Calvo Lana

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Structure of the presentation

Introduction.

What risk assessment is.

The methodology to assess the pipeline risk.

Criteria for accepting risk assessment results.

Risk reduction options: influence of maintenanceand inspection.

References.



Introduction

Pipelines is one of the safest ways totransport hazardous materials.

The safety record of the pipeline

industry is improving each year, asdemonstrated by the leakfrequencies shown by the main

industrial organizations.



Spill frequency for oil pipelines

Performance of European crosscountry oil pipelines. Statistical summary of reported spillagesin 2005 and since 1971, CONCAWE, R04/07, May 2007 (www.concawe.be).



Leak frequency for high pressure gas

pipeline

6th EGIG report 1970 – 2004. Gas pipeline incidents, EGIG, 05.R.002, December 2005

(www.egig.nl)



Introduction (2)

Nevertheless, thepossibility of an accidentis always present andsometimes the accidentshappens.

For this reason, it isnecessary to assess therisk and check that it isbelow a minimum

considered acceptable.

Ghislenghein incidents, Belgium. July 2004.

Rupture of a high pressure pipeline due to a third party aggression.

(source: http://picture.belga.be)



Remarks

This presentation will be mainly focus in thea sse s sm e n t o f r i s k on high pressure gas pipelines,although many of the content is directly applicableto oil pipelines.

Most of the information shown is based in thePIPESAFE software package, developed by

Advantica (UK) for a international group of gascompanies.

This software develops a methodology speciallydesigned to assess the risk on gas pipelines andthe mathematical model for calculating the effectsof an accident have been validated against a wideset of field scale test.



What is risk assessment?

Risk Assessment = Quantification of Risk

It is important to distinguish between:•Hazard: the potential to cause harm

•Risk: realisation of the hazard

Risk =

= f(Failure Frequency, Failure Consequence)



Risk assessment/management

Hazard Identification

Hazard Reduction

Quantification of Frequencies

Quantification of Consequences

Risk Reduction and MitigationApplication of Criteria

RA

RM



Hazard of oil and gas pipelines

In hydrocarbon products accidents, onlythermal radiation, if release ignites, is

normally considered a hazard to people.

Toxic effects are not expected, except ifpeople goes inside the smoke cloud afterignition. Normally, this is not taken intoaccount.

Permanent environmental damages shouldbe taken into account in case of oilpipelines.



Steps in a risk analysis

•To define a failure cause and mode.

•To calculate / estimate the failure frequency.

•To calculate the failure consequences.

•To calculate the risk.

IMPORTANT:

The risk result calculated is highly influenced

by the methodology and the mathematicalmodels utilised in the calculation.



Steps in a risk analysis

PIPESAFE software package, risk calculation flow



Data needed for a RA

•Pipeline geometry

•Pipeline material

•Pipeline operating conditions

•System data

•Site details

•Environmental/weather

Diameter

Wall thickness

Pressure

Cover

Compressor Valves PRS



Failure causes

Corrosion•Internal corrosion: normally in gathering pipelines.

•External corrosion: main corrosion in transport pipelines.

Fatigue•Due to cycles in the internal pressure.

Construction Defects•Each year lest important due to the improvements in quality

control in construction.Material Defects

•Each year lest important due to the improvements in qualitycontrol in material production.

Ground Movement

•Dependant of the pipeline trace, it could be controlled with theappropriate methods and selection of the route.

External Interference•Main cause of failure nowadays (50 % in gas pipelines).

•Difficult to control, mainly with organisational measures.



Failure modes

Leak:•Loss of product through punctures of different

sizes.•Normally less than 50 mm diameter. Greaterdiameter, at least in gas pipelines at highpressure, could lead to a rupture.

Rupture•Full bore rupture of the pipeline

•In gas pipelines, the length of the rupture uses

to be 1 line pipe length (about 12 m).•In gas pipelines, in the case of low grade steel,rupture length could be longer.



Failure Frequency calculations (1)

It is needed to know the failure frequencyfor each mode and cause of failure.

FF can be calculated/estimated in base to:Historical data

•EGIG (EU), CONCAWE (EU), DoT (USA).

•Company correlations.

Mathematical models:

•Based on Operational data on damage frequency,

type and size.•Fracture mechanics techniques.

•Prediction of failure frequencies for all pipelines.



Failure Frequency calculations (2)

Advantages / DisadvantagesHistorical data

•A: it covers all the failure causes.

•D: database of incidents is quite small, this meanslow statistical reliability.

•D: it is difficult to investigate the influence ofdifferent parameters in FF:

–diameter, depth of cover, wall thickness, pressure,materials, effect of surveillance, ...

Mathematical models:

•A: it could consider pipeline characteristics:–diameter, depth of cover, wall thickness, pressure,materials, effect of surveillance, ...

•D: it is necessary a model for each failure cause.



Failure consequences

Main difference between oil and gas pipeline:The behaviour of gas and liquid after the rupture is quitedifferent, due to the outflow pattern after the failure and the

type of fire produced.

Ruptures:•Gas flow rate decaying with time after rupture.

•Liquid flow rate quite constant after rupture and formationof liquid pool.

Leak:•Jetfire in case of gas pipelines, could be almost constant

with time, depending the leak size and operationalparameters.

•Jetfire initially in case of oil pipelines that can finish as apool fire after the lost of internal pressure in the pipeline.



Gas outflow calculation after apipeline rupture

Gas Outflow (PBREAK)

Upstream

Downstream

Total flow

F l o w ( k

g / s )

Time (s)

0

2000

4000

6000

8000

0 200 400 600 800 1000

Gas outflow after the rupture of a high pressure gas pipeline.PBREAK model, PIPESAFE software package.



Leak / Puncture Fire

•Jet fire.

•Steady state gas

outflow and radiationlevels.

Jet fire in an underground gas

pipeline(source: PIPESAFE group experiments)



Rupture Fire

Gas pipeline•Initial fireball for immediateignition.

•Decaying crater fire afterignition or delayed ignition.

Oil pipeline•Steady pool fire after ignition.

Fireball in an underground

pipeline (source: PIPESAFE

group experiments)



Rupture Fire (2)

Gas pipeline•Decaying crater fire after ignition or delayed ignition.

Ghislenghein incident (source: http://picture.belga.be)



Radiation Levels ( 0.000 m/s wind) -Immediate Ignition

16.0 s. 19.0 s. 30.0 s. 60.0 s. 90.0 s.

120.0 s. 180.0 s. 300.0 s. 900.0 s.

R a d i a t i o n ( k W / m ² )

Distance (m)

0

10

20

30

40

50

0 500 1000 1500 2000 2500

Thermal radiation after the rupture of a high pressure gas pipeline.IMPJET & CRISTAL models, PIPESAFE software package.

Thermal radiation calculation after a gas pipelinerupture



Consequences on people

•The effect of thermal radiation on people is done inbase to the Probit methodology.

•The Probit methodology takes into account thethermal radiation doses received by a person.

•The result is % of harm (normally lethality) at agiven distance.

•Some refinement can be done:

–Possibility of escaping from accident site.–Reaction time.

–Time of ignition of the release.

–Possibility of finding a refuge/shelter. In this case, theeffect of thermal radiation on the shelter should beconsidered.

•The change of the casualty probability with distancethe safe distance for people and the resistance of ashelter are the result of the calculation.



Consequences on people (2)

(source: Advantica)



Types of risk

Individual RiskThe frequency at which an individual may be expected tosustain a given level of harm from the realisation of specifiedhazards.

Societal RiskThe relationship between frequency and the number of peoplein a given population suffering from a specified level of harm

from the realisation of a given hazard.

The main difference of risk in pipelines comparedto other industrial risks, is due to the fact that we

have a linear hazard source, while in normalindustrial sites we normally has a punctual hazard.



Risk in an industrial site.

• Punctual risk.

• For a specificdistance, the

hazard (thermalradiation) could beconsideredconstant withtime.

I

(kW/m2)

d (m)

k l ( )



Risk in pipelines (1)

•Mainly based in UK experience (IG/TD/1) andimplemented in PIPESAFE methodology.

•Risk at a given distance is not only due to a singlepoint, but a series of points:

–d < dmax: CP > 0

–d > dmax: CP = 0

•This maximum distance defines the I N T ERACT I ON

LENGHT .

d

IL

dmax

Ri k i i li (2)



• It is necessary to calculate the averageCasualty Probability at a given distance.

•

Additionally, for gas pipelines is necessaryto take into account that thermal radiationis a function of time.

Risk in pipelines (2)

I

(kW/m2)

d (m)

time



Individual risk in pipelines

Individual risk at a distance d from the pipeline:

IR(d) = FF × IL(d) × PIGN

× CP(d)where:

IR(d): individual risk at distance d (1/year)FF: failure frequency (1/(km × year)IL(d): interaction length at distance d (km)

PIGN: ignition probabilityCP(d): average casualty probability at distance d

IL

d



Individual risk results

Individual risk is normally presentedas a isorisk contour.

In pipelines is more useful to present

the risk transect.

Risk transect: variation of risk with

distance perpendicular to pipelineaxis.



Individual risk results (2)

1.E-13

1.E-12

1.E-11

1.E-10

1.E-09

1.E-08

1.E-07

1.E-06

1.E-05

0 50 100 150 200 250 300 350 400 450

Dis t. (m)

I R ( y

- 1 )

DN26- rur al DN26- subur ban DN26- rur al DN20- rur al DN6- rur al DN48- rur al

Calculations done with PIPESAFE software package





Societal risk in pipelines (2)

F1N1

(source: Advantica)




FnNn

(source: Advantica)




1 10 100 1000

Number of Casualties, N

1.0E-10

1.0E-9

1.0E-8

1.0E-7

1.0E-6

1.0E-5

1.0E-4

F r e q u e n c y

o f N

o r m o r e p

e r y e a r

F-N Curve calculated with the PIPESAFE sotware package(source: Advantica)



Risk acceptability criteria

•There is not only a criteria accepted worldwide.•The acceptability criteria for risk is a country or company

policy.

•Criteria can be different for workers at the industrial site

than for general people living/staying around the industrialsite: voluntary or nor voluntary risk concept.

•Criteria for IR can be found in many countries.– A general accepted reference level is 10-6 y-1.

•Criteria for SR are lest extended, but some countries andcompanies has developed some references for F-N curves orother.

•Taking into account the accuracy and uncertainty of modelsand methodology used, the ALARP criteria is recommended.

– As Low As Reasonable Possible– If the pipeline has been built following regulations or

recognised standards or guidelines,it is possible to justify thatthe risk level is ALARP.

– A Cost Benefit Analysis could justify that additional investment

are not reasonable for the reduction in risk gained



Individual Risk acceptance levels

1E-4 per year

1E-6 per year

Risk Level

ALARP Region

Broadly Acceptable Region

Unacceptable Region

ALARP limits for IR adopted in UK



F-N curve

It is possible to finddifferent F-N curves

in different countriesand for differentpurposes.



Societal risk acceptance levels

Acceptability of risk inside a LNG plantEN 1473:2007

Installation and equipment for liquefied natural gas.

Design of onshore installations.

Influence of



Influence ofmethodology

Influence on the individual riskcalculated.

The influence of the differentparameters applied to the same

mathematical models, produceddifferent risk transect:

• Exposure time considered inthe calculation.

• Possibility of escape.

• Safe radiation level.

• Existence of refuges.

• ...

In the example all the

calculation has been made withPIPESAFE software package.

PIPESAFE allows to changesome parameters in themethodology for riskcalculation, in order to fulfil,i.e., national regulations.

Pipeline:

610 mm

55 barg

X52

9.52 mm

F = 0.49

Ri k t lt



Risk assessment results

Once RA is finished, it is possible to list thepipeline in three categories:

•Risk acceptable: no additional measures are needed.

•Risk ALARP: it is necessary to study if the improvement inthe design and maintenance of pipelines will reduce therisk without unreasonable efforts.

•Risk unacceptable: it is necessary to change design ortake additional measures to reduce risk.

This list will give a ranking of pipelines withmore/less maintenance and inspection needs.

It is assumed that any pipeline with a high risklevel will need additional efforts in maintenanceand inspection works.

Wh t f d i i k



Where to go for reducing risk

If the risk assessed is above the acceptablelevel, there are two point were is possible

to work:•Failure frequency

–It is possible to reduce the FF assuming organisationaland physical measures to reduce it.

•Failure consequences–Except in the design phase of a pipeline, it is difficult totake measures to reduce the consequences of theaccident, mainly due to commercial and/or operational

constrains.

T d f il



To reduce failure consequences

In design phase:•To reduce the maximum operational pressure in gaspipelines.

•To reduce pipeline diameter.

•To lay the pipeline furthest from the population.

In operation:•To reduce operational pressure.

•To change the route of the pipeline.

•To install additional shut-down valves remotelyoperated.

To ed ce fail e f eq enc (1)



To reduce failure frequency (1)

It is in reducing the FF, where the maintenanceand inspection of pipelines have an importantpaper.

The actions taking into account will depend on thecause of failure to reduce.

It is necessary to develop a method to quantifythis risk reduction of the different actions:

•Using mathematical models able for this purpose.

•Applying a methodology which allows to estimate the riskreduction in qualitative and/or quantitative way.

This is the difficult point.





Third party interferenceMeasures for increasing the resistance of the pipeline oravoiding the possibility of an interference:

•To increase depth of cover.•To install slabs.

•To increase surveillance frequency.

•Higher wall thickness of pipeline (only in design).

•To install remote detecting system of TPI.Currently, there are several technologies in developmentto prevent/alert of a TPI in real/short time:

–Utilisation of fibre optic cable to detect TPI.

–To detect the noise of a leak or hit on the pipeline

measuring the noise produced.–UAV/Satellite surveillance with image processed software.

–...





Corrosion

Measures to prevent the possibility of corrosion in

the pipeline:•To avoid, as much as possible, route parallel torailway systems and power lines: straight currents.

•To assure the good performance of cathodic

protection system.•To inspect the integrity of the coating in thosepipelines installed in more aggressive terrains andenvironment.

•To pass intelligent pigs to detect any loss ofthickness or defect in the pipeline.

Effect of On-Line Inspection in FF



p

The information gained in the On-Line Inspection may be used to reassess theprobability of failure and enable remedial action to be taken to reduce the FF,for instance, by repairing defects greater than a specific size.

Since the effect of the inspection and repair activities is to reduce the FF, themaximum value of FF will occur immediately before the inspection is conductedand the remedial measures are undertaken.





Ground movement

Measures to prevent the possibility of failure in the

pipeline:•To avoid, as much as possible, route in areasusceptible of ground movements: land slide, miningsubsidence.

•To install appropriate anchorage systems in unstablelandslide.

•To increase the frequency of surveillance in unstableareas.

•To install ground movement sensor.

•To install pipeline stress sensors.

References



References

Performance of European crosscountry oil pipelines. Statistical summary of reported spillages in 2005and since 1971, CONCAWE, R04/07, May 2007 (www.concawe.be).

6th EGIG report 1970 – 2004. Gas pipeline incidents, EGIG, 05.R.002, December 2005 (www.egig.nl)

Acton, M., Baldwin, P, Baldwin, T. & Jager, E., The development of the PIPESAFE risk assessment package for gas transmission pipelines. International Pipeline Conference, ASME, Calgary, Canada,1998.

Acton, M., Baldwin, T. & Jager, E., Recent developments in the design and application of the PIPESAFErisk assessment package for gas transmission pipelines. International Pipeline Conference, ASME,Calgary, Canada, 2002.

Cleaver, R.P., Acton, M. & Haltford, A., Modelling the effects of pipeline fire and response of people inlarge buildings. International Pipeline Conference, ASME, Calgary, Canada, 2006.

The Institution of Gas Engineers, Steel pipelines for high pressure gas transmission. IGE/TD/1, Ed. 4,United Kingdom, 2001.

Jager, E., Kuik, R., Stallenberg, G. & Zanting, J., The influence of land use and depth of cover on thefailure rate of gas transmission pipelines, International Pipeline Conference, ASME, Calgary, Canada,

2002.

Guidelines for Quantitative Risk Assessment (Purple Book), CPR 18E, Committee for the Prevention ofDisasters, 1ª Ed., 1999 (The Nederlands).

Mulhbauer, W.K., Pipeline risk management manual , 2nd Ed., Gulf Publishing Co., Houston, USA, 1996.

Acknowledges



Acknowledges

I wish to thank to all my colleagues and theircompanies (Advantica, Enagás, Energinet.dk , Fluxys ,Gasunie, National Grid, StatoilHydro, TransCanada)

whose collaboration in the development of thePIPESAFE software package and methodology hasmade possible for me to collect most of the informationshown in this presentation.

Thank you for your attention

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