Abstract
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 recognised onshore pipeline design codes. Where the proposed design falls outside the guidance in the codes, quantitative risk assessment 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 and IGE/TD/1 do not provide guidance on the design of pipelines with design pressures exceeding 100barg. Experience from other projects indicates that it is important to consider the implications of such high design pressures early in a project.
The quantitative risk assessment 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 summarised 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 100barg gas transmission pipeline. The individual risk was in the broadly accepted region of risk, as defined by the Health and Safety Executive, and the societal risk was below the acceptance criterion given in IGE/TD/1.
