Reliability Based Design for Pipelines – Canadian Standard Association Approach, Industry Response, and Comparison
with ISO 16708
International ISO Standardization Seminar for
the Reliability Technology and Cost Area
NEN - Vlinderweg 6 - 2623 AX Delft
29th March 2017
Maher Nessim
Francisco Alhanati
C-FER Technologies
Current Onshore Pipeline Design Approach
Applied hoop stress Specified MinimumYield Strength
Safety factor(Design factor x location factor)
Prevent yielding / rupture of new pipe under internal pressure
SMYSt
PD
2
Pipelines are designed using the Barlow Equation
2ISO Standardization Seminar - Delft NLMarch 2017
Pipeline Failure Stats
Most failures are associated with mechanical damage by external forces, corrosion and other deterioration mechanisms
36%
26%
6%
11%
4%
5%1%
11%
External Interference
External Corrosion
Internal corrosion
Manufacturing Defects
Geotechnical Hazard
Construction Defects
Operator Error
Other
Reportable Incidents for Natural Gas PipelinesUS DOT (2002 – 2008)
3ISO Standardization Seminar - Delft NLMarch 2017
Key Limitation
• Pipeline reliability with respect to the dominant failure mechanisms is far more sensitive to wall thickness than to other parameters, such as hoop stress
• The current design approach is not the most effective safety control parameter – results in widely varying risk levels for different pipelines
ISO Standardization Seminar - Delft NL 4March 2017
Implied Safety Levels
ISO Standardization Seminar - Delft NL 5March 2017
Resistance to dominant failure causes is more dependent on the wall thickness than the hoop stress factor
Hoop stress design factor not the most effective safety control parameter
Reliability Based Design
• Key features– Design for actual failure mechanisms (limit states)– Use reliability as a safety control parameter– Evaluate options based on meeting a specified reliability target
• Benefits– Known and consistent safety levels– Guidance for all relevant design and assessment conditions– Effective allocation of resources to maximize safety– Well suited to new situations (new technologies, materials or loads)
• Limitations– Requires probability calculations (data / expertise / effort)– Potential for different users to get different answers
ISO Standardization Seminar - Delft NL 6March 2017
Reliability Based Design Standards
• Reliability based design is permitted in many standards, e.g.– ISO 13623 / CSA Z662 / IGE TD1 / AS 2885.1
• Guidance is provided in a few standards, e.g.
– CSA Z662 (1995). Oil and gas pipeline systems – Annex C: Limit States design
– IGE/TD/1 (2001) – Steel pipelines and associated installations for high pressure gas transmission – Appendix 4: Structural reliability analysis
– ISO 16708 (2006) - Petroleum and natural gas industries - Pipeline transportation systems - Reliability-based limit state methods
– NEN 3650-1 (2006) – Requirements for pipeline systems – Section 8: Structural design
– CSA Z662 (2007). Oil and gas pipeline systems – Annex O: Reliability based design and assessment of onshore natural gas pipelines
ISO Standardization Seminar - Delft NL 7March 2017
Comparison Between ISO and CSA
Topic ISO CSA
Scope - pipelines All pipelinesBuried onshore pipelines (no crossings or
above-ground sections)
Scope - fluids All oil and gasSpecific fluids (Natural Gas / non-volatile
LVP / more to come)
Reliability targetsTo be defined by user – optional specific
guidance given for some casesPrescribed – defined as function of pipeline and location parameters
Loads, load combinations and
limit states
Generic definitions with illustrative examples
Comprehensive listing of potentially applicable loads, load combinations and
corresponding limit states
Reliabilityestimation
Detailed description of distribution and reliability theories – implementation left
to the user
Reference to reliability texts – specific limit state functions and input
distributions for key design conditions
Reliability checking
Generic checkSpecific methodology addressing pipeline
segmentation and length averaging
8ISO Standardization Seminar - Delft NLMarch 2017
CSA Approach - Highlights
• Limit States
• Reliability targets
• Reliability checking (demonstrating compliance)
ISO Standardization Seminar - Delft NL 9March 2017
Loads and Limit States
ISO Standardization Seminar - Delft NL 10
Life Cycle
Phase
Pipe
Configuration
Companion
LoadsLimit State
Limit State
Type
Stress
limit
Strain
limit
Time
Dependent
1 Cyclic bending Fatigue crack growth SLS Yes
2 Stacking weight Ovalization SLS No
Plastic collapse SLS No
Local Buckling SLS No
Girth weld tensile rupture SLS No
Local buckling SLS No
Testing All 3 Hydrostatic test Excessive plastic deformations SLS No
All 6 Internal pressure Burst of defect free pipe ULS No
7 Equipment Impact 6 Burst of a gouged dent2 ULS No
Local buckling SLS or ULS1
No
Upheaval buckling SLS or ULS1
No
Local buckling SLS or ULS1
Yes
Girth weld tensile rupture ULS Yes
Local buckling SLS or ULS1
Yes
Girth weld tensile rupture ULS Yes
Local buckling SLS or ULS1
Yes
Girth weld tensile rupture ULS Yes
Local buckling SLS or ULS1
No
Girth weld tensile rupture ULS No
Local buckling SLS or ULS1
Yes
Girth weld tensile rupture ULS Yes
Failure of a weld defect ULS Yes
Plastic collapse SLS or ULS1
No
Ovalization SLS No
Dynamic instability SLS or ULS1
No
Formation of mechanism by yielding SLS or ULS1
No
Local buckling SLS or ULS1
No
Girth weld tensile rupture ULS No
Waterway
crossing or
wetlands
16 Buoyancy 6,8 Floatation SLS or ULS1 No
Formation of mechanism by yielding SLS or ULS1
No
Local buckling SLS or ULS1
No
Girth weld tensile rupture SLS or ULS1
No
Local buckling SLS or ULS1
Yes
Girth weld tensile rupture ULS Yes
Dynamic instability SLS or ULS1
No
Burst of crack by fatigue ULS Yes
1 Starts as a serviceability limit state, but could progress to an ultimate limit state
Primary Load
Transportation
All
Installation
4 Bending during installation
Buried (installed
by directional
drilling)
5Directional drilling tension and
bending
9 Slope instability, ground movement 6,8,12
Operation
Buried
8 Restrained thermal expansion 6
10 Frost heave 6,8.12
12 Seismic loads6,8, 9 or10
or 11
Waterway
crossings15 River bottom erosion 6,8,16
Wind loads
11 Thaw settlement 6,8,12
13Loss of soil support (e.g.,
subsidence)6,8
Buried rail or road
crossings, or in
farmland
14 Overburden and surface loads 6
6,17
Above ground
17 Gravity loads 6
18 Support settlement 6,17
19
March 2017
Loads and Limit States
ISO Standardization Seminar - Delft NL 11
Life Cycle
Phase
Pipe
Configuration
Companion
LoadsLimit State
Limit State
Type
Stress
limit
Strain
limit
Time
Dependent
1 Cyclic bending Fatigue crack growth SLS Yes
2 Stacking weight Ovalization SLS No
Plastic collapse SLS No
Local Buckling SLS No
Girth weld tensile rupture SLS No
Local buckling SLS No
Testing All 3 Hydrostatic test Excessive plastic deformations SLS No
All 6 Internal pressure Burst of defect free pipe ULS No
7 Equipment Impact 6 Burst of a gouged dent2 ULS No
Local buckling SLS or ULS1
No
Upheaval buckling SLS or ULS1
No
Local buckling SLS or ULS1
Yes
Girth weld tensile rupture ULS Yes
Local buckling SLS or ULS1
Yes
Girth weld tensile rupture ULS Yes
Local buckling SLS or ULS1
Yes
Girth weld tensile rupture ULS Yes
Local buckling SLS or ULS1
No
Girth weld tensile rupture ULS No
Local buckling SLS or ULS1
Yes
Girth weld tensile rupture ULS Yes
Failure of a weld defect ULS Yes
Plastic collapse SLS or ULS1
No
Ovalization SLS No
Dynamic instability SLS or ULS1
No
Formation of mechanism by yielding SLS or ULS1
No
Local buckling SLS or ULS1
No
Girth weld tensile rupture ULS No
Waterway
crossing or
wetlands
16 Buoyancy 6,8 Floatation SLS or ULS1 No
Formation of mechanism by yielding SLS or ULS1
No
Local buckling SLS or ULS1
No
Girth weld tensile rupture SLS or ULS1
No
Local buckling SLS or ULS1
Yes
Girth weld tensile rupture ULS Yes
Dynamic instability SLS or ULS1
No
Burst of crack by fatigue ULS Yes
1 Starts as a serviceability limit state, but could progress to an ultimate limit state
Primary Load
Transportation
All
Installation
4 Bending during installation
Buried (installed
by directional
drilling)
5Directional drilling tension and
bending
9 Slope instability, ground movement 6,8,12
Operation
Buried
8 Restrained thermal expansion 6
10 Frost heave 6,8.12
12 Seismic loads6,8, 9 or10
or 11
Waterway
crossings15 River bottom erosion 6,8,16
Wind loads
11 Thaw settlement 6,8,12
13Loss of soil support (e.g.,
subsidence)6,8
Buried rail or road
crossings, or in
farmland
14 Overburden and surface loads 6
6,17
Above ground
17 Gravity loads 6
18 Support settlement 6,17
19
March 2017
Risk Based Reliability Targets – ULS
• Based on benchmarking to current practice
– Match or exceed average safety associated with a new pipeline network designed to acceptable standards and operated to best industry practices
– Maintain a uniform safety level for all pipelines
ISO Standardization Seminar - Delft NL 12March 2017
Risk Benchmarking Example –Total Societal Risk
1E-10
1E-09
1E-08
1E-07
1E-06
1E-05
1E-04
1E-03
1E-02
1.E+05 1.E+06 1.E+07 1.E+08 1.E+09
PD3 (psi-in
3)
Av
era
ge 5
0-y
r R
isk
(per
km
-yr)
Class 1Class 2Class 3Class 4Weighted average risk - 1.6E-5
1000 psi, 10 in 1200 psi, 20 in 1400 psi, 42 in
Calculated Risk Levels for Wide Range of Natural Gas Pipeline Designs and
Corresponding Average Risk Level and Length-weighted AverageISO Standardization Seminar - Delft NL 13March 2017
1.E-09
1.E-08
1.E-07
1.E-06
1.E-05
1.E-04
1.E-03
1.E-02
1.E+06 1.E+07 1.E+08 1.E+09 1.E+10 1.E+11 1.E+12 1.E+13
Allo
wab
le P
rob
abili
ty o
f Fa
ilure
(pe
r km
-yr)
rPD3 (people/ha-Mpa-mm3)
Allowable Failure Probabilities –Natural Gas
14ISO Standardization Seminar - Delft NLMarch 2017
Allowable Failure Probabilities –Non-volatile LVP Liquids
15
1.E-07
1.E-06
1.E-05
1.E-04
1.E-03
1.E-02
1.E+02 1.E+03 1.E+04 1.E+05 1.E+06
Allo
wab
le P
rob
abili
ty o
f Fa
ilure
(pe
r km
yr)
b D1.6 (mm)
ISO Standardization Seminar - Delft NLMarch 2017
Reliability Checking – Issues
• Pipeline segmentation based on potential consequence severity– Population density for natural gas– Environmental sensitivity for liquids
• Reliability checking for different threat types– Localized threats – point source (moving slope)– Distributed threats
• Continuous (internal pressure)• Randomly located (equipment impact)
• Reliability checking for different failure modes– Leaks– Ruptures
ISO Standardization Seminar - Delft NL 16March 2017
Validation and Scrutiny
• Developed under PRCI project – directed and supervised by industry
• Tested extensively to evaluate the impact on design and operational decision making
• Published in a series of 7 conference and 2 journal peer-reviewed papers –more to come
• Reviewed by 3 independent consultants and researchers
• Presented and debated in multiple sessions of the CSA Z662 Technical Committee
• Debated in a public forum sponsored by CSA in 2005
• Approved unanimously by the Z662 Technical Committee for adoption in 2007 edition of the Standard
ISO Standardization Seminar - Delft NL 17March 2017
Application
• Adoption initially slow– Apprehension about the use of firm reliability targets– Skepticism about the required probabilistic calculations– Lack of expertise in potential user organizations
• First applications were for arctic pipeline design against frost heave and thaw settlement loads because the current standards do not provide any guidance in this area
• Significant momentum over the past 2 to 3 years for application to conventional pipeline issues such as class location changes and management or corrosion and cracks– Heightened public awareness of pipeline risk– More recognition of the benefits of reliability– Improvements in data acquisition techniques
ISO Standardization Seminar - Delft NL 18March 2017
Future Direction
• Include non-volatile liquid in Annex O of full reliability based design and assessment (2019)
• Adopt a new version of Annex C on limit states design (2019)
• Develop a new risk based safety class and design factor system for the main body of the standard (2023?)
ISO Standardization Seminar - Delft NL 19March 2017
Questions ?
March 2017 ISO Standardization Seminar - Delft NL 20
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