A critical review of quantitative risk analysis (QRA) models used in the pipeline industry was conducted as part of a project titled “Critical Review of Candidate Pipeline Risk Models”, which was carried out for the U.S. Department of Transportation Pipeline and Hazardous Materials Safety Administration (PHMSA). Guidelines for the development and application of pipeline QRA models were developed as a part of this project, following an extensive literature review and an industry survey. The guidelines provide a framework for performing QRA for natural gas and hazardous liquids transmission pipelines, and address risk estimation, which involves estimating the failure frequency and failure consequences. They are intended to assist operators in developing new QRA models, and in identifying and addressing gaps in their existing models. They are also intended to help regulators evaluate the accuracy, completeness, and effectiveness of the QRA models developed by operators.

Accurate defect sizing is crucial for maintaining effective pipeline safety and operation. Under growing pressure from local, national and world organizations, pipeline operators demand improved magnetic flux leakage (MFL) metal-loss sizing accuracy and classification from in-line inspection (ILI) tools. The axial MFL field response in pipeline steel near a metal-loss defect is a very complex phenomenon. Although critical for proper sizing model development, the effects of tool speed due to product flow is very difficult to model during finite element analysis (FEA) and therefore is often overlooked. However, understanding the dynamic MFL response is crucial for proper ILI tool design and the development of accurate defect sizing algorithms. T.D. Williamson (TDW) utilizes dynamic computer simulation modeling, paired with laboratory testing, to develop the complex parametric relationships between metal loss geometry, pipeline material and ILI tool speed. The blend of simulation and physical test results allow for TDW to iterate more quickly across multiple physics variables with simulation models, while maintaining a firm footing in reality with physical test validation. Accurately simulating magnetic field responses of metal loss under dynamic conditions produces the data necessary to identify optimal magnetizer design, including optimizing sensor spacing and placement for metal-loss defect sizing and characterization. This paper will provide an overview of advances in the use of computer simulation modeling for predicting dynamic flux leakage field response. Besides increasing accuracy, results from this work will extend specifications beyond optimal speed ranges and provide the basis for general corrosion profilometry predictions from decomposition of the full MFL signal.

Full-bore decompression of an initially highly pressurized pipe has been studied extensively in recent years. The main aim of this effort has been to estimate the speed of the decompression wave and its relationship to the speed of a travelling fracture in the pipe wall. It has been demonstrated that the speed of the decompression wave is influenced by the friction at the gas-solid interface, and also by the pipe size (diameter). The numerical value of the friction factor has been traditionally estimated using known relationships such as the Haaland formula. However, it has also been noticed that the friction factor calculated in this way has to be increased many-fold to achieve agreement between theory and experiment. To date, there is no physical justification for this increase. The present paper proposes an explanation by modelling the full-bore decompression as a ‘transient Fanno’ flow. The model development is based on the observation that the flow at the exit plane always tends to approach a ‘choked’ condition (sonic velocity). It is shown that a re-interpretation of the Fanno flow formula allows an estimation of the irreversibility, and therefore the friction factor, in the evolving flow. When averaged over space and time, the friction factor attains a value that need not be artificially adjusted. This value of the friction factor can be used in one-dimensional models of the decompression process. Also, the role of the ‘second coefficient of viscosity’ during the initial instants of the highly transient flow is examined.

This paper presents the Con Edison Gas Control experience in developing a simulator-based training program. The simulator-based training is now part of the Con Edison safety training as it allows the gas controllers to get familiar with abnormal and emergency conditions and learn to react promptly to contain the problem. The process of developing a training course required a sustained and dedicated effort. A number of iterative steps were necessary as we learned that the development of models and scenarios for training is a specific activity which is different from other activities such as simulator-based studies. The simulator-based training course we developed has two parts: basic concepts and Con-Edison specific lessons. Each part required a different lesson format and issues related to the development of the lessons are discussed.

This paper presents the development of a new, simplified criterion, known as PCORRC, for prediction of the remaining strength of corrosion defects in moderate- to high-toughness pipeline steels that fail by plastic collapse. Comparisons against an experimental database indicate that, when toughness is sufficient, the PCORRC criterion reliably predicts the remaining strength of blunt defects using only the maximum depth and maximum length of the defects with less excess conservatism than existing criteria. The value of PCORRC is demonstrated in comparisons that show it capable of reducing excess conservatism significantly in the class of defects that fail by plastic collapse, potentially resulting in significant reductions in pipeline maintenance and repair costs. This new criterion was developed at Battelle under sponsorship of the Line Pipe Research Supervisory Committee of PRC international. The new simplified criterion was developed from a finite-element software analysis model. The analysis software was applied in a parametric investigation to evaluate the influence of geometry and material characteristics on the remaining strength of corrosion defects in moderate- to high-toughness steels that fail by plastic collapse. The model development and parametric investigations demonstrated that: • The failure of this class of defects is controlled by the ultimate tensile strength rather than yield strength or flow stress; • Defect depth and length are the most critical defect geometry variables; • Defect width and material strain hardening are of lesser importance.

Motivated by the inability to accurately address non-pressure related stresses within the framework of current assessment guidelines, a three phase study aimed at the progressive development of a reliable and readily-useable procedure suitable for the analysis of internally pressurized degraded pipes which sustain large settlement and/or axial loads was performed. To ensure accuracy of the resulting procedure, full-scale experiments and finite element numerical simulations of artificially corroded 48-inch (122-cm) diameter X65 pipes subjected to combined loadings were designed to produce upper and lower bound rupture and global buckling failure envelopes for a given set of representative corrosion dimensions. The evaluation model accommodates combined stresses arising from internal pressure, axial bending, and axially compressive loadings to predict operational margins of safety for a pipe containing discrete or multiple metal loss regions guided by failure criteria which considers two critical failure modes: 1) a von Mises type failure criterion for rupture moment capacity determination, and 2) a global buckling failure criterion for identification of the critical moment capacity approximating collapse of the pipe mid-section due to a reduction in bending stiffness attributed in part to ovalization of the cross-section. The new methodology has been incorporated in the personal computer based program SAFE (Shell Analysis Failure Envelope), developed by Southwest Research Institute (SwRI) for the Alyeska Pipeline Service Company. The user-friendly program allows for definition of combined applied stresses and geometry of the degraded region through implementation of field-obtainable pre-or post-excavation measurements, and employs unique features which provide for the examination of pipe sections exhibiting distinct areas of general corrosion, or “patches,” separated both longitudinally and circumferentially, in a single analysis run. This paper outlines the model development and validation with supporting experiments and numerical analyses, and extension of the new procedure through sophisticated numerical techniques embodied in SAFE to actual corrosion profiles and service loadings. Detailed information included in the review are the finite element and SAFE program failure predictions for pipes analyzed with a given set of corrosion dimensions and load magnitudes, and a thorough discussion of the practical application of the SAFE program.

Increasing concerns and attention to pipeline safety have engaged pipeline companies and regulatory agencies to extend their approaches to pipeline integrity. The implementation of High Consequence Areas (HCAs) has in particular had an impact on the development of integrity management protocols (IMPs) for pipelines. These IMPs can require that a risk based assessment of integrity issues be applied to specific HCA risk factors. This paper addresses the development of an operational risk assessment approach for pipeline leak detection requirements for HCAs. A detailed risk assessment algorithm that includes 25 risk variables and 28 consequence variables was developed for application to all HCA areas. The significant likelihood and consequence factors were chosen through discussions with the Leak Detection Risk Assessment Model Working Group and subject matter experts throughout Enbridge. The leak detection algorithm focuses on sections of pipe from flow meter to flow meter, as these are the locations that impact the leak detection system used by Enbridge. Each section of pipe is evaluated for likelihood, consequence and risk. When a high or medium risk area has been identified, an evaluation of potential Preventive and Mitigative (P&M) measures will be undertaken. A P & M Matrix has been developed to identify potential mitigation strategies to be considered for higher risk variables, called risk drivers, in the model. The matrix has been developed to identify potential risk mitigation strategies to consider for each variable used in the HCA Leak Detection Risk Assessment. The purpose of the matrix is to guide the user to consider actions identified for variables that drive the risk for the particular location. Upon review of the matrix, the user determines feasibility of the risk mitigation strategies being considered to identify an action. The paper will describe the consultative process that was used to workshop the development of this algorithm. Included in this description is how the process addressed various methods of leak detection across a wide variety of pipelines. The paper closes with “development challenges” and future steps in applying operation risk assessment techniques to mainline leak detection risk management.

Geologic hazards pose a significant threat to pipeline integrity. As an existing pipeline system ages, targeted analysis and positioning of maintenance resources become increasingly important to remediating problem pipeline sections and to ensure timely response to system failures. A geographic information system (GIS) now is commonly used to model pipeline systems. Significant geologic hazards can be mapped and effectively managed in a GIS database as a way to assess risk and to target pipeline remediation resources. In particular, the potential for soil corrosion is a significant threat to pipelines. In the U.S., digital soil maps from the United States Department of Agriculture, Natural Resources Conservation Service (USDA NRCS) have been compiled into the Soil Survey Geographic (SSURGO) database. Numerous soil attributes are stored in the database allowing for a detailed examination of soil characteristics. SSURGO data is largely consistent in quality and geographic extent across the U.S. and is the best available database for a national assessment of soil corrosion potential. We describe the development of a national database for the collection of locations of known corrosion from pipeline system managers. This database can be compared to soil conditions, as noted in SSURGO or other supporting soil data, for the development of a model of soil parameters that may indicate the future potential for buried pipeline corrosion. This paper outlines the need for such a database, significant design considerations and the proposed process for model development.

While the formation of a wrinkle in an onshore pipeline is an undesirable event, in many instances this event does not have immediate pipeline integrity implications. The magnitude or severity of a wrinkle formed due to displacement controlled loading processes (e.g. slope movement, fault displacement, frost heave and thaw settlement) may increase with time, eventually causing serviceability concerns (e.g. fluid flow or inspection restrictions). Pipe wall cracking and eventually a loss of containment involves contributions from the wrinkle formation process, as well as wrinkle deformations caused by in-service line pressure, temperature and seasonal soil displacements. The objective of this paper is to provide an overview of the ongoing research efforts, sponsored by TransCanada PipeLines Ltd, towards the development of a mechanics based wrinkle ultimate limit state that may be used in future to evaluate the long term integrity of wrinkled pipeline segments. The research efforts include testing and non-linear finite element modeling of a full scale wrinkled pipeline segment. This paper outlines the development of the full scale finite element model, including the detailed material model development, used to estimate the fatigue life of the experimental full scale fatigue test specimen. A comparison is then carried out between the experimental results and the results from the finite element analysis.

Inspection has revealed pipeline buckles and wrinkles promoted by thermal loads, differential settlement, slope movement and other pipe-soil interaction modes, as well as, cold field bends during construction. While all agree that pipeline wrinkles are undesirable, the urgency of their repair is not commonly understood. In general, it is accepted that the onset of wrinkling does not result in a loss of integrity because pipeline steels are adequately ductile to support large monotonic strains. It is also known that loading is displacement-controlled, thus applied load relief occurs during wrinkle formation. Although failure can occur with only a few strain reversals, the low loading frequency provides time to react. This paper will describe the steps and tools required to define the maintenance requirements for a pipeline wrinkle or to evaluate the effectiveness of remediation techniques. The paper will focus on the results of a preliminary wrinkle model development project aimed at assembling a practical technique capable of predicting the service life of a buckled or wrinkled pipe segment. The LS-DYNA non-linear finite element (FE)-based numerical wrinkle and buckle formation and growth model, developed at BMT Fleet Technology Limited, will be described along with its validation through comparison with full-scale trials and existing design criteria. The paper also discusses the use of the FE model predicted through-life wrinkle behavior to estimate the wrinkle service life and describe the way forward for the further development and implementation of this approach.