging under installed conditions by unidirectional
compression loading. The compression loading deformation is limited
by centralizers. Worst case deformation is likely to occur in the
pipe straightener during reel-lay; however this is prior to aging.
Subsequent in-situ deformations are probably less, but the material
will be thermally aged.
The testing of the thermal insulation has a number of specific
objectives, as follows:
To evaluate the thermal insulation of the XHPHT PIP system;
Obtain thermal conductivity at different levels of compression
and different mean temperatures;
Ensure no long-term degradation of the thermal properties of the
aerogel insulation, such as thermal conductivity;
Mechanical testing of the material to understand how it behaves
under compression;
Ensure that compressive loads are not detrimental to the thermal
performance;
Assess thermal aging effects on structural integrity of the
aerogel.
The following tests were successfully undertaken on aerogel
materials:
Thermal conductivity; Compressive strain recovery after static
loading - resilience; Hydrophobic threshold;
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6 Copyright 2008 by ASME
Long-term exposure of high-temperature on shrinkage; Aging
effect of high-temperature on thermal conductivity
and mechanical integrity. Nanogel Aerogel Thermal Insulation
Nanogel aerogel from Cabot Corporation is a particularly
thermally efficient insulation material. It is an extremely
lightweight and ultra-high performance insulation material that can
be used in PIP systems as a substitute for typical insulation
materials, such as PUF. Nanogel aerogel is produced by drying a gel
to produce a solid material that consists of a lattice structure of
the gel material with nanometer-sized pores dispersed throughout
the material. The size of the pores (~20-40 nm) is smaller than the
mean free path of air (~60-100 nm) and consequently gas phase
conduction is greatly reduced as a heat transfer mechanism. The
thermal conductivity ranges from 0.008-0.013 BTU/hr.ft.F (14 - 22
mW/m.K).
The important salient features of aerogel are as follows: Pure
aerogel in granular form Worlds best insulating solid Lightweight
Hydrophobic (water repellant) Highly porous Unique microstructure
(fractal) Elastically compressible (springy)
Fig. 8: Lattice arrangement of Nanogel Aerogel
The lattice arrangement of Nanogel aerogel is shown in Figure
8.
The use of opacifiers, such as carbon black or titanium dioxide,
are introduced into the aerogel to minimize radiation effects. A
number of
thermal conductivity and mechanical property tests were
undertaken (11) as described in the following sections. Thermal
Conductivity Tests
The first step of the test method is aging of the opacified
aerogel. The most extreme operational thermal gradient that the
aerogel will experience in the XHPHT pipe-in-pipe system is 310F
(154C), based on 350F (177C) internal contents temperature, 40F
(4C) seawater on the outside of the carrier. The samples of aerogel
were conservatively aged at 350F (177C) in glass containers, under
0% compression, in an oven for 0, 1, 2 and 4 weeks to evaluate
effects of thermal aging.
The first set of thermal conductivity measurements was
undertaken at 0% material compression. Tests were undertaken in
accordance with ASTM C518. Conductivity measurements were made over
a range of mean sample temperatures of 14F, 55F, 100F, 145F, and
176F (-10C, 13C, 38C, 63C, and 80C) with the hot and cold plate
boundary temperatures.
The maximum mean testing temperature equipment was limited to
176F (80C) whereas the mean temperature of the XHPHT system is 195F
(91C) (assuming seawater at 40F (4C) and product at 350F (177C)).
This compromise is considered to have negligible impact on the
results.
Thermal conductivity tests were also undertaken at 15% and 30%
compression, to represent the expected levels of installed
compression.
The results did show a downward trend for the tests aged for
four weeks, however the trend was not statistically significant.
Figure 9 and 10 show typical set of results for thermal
conductivity for 0% and 30% compression respectively. The graphs
also show the effect of age and temperature on the thermal
conductivity.
Fig. 9: Thermal Conductivity (mW/mK) for
0% Compression
The results of the thermal conductivity testing demonstrated; A
very tight standard deviation in the test results. Thermal
conductivity increases with temperature Thermal conductivity was
not affected by aging. Effect of compression on thermal
conductivity
demonstrated some improvement in k-factor due to pore-size
reduction
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7 Copyright 2008 by ASME
Fig. 10: Thermal Conductivity (mW/mK) for
30% Compression Mechanical Integrity Tests
Ageing tests were undertaken at 0%, 15% and 30% compression.
Aging effects were investigated in material sample holder with
different compression levels. The material sample holder consisted
of polytetrafluoroethylene (PTFE) cylinder, 1.52 inner diameter,
and two cylindrical, aluminum plates locked in place with machine
screws. By varying the quantities of aerogel material it was
possible to produce samples with different compression levels, as
shown in Figure 11.
Fig. 11: Sample holders for mechanical integrity testing
The aging system consisted of placing the mechanical test
specimens in the cold/hot plate system. Thermocouples were used to
measure the temperature. Figure 12 shows a typical sketch of the
aging setup for mechanical integrity test samples.
The Youngs Modulus for the test specimens was determined using
an Instron 5500R uniaxial mechanical testing machine. The
compressive testing consisted of ten, 5% strain compression cycles.
The 5% strain level represents the level of strain experienced by
the aerogel during laying and operation. Compression cycles for
various aged samples were 0, 1, 2 and 4 weeks at 0%, 15% and 30%
pre-compression. The results are shown in Figure 13.
Fig. 12: Aging setup for mechanical integrity test samples
Fig. 13: Young s Modulus (MPa) for 0%, 15%, 30%
compression over four weeks aging
Results of mechanical testing of aerogel material showed the
following;
Youngs Modulus increased with the level of compression; Aerogel
aged up to four weeks at 350F (177C) does not
show any statistically significant aging effects on mechanical
stiffness;
Cabots Nanogel aerogel material does not thermally age while
operating continuously at temperatures up to 350F (177C).
The tests were successful and it can be concluded that Cabots
Nanogel aerogel is suitable as thermal insulation for XHPHT PIP
systems. Mechanical Clamp Loadshare Tests
A mechanical radial clamp will be inserted in the annulus of the
PIP. The purpose of testing of a mechanical clamp loadshare is to
ensure performance as a loadshare component in the PIP system. Load
tests were successfully performed on the loadshare.
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8 Copyright 2008 by ASME
Fig. 14: A typical arrangement of a load share clamp
Load Test. The maximum expected axial load for the loadshare was
determined using finite element analysis FEA (7, 8). For a water
depth of 4500ft (1372 m), the test load was 193.6Te (1900kN) and
this included a load factor of 1.1. The load was applied using a
series of four calibrated hydraulic pistons and a calibrated
hydraulic hand pump. The full test load was applied for one
hour.
Figure 15 A loadshare clamp axial load versus
clamp activation chart The results showed no slippage of the
clamp. No further movement occurred, as shown in Figure 15. No
buckling of the inner pipe occurred, and the test was successful.
CONCLUSIONS
This paper describes a qualification testing programme for the
testing of PIP components for 350F (177C) service, and includes the
testing of centralizers, waterstop seals, thermal insulation and
loadshares. Conclusions from the testing program are;
Centralizers. The test program was not successful. The main
challenge is finding a material suitable to 350F. Materials tested
to date have failed due to lack of ductility (brittle
behavior).
Waterstop Seals. Waterstop seals were tested for structural
loading and thermal testing, and the seal passed all aspects of the
testing.
Thermal Insulation. The Nanogel aerogel material tested does not
thermally age while operating continuously at temperatures up to
350F (177C). The material is very well suited for PIP insulation
applications in XHPHT systems.
Loadshares. The tested design is suitable for accepting a load
of 176Te.
The qualification testing of the components presented within
this paper extends the boundaries of what is possible with PIP
designs and opens up the possibility of XHPHT field developments in
the GOM.
ACKNOWLEDGMENTS The author would like to thank all that have
provided input into
this work, especially BP, Cabot Corporation, TEKMAR and Devol
Engineering Ltd.
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[9] Devol Engineering Ltd, HPHT Pipe-in-Pipe Centralizer
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