PL Safety and Essentials of Risk Assessment

PL Safety and Essentials of Risk Assessment

Following the Essential Elements

Background

© Det Norske Veritas AS. All rights reserved. 2

Kalamazoo River, 2010

10ft creek

CoF: $1B
PoF: 1/1000yr

Expected Loss: $1M/yr for
~3m of pipeline!

$1,000,000,000 spent


Reality Check
 RM is not new; requires RA
 Risk-based decision-making is complex
- Because the real world is complex, measuring risk is
complex
- RM is even more complex than RA

 Dealing with the complexity is worthwhile
- increases understanding
- shows full range of options; many opportunities to impact risk
- cheaper than prescriptive ‘solutions’
- Improves decision-making
- the key to improving PL safety


Reality Check, Part Two

If you put tomfoolery into a computer, nothing comes out
of it but tomfoolery. But this tomfoolery, having passed
through a very expensive machine, is somehow
ennobled and no-one dares criticize it.
- Pierre Gallois

The Illusion of Knowledge


How good is PL RA now?

Pockets of strengths
But
Weaknesses are apparent
- A complicated topic--incomplete understanding is common
- Lack of standardized RA approaches
- Errors in some industry standards
- New demands by regulators and other stakeholders
- Myths and misconceptions


PL Risk Modeling Confusion

ASME B31.8s
•Subject Matter Experts
Qualitative
•Relative Assessments
Quantitative
•Scenario Assessments
Semi-quantitative
•Probabilistic Assessments
Probabilistic
Deterministic


Regulations: IMP Objectives vs RA Techniques
Objectives
(a) prioritization of pipelines/segments for scheduling integrity assessments and mitigating action
(b) assessment of the benefits derived from mitigating action
(c) determination of the most effective mitigation measures for the identified threats
(d) assessment of the integrity impact from modified inspection intervals
(e) assessment of the use of or need for alternative inspection methodologies
(f) more effective resource allocation
Techniques
• Subject Matter Experts
• Relative Assessments
• Scenario Assessments
• Probabilistic
Assessments
Numbers Needed
•Failure rate estimates for each threat on each PL segment
•Mitigation effectiveness for each contemplated measure
•Time to Failure (TTF) estimates (time-dep threats)


“Threat Interaction” Confusion
 Time Dependent Threats  Stable Threats Potential Weaknesses
- Corrosion  Manufacturing-related flaws in
- External
- Pipe body
- Internal
- Pipe seam
- Cracking
- Fatigue  Welding / Fabrication-caused flaws in
- EAC - Girth welds
- Fabrication welds
 Time Independent Threats - Wrinkled / buckled bend
- Third party - Threads / couplings
- Geohazards  Defects present in equipment
- Incorrect operations - Gaskets, O-rings
- Sabotage - Control / relief devices
- Seals, packing
- Other equipment


Myths: Data Availability vs Modeling Rigor
Myth:
 Some RA models are better able to accommodate low data availability

Reality:
 Strong data + strong model = accurate results
 Weak data + strong model = uncertain results
 Weak data + weak model = meaningless results

11

Myth: QRA / PRA Requirements
Myth:
 QRA requires vast amounts of incident histories

Reality:
 QRA ‘requires’ no more data than other techniques
 All assessments work better with better information

 Footnotes:
- Some classical QRA does over-emphasize history
- Excessive reliance on history is an error in any methodology

12

Removing the Weaknesses—The New Look of PL RA

PoF (len adjusted)

140

120

100
Frequency

80

60 PoF (unitized)

40 12.0%

20 10.0%

8.0%
0
6.0%
0. 0 1
0. 01
0. 04

0. 7

0. 13
0. 16
0. 19
0. 22
0. 25
0. 28

1
e
00

03

or
00
0
0

0
0
0
0
0
0

M
00
00
00

00
00
00
00
00
00
00

4.0%
0.

Bin 2.0%

0.0%
0 20000 40000 60000 80000 100000 120000 140000
station


Essential Elements


Essential Elements
 The Essential Elements are meant to
- Minimize the weaknesses in current PL RA practice
- Be common sense ingredients that make risk assessment meaningful, objective, and
acceptable to all stakeholders
- Be concise yet flexible, allowing tailored solutions to situation-specific concerns
- Lead to smarter risk assessment

 The elements are meant to supplement, not replace, guidance, recommended
practice, and regulations already in place


The Essential Elements
Measurements in Verifiable Units

Proper Probability of Failure Assessment

Characterization of Potential Consequences

Full Integration of Pipeline Knowledge

Sufficient Granularity

Bias Management

Profiles of Risk

Proper Aggregation


Measure in Verifiable Units
Probability of
Measure in Fully
Failure Integrate Incorporate
Characterize Profile the Risk Unmask
Verifiable Grounded in
Consequence of
Pipeline Sufficient Control the Bias
Aggregation
Engineering Knowledge Granularity Reality
Units Failure
Principles

 Must include a definition of “Failure”
 Must produce verifiable estimates of PoF and CoF in
commonly used measurement units
 PoF must capture effects of length and time
 Must be free from intermediate schemes (scoring, point
assignments, etc)
“Measure in verifiable units” keeps the
process transparent by expressing risk
elements in understandable terms that
can be calibrated to reality


Measure in
Verifiable
Units

Risk Estimates as Measurements

Risk = Frequency of consequence
- Temporally
- Spatially
TTF = time to failure
•Incidents per mile-year remaining life estimates in
years
•fatalities per mile-year

•dollars per km-decade

conseq prob


Measure in
Verifiable
Units

Why measurements instead of scores?

Direct measurements are efficient
- Less subjective
- Anchored in ‘real world’, able to capture real world
phenomena
- Defensible, auditable, transparent
- Avoids need for standardization
- Avoids erosion of score definitions
- Allows calculation of costs and benefits
- Supports better decisions


Probability of Failure Grounded in Engineering Principles
Probability of
Measure in Fully
Consequence of
Aggregation
Units Failure
Principles

 All plausible failure mechanisms must be included in the
assessment of PoF
 Each failure mechanism must have the following elements
independently measured:
- Exposure
- Mitigation
- Resistance

 For each time dependent failure mechanism, a theoretical
remaining life estimate must be produced


Probability of
Failure Grounded
in Engineering
Proper PoF Characterization Principles

Independent Evaluations of:

 Exposure: likelihood and aggressiveness of a failure mechanism reaching the pipe when no

mitigation applied (ATTACK)

 Mitigation: prevents or reduces likelihood or intensity of the exposure reaching the pipe

(DEFENSE)

 Resistance: ability to resist failure given presence of exposure (SURVIVABILITY )


Probability of
Failure Grounded
in Engineering
Simple and Robust Relationships are Available Principles

Probability of Failure (PoF) = Exposure x (1 - Mitigation) x (1 – Resistance)

Probability of Damage

TTF = exposure * (1 – mitigation) / resistance
PoF = f (TTF)


Probability of
Failure Grounded
in Engineering
Estimating Threat Exposure Principles

Events per mile-year for time independent
mechanism
- third party
- incorrect operations
- weather & land movements

MPY for degradation mechanisms
- Ext corr
- Int corr
- Cracking (EAC / fatigue)


Estimating Mitigation Measure Effectiveness
Strong, single measure
Or
Accumulation of lesser measures

Cathodic Public Maint Pigging
protection Patrol Education
system

Coating Depth of Casing Training & Chem Inhibition
system cover Competency

Exposure Damage

Slide 27

Probability of
Failure Grounded

Estimating Resistance in Engineering
Principles

 Pipe spec (original)  Required pipe strength
- Normal internal pressure
 Historical issues - Normal external loadings
- Low toughness
- Hard spots
- Seam type
- Manufacturing

 Pipe spec (current)
- ILI measurements
- Calcs from pressure test
- Visual inspections
- Effect of estimated degradations


Probability of
Failure Grounded
in Engineering

Best Estimate of Pipe Wall Today Principles

Adjust measurements for age and accuracy

Measurement error Degradation Since Meas

Current Estimate

Press Test
1992
8 mpy x 21 yrs = 168 mils
(inferred) +/- 5%

ILI
2005
8 mpy x 8 yrs = 64 mils
+/- 15%


PoF: Critical Aspects


Fully Characterize Consequence of Failure
Probability of
Measure in Fully
Consequence of
Aggregation
Units Failure
Principles

 Must identify and acknowledge the full range of possible
consequence scenarios
 Must consider ‘most probable’ and ‘worst case’ scenarios

HCA

Spill path
PL Hazard
Zone


Fully
Characterize
Consequence
Consequence Estimation Overview of Failure

Sequence of Analysis
1. Chance of failure (threat models)
Probability
2. Chance of failure hole size
3. Spill size (considering leak detection and reaction scenarios)
- Volume Out
2 4 5 6
4. Chance of ignition Product Hole size
Hole size
Ignition scenario
Ignition
Distance thermal
from source hazard
Contaminati
on hazard
Total
probability
of hazard
probability probability (ft)
- Immediate immediate ignition 5%
(ft)
0
zone (ft)
400
zone (ft)
0 400
zone
0.2%
- Delayed rupture 4% delayed ignition
no ignition
10%
85%
600
600
500
0
400
900
1100
1500
0.4%
3.4%
- None immediate ignition 2% 0 200 0 200 0.3%
oil medium 16% delayed ignition 5% 200 300 200 500 0.8%
no ignition 93% 200 0 500 700 14.9%
5. Spill dispersion immediate ignition 1% 0 50 0 50 0.8%
delayed ignition 2% 80 100 0 180 1.6%
- Pipeline/product characteristics small 80%
no ignition 97% 80 0 80 160 77.6%
- Topography (if liquid release)
- Meteorology (if gaseous release)
6. Hazard area size and probability (for each scenario)
7. Chance of receptor(s) being in hazard area (counts, density, or area)
8. Chance of various damage states to various receptor (including consequence mitigation)
9. Calculate Expected Loss (Prob x Consequence $)


Integrate Pipeline Knowledge
Probability of
Measure in Fully
Consequence of
Aggregation
Units Failure
Principles

 The assessment must include complete, appropriate, and
transparent use of all available information
 ‘Appropriate’ when model uses info as would an SME


Integrate
Pipeline

External Corrosion Model Knowledge

EC POF (prob/mile-yr)

EC TTF (Years –assuming a per mile basis )

Available Pipe Wall (in) Growth Rate (mpy)
Estimate x Adjustment

Estimate (in) Adjustments (%) Estimate (mpy)
Total mpy x (1-Mitigation) Measured (mpy)

Max based on:
Cumulative:
1. NOP Environment (mpy) Mitigation (%) based on Active
1. Joint Type Direct measurements
2. Hydrotest Sum Corrosion Locations
2. Reinforcements adjusted by
3. NDE/ILI
3. Manuf & Const Confidence
2&3 adjusted for
4. Pipe Type
mpy growth since 1. Above/Below Ground
5. Toughness CP Gaps (Prob of gaps/ft)
measurement 2. Atmospheric CGR (mpy)
6. Flaws Sum of gaps/mi converted to probability External Coating Holiday Rate
7. External Loads3. Electrical Isolation (%)
8. Spans 4. Soil based CGR (mpy)
1. Corrosivity
2. Moisture Content CP Effectiveness CP Interference Estimated (defects/mi)
3. MIC 1. Defects/mi adjusted by
5. Mitigated AC Induced confidence
CGR (mpy) Measured Gaps /mi Locations/mi: Measured (defects/mi)
1. CP Readings 1. DC Sources 1. Defects/mi adjusted by
adjusted by (mitigated) confidence and age
confidence 2. Coating
Estimated Gaps/mi Shielding
1. Distance from 3. Casing
test station Shielding
2. PL Age
3. Criteria
4. Rectifier out of
service history

Incorporate Sufficient Granularity
Probability of
Measure in Fully
Consequence of
Aggregation
Units Failure
Principles

 Risk assessment must divide the pipeline into segments
where risks are unchanging
 Compromises involving the use of averages or extremes
can significantly weaken the analysis and are to be avoided


Incorporate
Sufficient

Dynamic Segmentation Granularity

Due to the numerous and constantly-varying factors
effecting the risk to the pipeline, proper analysis will
require at least 10 segments per mile
(not uncommon to have thousands of segments per mile)

Steel Pipe wall 0.320” Pipe wall 0.500”

1995 1961
Landslide Threat
Population Class 3


Control the Bias
Probability of
Measure in Fully
Consequence of
Aggregation
Units Failure
Principles

 Risk assessment must state the level of conservatism
employed in all of its components
 Assessment must be free of inappropriate bias that tends to
force incorrect conclusions


Control the
Bias
Certainty

“Absolute certAinty is
the privilege of fools
And fAnAtics.”


Control the

Understanding Conservatism and Uncertainty Bias

A way to measure and communicate conservatism in risk estimates
- PXX
- P50
- P90
- P99.9
Useful in conveying intended level of conservatism


The Role of Historical Incidents Control the
Bias

Problems:
 Historical data usefulness in current situation
 Small amount of data in rare-event situations
 Representative population
 Behavior of the individual vs population

weightings


Profile the Risk Reality
Probability of
Measure in Fully
Consequence of
Aggregation
Units Failure
Principles

 The risk assessment must be performed at all points along
the pipeline
 Must produce a continuous profile of changing risks along
the entire pipeline
 Profile must reflect the changing characteristics of the pipe
and its surroundings


Risk Profile: Passing the ‘Map Point’ Test
Profile the
Risk Reality


Profile the

Profile to Characterize Risk Risk Reality

Scenario 1
100 km oil pipeline
widespread coating failure
river parallel
remote

Scenario 2
50 km gas pipeline
2 shallow cover locations
high population density
high pressure, large diameter


Profile the
Risk Reality

Risk Characterization

Scenario 2
Scenario 1 50 km gas pipeline
100 km oil pipeline 2 shallow cover locations
widespread coating failure high population density
river parallel high pressure, large diameter
remote location

EL
EL

km km

Very different risk profiles


System Profiles Compared


Proper Aggregation
Probability of
Measure in Fully
Consequence of
Aggregation
Units Failure
Principles

 Proper process for aggregation of the risks from multiple
pipeline segments must be included
 Summarization of the risks from multiple segments must
avoid simple statistics or weighted statistics that mask the
actual risks


Unmask
Aggregation
Aggregating Risks for Collection of Pipe Segments

PoF total = PoF1 + PoF2 + PoF3 + PoF4 + …. PoFn

PoF total = 137% . . . ?

Simple sum only works when values are very
low.
Len-weighted avg masks ‘weak link in chain’


Unmask

Aggregating Risks Aggregation

PoF total = Avg(PoF1, PoF2, …PoFn)

Avg PoF = Avg PoF
But

PoF PoF

≠

KM KM


Unmask

Aggregating Risks Aggregation

PoF total = Max(PoF1, PoF2, …PoFn)

Max PoF = Max PoF
But

PoF PoF

≠

KM KM


Aggregating Risks

PoF total = Max(PoF1, PoF2, …PoFn)

Max PoF = Max PoF
But

PoF PoF

≠

KM KM


Unmask
Aggregation
Aggregating Failure Probabilities

Overall PoF is prob failure by [(thd pty) OR (corr) OR (geohaz)…]

PoS = 1 - PoF

Overall PoS is prob surviving [(thd pty) AND (corr) AND (geohaz)….]

So…

PoF overall = 1-[(1-pfthdpty) x (1-pfcorr) x (1-pfgeohaz) x (1-pfincops)]


The Essential Elements
Measurements in Verifiable Units

Proper Probability of Failure Assessment

Characterization of Potential Consequences

Full Integration of Pipeline Knowledge

Sufficient Granularity

Bias Management

Profiles of Risk

Proper Aggregation


The New Look of PL RA

PoF (len adjusted)

140

120

100
Frequency

80

60 PoF (unitized)

40 12.0%

20 10.0%

8.0%
0
6.0%
0. 0 1
0. 01
0. 04

0. 7

0. 13
0. 16
0. 19
0. 22
0. 25
0. 28

1
e
00

03

or
00
0
0

0
0
0
0
0
0

M
00
00
00

00
00
00
00
00
00
00

4.0%
0.

Bin 2.0%

0.0%
0 20000 40000 60000 80000 100000 120000 140000
station


Intended Outcomes


Intended Outcomes of Application of EE’s
 Efficient and transparent risk modeling
 Accurate, verifiable, and complete results
 Improved understanding of actual risk
 Risk-based input to guide integrity decision-making: true risk management

 Optimized resource allocation leading to higher levels of public
safety
 Appropriate level of standardization facilitating smoother regulatory audits
- Does not stifle creativity
- Does not dictate all aspects of the process
- Avoids need for (high-overhead) prescriptive documentation

 Expectations of regulators, the public, and operators fulfilled


If you don’t have a number,
you don’t have a fact,
you have an opinion.


Safeguarding life, property
and the environment

www.dnv.com

Kent Muhlbauer
wkm@pipelinerisk.com


PL Safety and Essentials of Risk Assessment

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