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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.


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.


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).


Turner S.,Penspen Ltd | Uloko M.,Penspen Ltd
Pipeline Pigging and Integrity Management Conference, PPIM 2015 | Year: 2015

INTERNAL INSPECTION IS a key element of best practice in pipeline integrity management and strategic asset management planning. The information that can be collected on the condition of a pipeline is invaluable and can be used for many purposes. The key uses are: Immediate integrity assessment: To identify any requirement for pressure reduction, To identify locations requiring immediate local inspection and possible repair. Remnant life assessment for integrity management: To identify locations that require local inspection and possible repair in the future, To plan future internal inspections. Remnant life assessment for asset management planning: To estimate the useful remaining life of the pipeline, To plan future developments and possible requirements for rehabilitation or replacement. There are of course many other important uses of inspection data such as understanding the hazards affecting a pipeline, or determining the position of a pipeline. However for the purposes of this paper we will focus on the uses listed above, with reference to degradation mechanisms that can be monitored by inspection. Inspection data is not perfect and in particular, defects may be undersized or oversized. Depending on the inspection technology and the type of line pipe these errors may be significant. For example the inspection accuracy for a standard magnetic flux leakage tool measuring an internal corrosion defect in seamless pipe close to a girth weld may be in excess of 30% of pipe wall thickness at 80% confidence. These errors are real and there is plenty of evidence and experience in the industry of defects found in pipelines that are significantly deeper or shallower than the best estimate provided by the internal inspection contractor. Best practice requires that to ensure integrity and safety these errors are considered when assessing defects. This can lead to what appear to be very conservative assessments particularly when considering the longer term performance of a pipeline. It is proposed that consistent with best practice, measurement errors should be explicitly considered to determine requirements for pipeline integrity management activities, including dealing with immediate integrity issues and planning the next internal inspection. This approach will prevent failures and allow effective risk management. However, separate, less conservative assessments that are designed to give a best estimate of remnant life are more appropriate for longer term asset management planning. In this paper, an approach for dealing with inspection errors in a rational and justifiable manner is discussed. The paper considers how measurement uncertainty can be dealt with in a way which will ensure safe operation whilst allowing realistic long term planning. Illustrative examples are given. Copyright © 2015 by Clarion Technical Conferences, Tiratsoo Technical (a division of Great Southern Press) and the author(s).


Dafea M.,Noble Denton | Hopkins P.,Penspen Ltd | Palmer-Jones R.,Penspen Ltd | De Bourayne P.,Trapil | Blin L.,Societe du Pipeline Sud Europeen
Journal of Pipeline Engineering | Year: 2014

IN AUGUST 2009, there was a 2.5-m long rupture In the longitudinal seam weld of a crude oil pipeline in France.The failure caused a spillage of approximately 2000 cubic metres in a protected area.This rupture caused the authorities to withdraw the permit to operate a 260-km long section of this pipeline. The pipeline had a similar failure in August, 1980.The 1980 failure was attributed to a fatigue crack initiating at the inner side of the longitudinal weld. There was evidence of'roof topping' along this weld. Penspen Ltd was contracted by the pipeline operator Société du Pipeline Sud Européen (SPSE) to carry out an independent investigation into the cause of the 2009 failure, review and confirm the actions needed for safe short-term operation to allow internal inspection, and determine a safe future life for the pipeline. The failed pipe specimen was not immediately available for inspection. An initial analysis indicated that a purely analytical evaluation would not provide conclusive results, due to variability in material properties, geometry, and loading. It was decided that a better understanding of the behaviour of defects in the pipe, and the fatigue performance, was required. A detailed laboratory programme of burst and fatigue testing on a section of linepipe was recommended.The tests were carried out on a combination of'defect-free'1 ring specimens, and ring specimens with initial electric-discharge-machined (EDM) slits to represent crack-like defects.These tests showed: 1.Burst tests:The failure pressures of the burst tests could be predicted using a recognized industry model. Roof topping, laminations and inclusions, and toughness variations were found to have no noticeable effect on the defect size at failure. 2.Fatigue tests: The fatigue test results showed that defect-free rings had a fatigue life one order of magnitude longer than those containing an EDM slit, and that the fatigue life of a defect-free ring could be predicted using a standard S-N method. In addition, it was found that crack growth was conservatively predicted using standard fatigue-fracture mechanics. The fatigue test results showed that the 1980 and the 2009 failures were caused by a combination of cyclic pressure loading, roof topping, and a pre-existing weld defect (probably present when the pipeline went into service in 1972). This paper provides an overview of the failure investigation, with a discussion of the ring testing, supporting tests, and fracture surface inspection.


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.


Rumney P.,Penspen Ltd. | Goodfellow G.,Penspen Ltd.
Proceedings of the Biennial International Pipeline Conference, IPC | Year: 2012

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.Copyright © 2012 by ASME.


Goodfellow G.,Penspen Ltd. | Turner S.,Penspen Ltd. | Haswell J.,Pipeline Integrity Engineers Ltd. | Espiner R.,BP Sunbury
Proceedings of the Biennial International Pipeline Conference, IPC | Year: 2012

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.Copyright © 2012 by ASME.


Lockey A.,Penspen Ltd. | Young A.,Penspen Ltd.
Proceedings of the Biennial International Pipeline Conference, IPC | Year: 2012

Pipelines that cross mountainous areas are susceptible to ground movement loading from landslides. In-line inspection using inertial mapping tools provides an excellent method of evaluating the current pipeline integrity. A single inspection only gives an indication of the pipeline integrity at a single point in time. Multiple inspections over a period of time can be used to estimate positional change and the nature of the loading process. An essential element of pipeline integrity management in geohazard areas is the ability to determine future performance so that intervention methods are correctly designed and scheduled and resources are efficiently administered. This requires the reliable prediction of the future development of pipeline integrity based on trends in the mapping data from multiple inspections. The approach developed by the authors to predict the future integrity of pipelines affected by ground movements is set out in this paper. It involves inertial mapping data from multiple inspections and calculates future strains in the pipeline using finite element analysis. Unlike methods based on interpreting inspection data alone, the finite element model includes the effects of soil-pipe interaction and axial pipeline stress together with the operational loads to provide a more complete assessment of pipeline integrity. The method is illustrated through the use of a case study. Copyright © 2012 by ASME.


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.

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