OBJECTIVE:
As
water depths increase, there is growing interest in the use of composite
production risers instead of steel risers for deepwater production systems.
The MMS’s Deepwater Operating Plan (DWOP) requires that new technology
introduced in a deepwater development project must be shown to be as safe
as existing technology. The project will compare the risks of a composite
production riser for deepwater floating production systems with the risks
of a steel riser that has the same functional requirements and service
life, to demonstrate the safety of a composite riser relative to a steel
riser.
APPROACH:
A
Comparative Risk Analysis (CRA) will be conducted to compare the risks
of composite and steel production risers. The specific riser functional
requirements, service life, and configuration(s) for the composite riser
will be based upon results from DeepStar Project 6120 on permitting composite
risers, and will be subject to MMS approval. A configuration for a steel
riser with the same functional and service requirements will be developed,
and both will be designed in sufficient detail for analysis.
The
Study Team will include expertise in the areas of risk analysis, deepwater
production riser configuration and design, composite riser analysis, and
steel riser analysis. The Study Team will interact with experts from industry,
class societies, and regulatory authorities through a series of Workshops
to (1) develop the riser systems for the CRA; (2) determine appropriate
risk measures for this study; (3) identify hazards for the composite and
steel riser, and the resulting consequences of failure; and (4) estimate
the frequencies of such events.
The
Study Team will use this information to estimate the risks for the composite
and steel riser systems. Each riser system will be quantitatively analyzed
to determine its responses to hazards and the resulting risks. Existing
data will be sought to support the analyses. The resulting risks for the
two riser systems will be compared to determine the risks of the composite
riser relative to the steel riser. The study will be conducted such that
the larger contributors to risk can be identified so that appropriate risk
mitigation strategies and measures can be studied.
The
Study Team will review intermediate results with the industry, class society,
and regulatory experts at appropriate milestones to get their advice and
input as the study progresses.
DEPLOYMENT OF
RESULTS:
Results
from this CRA study will be shared with the Workshop Participants as part
of the study process, and will be documented in a Final Report that will
be available to the MMS, other regulatory authorities, Workshop Participants,
and the public. Results from this study could also provide a basis for
· Developing a process to qualify other new production or drilling risers,
· Developing any needed certification or testing requirements for composite
risers
· Identifying NDE methods that could be useful in sensing the ongoing
performance of composite risers during field service
ANTICIPATED PROJECT DURATION: 2 years
PROJECT PLAN
FOR YEAR 1 (2003-2004):
Scope of Work:
The
CRA for a composite riser configuration will be completed. The Study Team
will
· Develop the functional requirements, service life, configuration, and
design for the composite production riser
· Develop similar information for a steel riser with the same functional
and service requirements
· Identify appropriate risk measures for the production risers
· Identify hazards and estimate the corresponding frequencies and consequences
· Complete a quantitative risk analysis for each riser system
· Compare the risks and identify potential mitigation strategies and methods
as needed to manage risks
· Prepare a final report
The study will include a series of Workshops to interact with industry, class
society, and regulatory experts as shown in Figure 1.
Figure 1 Workshop Process
Anticipated Results:
The
Final Report will
1. Compare the risks for the specific composite production riser studied relative
to an equivalent steel riser
2. Suggest strategies and methods to mitigate any risks as might be needed
3. Suggest NDE techniques that could be useful to monitor the insitu field
performance of a composite riser
PROJECT PLAN
FOR YEAR 2:
Scope
of Work: This project could be continued to address
· Other composite production riser configurations
· Composite drilling risers
· Certification or testing requirements for composite risers
· Developing a process to qualify other new production or drilling risers
· Composite flowlines
Anticipated
Results: To be determined depending on Scope
SPONSORSHIP:
MMS
PRINCIPAL INVESTIGATOR
(S) & OTHERS INVOLVED IN PROJECT: (see Figure 2 below)
PI(s): E.
Ward, O. Ochoa, and R. Gilbert
Others: Dr.
E.B. Denison (consultant), Dr. Ochoa’s graduate student, Riser designer/analyst(s)
from Stress Engineering Services, Workshop Participants
Date: December 2005
Project Title: Comparative Risk Analysis of Composite & Steel
Production Risers
MMS Project: 490 TO Numbers: 73632/35985
PIs: E.G. Ward, O.A Ochoa, R. B. Gilbert (OTRC); C. Miller (Stress
Engineering Services), E.B. Denison (Consultant)
COTR: S. Buffington
Estimated
Completion Date: October 2005
Project
Description: As water
depths increase, there is growing interest in using
composite production risers instead of steel
risers for deepwater production systems. The MMS’s Deepwater
Operating Plan (DWOP) requires that new technology introduced in
a deepwater development project must be shown to be as safe as
existing technology. The project compared the risks of a composite
production riser (new technology) with the risks of a steel riser
(existing technology) that has the same functional requirements
and service life to demonstrate the safety of a composite riser
relative to a steel riser for deepwater floating production systems.
The Study Team included the expertise in composites, risk analysis,
riser design & analysis, and riser operations & hardware
from OTRC and industry.
Progress:
The analyses of the steel riser had been completed in the previous
year and those results are summarized in Table 1.
The
analyses of the composite liner have now been completed.
Special attention had to be given to sizing the steel liner in the
composite
tube. Global analyses of the riser response had been completed,
and were used as input to the more detailed analyses of the
composite riser, consisting of the composite tube and the steel liner.
The
composite tube was analyzed at the fiber and matrix level.
The analyses included load cases that addressed:
• maximum combined axial tension and bending moments
• burst
• collapse (buckling)
• fatigue
Results were documented in a report by W. Kim (see below) and are
summarized in Table 2.
Thermal effects on the composite riser were addressed by looking
at an extreme case that could happen during well start-up. Assume
that the annulus was filled with brine, a good conductor, and the
initial temperature was 40F (the ambient water temperature at the
seafloor). After start-up, heat from the produced fluids (180F)
could rapidly heat up the tubing, annular fluid, and liner to 180F.
Meanwhile the composite tube remained at near ambient temperature,
was a perfect insulator, and did not expand. The thermally induced
stress in the tubing would be 26 ksi, well below yield and thus
not be a concern.
The impact on
the tubing string was also examined. Assuming the 5 ½ inch
tubing was axially constrained at the surface and below the mudline
(via a hanger),
the heating and resulting expansion
of the tubing after starting up the well could result
in a stress reduction of 23 ksi and a tension reduction of 150
kips.
Depending
on the residual tension when the riser was installed,
this expansion could result in compression at the mudline and
helical
buckling,
but the tubing would not yield due to the modest compressive
stress. This tubing performance would be similar to that experience
in
insulated steel risers that are currently used in deep
water.
Comparing Tables 1 and 2, we conclude that both the steel and
composite risers can meet the prescribed design and operational
requirements.
The Final Report documenting this comprehensive comparative risk
analysis of a steel and composite production riser is being completed
and should be available for review by April 1.
Reports & Publications:
Risk Analysis of Steel Production Risers for Deepwater Offshore
Facilities (2004), thesis by Anubhav Jain under the supervision
of R.M. Gilbert, University of Texas, December
Structural Response
of Composite Production Risers (2005), W. K. Kim, O. O. Ochoa,
E. G. Ward, & C.
A. Miller, paper at Fourth International Conference
On Composite Materials for Offshore Operations,
Houston, TX, October 4-6, 2005.
Comparative Risk
Analysis of Composite and Steel Production Risers: Composite
Riser Response Assessment
(2005), report by Won K. Kim & Dr.
Ozden Ochoa, Texas A&M University, December
|
Table 1. Steel Riser
|
|
Hazard
|
Failure Mode
|
Allowable/ Design Target
|
Predicted Performance
|
Minimum Failure
|
Risk
|
Remarks
|
|
Kick control while drilling
|
Burst
|
8500 psi
|
8500 psi (60% of calculated minimum burst)
|
14,170 psi (minimum burst)
|
Loss of pressure containment
|
API RP-1111 Calculation, 12.5% mill tolerance, 0.050" corrosion and
wear allowance.
|
|
Tubing leak
|
|
Riser evacuation
|
Collapse
|
6,000 ft WD (2,660 psi)
|
2,660 psi (6,000 ft WD)
|
12,680 psi
|
API 5C3 Calculation, elastic collapse, using nominal wall.
|
|
Excessive riser axial stress
|
Axial yielding
|
64 ksi
(80% yield)
|
Max above SJ is 52 ksi,
max below TJ is 30 ksi (see Note 1)
|
80 ksi (yield)
|
Loss of pressure containment, parted
riser
|
100-year Hurricane, API RP 2RD
|
|
Max above SJ is 60 ksi,
max below TJ is 32 ksi (see Note 1)
|
100-year Loop current, API RP 2RD
|
|
Wave fatigue
|
Crack, parting
|
Minimum life = 200 years
|
Variable damage, minimum life of
200 years (see Note 2)
|
Cumulative Damage = 1.00 or calculated
life = 20 years or less
|
Damage calculations for 20 year life with factor of 10 for non-inspectable components. VIV
fatigue mitigated by suppression equipment.
|
|
VIV fatigue
|
No damage
|
|
Dropped objects
|
Denting, leakage in connector
|
|
|
|
Loss of pressure containment
|
This is typically not evaluated for riser systems. Tests have shown the
joints and connectors to be robust. No information exists
on riser joints that have been damaged in service by
external collisions or dropped objects.
|
|
Riser-to-riser collisions
|
|
Note 1:The stress joint above the seabed and the tensioner joint
just above the sea surface are specialty joints that
have not been carefully designed and analyzed for this
study. Results are emphasized here for the riser joints
only. The stress in the middle portion of the riser
is lower than at the two extremes noted in the table.
|
|
Note 2: Analyses show that with the normal practice of using forged steel
stress joints and tensioner joints,
achieving the required fatigue performance in the stress
joint and tensioner joint are not a problem. Results indicate that
the riser joint welds must be ground to achieve DNV C-curve
performance for the first 200 ft above the stress joint. Above
these few joints, unground welds
meeting the DNV F2 curve will achieve the needed fatigue
life.
|
|
Table 2. Composite Riser
|
|
Hazard
|
Failure Mode
|
Allowable/ Design Target
|
Predicted Performance
|
Minimum Failure
|
|
Remarks
|
|
Kick control while drilling
|
Burst
|
8500 psi
|
11,000 liner yield, body is significantly
stronger
|
18,000 psi matrix yield, 30,000 psi fiber
limit
|
Loss of pressure containment
|
|
|
Tubing leak
|
|
Riser evacuation
|
Collapse
|
6,000 ft WD (2,660 psi)
|
12,400 psi
(leak in outer liner, complete debonding of steel liner)
|
12,400 psi w/ debonded liner 29,400 psi w/ limited debonding
|
With no breach of outer structure, riser is stronger than the 29,400 psi figure.
|
|
Excessive riser axial stress
|
Axial yielding of liner
|
64 ksi
(80% yield)
|
Max at Top of Composite Riser (74
ft WD) is 31 ksi (Note 3)
|
80 ksi (yield)
|
100-year Hurricane, API RP 2RD, riser will remain intact even with yielded
liner.
|
|
Max at Top of Composite Riser (74
ft WD) is 23 ksi (Note 3)
|
100-year Loop current, API RP 2RD, riser will remain
intact even with yielded liner.
|
|
Wave fatigue
|
Crack, parting of liner
|
Minimum life = 200 years
|
Minimum life is 80,000 years (Composite
Section)
|
Cumulative Damage = 1.00 or calculated
life = 20 years or less
|
Results for composite riser section only (see Note 3). Steel sections (top & bottom)
designed using normal practices for all-steel risers.
Damage calculations for 20 year life of liner welds with
factor of 10 for non-inspectable components
using DNV E curve for unground welds. No
need for ground welds in composite joints. VIV fatigue
mitigated by suppression equipment. Composite body has
much longer predicted life.
|
|
VIV fatigue
|
No damage
|
|
Dropped objects
|
Denting, leakage in connector
|
|
|
|
Magnolia riser joints impact tested to 10 MJ.
|
|
Riser-to-riser collisions
|
|
Note 3: Composite riser section is between 102 ft, (54 ft above SJ) to 5926
ft (124 ft below bottom of TJ & 74 ft below MWL.
The max composite joint liner stress is near the surface
rather than near the stress joint above the seabed. The
composite structure is much stronger than the liner.
|
Return
to top
OTRC PROJECT STATUS REPORT
Date: June 2005
Project Title: Comparative
Risk Analysis of Composite & Steel
Production Risers
MMS Project: 490 TO
Numbers: 73632/35985
PI: E.G. Ward, O.A Ochoa, R. B. Gilbert (OTRC); C. Miller, E.B. Denison
(industry)
COTR: Andrew Konczvald
Estimated
Completion Date: October 2005
Project
Description: As water depths
increase, there is growing interest in
using composite production risers
instead
of steel
risers for deepwater production systems.
The MMS’s Deepwater
Operating Plan (DWOP) requires that new technology introduced in
a deepwater development project must be shown to be as safe as
existing technology. The project will compare the risks of a composite
production riser (new technology) with the risks of a steel riser
(existing technology) that has the same functional requirements
and service life to demonstrate the safety of a composite riser
relative to a steel riser for deepwater floating production systems.
The Study Team includes the expertise in composites, risk analysis,
riser design & analysis, and riser operations & hardware
from OTRC and industry.
Progress:
The comparative failure modes for steel and composite risers have
been considered. Failure for the steel riser has been defined as
a through-wall crack that leads to a leak or riser failure. Failure
modes for the composite riser are very different. The composite
riser depends upon the steel liner and the outer elastomeric layer
for pressure containment since the composite tube itself will weep.
A crack in the liner can lead to a loss of pressure containment.
A hole in the outer elastomeric covering could lead to external
pressure on the liner causing a collapse and perhaps even a crack
that would result in loss of pressure containment.
Continuing research focused on the composite riser. Further study
of the steel liner for the composite riser focused on the girth
welds of the liner. The liner thickness for the study riser was
increased to mitigate concerns regarding undetectable weld flaws
that could lead to through-wall cracks, and the study riser was
resized.
Global riser analyses were completed to predict the composite
riser responses under a variety of important design cases, including
100-year hurricane conditions, 100-year loop current conditions,
and the 1-year winter storm case.
The computed distributions of tensions and bending moments are
being used as the basis and boundary conditions for detailed local
analyses of the composite tube. These local analyses will investigate
the expected amount of fiber failure and matrix cracking in layers
of the composite tubular under different loading conditions. These
analyses will be used to examine the likelihood and degree of failure
in the layers of the composite tubular, and the remaining strength
of the riser.
Reports & Publications:
Risk
Analysis of Steel Production Risers for Deepwater Offshore Facilities
(2004), thesis by Anubhav Jain under the supervision
of R.M. Gilbert, University of Texas, December.
Return
to top
OTRC PROJECT STATUS REPORT
Date: December, 2004
Project Title: Comparative Risk Analysis of
Composite & Steel
Production Risers
MMS Project: 490 TO Numbers: 73632/35985
PI: E.G. Ward, O.A Ochoa, R. B. Gilbert (OTRC); C. Miller, E.B.
Denison (industry)
COTR: Julie McNeil
Estimated
Completion Date: July 2005
Project
Description: As water depths increase,
there is growing interest in using
composite production risers instead of
steel risers for deepwater production systems.
The MMS’s Deepwater
Operating Plan (DWOP) requires that new technology introduced
in a deepwater development project must be shown to be as safe
as existing technology. The project will compare the risks of
a composite production riser (new technology) with the risks
of a steel riser (existing technology) that has the same functional
requirements and service life to demonstrate the safety of a
composite riser relative to a steel riser for deepwater floating
production systems. The Study Team includes the expertise in
composites, risk analysis, riser design & analysis, and riser
operations & hardware from OTRC and industry.
Progress: Preliminary analyses of the steel riser design being
used for this study were completed. These analyses included global
analyses to predict the overall response of the risers to various
storm and operational conditions that represented the design
load cases. Analyses of riser responses under operational conditions
were also completed to define the long term fatigue loading on
the riser.
A risk analysis
of the steel riser was completed to develop the
methodology and
framework to compare the risks of steel versus
composite production risers, and provide preliminary
results for the steel riser. Failure was defined as a through
wall crack,
and the risks of a through wall crack developing
during the design life were evaluated for a number load scenarios
including
burst(kick,
production tubing leak), collapse (hydrostatic pressure),
yield (high tension or compression, dropped objects), and fatigue
(wave
loading – it was assumed that VIV could be
suppressed through strakes). The results are reasonable
for the
steel riser.
The steel liner for the composite riser was further studied
and focused on the girth welds of the liner. Concerns centered
on the ability to sizes of flaws in the weld that could be detected
versus the size of a flaw that could lead to through wall cracks
during the design life. A preliminary wall thickness was selected
for further study. The composite riser was resized for this liner
thickness, and sectional properties were developed and used to
complete preliminary global analyses.
Failure modes for the composite riser continued to be studied
along with detailed analyses of the composite riser under various
loading scenarios.
Reports & Publications:
Risk Analysis of Steel Production Risers for Deepwater Offshore
Facilities (2004), thesis by Anubhav Jain under the supervision
of R.M. Gilbert, University of Texas, December
Return
to top
OTRC
PROJECT STATUS REPORT
Date: June
2004
Project
Name: Comparative Risk Analysis of Composite and Steel
Production Risers for a Deepwater Floating Production System
Project
Number: 490 Task Order: 73632
Principal
Investigators: E.G. Ward, O.A Ochoa, R. B. Gilbert
(OTRC); C. Miller, E.B. Denison (industry)
Estimated
Completion Date: July 2005
Project
Description:
As
water depths increase, there is growing interest in
using composite production risers instead of steel risers
for deepwater
production
systems. The MMS’s Deepwater Operating Plan (DWOP) requires
that new technology introduced in a deepwater development project
must be shown to be as safe as existing technology. The project
will compare the risks of a composite production riser (new technology)
with the risks of a steel riser (existing technology) that has
the same functional requirements and service life to demonstrate
the safety of a composite riser relative to a steel riser for
deepwater floating production systems. The Study Team includes
the expertise in composites, risk analysis, riser design & analysis,
and riser operations & hardware from OTRC and industry.
Progress:
The
functional requirements and design parameters for the risers
have been established. The riser will be a single-casing production
riser for a TLP in 6000 ft. Workover operations will be conducted
through the riser. A standard steel riser is being used for the
study.
A “design” for
the composite riser has been completed. Properties
of the composite materials (fiber and matrix) and the stacking
sequence
have been
established from available literature. Containment
capabilities
of steel and production risers are quite different,
and considerable effort has been focused on developing a
composite
riser design
that is sufficient to capture these differences and
serve as a basis for comparing the risks without becoming
too detailed
(as in a specific final design). A riser with a steel
liner, composite body, rubber barrier, and epoxy coating
will be studied.
The bottom stress joint and the tensioner and first
riser joint (to below the water line) will be steel for the
composite
riser.
The
analyses and the load cases have selected. The hurricane and
loop current environments are being specified, and the cases
have been developed and planned. Containment capabilities of
steel and production risers are quite different, and considerable
effort has been focused on developing a composite riser design
for this study that is sufficient to capture these differences
and serve as a basis for comparing the risks without becoming
too detailed (as in a specific final design).
The analyses of both the steel and composite risers have been initiated.
Load cases have been selected for comparing the risks. Planning for the
comparative risk analyses is nearing completion.
We
have consulted with industry in developing some of study parameters
and assumptions. In the next Quarter, we will invite industry
and class society experts to a meeting to review the study progress
and provide feedback.
Reports & Publications: None
Return
to top
OTRC
PROJECT STATUS REPORT
Date: December
2003
Project
Name: Comparative Risk Analysis of Composite and Steel
Production Risers for a Deepwater Floating Production System
TEES Project
Number: 32558-60280
MMS Task Order: 73632 MMS
Project Number: 490
Principal
Investigators: O.A Ochoa, R. B. Gilbert, E.G. Ward
Estimated
Completion Date: May 2003
Project
Description: As
water depths increase, there is growing interest in the
use of composite production
risers instead of steel risers for deepwater production systems.
The MMS’s Deepwater Operating Plan (DWOP) requires
that new technology introduced in a deepwater development
project
must be
shown to be as safe as existing technology. The project will
compare the risks of a composite production riser for deepwater
floating
production systems with the risks of a steel riser that has
the same functional requirements and service life, to demonstrate
the safety
of a composite riser relative to a steel riser and the use
of
Comparative Risk Analysis to demonstrate the safety of new
technology.
Progress: A plan and a Study
Team have been developed. A Study Team combining the talents and
experience of OTRC faculty and industry experts has been set up:
o Composite riser analysis – O.A. Ochoa (Texas A&M)
o Risk analysis – R.B. Gilbert (U. Texas)
o Steel riser design & analysis – C. Miller (Stress
Engineering)
o Production riser operations & hardware – E.B.
Denison (consultant) The
Study Team will proceed to:
o Obtain the functional & service requirements, configuration,
and design for the composite production riser from industry sources
o Develop similar information for a steel riser with the same functional
and service requirements
o Identify appropriate risk measures for the production risers
o Identify hazards and estimate the corresponding frequencies and consequences
o Complete a quantitative risk analysis for each riser system
o Compare the risks and identify potential mitigation strategies and methods
as needed to manage risks
The study will include a series of Workshops to interact with industry, class
societies, and the MMS to gather information and review progress. Information
on the composite riser is being compiled, and the OTRC faculty has initiated
studies on riser mechanics and the application of risk analysis methodologies
to risers.
Reports & Publications:
None
