The Use of QRA To Inform the Design of a High-Pressure Onshore Pipeline

Abstract

Summary The management of onshore-pipeline safety in the United Kingdom is governed by the Pipelines Safety Regulations, 1996. This requires pipeline operators to design, build, and operate pipelines to ensure that they are safe, so far as is reasonably practicable. This is achieved, in part, by applying good practice and designing the pipeline to recognized onshore-pipeline design codes. Where the proposed design falls outside code guidance, a quantitative risk assessment (QRA) provides an effective means of demonstrating a safe design. This paper describes a study that was carried out to define the design requirements for the onshore section of a multiphase pipeline. The proposed pipeline will have a design pressure of 380 barg. However, onshore design codes PD 8010-1 (2004) and IGE/TD/1 (Steel Pipelines 2001) do not provide guidance on the design of pipelines with pressures exceeding 100 barg. Experience from other projects indicates that it is important to consider the implications of such high design pressures early in a project. The QRA considered a number of different design options. The safety risks of the proposed pipeline options were compared with those from a typical 100-barg-gas-transmission pipeline of the same diameter. This means that the risk of the proposed pipeline can be compared in a relative manner, to an acceptable design, and in an absolute manner to limits on individual and societal risk. The results of QRAs of the different design options are summarized and discussed. The effects of mitigation measures, such as reducing the pipeline-design factor (the ratio of the hoop stress to the specified minimum yield strength), increasing the wall thickness, and incorporating a pressure-limiting system at the landfall, are illustrated. It is shown that the proposed design is feasible. The individual and societal risks for the proposed design were lower than that of a typical 100-barg-gas-transmission pipeline. The individual risk was in the broadly accepted region of risk, as defined by the UK Health and Safety Executive (HSE), and the societal risk was below the acceptance criterion given in IGE/TD/1 (Steel Pipelines 2001).