mangold essential elements of risk assessment

Essential Elements of Risk Assessment

David Mangold and Kent [email protected] [email protected]

mailto:[email protected]

mailto:[email protected]

© Det Norske Veritas AS. All rights reserved.

Risk Assessment: Regulations vs Guidance Docs

(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

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)

• Subject Matter Experts• Relative Assessments• Scenario Assessments• Probabilistic

Assessments

Techniques

Objectives

ASME B31.8S, Section 5

© Det Norske Veritas AS. All rights reserved. 3

Risk Assessment Essential Elements

The Essential Elements are meant to- Be common sense ingredients that make risk assessment meaningful, objective, and

acceptable to all stakeholders- Be concise yet flexible, allowing tailored solutions (not a recipe) 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

http://theneveraloneprincess.com/wp-content/uploads/2013/03/recipes.jpg


Risk Assessment Essential Elements

Proper Aggregation

Bias Management

Sufficient Granularity

Full Integration of Pipeline Knowledge

Profiles of Risk

Characterization of Potential Consequences

Proper Probability of Failure Assessment

Measurements in Verifiable Units


Risk Assessment Essential ElementsMeasurements in Verifiable Units

The risk assessment must include a definition of ‘failure’ and produce verifiable estimates of failure potential. Therefore, the risk assessment must produce a measure of probability of failure (PoF) and a measure of potential consequence.

Both must be expressed in verifiable and commonly used measurement units, free from intermediate schemes (such as scoring or point assignments). Failure probability, which can also be expressed as a frequency, must capture effects of length and time, leading to a risk estimates such as:

Measure in Verifiable

Units

Probability of Failure

Grounded in Engineering Principles

Fully Characterize

Consequence of Failure

Profile the Risk Reality

Integrate Pipeline

Knowledge

Incorporate Sufficient

GranularityControl the Bias Unmask

Aggregation

• Incidents per mile-year

• Fatalities per mile-year

• Dollars per km-decade

conseq prob


Risk Assessment Essential ElementsProper Probability of Failure Assessment

All plausible failure mechanisms must be included in the assessment of PoF. Every failure mechanism must have the following three elements independently measured:- Exposure (attack) – The type and unmitigated aggressiveness of the force or process that may

precipitate failure. Example measurement units are ‘events per mile-year’ or ‘mils per year metal loss’.- Mitigation (defense) – The type and effectiveness of every mitigation measure designed to block or

reduce an exposure. The benefit from each independent mitigation measure, coupled with the combined effects of all mitigations, is to be estimated.

- Resistance (survivability) – The inherent ability of a pipeline to sustain forces and deformations in the event of mitigation failure. Resistance characteristics are to be evaluated separately to determine the probability of ‘damage without failure’ vs. ‘damage resulting in failure’.


Units



Fully Characterize



Integrate Pipeline

Knowledge



Aggregation

Exp

osur

e

Mitigation Resistance

Release

Detection and ControlBarriers

Miti

gate

d C

onse

quen

ces

E/M/R


Risk Assessment Essential ElementsProper Probability of Failure Assessment (continued)

Estimating Threat Exposure- Events per km-year (mile-yr) for time independent mechanism

- Third party- Incorrect operations- Weather & land movements

- mm/yr (MPY) for degradation mechanisms- External corrosion- Internal corrosion- Cracking (EAC / fatigue)


Units



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Integrate Pipeline

Knowledge



Aggregation



Measuring Mitigation

Strong, single measure

Or

Accumulation of lesser measures

Mitigation % = 1 - (remaining threat)

Remaining threat = (remnant from mit1) AND (remnant from mit2) AND (remnant from mit3) …

Mitigation % = 1-[(1-mit1) x (1-mit2) x (1-mit3)…]


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Integrate Pipeline

Knowledge



Aggregation

Miti

gate

d E

xpos

ure

Exp

osur

e

Mitigation

CPCoating



Estimating Resistance- Pipe spec (original)- Historical Issues

- Low toughness- Hard spots- Seam type- Manufacturing

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

- Required pipe strength- Normal internal pressure- Normal external loadings


Units



Fully Characterize



Integrate Pipeline

Knowledge



Aggregation




Units



Fully Characterize



Integrate Pipeline

Knowledge



Aggregation

Probability of Damage (PoD) = exposure x (1 - mitigation)

Probability of Failure (PoF) = PoD x (1- resistance)

{PoF = exposure x (1 - mitigation) x (1 - resistance)}

PoF (time-dependent) = 1-e-1/TTF

= exposure * (1 – mitigation) / resistance (example only)

Exposure PoD*

Mitigation PoF

Resistance




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Integrate Pipeline

Knowledge



Aggregation

Example:- Soil corrosivity studies have been used to calculate an unmitigated CGR of

5 mpy - Previous DCVG has been used to determine 85% of the coating is holiday

free- CP is believed to be providing only 60% coverage due to seasonal moisture

fluctuations- Average wall thickness at this location is estimated to be 0.21” with no

known manufacturing/construction concerns

= = = 700 yearsPoFEC =1-e-1/TFF = 0.14%PoF/mile-yr ≈0.0014failures/mile-yr


Risk Assessment Essential ElementsCharacterization of Potential Consequences

The risk assessment must identify and acknowledge the full range of possible consequence scenarios associated with failure, including ‘most probable’ and ‘worst case’ scenarios.


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Integrate Pipeline

Knowledge



Aggregation

Common Consequences of Interest:- Human health- Environment- Costs

Other Consequences of Interest:- Service Interruption- Production/transportation loss- Repair costs- Resumption of service- Contract penalties- Legal costs- Increased regulatory oversight- Corp reputation


Risk Assessment Essential ElementsCharacterization of Potential Consequences (continued)

Example (Continued):- Scenarios:

- HPA:

- ESA:

- CNW:

) = 0.10 x $62,500+0.9 x $770,550=$700,145 = $700k x 0.14% PoF/mile-yr= $999 / mile-yr= $7.6/year for 1 joint


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Integrate Pipeline

Knowledge



Aggregation

Ign

Cont

Ignition 10 % ProbabilityContamination 90 % Probability

Hazard Area (ign/cont) 20 / 1500 ft2

Value $5,000,000 val/receptorDensity 0.01 receptors/ft2

Damage rate (ign/cont) 0.1 / 0.001 % Per Scenario


Value $500 val/ft2

Density 1 receptors/ft2

Damage rate (ign/cont) 30 / 90 %/ft2


Value $200 val/ft2

Density 1 receptors/ft2

Damage rate (ign/cont) 90 / 1 %/ft2


Risk Assessment Essential ElementsFull Integration of Pipeline / Facility Knowledge

The assessment must include complete, appropriate, and transparent use of all available information. Appropriateness is evident when the risk assessment uses all information in substantially the same way that a subject matter expert (SME) uses information to improve their understanding of risk.


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Integrate Pipeline

Knowledge



Aggregation


Risk Assessment Essential ElementsSufficient Granularity

For analysis purposes, the risk assessment must divide the pipeline into segments where risks are unchanging (i.e. all risk variables are essentially unchanging within each segment). Due to factors such as hydraulic profile and varying natural environments, most pipelines will necessitate the identification of at least ten to twenty segments per km with some pipelines requiring thousands per km. - For the other assets such as facilities, dynamic segmentation is applied for equipment items

with identical characteristics.- Compromises involving the use of averages or extremes (i.e. maximums, minimums) to

characterize a segment can significantly weaken the analyses and are to be avoided.


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Aggregation


Risk Assessment Essential ElementsBias Management

The risk assessment must state the level of conservatism employed in all of its components – inputs, defaults (applied in the absence of information), algorithms, and results. The assessment must be free of inappropriate bias that tends to force incorrect conclusions for some segments. - For example, the use of weightings based on historical failure frequencies may misrepresent

lower frequency albeit important threats.

A way to measure and communicate conservatism in risk estimates- PXX

- P50- P90- P99.9

- Useful in conveying intended level of conservatism


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Integrate Pipeline

Knowledge



Aggregation


Risk Assessment Essential ElementsProfiles of Risk

The risk assessment must produce a continuous profile of changing risks along the entire pipeline, recognizing the changing characteristics of the pipe and its surroundings. The risk assessment must be performed at all points along the pipeline.


Units



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Integrate Pipeline

Knowledge



Aggregation

Scenario 1100 km oil pipelinewidespread coating failureriver parallelremote

Scenario 250 km gas pipeline2 shallow cover locationshigh population densityhigh pressure, large diameter

EL

km

EL

km


Risk Assessment Essential ElementsProfiles of Risk (continued)

Passing the ‘Map Point’ Test


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Knowledge



Aggregation


Risk Assessment Essential ElementsProper Aggregation

A 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

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

PoF total = Avg(PoF1, PoF2, … PoFn)

Overall PoF is probability of failure by [(thd pty) OR (corr) OR (geohaz)…]Ps = 1 - PoF

Overall Ps is probability of surviving [(thd pty) AND (corr) AND (geohaz)….]

So…

PoFoverall = 1-[(1-PoFthdpty) x (1-PoFcorr) x (1-PoFgeohaz) x (1-PoFincops)]


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Integrate Pipeline

Knowledge



Aggregation


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


Safeguarding life, property and the environment

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