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Goodfellow G.D.,Penspen Ltd | Haswell J.V.,Pipeline Integrity Engineers Ltd. | Jackson N.W.,UK National Grid Corporation | Ellis R.,Essar Oil UK Ltd.
Proceedings of the Biennial International Pipeline Conference, IPC | Year: 2014

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. Quantitative risk assessment (QRA) is used by operators in the UK to determine if individual and societal risk levels at new developments adjacent to existing pipelines are as low as reasonably practicable (ALARP). In 2008 the UKOPA Risk Assessment Working Group developed codified advice on the use of QRA applied to land use planning assessments, which was published by the Institution of Gas Engineers & Managers (IGEM) and the British Standards Institute (BSI). This advice was designed to ensure a standard and consistent approach, and reduce the potential for disagreement between stakeholders on the acceptability of proposed developments. Since publication of IGEM/TD/2 and PD8010-3 in 2008, feedback from users of the guidance together with new research work and additional discussions with the UK safety regulator, the Health & Safety Executive (HSE), have been undertaken and the codified advice has been revised and reissued in June 2013. This paper describes the revisions to the guidance given in these codes in relation to: • Clarification on application • Update of physical risk mitigation measures (slabbing and depth of cover) • Update of HSE approach to Land Use Planning • Update of failure frequency data: o Weibull damage distributions for external interference o Generic failure frequency curve for external interference o Prediction of failure frequency due to landsliding The revised codes, and their content, are considered to represent the current UK best practice in pipeline QRA. Copyright © 2014 by ASME. Source


Gonzalez-Franchi G.,Penspen Ltd | Leek N.,Penspen Ltd | Palmer-Jones R.,Penspen Ltd | Lewis T.,ExxonMobil
Pipeline Pigging and Integrity Management Conference, PPIM 2015 | Year: 2015

PINHOLE FEATURES ARE DIFFICULT to detect and size accurately using standard inline inspection (ILI) tools, such as Magnetic Flux Leakage (MFL) and Ultrasonic Wall Thickness Measurement (UTWM) due to the small volume and area of metal loss. Pinhole type features can be caused by certain types of corrosion such as microbial induced corrosion (MIC) as well as other hazards such as illegal tapping. It is therefore desirable to be able to detect small diameter pits, or pinholes of just a few millimetres (mm) in diameter. The potential for very small diameter metal loss features was identified on an onshore multiproduct pipeline operated by ExxonMobil in the UK. Two types of ILI tools were considered, pitting ultrasonic (UT) and high resolution MFL tools. For the particular pipe geometry of interest, the specifications for pinhole detection were comparable at a 90% Probability of Detection (PoD). In order to gain a better understanding of the relative detection performance and measurement accuracy, a series of 'blind' pull through tests were performed. A test spool was manufactured containing a set of artificial features including: straight hole, internal and external conical defects, some of which were beyond the detection specifications of the ILI tools used. Finally, MFL and UT ILI tools were pulled through the test spool. The performance of the tools was analysed using the confidence interval analysis (Clopper-Pearson Method), Pearson correlation, Mean Square Error (MSE), and average sizing error. The results of the findings, including comparisons of as-reported depths versus as-manufactured depths are discussed. Overall conclusions on the ability of MFL and UT tools to detect and size pinhole features are presented. Copyright © 2015 by Clarion Technical Conferences, Tiratsoo Technical (a division of Great Southern Press) and the author(s). Source


Lockey A.,Penspen Ltd | Jackson N.,UK National Grid Corporation | Palmer-Jones R.,Penspen Ltd | Ellis R.,Essar Oil UK Ltd.
Proceedings of the Biennial International Pipeline Conference, IPC | Year: 2014

Pipelines can be dented, but shallow dents with depths less than 2% of the pipe diameter have only recently begun to be reported reliably by high resolution in-line geometry inspections. Most thin-walled onshore pipelines around the world are found to contain these shallow dents, many on welds of unknown toughness, or subject to severe pressure cycling. Much of the existing guidance for dent management was published before such shallow dents were being reported, and did not necessarily consider them. Furthermore, recent failures in Canada have demonstrated that the existing guidance can be non-conservative when a shallow dent is combined with fatigue loading or other undetected damage. The United Kingdom Onshore Pipeline Operators Association (UKOPA) is developing a strategy for the management of dents to provide guidance to operators based on published best practice. The aim of the work is to ensure that dents now identified but not sized by MFL inspection tools are appropriately inspected, investigated, assessed and repaired. UKOPA's methodology allows shallow dents to be screened and assessed without the requirement for numerous feature investigations. This management strategy is: Stage 1: Use previously published UKOPA guidance on the prioritization of dents. This involves following a series of flow charts, leading the operator from dent discovery, through decisions affecting assessment and possible repair. Stage 2: This Stage provides a series of criteria to indicate whether a weld is likely to be of sufficient toughness to withstand shallow denting, then gives a method to carry out an engineering assessment of a dent based on finite element analysis. This paper presents the background and justification of 'Stage 2', and updates 'Stage 1'. It includes a review of recent published work covering dents on welds, including analytical studies, finite element analyses, testing and failures. The results of this work by UKOPA will form an input to the planned updates to the Pipeline Defect Assessment Manual (PDAM). The paper then applies the updated guidance to operational dent assessment problems provided by UKOPA members. Finally, an example of a dent assessment under the previous and updated guidance, including a finite element analysis, is given to illustrate how a shallow dent on a weld of unknown toughness may be re-categorized as not requiring repair. Copyright © 2014 by ASME. Source


Lockey A.,Penspen Ltd | Santamaria W.,ExxonMobil | Gonzalez G.,Penspen Ltd
Proceedings of the Biennial International Pipeline Conference, IPC | Year: 2014

Modern in-line inspections can detect shallow dents in pipelines, with depths less than 2% of pipeline diameter. These dents are very common in thin-walled, small diameter refined and multiproduct lines, and frequently coincide with longitudinal welds and girth welds. Traditional dent assessment methods (such as the EPRG approach) can be conservative. Dents can have short predicted fatigue lives, but shallow dents are not known to be a major cause of pipeline failure, unless they are associated with a weld, a gouge, a crack, or severe pressure cycling. The conservatism affects both static failure assessments and fatigue assessments, resulting in high repair rates for shallow dents. This conservatism is partly due to: Limitations of how the dent shape is modelled in the assessment methods; Simplifications of the modelling of the stresses range; Limitations of the calculation of strains in a dent based on inspection measurements; Inability to model the changing cyclic stress range with changing dent shape. This paper shows that high resolution geometry inspection data contains irregularities which need to be filtered and smoothed. Advanced local regression methods are shown to give effective smoothing by removing errors but retaining the important elements of the real dent shape. The smoothed dent shape is used with the strain estimation methodology given by ASME B31.8 Appendix R, and an appropriate strain limit (based on likely weld quality), to assess whether cracking is likely to have initiated during dent formation. A methodology is then presented, based on Finite Element Analysis (FEA), which improves the accuracy of cyclic stress assessments of shallow smooth dents. The FEA model geometry is provided by the smoothed version of the measured dent shape. The pressure at which the dent shape was measured affects the calculated dent shape and stress as internal pressure varies: this effect is included in the model. The calculated cyclic stresses are used with S-N curves, such as those in BSI PD 5500, to estimate dent fatigue life. This methodology is then applied to 88 dents in two pipelines operated by ExxonMobil in the UK, using detailed high resolution geometrical in-line inspection data, comprehensive pressure cycle measurement data and enhanced dent assessment using the FEA method. It is concluded that this methodology can significantly improve the operator's pipeline integrity strategy. Copyright © 2014 by ASME. Source


Marcoulaki E.C.,Greek National Center For Scientific Research | Papazoglou I.A.,Greek National Center For Scientific Research | Pixopoulou N.,Penspen Ltd
Chemical Engineering Research and Design | Year: 2012

This work presents an optimisation framework for the routing and equipment design of main pipelines to be used for fluid transmission. There are many considerations in these design problems, involving various constraints, decisions and the associated costs for the construction, operation, maintenance, etc., of the system. In practice, engineers rely on experience, try out various design alternatives, and use simulators for engineering calculations, cost models, geographical information systems and equipment databases to identify promising options. The present approach proposes a systematic search for optimal and near-optimal solutions. The search is based on stochastic optimisation, and assumes that the same information and simulation tools as in the case of design by trial and error are available. An application example is used to demonstrate the approach and test the robustness of the optimal search using Simulated Annealing. © 2012 The Institution of Chemical Engineers. Source

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