Loss of Containment of North Sea Pipelines
Authors: Williams K.A.J. , Ellinas C.P. , Brown P. 
Published: October 2008

ABSTRACT
This paper summarises the findings of a study on loss of containment of North Sea offshore pipelines was commissioned by the United Kingdom Offshore Operators Association. Incident and pipeline databases were assembled and used to assess the frequency of loss of containment associated with operation of North Sea pipelines and to determine significant factors affecting loss of containment. The results obtained from the study are unique in that they represent up to date information on the frequency of loss of containment of North Sea pipelines, and as such can form the basis of safety assessments and risk analysis studies of subsea pipelines.

INTRODUCTION
Following the Piper Alpha Incident, the United Kingdom Offshore Operators Association (UKOOA) commissioned a study on the incidence of loss of containment from pipelines in the North Sea. The main objective of the study was to update and improve confidence in the statistical information available to assess the frequency of loss of containment associated with operation of North Sea pipelines. In order to achieve this, two databases were compiled:A pipeline database, which contains details of all the pipelines installed in the North Sea.An incident database, which contains a description of each reported incident and related data on the pipeline or lines affected. Incidents which directly resulted or threatened to result in loss of containment of an operating pipeline were considered in the study and are addressed in the project report1. Combining the information from both databases enabled the frequency of incidents to be related to the pipeline population as a whole in terms of incidents per year or per km-year, as appropriate. The databases contain information collected until the end of 1989.
The basis of the study was a review of information held by Regulatory Authorities and Pipeline Operators. A literature review was also undertaken, which included Trade Journals and published papers and reports from earlier studies in this area. Throughout the study, considerable care was taken to ensure that data collected were as accurate and complete as possible, in order that the frequencies derived were representative of North Sea conditions. Extensive cross-checking and verification of records from different sources was carried out and wherever discrepancies were identified, careful engineering considerations were used to determine which source was most likely to be correct.
A detailed report describing the work involved in the study is available to UKOOA members and it will soon be published by HMSO1. The report describes the information available to the project and the methods by which data were checked and evaluated are described. It also describes the results of an analysis of the extended databases to develop incident frequencies appropriate to pipelines, risers and topsides pipework for platforms in the North Sea, concentrating on incidents which gave rise to loss of containment. Trends in the recorded data have also been investigated and the report indicates how incident frequencies vary with location, cause of failure, line type, line size and consequence.