The Use of QRA To Inform the Design of a High-Pressure Onshore Pipeline
- Stacy Nelson (Total E&P) | Margaret Caulfield (Vectra Group Limited) | Andrew Cosham (Atkins Boreas)
- Document ID
- Society of Petroleum Engineers
- SPE Projects, Facilities & Construction
- Publication Date
- September 2008
- Document Type
- Journal Paper
- 1 - 12
- 2008. Society of Petroleum Engineers
- 4.6 Natural Gas, 4.1.2 Separation and Treating, 6.3.2 Safety in Design and Engineering, 2.4.3 Sand/Solids Control, 4.2.2 Pipeline Transient Behavior, 5.1.2 Faults and Fracture Characterisation, 4.3.4 Scale, 4.1.4 Gas Processing, 1.10.1 Drill string components and drilling tools (tubulars, jars, subs, stabilisers, reamers, etc), 4.5 Offshore Facilities and Subsea Systems, 4.1.5 Processing Equipment, 4.2 Pipelines, Flowlines and Risers, 4.2.3 Materials and Corrosion, 4.2.5 Offshore Pipelines, 7.2.1 Risk, Uncertainty and Risk Assessment
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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).
In the United Kingdom, the management of pipeline safety is governed by the Pipelines Safety Regulations, 1996. These regulations consist of goal setting and encompass a risk-based approach to safety. They require pipeline operators to design, build, and operate pipelines to ensure that they are safe, so far as is reasonably practicable (Chatfield 2005). The safety of the pipeline is achieved in part by applying recognized onshore-pipeline design codes. However, in some cases, there is a need to demonstrate the safety of the pipeline by quantifying the risks associated with the pipeline installation and ensuring that the risks in the vicinity of the pipeline are as low as reasonably practicable.
This paper describes a case study that was conducted at the early stages of a development project to identify the risks associated with a high-pressure onshore pipeline. The development involved a gas field located approximately 125 km northwest of the Shetland Islands, UK. The produced gas, wet natural gas of approximately 86% methane, was assumed to be transported to a gas-processing plant on the Shetland Islands by two new 16-in. import pipelines. The pipelines were assumed to have a design pressure of 380 barg, equal to the wellhead shut-in pressure from the gas field. However, the normal operating pressure was expected to be 63 barg. Two main import routes were investigated by the project. One route involved a mainly offshore route, with a short onshore section where it came into the gas plant. The other route, which is the subject of this paper, included a 19-km section of onshore pipeline.
The UK has approximately 7,000 km of high-pressure onshore gas-transmission pipelines operating in the range of 70 to 85 barg. There are several precedents for short onshore gas pipelines with design pressures greater than 100 barg [e.g., the Central Area Transmission System (CATS) pipeline, the Interconnector Pipeline from Belgium to the UK, and the BBL Pipeline from The Netherlands to the UK]. (The definition of the boundary between onshore and subsea pipelines in PD 8010-1 means that all subsea pipelines that go to an onshore terminal have a short onshore section.) However, the proposed pipeline is atypical because of the high pressure (up to 380 barg) and the relatively long onshore sections (up to 19 km) that will traverse through areas that are not within, or adjacent to, a gas-processing terminal.
In view of the potentially sensitive nature of such a high-pressure pipeline--the history of the Corrib development (Corrib Gas Development 2005) is instructive in this regard--it was considered important to investigate the implications of the proposed onshore pipeline in the early stages of the project. The results of this study would inform the decision on which potential routes to take forward to detailed design. Consequently, a QRA was conducted of various options for the proposed onshore pipeline. It is normally unusual to conduct this level of risk analysis at such an early stage of a project.
The main aspects of the case study are described in the paper:
- Identification of the main requirements of the pipeline-design codes
- Definition of the proposed pipeline-design cases
- Description of the methodology used for conducting the QRA
- Discussion of the results obtained for the individual and societal risk
|File Size||2 MB||Number of Pages||12|
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