REPORT
623
Lifetime Extension of
Flexible Pipe Systems
extend
operation
DECEMBER
2019
Acknowledgements
This document was prepared by the Flexible Pipe Subcommittee of
IOGP’s Subsea Committee.
Front cover photography used with permission courtesy of
Johan Castberg / © Equinor and ©mikeuk/iStockphoto
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REPORT
623
Lifetime Extension of
Flexible Pipe Systems
Revision history
VERSION
DATE
AMENDMENTS
1.0
December 2019
First release
DECEMBER
2019
Lifetime Extension of Flexible Pipe Systems
Contents
Scope
5
1. Lifetime Extension
6
2. Methodology
8
2.1 System Identification
8
2.2 Failure Mode, Effects and Criticality Assessment (FMECA)
8
2.3 Input Integrity Data
9
2.4 Engineering Analysis
10
2.5 Risk Assessment
11
2.6 Document Work and Implementation Actions
12
2.7 General Recommendations
12
Appendix A: Sample list of Failure Modes and Mechanisms
13
Appendix B: Sample list of analyses and checks to be
performed in LTE studies
15
Appendix C: Examples of Recommended Assessment
Process for the LTE
17
Glossary
19
References
20
4
Lifetime Extension of Flexible Pipe Systems
Scope
This guideline provides a framework to assist companies and contractors in
extending the product lifetime of unbonded flexible pipe systems (including
ancillary components) as per API 17J and API 17L1/L2. This FPLEN Guideline is
intended for incorporation into API 17B, Section 11 - Integrity Management.
5
Lifetime Extension of Flexible Pipe Systems
1. Lifetime Extension
Lifetime Extension (LTE) is a procedure that uses a risk-based engineering assessment
to extend operation of a flexible pipe system beyond the service life for which it has been
originally designed. During the LTE process, actual operating conditions are considered
to be input data. The process utilizes advanced predictive tools to provide an increased
understanding of degradation mechanisms, taking into account historic and future service
conditions for key degradation mechanisms. As such, the LTE provides a risk-based
assessment of the flexible pipe systems’ remaining operational life. Mitigation and control
measures may then be used as a basis to maintain the sufficiently low probability of failure
of the flexible pipe system for the new service life.
The potential for Lifetime Extension is greatly enhanced by ensuring that flexible pipe
system integrity is formally managed and documented during the current operational
lifetime.
A schematic representation of Lifetime Extension is presented in Figure 2.1. The figure
shows the integrity level in the vertical axis vs the time in the horizontal axis. The Expected
Degradation line represents the degradation models at the time of original service life
assessment (when the pipe was designed). The New Degradation Model displays a newer,
updated degradation model at the time of Lifetime Extension. The New Degradation Model
may include increased understanding of degradation mechanisms, better predictive tools,
or intervention methods that reduce the rate of degradation. The New Degradation Model
may, together with historical operational data, make a further Lifetime Extension possible.
Safety
Level
New Degration
Model
Expected
Degration
Acceptance
Level
Original Service
Life
New Service
Life
Time
Installation
Lifetime Extension
Evaluation
Figure 2.1: Lifetime Extension schematic sketch, integrity level vs time.
6
Lifetime Extension of Flexible Pipe Systems
The Lifetime Extension should be triggered at a set period before the end of the originally
designed lifespan, to allow sufficient time to perform lifetime studies, implement
mitigations, formulate alternative strategies, and engage regulators. These activities may
take up to three years to perform.
A Lifetime Extension study usually addresses a complete flexible pipe system and can cover
multiple assets. Due to the size of such an extensive study, a systematic methodology is
important. Some of the documents that could be referred to during such exercises are
listed in the references section of this guideline.
7
Lifetime Extension of Flexible Pipe Systems
2. Methodology
Lifetime Extension of flexible pipe systems involves the following steps:
1)
System Identification
2)
Failure Mode, Effects, and Criticality Analysis (FMECA)
3)
Input Integrity Data
4)
Engineering Analysis
5)
Risk Assessment
6)
Document Work and Implement Actions
Flexible Pipe
System
Identification
2.1
Failure Mode,
Effects and
Criticality
Analysis
(FMECA)
Input Integrity
Data:
Detailed
Engineering
Analysis
including (e.g.
extreme and
fatigue,
degradation
modeling)
Historic and
Future Forecast
(motion,
production
history, annulus
condition, etc.)
Risk
Assessment
and
Identification
of Mitigating
Actions
Documentation:
Report Results
and
Implementation
of Mitigation
Plan (monitoring,
inspection,
change out etc.)
System Identification
The first step in the Lifetime Extension of a flexible pipe system should be the identification
of the components and equipment that are targeted for Lifetime Extension. Every pipe
section, end fitting, and associated ancillary equipment and accessory should be identified,
as well as their interfaces. Datasheets of the pipe structures and drawings of accessories
and ancillary components should be collected. All relevant information (including main
operational parameters) on the flexible pipe system should be collected to allow the
most accurate assessment. It is suggested that assessors develop a complete asset and
component register to clearly define the scope and boundaries of the assessment.
Additional requirements defined by local agencies should also be identified at this point.
2.2
Failure Mode, Effects and Criticality Assessment (FMECA)
The second step in the Lifetime Extension of a flexible system pipe should be a Failure
Mode, Effects, and Criticality Analysis (FMECA) of the system and all of its components. The
analysis should be based on the information gathered during Step 1, System Identification.
The FMECA should identify the applicable failure modes and mechanisms for each
component and the parameters that affect them. It is recommended to perform the FMECA
based on the state of the art understanding of failure modes and mechanisms that may
have been unknown when the system was designed or last analysed.
8
Lifetime Extension of Flexible Pipe Systems
The FMECA should have an associated risk score (based on likelihood, failure detectability,
and consequence) for each failure mode or mechanism identified.
Given the multilayered construction of the flexible pipe, it is recommended to identify the
failure modes and mechanisms based on each layer when considering the pipe tubular
body and end fittings. The prime reference for failure modes is presented in API 17B. This
may be supplemented with references containing a more exhaustive list of failure modes,
such as the one found in the Handbook on Design and Operation of Flexible Pipes (see
references at the end of this document).
The result of the FMECA should be a list of failure modes and mechanisms applicable to
the system with an associated risk score and the list of relevant parameters.
Depending on the result of the FMECA, specific inspection and monitoring tasks or tests
may have to be performed to verify the actual condition of components or obtain key data
for the Lifetime Extension analysis.
The results from the FMECA will decide which engineering studies and checks will be
necessary to be performed during the LTE study.
One should note that while a comprehensive FMECA for a flexible pipe system may include
numerous failure modes and mechanisms, performing such activity from scratch at every
LTE process will be time consuming. Instead, it is recommended to develop a general
FMECA targeting the typical flexible pipe systems and use it as a guide to see what would
be applicable for the identified system given its specific characteristics and operational
data. In other words, during each LTE process the general and comprehensive FMECA
would be mapped onto a more focused case with reclassification of the associated risks.
Another approach would be to perform a series of FMECA with updates reflecting the
latest events related to the system. For example, the first FMECA implementation
reflecting design conservatism and manufacturing non-conformances can be prepared
and reported by flexible pipe OEM and delivered as part of the Flexible Pipe Operation
Manual. The second FMECA implementation can modify the first one by reflecting
Installation irregularities, damages and repairs. The third FMECA implementation can
modify the second one by reflecting incidents, accidents, and exceedance of design
parameters, encountered during operation. A LTE FMECA implementation can modify those
implemented during manufacturing, installation and operation.
See Appendix A of this document for a sample, detailed list of Failure Modes and
Mechanisms.
2.3
Input Integrity Data
The third step in the Lifetime Extension of a flexible pipe system should be the gathering of
input data. The input data to be gathered should target the parameters identified during the
FMECA, and should specifically target the evolution of the degradation mechanisms that
influence the critical failure modes.
The input to integrity data should include both the past operating conditions and future
operating conditions envisioned for the system assessed for LTE.
9
Lifetime Extension of Flexible Pipe Systems
Historic data for flexible pipe Lifetime Extension analysis may include the following:
• Purchasing documentation (i.e., design reports, material reports, manufacturing
record book inclusive of as built data and drawings, and operation manual)
• Reports describing installation irregularities, damages and repairs
• Operational data (e.g., temperature, pressure, fluid composition, flow velocity)
• External environment data (e.g., metocean data, water depth and temperature)
• Interface data (e.g., floating point unit movements, riser loads, position monitoring)
• Previous integrity assessments reports
• Inspection, monitoring and testing data
• Reports from root cause failure analyses
• Reports from repairs and modifications of the flexible pipe system, including ancillary
items
Where historic input data is assumed, it should be highlighted to ensure that this
uncertainty is adequately bounded in subsequent engineering activities.
The future operating conditions shall be defined based on the parameters identified in the
FMECA. For any new project, conditions shall be defined per operator rules and as per API
17J’s functional and design requirements.
2.4
Engineering Analysis
Engineering analysis, the fourth step, should evaluate the degradation of components and
the impact of that degradation on the critical failure modes and mechanisms identified
in the FMECA. Assessment of failure modes for historic conditions should be refined and
compared to the original design by using actual values instead of design assumptions
(e.g., monitored data such as pressure and temperature, sampled fluids, riser loads and
response, metocean criteria, etc.). Typical engineering studies shall assess the capacity
of all permanent ancillary components to resist all loads expected during the lifetime
extension.
The applicable failure modes or mechanisms identified in the FMECA (2.2) should be
assessed by an appropriate method, e.g., with engineering calculation/analysis or with
engineering judgement. Engineering analysis methods should be verified, and analysis
tools should be validated against test data. The failure modes or mechanisms that cannot
be ruled as not applicable or with negligible risk should be evaluated in line with latest
industry standards.
Annulus composition may affect a great number of failure modes and mechanisms;
therefore, annulus prediction is a key part of the Engineering Analysis. The annulus
environment prediction should be performed through validated tools and account for both
intact and breached external sheath conditions as per API 17J requirements, as applicable.
The flexible pipe system is designed according to applicable design rules and standards at
time of design. A gap analysis between the current industry standard requirements and that
at the time of the previous life extension analysis, and/or initial flexible pipe system design
should be performed to aid in the assessment of the current flexible pipe system status and
10
Lifetime Extension of Flexible Pipe Systems
overall risks to operation. It should be noted that updated models may show more rapid
degeneration, reducing design life. LTE may still be possible due to less severe operating
conditions than originally anticipated.
The same applies to design methodology and degradation models.
After assessing the current state of degradation of the system components, the
Engineering Analysis should establish the new service life and operating limits based
on the future data expected for the specific system. This analysis shall encompass
calculations, analysis, or engineering judgement regarding the failure modes and
mechanisms identified as applicable and non-negligible in the FMECA.
See Appendix B of this document for a detailed list of analyses and checks that may be
performed in LTE studies.
2.5
Risk Assessment
With the results of the Engineering Analysis available, a risk assessment of the flexible
pipe system should be performed. The risk assessment should provide a clear overview
of risk related to each failure mode and mechanism previously categorised as applicable
and highlight whenever current requirements are not met. In this case, mitigations and/
or controls should be specified to maintain the adequate safety level for the duration of the
Lifetime Extension.
The Risk Assessment may result in new monitoring, inspection or regular testing
requirements, for example in preparation for consequent LTE and RA, or to maintain safety
level that is adequate for the duration of LTE but lower than the safety level assumed in the
original design. Depending on the analysis, different operational limits may be specified for
critical variables. Examples of this include:
• System derating (pressure, temperature, bore conditions)
• Reduced service life
• Special operating procedures
• Additional monitoring and/or testing
• Specialised inspection
• Modifications and/or partial replacements
• New safety or utilisation factors (shown by reliability analysis)
It is important to ensure that all mitigations and controls can be implemented. For
example, if the Lifetime Extension assessment of a flowline is dependent on inlet
temperature, it is important that an accurate value can be established either by direct
measurement or from system modelling.
The Risk Assessment should be complete after all applicable risk ratings are reviewed
based on the proposed mitigation actions. Acceptance criteria should be based on
demonstrating safety levels that are adequate for the duration of Lifetime Extension, which
in turn should be cross-checked for compliance with local regulations.
11
Lifetime Extension of Flexible Pipe Systems
With the conclusion of the Risk Assessment, the Operating Envelope and the Integrity
Management program or strategy should be updated considering the risks and associated
mitigation actions.
The Risk Assessment should also establish the period for which the current assessment
is valid and after which the Lifetime Extension analysis should be restarted. The validity
period of the risk analysis may be based on previous experiences and engineering
judgement and should not exceed the new service life.
See Appendix C of this document for examples of Recommended Assessment Process for
the LTE.
2.6
Document Work and Implementation Actions
The work performed for the Lifetime Extension should be documented in a Lifetime
Extension Report. This report should clearly state the new service life and operational
limits for the new scenario.
The report should contain the historic data and predicted future data used to evaluate the
degradation of the system components. The report should also contain, or reference, all the
necessary evidence that supported the Lifetime Extension process, such as the engineering
analysis and risk assessment, as well as the mitigation actions.
The asset control and integrity management system, including any asset registers and
maintenance/operational documentation, should then be updated with the revised limits
of operational conditions, consistent with the basis of the Lifetime Extension. Flexible Pipe
Operating Manuals and Design Reports may need amendments based on the Lifetime
Extension Report.
2.7
General Recommendations
The potential for Lifetime Extension of flexible pipe systems may be greatly enhanced
by the use of detailed historical data. Therefore, it is highly recommended that the
main parameters involved in the Lifetime Extension of flexible pipes are monitored and
registered since the beginning of operation. This may also need adjustments in the design
requirements of pipes to allow proper monitoring.
The flexible pipe cross section and system is complex, with interacting degradation
processes. This has to be duly considered in the LTE process.
12
Lifetime Extension of Flexible Pipe Systems
Appendix A: Sample list of Failure Modes
and Mechanisms
Corrosion/degradation of riser:
• Corrosion of tensile- and pressure armour - outer sheath damage case
• Corrosion of tensile- and pressure armour - intact outer sheath case
• Corrosion of carcass
• External corrosion of topside end fittings
• External corrosion of bottom end fittings (cathodic protection failure)
• Tensile and pressure armouring HIC (hydrogen induced cracking), SSC (sulphide stress
cracking) and SCC (Stress Corrosion Cracking)
• Tensile and pressure armouring HISC (hydrogen induced stress cracking)
• HISC (hydrogen induced stress cracking) on ancillary equipment (bolts, trunnions, etc.)
Fatigue of riser structure and components:
• Fatigue of dynamic riser structure (tensile- and pressure armour), possibly in combination
with local corrosion
• Fatigue of hang-off
• Fatigue of bending stiffener fixation, female and male parts
• Fatigue of bending stiffener adaptor
• Fatigue of bending stiffener internals/stud bolts
• Fatigue of MWA anchoring and structural components
• Fatigue of vertical anchoring arrangement (clamp and tether pad eye connection, tether)
• Fatigue of gravity anchor (vertical tether trunnion connection and wire connection)
• Fatigue of horizontal anchoring arrangement (clamp and tether pad eye connection, wire
sling, chain connection to turning point)
• Fatigue of horizontal end fitting anchoring clamp
Erosion:
• Erosion of carcass
• Erosion of internal cladding in the top and bottom end fitting areas
Chemical degradation of polymers:
• Degradation of pressure barrier
• Ageing/degradation of anti-wear tape
• Wear/degradation of anti-wear tape
• Degradation of outer sheath
• Degradation of bend restrictor/bend stiffener
13
Lifetime Extension of Flexible Pipe Systems
Dynamic behaviour:
• Global load increase
• Wear of outer sheath
• On bottom stability/thermal expansion
• Condition of vertical anchoring arrangement
• Condition of horizontal anchoring arrangement
• Changes in riser number or arrangements over MWAs
• Condition of buoyancy section (reduced total buoyancy)
Structural:
• Pull-out of pressure barrier from end fitting
• Collapse of pressure barrier in smooth bore pipes
• Crack growth of pressure barrier at end fitting
• Mechanical wear, pressure barrier
• Environmental stress cracking (ESC), outer sheath
• Carcass tear due to hydrate plug
• Carcass failure due to collapse (due to hydrostatic pressure)
• Carcass failure due to collapse (due to hydrate in carcass structure)
• Carcass failure due to rapid depressurisation
• Lack of annulus vent
• Bird caging (compressive failure)
• Lateral buckling
• Over bending failures (sheaths, carcass, pressure vault)
Structural – Accessories and Ancillaries:
• Corrosion of end fitting groove and J-tube hang-off flange, inside in J-tube
• Corrosion of split-ring
• Corrosion of bending stiffener fixation female/male parts
• Corrosion of bending stiffener adaptor (spool)
• Polyurethane bending stiffener - lack of support (hydrolysis)
• Corrosion of vertical anchoring clamp arrangement
• Wear of structural fibres of vertical tether including sideways loads on shackle
• Corrosion of vertical gravity anchor arrangement
• Corrosion of horizontal anchoring clamp arrangement
• Corrosion of turning point gravity arrangement
• Reduced bending restrictor capacity/corrosion of end fitting interface steel part
Third party:
• Mechanical impact, damage outer sheath
• Mechanical impact, armouring layers
14
Lifetime Extension of Flexible Pipe Systems
Appendix B: Sample list of analyses and
checks to be performed in LTE studies
Assessment of operational/design data (example of relevant check actions):
• Evaluation of operational data (design envelope, historical and future)
• Check validity of metocean data
• Injected chemicals (type, frequency, amount)
• Design data including gap analysis/requirements
• Sand rates and possible sand erosion
• Slugging in production lines
• Integrity of outer sheath (dropped object incidents, etc.)
• Check H2S and CO2 level in bore for sour service compatibility of armour wires
Analysis for flexible risers / topside jumpers:
• Diffusion analysis (determine annulus environment)
• Calculate pressure build-up in annulus in case of blocked vent ports
• Evaluate results of Annulus Pressure Monitoring
• Ageing assessment of polymer materials
• Dynamic strength and fatigue analysis of riser
• Corrosion assessment (material loss, HIC/SSC) and associate pipe strength degradation
• FLIP analysis
• Wear of outer sheath assessment
• Pull-out analysis of liner from end fitting
• Calculate bird caging
• Crack growth prediction analysis for polymer materials
Analysis for flowlines / subsea jumpers:
• Diffusion analysis (determine annulus environment)
• Calculate pressure build-up in annulus in case of blocked vent ports
• Ageing assessment of polymer materials
• Corrosion assessment (material loss, HIC/SCC, pitting, CO2 and O2 effects, water
condensation in annulus and vent system)
• Wear assessment of outer sheath
• Pull-out analysis of liner from end fitting
• Calculate bird caging
• Crack growth prediction analysis for polymer materials
• Free span analysis
15
Lifetime Extension of Flexible Pipe Systems
Analysis for ancillary equipment:
• Status of cathodic protection (anode consumption at end-fittings, clamps etc.)
• Status of annulus vent clamp
• Status of bend restrictors (steel/polymer)
• Integrity of piping between topside end fitting and emergency shutdown valve
• Integrity of hang off structure including fatigue analysis
• Crack growth analysis for metallic component and polymer
• Integrity of riser guide tube
• Integrity of bending stiffener polymer/steel parts including fatigue analysis
• Riser configuration equipment (buoyancy elements, anchors, mid water arch etc.)
16
Lifetime Extension of Flexible Pipe Systems
Appendix C: Examples of Recommended
Assessment Process for the LTE
These is an example of a recommended assessment process with specific analytical checks for the
LTE. Note that this is not an exhaustive list and this process may expand further for each LTE case.
Pressure Sheath Ageing
1)
Data collection
a) Operating temperature along length of flexible
b) pH variations over time
c)
Chemical injection history (particularly methanol)
2)
Calculate CIV based on previously performed ageing tests
3)
Calculate % utilisation of pressure sheath available lifetime
4)
Extrapolate remaining service life based upon expected future conditions
5)
Compare theoretical calculations to measurements, if coupon samples are available.
Example:
Operating Temp [C]
pH
Actual Duration
Allowable
Duration
% Utilization
Normal Operating 1
40
6
10
100
10.0
Normal Operating 2
45
6
2
90
2.2
Normal Operating 3
50
6
2
60
3.3
Normal Operating 4
55
6
2
35
5.7
Design
65
6
1
20
5.0
Methanol Injection
20
N/A
1
20
5.0
Total
18
Expected
Remaining Life
39.6
Case
17
31.3
years
Lifetime Extension of Flexible Pipe Systems
Annulus Corrosion / Corrosion Fatigue
1)
Data collection
a) Operating temperature history
b) Operating pressure history
c)
Fluid composition history
d) Vessel motion history
2)
Determine annulus condition history (SN curve determination)
a) Review annulus test reports over the life, or other annulus integrity test data
b) Perform gas diffusion analysis based upon as-experienced service conditions
3)
Determine local state of pressure and tensile armour wires
a) Calculate corroded thickness of pressure and tensile wires based upon asexperienced service conditions
b) Alternately, determine corroded thickness through direct inspection means
4)
Perform global dynamic analysis, and local fatigue analysis based upon outs of steps
1, 2, and 3
5)
Determine riser remaining life
End Fitting Tensile Wire Fatigue
1)
Similar to above
2)
Additional step for determining stress concentration factors to be considered in the
analysis.
18
Lifetime Extension of Flexible Pipe Systems
Glossary
Service Life (SL)
Period of time during which the flexible pipe is expected to fulfil all specified performance
requirements.
Design Life
Period of time during which the flexible pipe is designed to fulfil all specified performance
requirements. Design Life can be longer than Service Life, for example when the required
fatigue life is 10 times the duration of the service life.
Lifetime Extension (LTE)
A risk based engineering assessment to extend flexible pipe operation beyond the service
life it has been originally designed to.
19
Lifetime Extension of Flexible Pipe Systems
References
[1] American Petroleum Institute. API Spec 17J - Specification for Unbonded Flexible Pipe, Fourth Edition.
[2] American Petroleum Institute. API RP 17B - Recommended Practice for Flexible Pipe, Fifth Edition.
[3] American Petroleum Institute. API Spec 17L1 - Specification for Unbonded Flexible Pipe Ancillary
Equipment, First Edition.
[4] American Petroleum Institute. API RP 17L2 - Recommended Practice for Flexible Pipe Ancillary
Equipment, First Edition.
[5] Norsok Y-002, Life Extension For Transportation Systems
[6] Norsok U-009, Life Extension For Subsea Systems
[7] Handbook on Design and Operation of Flexible Pipe. Fergestad D and Løtveit SA, eds. Trondheim:
Marintek, 2014.
[8] Wood Group. “Flexible Pipe Integrity Management Guidelines and Good Practices”. Prepared for the
Sureflex JIP. 2017.
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23
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This guideline provides a framework
to assist companies and contractors
in extending the product lifetime
of unbonded flexible pipe systems
(including ancillary components) as
per API 17J and API 17L1/L2. This
FPLEN Guideline is intended for
incorporation into API 17B, Section
11 - Integrity Management.
www.iogp.org