Dents in buried pipelines can occur due to a number of potential causes; the pipe resting on rock, third party machinery strike, rock strikes during backfilling, amongst others. The long-term integrity of a dented pipeline segment is a complex function of a variety of parameters, including pipe geometry, indenter shape, dent depth, indenter support, pressure history at and following indentation. In order to estimate the safe remaining operational life of a dented pipeline, all of these factors must be accounted for in the analysis. The paper discusses the full-scale dent testing being completed to support the development of pipeline integrity management criteria and is a continuation of the work discussed in previous IPC papers [1,2]. The material and structural response of the pipe test segments during dent formation and pressure loading has been recorded to support numerical model development. The full scale experimental testing is being completed for pipe test specimens in the unrestrained and restrained condition using different indentation depths and indenter sizes. The dents are pressure cycled until fatigue failure in the dent. This paper presents typical data recorded during trial including indentation load/displacement curves, applied pressures, strain gauges along the axial and circumferential centerlines, as well as dent profiles. The use of the full-scale mechanical damage test data described in this paper in calibrating and validating a finite element model based integrity assessment model is outlined. The details of the integrity assessment model are described along with the level of agreement of the finite element model with the full scale trial results. Current and future applications of the integrity assessment model are described along with recommendations for further development and testing to support pipeline integrity management.

Dents in buried pipelines can occur due to a number of potential causes; the pipe resting on rock, third party machinery strike, rock strikes during backfilling, amongst others. The long-term integrity of a dented pipeline segment is a complex function of a variety of parameters, including pipe geometry, indenter shape, dent depth, indenter support, pressure history at and following indentation. In order to estimate the safe remaining operational life of a dented pipeline, all of these factors must be accounted for in the analysis. The goal of the full scale experimental program described in this paper is to compile a database of full scale dent test results that encompasses many of the dent types seen in the field, including plain dents, dents interacting with girth and long seam welds, and dents interacting with metal loss features, in both the unrestrained and restrained condition. The dents are pressure cycled until a fatigue failure occurs in the dent. Typical data recorded includes indentation load/displacement curves, applied pressures, pipe wall OD strains along the axial and circumferential centerlines, and axial and circumferential dent profiles. The full scale tests are being performed on behalf of PRCI and US DoT. This paper is intended to show the matrix of dents considered to date and present a representative summary of the data recorded. In addition to presenting the full scale test program and resulting data, this paper summarizes ongoing efforts to develop a validated pipeline dent integrity assessment model. The model under development makes use of the aforementioned full scale experimental data, to validate a finite element model of the denting and re-rounding process for a variety of dent scenarios (i.e. depths, restraints, indenter sizes). The paper discusses the efforts under way to develop and validate the finite element model with the goal being to estimate the fatigue life. The paper is an extension of work discussed in a previously presented IPC paper [1].

Detectable dents in buried pipelines can occur due to a number of potential causes; the pipe resting on rock, third party machinery strike, rock strikes during backfilling. The integrity of a dented pipeline segment is a complex function of a variety of parameters, including pipe geometry, indenter shape, dent depth, indenter support and pressure history at and following indentation. In order to estimate the safe remaining operational life of a dented pipeline, all of these factors must be accounted for in the analysis. The following paper summarizes ongoing efforts to develop a validated pipeline dent integrity assessment model. The model under development makes use of experimental tests to validate a finite element model of the denting and re-rounding process for a variety of dent scenarios (i.e. depths, restraints, indenter sizes). The results of the finite element model are then used in conjunction with the estimated pressure-time history in an integrity assessment procedure to estimate the safe remaining operational life of the pipe segment. The paper presents a discussion of the full scale fatigue tests carried out on dented pipeline segments and the efforts under way to develop and validate a finite element model of the experimental specimens with the goal of estimating the experimental fatigue life.

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.

Pipeline design and integrity management programs are employed to ensure reliable and efficient transportation of energy products and prevent pipeline failures. One of the failure modes that has received attention recently is pipeline fatigue due to pressure cycling in liquid pipelines, promoting through wall cracking and the release of product. Being able to estimate the leakage rate and/ total release volume are important in evaluating the consequence of developing a through wall crack, operational responses when incidents occur, and remedial action strategies and timelines. Estimates of leak rates can be used in pipeline system threat and risk assessment, evaluation of leak detection system sensitivity, development of Emergency Response Plans and strategies, and post-event evaluation. Fracture mechanics techniques consider the response of crack-like features to applied loading such as internal pressure, including estimation of crack mouth opening. Considering the differential pressure across the pipe wall and the crack opening area, estimated from the crack mouth opening, the flow of fluid through the crack can be conservatively estimated. To understand the conservatism of this analytical estimate of leakage rate, full-scale testing has been completed to evaluate the leakage rate through dent fatigue cracks of differing lengths under a range of internal pressures, and compare the empirical measured results to the analytical/theoretical estimates. The test procedure employed cyclic internal pressure loading on an end-capped pipe with a dent to grow fatigue cracks through the pipe wall thickness. Once a through wall crack was established, the internal pressure was held constant and the leakage rate was measured. After measuring the leakage rate, cyclic loading was employed to grow the crack further and repeat the leakage rate measurement with the increased crack length. The results of this experimental trial illustrate that the tight fatigue crack resulted in a discontinuous relationship between leakage rate and pipe internal pressure. Measureable leakage did not occur at low pipe internal pressures and then increased in a nonlinear trend with pressure. These results illustrate that a liquid pipeline with a through wall fatigue crack operating at a low internal pressure, or one having taken a pressure reduction, can have low leakage rates. The data and results presented in this paper provide a basis for an improved understanding and describing the leakage rate estimates at pipeline fatigue cracks, and providing insights into leakage rates and how to conservatively estimate them for fatigue crack consequence evaluation.