Quantified risk assessments (QRAs) are widely used in the UK to assess the significance of the risk posed by major accident hazard pipelines on the population and infrastructure in the vicinity of the pipeline. A QRA requires the calculation of the frequency of failures and the consequences of failures. One of the main causes of failures in onshore pipelines is mechanical damage due to external interference, such as a dent, a gouge, or a dent and gouge. In the published literature, two methods have been used to calculate the probability of failure due to external interference: • historical failure data and • limit state functions combined with historical data (i.e. structural reliability-based methods). Structural reliability-based methods are mathematically complicated, compared to using historical failure data, but have several advantages, e.g. extrapolation beyond the limited historical data, and the identification of trends that may not be apparent in the historical data. In view of this complexity, proposed supplements to the UK pipeline design codes IGE/TD/1 (natural gas) and PD 8010 (all substances) — on the application of QRAs to proposed developments in the vicinity of major accident hazard pipelines — include simple ‘reduction factors’ for use in ‘screening’ risk assessments. These ‘reduction factors’ are based on a comprehensive parametric study using a structural reliability-based model to calculate the probability of failure due to mechanical damage, defined as: gouges, and dents and gouges. The two ‘reduction factors’ are expressed in terms of the design factor and wall thickness of the pipeline. It is shown that, through appropriate normalisation, the effects of diameter, grade and toughness are secondary. Reasonably accurate, but conservative, estimates of the probability of failure can be obtained using these ‘reduction factors’. The proposed methodology is considerably simpler than a structural reliability-based analysis. The development and verification of these ‘reduction factors’ is described in this paper.
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2008 7th International Pipeline Conference
September 29–October 3, 2008
Calgary, Alberta, Canada
Conference Sponsors:
- International Petroleum Technology Institute and the Pipeline Division
ISBN:
978-0-7918-4860-9
PROCEEDINGS PAPER
Reduction Factors for Estimating the Probability of Failure of Mechanical Damage Due to External Interference Available to Purchase
Andrew Cosham,
Andrew Cosham
Atkins Boreas, Newcastle upon Tyne, UK
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Jane Haswell,
Jane Haswell
Pipeline Integrity Engineers, Newcastle upon Tyne, UK
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Neil Jackson
Neil Jackson
National Grid, Newcastle upon Tyne, UK
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Andrew Cosham
Atkins Boreas, Newcastle upon Tyne, UK
Jane Haswell
Pipeline Integrity Engineers, Newcastle upon Tyne, UK
Neil Jackson
National Grid, Newcastle upon Tyne, UK
Paper No:
IPC2008-64345, pp. 373-388; 16 pages
Published Online:
June 29, 2009
Citation
Cosham, A, Haswell, J, & Jackson, N. "Reduction Factors for Estimating the Probability of Failure of Mechanical Damage Due to External Interference." Proceedings of the 2008 7th International Pipeline Conference. 2008 7th International Pipeline Conference, Volume 4. Calgary, Alberta, Canada. September 29–October 3, 2008. pp. 373-388. ASME. https://doi.org/10.1115/IPC2008-64345
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