Gerald Laheij | March 8th 2006Risk assessment on pipelines The Dutch approachWorkshop UN ECE

High pressure natural gas pipelinesTotal length: 12000 kilometre

Main transport pipelines18- 48 inch (66 bar)Average depth of cover 1.75 meter

Regional transport pipelines2-16 inch (40 bar)Average depth of cover 1.2 meter

Workshop UN ECE

Prevention of accidents

Risk reduced as much as is reasonably practicable through measures at the sourceNumber of people exposed is reduced by a risk based zoning policyIndividual risk, creates distance between potential hazardous source and its surroundingsSocietal risk, limits the population density around the potential hazardous source

Risk measuresIndividual riskChance that an unprotected person residing permanently at a fixed location is killed as a result of an accident Presented as risk contours on a mapLimit for dwellings and vulnerable destinations, guidance value for less vulnerable destinations (10-6 per year)

Workshop UN ECE

Risk measuresSocietal riskChance that in a single accident a certain number of victims is exceededPresented in a F-N curveJustification of new developmentsGuidance value, per km pipeline

Workshop UN ECE

Standardised method

Guidelines for quantitative risk assessment (QRA) are given in the Purple Book loss of containment events source term and dispersion exposure and damage calculation and presentation of results

Guideline is reviewed, use of a single computer code

Workshop UN ECE

Current building distances

Building distances derived in 1984Building distance depends on diameter, pressure of pipeline, and vulnerability of objects (4 60 meter)Construction (wall thickness) of new pipelines depends on area classification

Building distances are currently under revision

Workshop UN ECE

Loss of containmentFull bore ruptures dominate the risk of natural gas pipelinesExternal interference main cause of failureFailure frequency depends on depth of cover and wall thickness

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Source term and dispersionPipeline rupture results in vertical jet which can igniteSource term, average release (first 20 seconds) Exposure dominated by effects of heat radiation

Workshop UN ECE

Probability of ignition

Casuistic available for rural areas, depends on diameter and pressure (5-80%)Influence build-up area not knownLarge scale experiments are planned

ConsequencesWorkshop UN ECEExample for a 12 inch pipeline

Chart4

14755

14655

14405

14105

14105

14105

14105

current distance 1984

Minimum wall thickness

Maximum wall thickness

Depth of cover (m)

Distance

Sheet1

Diepteliggingcurrent distance 1984Minimum wall thicknessMaximum wall thickness

0.814755

114655

1.214405

1.414105

1.614105

1.814105

214105

Sheet1

current distance 1984

Minimum wall thickness

Maximum wall thickness

Diepteligging (m)

Zoneringsafstand (m)

Sheet2

Sheet3

Additional measures

Building distances (1984) normative distance for new building developments, additional measures at source may be necessary Obligatory one-call systemSupervision of pipeline operator (dangerous substance) Concrete slabs and warning tapes Warning marks, camera surveillance

For new pipelines depth of cover and wall thickness are chosen such that distance to individual risk contour of 10-6 per year is less or equal to building distance of 1984.Workshop UN ECE