The United Kingdom Onshore Pipeline Operators Association (UKOPA) was formed by UK pipeline operators to provide a common forum for representing operators interests in the safe management of pipelines. This includes providing historical failure statistics for use in pipeline quantitative risk assessment and UKOPA maintain a database to record this data. The UKOPA database holds data on product loss failures of UK major accident hazard pipelines from 1962 onwards and currently has a total length of 22,370 km of pipelines reporting. Overall exposure from 1952 to 2010 is of over 785,000 km years of operating experience with a total of 184 product loss incidents during this period. The low number of failures means that the historical failure rate for pipelines of some specific diameters, wall thicknesses and material grades is zero or statistically insignificant. It is unreasonable to assume that the failure rate for these pipelines is actually zero. However, unlike the European Gas Incident data Group (EGIG) database, which also includes the UK gas transmission pipeline data, the UKOPA database contains extensive data on measured part wall damage that did not cause product loss. The data on damage to pipelines caused by external interference can be assessed to derive statistical distribution parameters describing the expected gouge length, gouge depth and dent depth resulting from an incident. Overall 3rd party interference incident rates for different class locations can also be determined. These distributions and incident rates can be used in structural reliability based techniques to predict the failure frequency due to 3rd party damage for a given set of pipeline parameters. The UKOPA recommended methodology for the assessment of pipeline failure frequency due to 3rd party damage is implemented in the FFREQ software. The distributions of 3rd party damage currently used in FFREQ date from the mid-1990s. This paper describes the work involved in updating the analysis of the damage database and presents the updated distribution parameters. A comparison of predictions using the old and new distributions is also presented.
The approach to gas pipeline risk and integrity management in the US, involving the development of integrity management plans for High Consequence Areas (HCA), is usually qualitative, as outlined in ASME B31.8S. Depending on the engineering judgement of the assessment team this can lead to a wide variety of results making risk comparison between pipelines difficult. Qualitative risk ranking methods are popular in Europe, but quantitative risk assessment (QRA) is also used for setting acceptable risk levels and as an input to risk and integrity management planning. It is possible to use quantitative risk assessment methods to compare the levels of risk inherent in different pipeline design codes. This paper discusses the use of pipeline quantitative risk assessment methods to analyse pipelines designed to ASME B31.8 and UK IGE/TD/1 (equivalent to PD 8010, published by BSI, for the design of gas pipelines) codes. The QRA utilises predictive models for consequence assessment, e.g. pipeline blowdown and thermal radiation effects, and failure frequency, in determining the risk levels due to an operational pipeline. The results of the analysis illustrate how the risk levels inherent in the two codes compare for different class locations & minimum housing separation distances. The impact of code requirements on design factor, depth of burial, population density and the impact of third party activity on overall risk levels are also discussed.
Expansion of existing residential and commercial areas, or the construction of new developments in the vicinity of high pressure gas transmission pipelines can change a Location Class 1 into a Class 2 or Class 3 location. Operators are left with a pipeline that no longer meets the requirements of its design code. Reducing the maximum allowable operating pressure of a pipeline, or re-routing it away from the population, can meet the requirements of a design code, such as CSA Z662 or ASME B31.8, but such options have both high costs and significant operational difficulties. Quantitative risk assessment has been employed successfully for many years, by pipeline operators, to determine risk based land use planning zones, or to justify code infringements caused by new developments. By calculating the risk to a specific population from a pipeline, and comparing it with suitable acceptability criteria, a pipeline may be shown to contribute no more risk to a population than other pipelines operating entirely in accordance with the design codes. Risks may be demonstrated to be ‘as low as reasonably practicable’, through the use of cost benefit analysis, without additional mitigation, allowing precious pipeline maintenance funds to be spent most effectively in areas where they will have the highest impact on risk. This paper shows how quantitative risk assessment may be used to justify continued safe operation of a pipeline at its original operating stress following a change of class designation, illustrated with a case study from Western Europe.
This paper presents an overview of the various components of an emergency pipeline repair system which should be in place in order to act effectively and efficiently during an emergency pipeline repair scenario. The condition of pipelines during operation is typically monitored by means of external and internal inspections. These inspections allow for planned intervention when a pipeline is found to be deteriorating. A failure to inspect adequately for time dependent threats, or randomly occurring events such as third party interaction, could result in a pipeline failure, leading to a requirement to rapidly return to operation and thus the need for an emergency repair. An Emergency Pipeline Repair System (EPRS) is therefore an essential part of a pipeline integrity management system. The primary purpose of the EPRS is to ensure that pipeline operators have the necessary level of readiness to allow an emergency repair to be carried out, thus minimising the economic consequences of having a pipeline out of service, whilst optimising the cost of purchasing and maintaining equipment and spares. In general, pipeline operators will have some emergency repair procedures to cater for unplanned or unexpected incidents. However, to complete an emergency repair efficiently and effectively, the availability of adequate spare materials and timely access to the damage location is required. For a large pipeline network, satisfying these requirements can be challenging. This paper discusses some basic elements of an EPRS and describes a case study of the development of a risk based EPRS strategy for an offshore pipeline operator. This approach involves the identification of credible hazards that can lead to damage requiring an emergency repair, and identification of repair options. The relative importance of the individual pipelines, in terms of their availability requirement, and the expected time required to complete an emergency repair are then taken into account. This enables the pipelines to be ranked based on the consequence of failure. Pipelines with consequence rankings that are considered unacceptable are therefore highlighted, and EPRS readiness related to those pipelines can subsequently be optimised. Recommendations for the development of an EPRS for an onshore or offshore pipeline network are also made.
The United Kingdom Onshore Pipeline Operators Association (UKOPA) was formed by UK pipeline operators to provide a common forum for representing pipeline operators interests in the safe management of pipelines. This includes ensuring that UK pipeline codes include best practice, and that there is a common view in terms of compliance with these codes. Major hazard cross country pipelines are laid on 3rd party land, and in general have an operational life typically greater than 50 years. The land use in the vicinity of any pipeline will change with time, and buildings will be constructed adjacent to the pipeline route. This can result in population density and proximity infringements, and the pipeline becoming non-compliant with the code. Accordingly, a land use planning system is applied so that the safety of, and risk to, developments in the vicinity of major hazard pipelines are assessed at the planning stage. In the UK, the Health & Safety Executive (HSE) are statutory consultees to this process, and they set a quantitative risk-based consultation zone around major hazard pipelines, where the risks to people and developments must be assessed. Quantitative risk assessment (QRA) requires expertise, and the results obtained are dependent upon consequence and failure models, input data, assumptions and criteria. UKOPA has worked to obtain cross-stakeholder agreement on how QRA is applied to land use planning assessments. A major part of the strategy to achieve this was the development of supplements for the UK design codes IGE/TD/1 and PD 8010, to provide authoritative and accepted guidance on the risk analysis of: i) Site specific pipeline details, for example increased wall thickness, pipeline protection (such as slabbing), depth of cover, damage type and failure mode, and ii) The impact of mitigation measures which could be applied as part of the development. The availability of this codified advice would ensure a standard and consistent approach, and reduce the potential for disagreement between stakeholders on the acceptability of proposed developments. This paper describes the guidance given in these code supplements in relation to consequence modelling, prediction of failure frequency, application of risk criteria, implementation of risk mitigation and summaries the assessment example provided.
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