Pipeline Risk Management

Modeling of Corrosion

NACE ECDA Seminar

Jan 2009

What can a risk assessment do?

• where will the next failure

happen?

• when will a failure occur?

• how many failures next year?

where are the hot spots?

what is the best use of my resources?

what are the priorities?

Key Concepts

• Risk = (hazard likelihood) X (hazard consequence)

• Probability = Degree of Belief

• Risk Assessment -- Risk Management

• Management = choices in resource allocation

Historical (Informal) Risk Mgmt

ADVANTAGES:

• simple/intuitive

• consensus is often sought

• utilizes experience and engr judgment

• successful

Historical (Informal) Risk Mgmt

REASONS TO CHANGE:

• more at stake from mistakes

• inefficiencies/subjectivities

• lack of consistency

• need to consider complicated factors

• regulatory mandates

Gas IM Rule

Objectives• Prioritize pipeline segments

• Evaluate benefits of mitigation

• Determine most effective mitigation

• Evaluate effect of inspection intervals

• Assess the use of alternative assessment

• Allocate resources more effectively

ASME B31.8S, Section 5

Gas IM Rule

Points to consider• Account for relevant attributes

• Use conservative defaults for unknown data

• Identify significant risk-driving factors

• Sufficient segment discretization or resolution

• Predictive or “what-if” capability

• Updateable to reflect changes or new information

• Populating risk model is resource intensive

• Validate model, show to be plausible with respect to known

history and significance of threats

ASME B31.8S, Section 5

Threat Categories

• ASME B31.8 Supplement considers 3 categories

of threat:

– Time Dependent – May worsen over time;

require periodic reassessment

– Time Stable – Does not worsen over time; one-

time assessment is sufficient (unless conditions

of operation change)

– Time Independent – Occurs randomly; best

addressed by prevention

Bathtub Curve

Failures

Time

Threat Categories

Time Dependent Threats

• External corrosion

• Internal corrosion

• Stress-corrosion cracking (SCC)

• (Fatigue)

Threat Categories Time Independent

(Random) Threats

• Third-party/Mechanical damage

– Immediate failure

– Delayed failure (previously damaged)

– Vandalism

• Incorrect operations

• Weather related

– Cold weather

– Lightning

– Heavy rain, flood

– Earth movement

Threat CategoriesTime Stable Threats (resistance)

• Manufacturing-related flaws in

– Pipe body

– Pipe seam

• Welding / Fabrication-caused

flaws in

– Girth welds

– Fabrication welds

– Wrinkled / buckled bend

– Threads / couplings

• Defects present in equipment

– Gaskets, O-rings

– Control / relief devices

– Seals, packing

– Other equipment

ASME B31.8s

• Subject Matter Experts

• Relative Assessments

• Scenario Assessments

• Probabilistic Assessments

Better Way to Conceptualize

• Types of Models

– Absolute Results

– Relative Results

• Tools for All Models

– Probabilistic methods

• Scenarios

• Trees

– SME (input and validation)

Relative, Index, Scoring Models

• intuitive

• comprehensive

• ease of setup and use

• optimum for prioritization

• mainstream

• served us well in the past

Scoring Model Issues

• Difficult to anchor

• Potential for masking

• Technical compromises

– weightings

– scale direction

– interactions of variables (dep vs indep)

• Validation (reg reqmt)

• New Uses

Index Sum vs. Fail Probability

Scenario 1 Scenario 2

Index Score

Probability of Failure Score

Index Score

Probability of Failure Score

Third Party Damage 60 90

Corrosion 70 10

Design 80 90

Operations 70 90

280 280

Index Sum vs. Fail Prob

Scenario 1 Scenario 2

Index Score

Probability of Failure Score

Index Score

Probability of Failure Score

Third Party Damage 60 0.4 90 0.1

Corrosion 70 0.3 10 0.9

Design 80 0.2 90 0.1

Operations 70 0.3 90 0.1

280 76.5% 280 92.7%

Now

• plan for centerpiece of public scrutiny

• plan for legal challenges

• support integrity verification schedule

• determine appropriate reaction to risk

• anticipate desire for anchoring the numbers

• few computer limitations

Enhanced Modeling Approach

Probability of Failure

• Exposure

• Mitigation

• Resistance

Definitions

• Exposure: liklihood of an active failure mechanism reaching the pipe

when no mitigation applied

• Mitigation measure: prevents or reduces likelihood or intensity of the

exposure reaching the pipe

• Resistance: ability to resist failure given presence of exposure/threat

Information Use--Exposure, Mitigation, or

Resistance?

pipe wall thickness

air patrol frequency

soil resistivity

coating type

CP P-S voltage reading

date of pipe manufacture

operating procedures

nearby traffic type and volume

nearby AC power lines (2)

ILI date and type

pressure test psig

maintenance pigging

surge relief valve

casing pipe

flowrate

depth cover

training

SMYS

one-call system type

SCADA

geotech study

pipe wall lamination

wrinkle bend

Absolute Risk Values

Frequency of consequence

– Temporally

– Spatially

•Incidents per mile-year

•fatalities per mile-year

•dollars per km-decade

conseq prob

Dependent vs Independent

InteractionsAND Gates

– CP failure AND coating failure = failure of mitigation

– CP effectiveness = P/S reading AND P/S distance AND P/S age

OR gates

– PoF = PoF1 OR PoF2 OR PoF3

– Corr control = coating effectiveness OR CP effectiveness

Combination of Likely Events

0.8 AND 0.8 AND 0.8 AND 0.8 AND 0.8

= 0.8 x 0.8 x 0.8 x 0.8 x 0.8 = 0.3actually unlikely

0.8 OR 0.8 OR 0.8

= [1-(1-0.8) x (1-0.8) x (1-0.8)] = 0.992very likely

Failure Probabilities

Overall Pf is Prob Failure by [(Thd Pty) OR (Corr) OR (GeoHaz)…]

Ps = 1 - Pf

Overall Ps is Prob Surviving [(Thd Pty) AND (Corr) AND (GeoHaz)….]

So…

Pf overall = 1-[(1-Pfthdpty) x (1-Pfcorr) x (1-Pfgeohaz) x (1-Pfincops)]

Final PoF

PoF overall = PoFthdpty+ PoFTTF + PoFtheftsab+ PoFincops+ PoFgeohazard

PoF overall = 1-[(1-PoFthdpty) x (1-PoFTTF) x (1-PoFtheftsab) x (1-PoFincops) x

(1-PoFgeohazard)]

Guess PoF if 1%, 4%, 2%, 2%, 0%

Calc:

Probability of Failure

• Exposure

• Mitigation

• Resistance

Estimating Threat Exposure

• Events per mile-year for time independent /

random mechanism– third party

– incorrect operations

– weather & land movements

– equipment failures

• MPY for degradation mechanisms– ext corr

– int corr

– SCC / fatigue

Failure Rates

Failures/yr Years to Fail Approximate Rule Thumb

1,000,000 0.000001 Continuous failures

100,000 0.00001 fails ~10 times per hour

10,000 0.0001 fails ~1 times per hour

1,000 0.001 fails ~3 times per day

100 0.01 fails ~2 times per week

10 0.1 fails ~1 times per month

1 1 fails ~1 times per year

0.1 10 fails ~1 per 10 years

0.01 100 fails ~1 per 100 years

0.001 1,000 fails ~1 per 1000 years

0.0001 10,000 fails ~1 per 10,000 years

0.00001 100,000 fails ~1 per 100,000 years

0.000001 1,000,000 One in a million chance of failure

0.0000000001 1,000,000,000 Effectively, it never fails

Time Dependent Mech

PoF time-dep = f (TTF)

where

TTF = “time to failure”

TTF = (available pipe wall) / [(wall loss rate) x (1 – mitigation

effectiveness)]

Advantages of New Exposure

Estimates• Estimates can often be validated over time

• Estimate values from several causes are directly additive. E.g. falling

objects, landslide, subsidence, etc, each with their own frequency of

occurrence can be added together

• Estimates are in a form that consider segment-length effects and

supports PoF estimates in absolute terms

• Avoids need to standardize qualitative measures such as “high”,

“medium”, “low” avoids interpretation and erosion of definitions over

time and when different assessors become involved.

• Can directly incorporate pertinent company and industry historical

data.

• Forces SME to provide more considered values. It is more difficult to

present a number such as 1 hit every 2 years

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) …

Measuring Mitigation

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

In words: mitigation % = 1 - (remaining threat)

remaining threat = (remnant from mit1) AND (remnant from mit2) AND (remnant

from mit3) …

What is cumulative mitigation benefit from 3 measures that independently produce

effectiveness of 60%, 60%, and 50%?

Coating-CP Interaction

PoD of coating

OR gate

CP effectiveness

Calibrating Coating Fail Rate

calibrate coating fail rate using DOT stats

coat defect rate

dia

A, sq-

ft/linear ft

A, sq-

ft/mi fail/mil-yr

% corr

fail

coating

fail fctr

fails/per

sq ft/yr

24 6.3 33,175 0.001 0.3 100 9.0E-07 0.003 fails per yr per 33K sq ft

12 3.1 16,588 0.001 0.3 100 1.8E-06

10 2.6 13,823 0.001 0.3 100 2.2E-06

8 2.1 11,058 0.001 0.3 100 2.7E-06

6 1.6 8,294 0.001 0.3 100 3.6E-06

assume 100x as many coating failures as corr failures

% bare from CP current demand….

or

PoD for Coating

12” diameter

PoD = 1 - EXP[-[surface area, ft2)x(failure rate per ft2)]

L = 1 ft L = 10 ft L = 100 ft L = 1000 ft L = 5280 ft

excellent 5.0E-07 0.00% 0.00% 0.02% 0.16% 0.83%

good 2.5E-06 0.00% 0.02% 0.18% 1.75% 8.91%

fair 3.2E-04 2.46% 22.1% 91.8% 100% 100%

poor 4.0E-02 11.8% 71.4% 100% 100% 100%

absent 1.0E+07 100% 100% 100% 100% 100%

Probability of Defect in Segment, per yeardefect rate

per sq ft

Coating

Score

Corrosion Control Effectiveness

Coating Condition

Coating Defect Type

Prob of Defect Type per sq ft

Is CP fully eff?

Prob of CP

protecting pipe

Scenario Prob

Resultant MPY

Y 0.9 99.99% 0 none 99.9%

N 0.1 0.01% 0

Y 0.9 0.09% 0 hole 0.1%

N 0.1 0.01% 16

Y 0.1 0.0% 0

excellent

shielding 0.0% N 0.9 0.0% 16

Final probability of 16 mpy damage rate per sq ft 0.01% 16

Final probability of 0 mpy damage rate per sq ft 99.99% 0

Damage vs Failure

• Probability of Damage (PoD) = f (exposure, mitigation)

• Probability of Failure (PoF) = f (PoD, resistance)

Exposure PoD

Mitigation PoF

Resistance

Estimating Resistance

• pipe spec (original)

• historical issues

– low toughness

– hard spots

– seam type

– manufacturing

• pipe spec (current)

– ILI measurements

– calcs from pressure test

– visual inspections

– effect of estimated degradations

• required pipe strength

– normal internal pressure

– normal external loadings

Best Estimate of Pipe Wall Today

Press Test

1992

ILI

2005

Measurement error Degradation Since Meas

8 mpy x 15 yrs = 120 mils

8 mpy x 2 yrs = 16 mils+/- 15%

+/- 5%(inferred)

2007 Estimate

Best Estimate of Pipe Wall Today

Press Test 1

Press Test 2

Bell Hole 1

Bell Hole 2

ILI 1

ILI 2

NOP

Best Est Today

ILI Capability Matrix

Dent/ Ovality/

Gouge Buckling

Aggressive 5 5 100 10 20 50 50 5 100

Routine 10 10 100 50 50 50 50 10 100

Min 15 15 100 100 50 50 50 15 100

Aggressive 10 10 100 50 50 50 50 10 100

Routine 15 15 100 100 50 50 50 15 100

Min 20 20 100 100 50 50 50 20 100

5 5 100 100 20 20 5 5 100

TFI 20 20 5 10 50 50 50 20 5

EMAT 50 50 10 10 50 50 10 50 10

50 50 10 10 50 50 10 50 10

100 100 100 100 5 5 100 100 100

Press test 5 5 5 5 2 2 2 5 5

Defect Type

External

Corrosio

Internal

Corrosio

Axial

Crack

Circum

Crack Lamin

Ultrasound

Ultrasound shear wave crack tool

Caliper, sizing, gauging, inertial

Max Surviving Defect

Metal Loss

Inspection

Type

Validation (Pig-

Digs) Protocol Crack

MFL high

resolution

MFL std

resolution

NOP & Integrity

+ Integrity info -Rupture potential

-Higher stress

-Fatigue

Time

PoF

TTF to PoF

Time

PoF

TTF to PoF

PoF: TTF & TTF99

time

PoF PoF=100%

PoF=1%

TTF99

Examples

• TTF = 0.160” / [(16 mpy) x (1 - 0.9)] = 100 years

• TTF99 = 0.160” / (16 mpy) = 10 years

• PoF => lognormal or other =>0.001%

• TTF = 0.016” / [(16 mpy) x (1 - 0.9)] = 10 years

• TTF99 = 0.016” / (16 mpy) = 1 year

• PoF = 1/TTF = 1%

Approach Advantages

• more intuitive

• better models reality

• distinguishes between unmitigated exposure to a threat,

mitigation effectiveness, and system resistance--better risk

management decisions

• eliminates need for unrealistic and expensive re-weighting of

variables for new technologies or other changes

• flexibility to present results in either absolute terms or relative

terms

• more audit friendly