by Glenn Petitt with comments acknowledged from Richard Espiner
This paper was presented at the IChemE Hazards XXIII Conference in November 2012. Proceedings for the conference can be found at the IChemE Shop.
Underground cross-country pipelines are widely used in the Oil & Gas and Petrochemical Industries to transport raw materials and products, e.g. crude oil, natural gas and gasoline. The loss of mechanical integrity of such pipelines has occurred on numerous occasions world-wide, due to a variety of causes such as corrosion, external impact, defects, operational errors and natural hazards. With materials being transported at very high pressures, pipeline failures may result in major releases of hazardous materials. An example is shown in Figure 1: the destruction of many houses after a major fire following a gas pipeline rupture in San Bruno, California, USA in September 2010. Such failures present a risk to people (in the case of ignition of high pressure gas) and the environment (in the case of oil and other liquid products).
There are a number of recognised failure rate databases for cross-country pipelines, such as CONCAWE (European liquid pipelines) , EGIG (European gas pipelines)  and the US DoT (both liquids and gas pipelines) . It is remarkable how close the base data from the different systems are, which leads to some confidence that the figures are sufficiently robust to be used in risk analyses.
For each database there is a number of failure modes included, such as corrosion, third party impact, material defects, natural hazards. For some of these failure modes, the databases have shown that there is a correlation between the failure rates and various risk reduction mechanism, such as heavy wall thickness. In particular, a reduction in failure rate can be applied for the corrosion and third party impact failure modes for heavy wall thickness.
However, for other failure modes, in particular material defects, the databases show no correlation between the failure rate and key risk reduction mechanisms such as heavy wall thickness. It would seem logical that the failure rate for material defects should decrease with increasing wall thickness, but for frequency assessments this has often been a constant in past studies, by simple use of statistics from the various databases.
The author has extensive experience of assessing the risks associated with pipeline systems, having been heavily involved in the design and subsequent operation of a number of high-profile pipelines world-wide (from a risk perspective). This experience has been applied to the analysis of the various failure modes in order to determine how various risk reduction techniques can reduce the frequency of failure. This includes the assessment of statistics where there is no immediate correlation from the various databases for specific failure modes.
The paper discusses how such data can be applied where logic would suggest that there should be a reduction in failure rates, although this is not immediately apparent from the various databases.
Read the full paper, with comments acknowledged from Richard Espiner (434Kb PDF )
1. CONCAWE, Performance of European Cross-country Oil Pipelines, Statistical summary of reported spillages in 2010 and since 1971, Brussels, December 2011, http://www.concawe.org/
2. European Gas Pipeline Incident Data Group (EGIG), Gas Pipeline Incidents, 8th Report of the European Gas Pipeline Incident Data Group, Doc. No. EGIG 11.R.0402, December 2011, http://www.egig.nl/