Surface cracks in pipelines under certain service conditions may grow due to fatigue, which is caused by pressure (cycles). The leak-before-break (LBB) assessment method is employed to avoid any catastrophic failure prior to a detectable leakage. In the LBB analysis, crack critical length is an essential element for determining the pipeline leak or rupture. The common approach regarding the evaluation of LBB is to calculate the critical crack length and through-wall length under iven pressure cycling conditions. If the critical crack length is less than the through-wall length, LBB conditions could occur and be detected if leak detection capability is high. This involves complex calculations in crack fatigue growth and could result in extensive analysis if thepipeline has a large crack population. This paper presents a simplified approach for assessing the leak-before-break of the flawed pipelines. This approach is based on industrial code API 579-1/ASME FFS-1 Fitness-For-Service. Through the investigation of effects for different parameters on crack growth, including crack initial geometry, pipeline materials, loading conditions, pipeline diameter and wall thickness, it was determined that the crack initial aspect ratio is a major factor influencing crack growth and geometry evolution. Based on these parameters, a crack fatigue growth map was developed. By comparing the behaviors of different cases, it was confirmed that the proposed method is a valid approach for the pipeline LBB analysis.

Ovality in a pipe results in a stress concentration and may present a pipeline integrity concern. If ovalization is generated during manufacturing or transportation and found during the girth welding process before the pipe is buried, replacement of the oval segment is usually the solution. However, ovalization is sometimes also found in buried pipelines via in-line-inspection (ILI) either before the pipeline is put into service or during regular pipeline maintenance. The mitigation and/or replacement of oval pipes after burial can be expensive. It is vital to identify what constitutes an unacceptable ovality level and to remediate only those that pose a threat of failure during the service life of the pipeline. The existing assessment approaches for oval pipes, such as that in API 579, generally require knowledge of the amount of ovality at zero pressure. However, the ovality of buried pipes usually is only available from ILI runs carried out at a non-zero internal pressure. The internal pressure tends to push the pipe back toward a circular shape, a phenomenon known as re-rounding. As a result, the ILI-reported ovality is smaller than that under zero pressure. Described in this paper is a new approach which can be used to assess the integrity of oval pipe segments based on ovality either as measured with no pressure in the pipe or as reported by ILI conducted at an elevated level of pressure. The approach considers both burst failure and fatigue damage. The accuracy of the approach was verified by finite element analysis (FEA). With the help of this new approach, a general discussion about the threat of ovalization to the integrity of a pipeline is provided. The analysis indicates that ovalization in amounts usually observed does not reduce the burst pressure in most pipelines, but fatigue damage could be a concern. The fatigue damage due to ovalization is sensitive to pipe geometry, amplitude of pressure variation, and the minimum pressure level within the pressure cycles.

Integrity Management Program (IMP) is a systematic and documented program for assuring asset integrity throughout the full life cycle of an asset. To ensure safe and reliable operation, the British Columbia Oil and Gas Commission (Commission) has been requiring its licensed pipeline operators through its regulations to develop and implement pipeline integrity management programs (IMPs) in accordance with Canadian Industry Standard CSA Z662. The auditing process, the collated results and findings from the IMP audit years (2011–15) were published in IPC 2016-64161[1]. Since 2016, the Commission has enhanced its IMP compliance assurance process, and aligned it with the management system approach using Deming’s model of plan-do-check-act (PDCA) for IMP components and incorporated a lifecycle approach that spans the entire lifecycle of a pipeline system from planning to abandonment. In addition, the Commission has adopted a multi-criteria decision-making approach when prioritizing which operators to audit. This method utilizes weighted rank approach and takes into account multiple factors, such as, previous IMP audit results, pipeline length and product, class location, incident frequency, and asset age. Through collaborative efforts with the University of British Columbia (Okanagan), an innovative risk based audit tool — Integrity Management Program Audit and Knowledge Tool (IMPAKT) has been developed to help evaluate the compliance of operators’ IMP in terms of the management system approach and its associated risk. This tool conducts three-dimensional analysis of IMP performance using the failure mode effect analysis (FMEA) technique and allows the Commission to generate a risk profile for each IMP component to determine which components are most critical, requiring immediate attention. The final audit results are presented as a Risk Priority Number (RPN), which is a product of severity, occurrence and action. An effective integrity management program requires a strong safety culture, therefore, safety culture aspects are incorporated into the risk based auditing tool, IMPAKT. This risk based evaluation process also allows the Commission to develop a compliance benchmark to make comparison between different operators’ IMP results for continuous performance improvement. This paper presents the innovative approach developed and implemented by the Commission for the IMP compliance oversight (auditing) process and implication of such changes.

High strength, butt-welded pipeline fittings are critical components for the construction of reliable and safe pipeline systems to extract, gather and transmit oil and gas products. Due to stringent safety and environmental requirements, fittings manufacturers are obliged to adhere to commonly accepted industry standards (e.g. CSA Z245.11, MSS-SP-75) and adopt supplementary operators’ specifications. Nevertheless, there have been several recent cases where fittings delivered by qualified manufacturers and available through local stock suppliers have not met the specified tensile properties, such that they failed during hydrostatic pressure tests or in-service operations. The issue has triggered concerns of operators and regulators (e.g. NEB SA 2016-01) warning about the use of substandard fittings. Although deficiencies in engineering design or operation beyond permissible conditions could be contributing factors, the root cause of the recent fittings failures was mainly associated with the underlying metallurgy and processing resulting in critically low yield strength and/or toughness levels. Further, existing standards and specifications are not stringent enough to screen out fittings with inadequate steel composition or improper manufacturing parameters. As such, a comprehensive modelling and experimental study has been launched to understand the interplay between the composition, grade, geometry and plant-specific processing parameters of quenched and tempered pipeline components. The experiment entailed plant trials using an instrumented NPS 36″ 3D elbow to measure the actual thermal response of the fitting during reheating, quenching and tempering cycles. Data was acquired from 36 different positions on the part in order to monitor any deviations from intended production parameters. Further, the metallurgical behaviour of the base steel plate, in terms of austenite grain growth, continuous cooling transformations (CCT) and temper softening of the as-quenched microstructure, has been established by dilatometric tests and microstructural characterization. The analysis and coupling of these diverse data sets is not trivial and requires scientific-based computational modelling. An integrated thermal-structure-properties finite element model was developed to predict the temporal and spatial evolution of the microstructure and provide a 3D strength map for any as-quenched and as-tempered fitting. This predictive engineering tool aids the selection of adequate steels and suitable heat treatment parameters such that target gauges and grades can be manufactured by a given plant to meet the specified requirements and standards. This paper describes the aforementioned methodology and highlights the challenges associated with the manufacture of fittings; in particular thick-wall pipeline components. Further, guidelines and existing knowledge gaps for improved specifications and standards will be discussed.

High pH Stress Corrosion Cracking (HpHSCC) is a significant threat to the buried pipelines, which are protected through simultaneous coating and cathodic protection strategies. In the past decades, extensive research has been devoted to assessing the influence of environmental and metallurgical factors on the susceptibility to HpHSCC. With reference to mechanical factors, previous studies employed either slow strain rate or constant amplitude testing methods. However, the pressure fluctuation data extracted from pipeline operations has indicated that pipelines experience highly variable amplitude loading conditions during their service. Accordingly, an important consideration in managing HpHSCC is load interaction. Statistics show a higher probability of HpHSCC failures within the 30 km downstream from pump/compressor stations where the pipeline steels experience elevated service temperatures, with incipient higher susceptibility to HpHSCC. However, the pipeline sections within the 30 km downstream from pump/compressor stations also experience the underload-type of pressure fluctuations that feature a maximum pressure close to the design limit, frequent and large amplitudes of depressurization, resulting in low stress ratio, R (minimum stress/maximum stress), and many smaller pressure fluctuations (minor cycles) with R ratio closer to +1.0. It has been well characterized that the underload-minor-cycle-type of pressure fluctuations has the significant acceleration effect on crack growth rates in near-neutral pH (NNpH) environments. However, the effect of the underload-type of pressure schemes on HpHSCC crack growth has not been well developed. In this research work, a cathodically protected X65 steel specimen in the developed high pH solution, composed of 1N Na 2 CO 3 and 1N NaHCO 3 , was subjected to different loading conditions. These loading waveforms simulate underload cycles (R = 0.5), minor cycles (R = 0.9) and variable amplitudes consisting of both underload and minor cycles, respectively. The HpHSCC test results showed that the highest and lowest crack growth rates were obtained in high and low R ratio constant amplitude loading conditions, respectively. Furthermore, an intermediate crack growth rate was obtained under variable amplitude loading condition. These results indicate that the underload cycles retard crack growth rate in high pH environments.

In the majority of liquid pipelines, the pump station discharge pressure ranges are much greater than the pressure ranges experienced at the suction end of the downstream pump station. Consequently, the cyclic pressure induced fatigue damage accumulation rate is greater at the discharge end than at the suction end of a given pipeline segment. In completing an integrity assessment of a fatigue susceptible feature, assuming that the pump station discharge cyclic pressure profile applies to all features in the line segment is conservative. This conservative assumption can lead to un-necessary repairs, unintentional damage from over-prescribed maintenance, or inefficient decisions regarding maintenance action prioritization. The following paper presents the results of a Canadian Energy Pipeline Association (CEPA) initiative to develop a simple approach to define the cyclic pressure history at any point in a liquid pipeline segment based on the bounding discharge and suction pump station Supervisory Control and Data Acquisition (SCADA) pressure time history data. The approach was developed based on collected operating pipeline SCADA pressure time history data for line segments with intermediate measurement points which could be used to validate the developed model. The pressure time histories for all the locations were analyzed using a Rainflow cycle counting technique to develop pressure range spectra (i.e. histograms of pressure range events) and the cyclic pressure severity of each of the time histories was characterized by the Spectrum Severity Indicator (SSI). The SSI represents the number of annual 90MPa hoop stress cycles required to accumulate the same fatigue damage as the actual pressure spectrums. The technique presented in this paper illustrates how to infer the pressure range spectra or SSI at intermediate locations. The technique is shown to be a significant improvement (i.e. higher location specific accuracy) than either applying the discharge pressure spectrum or applying a linear interpolation between discharge and suction conditions in fatigue life assessments. The liquid pipeline cyclic pressure characterization technique presented in this paper will permit integrity assessment or severity ranking of features along a pipeline to be based on an accurate local pressure profile rather than an upper bound. This understanding will help to improve the accuracy of defect loading, one of the three main pillars in integrity assessment (i.e., loading, geometry, materials) for defects susceptible to cyclic loading (e.g., cracking, mechanical damage).

Although stress corrosion cracking (SCC) growth is attributed to the synergistic effects of stress and corrosion, these two factors can just as easily become competing mechanisms, with stress cycles driving growth (hydrogen, the by-product of corrosion, may facilitate the growth), and corrosion working to blunt the crack tip and arrest growth. It follows that reducing the maximum pressure and cycling severity can slow down the crack growth or even stop it, and aggressive corrosion can further blunt the sharp crack tip. The Authors have observed, on a particular Polyethylene (PE) tape coated pipeline, instances where SCC has exhibited a propensity to corrode and convert into sharp edge corrosion. This is attributed to the combined effects of limited corrosion protection and low stresses. The focus of the paper is to assist operators in recognizing this phenomenon and integrate lessons learned into pipeline integrity management strategies.

Statistical data available from several international sources, such as the reports provided by the European institutions EGIG, CONCAWE and UKOPA, as well as by the American Department of Transportation – DOT, indicate that pipelines represent the safest mode of transportation for hydrocarbons and other dangerous products when compared to other alternatives, such as road, rail, waterway, etc. Operators ensure a high level of safety of their pipelines by investing large amounts of effort and resources in accident prevention, efficient contingency procedures, environmental protection and reliability along the life cycle of their assets. However, the pipeline industry, both in Brazil and abroad, is frequently asked to demonstrate their safety performance both by environmental and regulatory agencies, as well as by society, considering the assets already in operation and also those that will still be built (new pipelines). Such requests are based on the most opened and detailed communication between pipeline operators and the other stakeholders involved. In this context, the organized and standardized collection of data related to pipeline failure events, such as failure mechanisms and their consequences, along with relevant and specific data regarding the assets and their operations, is essential to foster the process of knowledge construction on this topic. It allows generating consistent information both to meet the stakeholders’ requests and to improve risk management of pipelines by the operators, ultimately supporting decision-making. Therefore, this work aims to create a Brazilian Pipeline Incident Database, considering firstly gas pipelines and oil pipelines operated by TRANSPETRO, a PETROBRAS Subsidiary. This research intends to study the characteristics, the architectures, the assumptions and the principles adopted by the international pipeline failure databases currently available, considered here as benchmarks, in order to propose an analogous and specific structure for the reality of the Brazilian Pipeline System.

Internal pressure fluctuations during pipeline operations could contribute to crack growth in steel pipelines. These pressure fluctuations create a variable amplitude loading condition with large amplitude cycles at near-zero stress ratio, R (minimum stress / maximum stress) and small amplitude cycles (minor cycles) at near +1 R ratio which can both affect crack propagation. Mean stresses fluctuate with pressure due to fluid friction losses proportional to the distance from the pump/compressor station. A deeper understanding of mean stress sensitivity on crack growth rate in steel pipelines is sought. The aim of this research is to retard crack growth in pipelines by prescribing pressure fluctuations, thus controlling mean stress effects on imperfection growth in steel pipelines under a near neutral pH environment. This study shows that prescriptive mean load pressure fluctuations can be used to reduce crack growth rates in steel pipelines, thus expanding pipeline integrity management methods.

The US regulations and Canadian standards require that a System Wide Risk Assessment (SWRA) be performed for all pipelines. Typically, an annual SWRA is performed by operators and used to identify high risk sections. Appropriate identification of these high risk sections is expected to avoid significant failures, particularly in higher consequence locations. With current heightened public awareness levels and related regulatory oversight even a failure, such as a rupture, with relatively low safety and environmental consequences is considered undesirable. Post failure analysis often examines SWRA results to investigate if SWRA is identifying such locations appropriately. Are SWRAs developed with the intention of avoiding these failures? How can we ensure SWRA achieves these expectations? This paper examines the purpose of SWRA and takes a data driven approach to critically assess its effectiveness. In the 21 st century, where vast amounts of data are being generated through inspections, patrolling, monitoring, and management systems, TransCanada’s approach seeks to leverage all the evidence or leading indicators of high risk and imminent failures. However, data and subject matter expert opinions are not perfect and complete. Understanding these limitations and inadequacies, yet optimizing in the face of them, requires an honest representation of reality with considerations to limits of applicability and probable blind spots, together with clear decision-making to achieve a well-defined purpose. This paper will describe the six-year evolution of a quantitative SWRA approach with a built in continuous improvement cycle. Examples of learning from failures, assessments, and analytical studies and how they were incorporated into the SWRA are demonstrated. Also the development of meaningful risk targets and their applications are explained. The particular details for scenarios where risk criteria have been exceeded in both high consequence and low consequence locations are examined and interpreted such that maintenance teams can address issues appropriately. The value of bringing all relevant data to a common risk platform is also demonstrated. In the 21st century, where data availability will only increase, appropriate holistic incorporation of these multiple data sets is critical to identify where multiple threats interact. Depending on how likelihood of failure and the consequences of failure are combined, the resultant risk could potentially be high (i.e. different risk measures). Therefore, it is important to cover all risk measures that are relevant and develop criteria that govern these risk measures. The implementation of a holistic SWRA to make the best optimized decisions possible is demonstrated in practical situations where inputs are imperfect and vast data sets need to be combed for meaningful indicators.

Reliability, Availability and Maintainability (RAM) models were first developed in Enbridge Liquids Pipelines in 2006 and in the last 3 years have contributed over $200 Million in capital cost avoidance while maintaining or improving the reliable design and operation of the pipeline system. These models constitute a very effective, factual and dependable tool to assess the throughput performance of a pipeline system over its entire life cycle or a specified time of interest. In addition, the RAM model cost is a small fraction of the overall monetary benefit, in the order of 1%, hence making RAM models a highly leveraged activity. The concept of a RAM model stems from Reliability Block Diagram methods (also known as Dependent Diagrams). Interaction of large, complex and multi layered systems can then be analyzed using the Monte Carlo simulation methods (or Stochastic Discrete Event Simulation) hence quantifying the output of the entire system with greater accuracy than other estimating tools or methods. Over 10 years, Enbridge Liquids Pipelines has developed its own failure database for equipment and operational events consequently almost all model inputs are based on in-house data rather than industry generic data, making the model output more robust, accurate and appropriate for internal use. Initially, in Enbridge Liquids Pipelines, RAM models were mainly built to assess and confirm the design capabilities of future pipelines designs and assist in the optimal selection of specific design options. Because of the effectiveness of the tool combined with the current cost constrained business environment, the company is moving towards building RAM models for assets already in operation in order to optimize their performance. This is proving to be an extremely cost effective addition to internal decision making processes. The approach has been used in risk based budgeting, asset maintenance, design modifications and throughput optimization initiatives. In various industries including Oil and Gas, RAM models have proven their worth over time as an effective cost avoidance tool. This approach has now been successfully deployed in the Pipeline Industry at Enbridge. As an example, a RAM model conducted during the design phase of a pipeline project saved $28 million in capital by proving that an additional storage tank and significant new infrastructure was not required. Another benefit of RAM models has been their ability to confirm or counter stated assumptions by internal stakeholders. Equipment upgrades and equipment sparing decisions are often seriously debated and costly decisions may not always be based on complete economical foundations but rather on avoiding past negative experiences or by following basic guidelines that are less than optimal. When a project or operational team needs to find an alternative, a RAM model is a tool of choice to evaluate, and justify the best option. Because of its proven value, RAM models are now an integral part of Enbridge Liquids Pipelines Design Standards and are used on all large projects. Models recently built for operational pipelines delivered similar value so in the near future the work will be expanded to encompass the entire existing network of integrated pipelines to improve on performance and operational costs.

Pipelines are the most efficient and common infrastructure for the transportation of oil and gas. For Canadian pipeline operators, CSA Z662 Annex N is considered the industry standard for the development and implementation of integrity management programs (IMP) which include essential elements of policy and commitment; planning (goals, targets, organizational structure, roles and responsibilities, hazard identification, risk assessment and control); implementation (management of change, training and competency, documentation and record management); checking and corrective action (inspection, measurement and monitoring, investigating and reporting incidents, and internal audits); and management review elements over the lifecycle of a pipeline asset. In 2006, the British Columbia Oil and Gas Commission (Commission) made CSA Z662 Annex N mandatory for pipeline operators within its regulation. This paper provides an overview of the Commission’s compliance assurance process through the assessment of British Columbia’s pipeline operators’ IMPs and presents findings from the first five year (2011–15) assessment cycle. The analysis and trends of findings are presented in detail along with tracking of corrective actions. This paper also discusses knowledge gained from the compliance assurance process, along with the areas of proposed improvement to the current process for the next five year cycle. This includes alignment of the assessment process with the management system approach (using a risk based assessment process), improving regulation and the processes of compliance assurance and enforcement.

Human Factors play an important role in the reduction of pipeline incidents. There has been little guidance specific to the Pipeline Industry related to Human Factors management, with the exception of Control Room Management, in the recent past. The Human Factors Working Group, formed during the 2013 Banff Pipeline Workshop, partnered with CSA Group to fill an identified gap in the industry related to Pipeline Human Factors. The result was the creation of an Express Document, CSA EXP248 Pipeline Human Factors. CSA EXP248 (EXP248) considers Human Factors through the life cycle of a pipeline asset. The main goal of this document is to improve pipeline safety performance through management of risks associated with Human Factors. It provides guidance to pipeline operators on the need and means to integrate Human Factors in all aspects of the Pipeline Life Cycle and Management System, with philosophy considerations for integration of Human Factors into a “fit for service” pipeline system. A review of EXP248 will illustrate how this document provides information that is scalable to organizations based on size and complexity. This paper reviews the new CSA Group Express Document process and its application for the Pipeline Industry. This paper will discuss kkey aspects of EXP248 that operators could apply and practical tips on the application of this guidance to the pipeline operating community. Areas highlighted during this review include elements of a Human Factors program, consideration of physical, organizational and cognitive demands of a job or task, and integration of Human Factors into Management Systems. Finally, the paper will describe next steps to create a CSA Group consensus standard for Pipeline Human Factors, where EXP248 will serve as a seed document. Lessons learned during the use of the new Express Document will be highlighted and the use of this new process for other applications explored.

Assurance Management is an essential aspect of a company’s governance. Assurance management can be defined as the “check” and “act” elements in any management system’s continual improvement cycle and is designed to provide stakeholders with current and accurate information about the adequacy, compliance, and effectiveness of its policies, programs, processes, and activities. An assurance management program may have activities that span beyond a particular management system’s scope, and often incorporates processes completed by various internal and external stakeholder groups. As such, it is vital to have a structured and disciplined approach to assurance management. Over the past few years, Enbridge Pipeline Inc. Liquid Pipeline Business Unit (Enbridge) has been actively working on the development, implementation, and continual improvement of its Assurance Management Program (AMP) and associated processes, as part of our Integrated Management System (IMS) framework. The alignment of existing processes within a single structured program within Enbridge will provide a more coordinated approach as well as clear accountabilities on assurance functions within the organization. Enbridge’s AMP consists of three layers of “Check” defenses and is linked to core “act” processes in an effort to drive overall continual improvement throughout the organization. The minimum requirements and considerations in establishing an adequate and effective AMP will be detailed within this paper based on the insight Enbridge has gathered through its journey in the implementation of its program within the organization. The paper will discuss the principles behind our AMP model as well as some of the challenges and successes experienced in implementing the AMP within Enbridge.

The soil response around a high temperature pipeline proposed for construction was evaluated. Infilling of backfill around pipelines at side bends subjected to temperature changes may accumulate during cyclic displacements leading to ratcheting and possibly buckling of the pipeline. A medium-scale laboratory model testing program was used to gain a better understanding of how silty sand backfill migrates around a pipeline when subjected to cyclic lateral loading. Several mitigation techniques using geosynthetics and compressible materials were evaluated in order to both delay and reduce the net downward soil movement from pipe displacement cycles.

In 1958, General Curtis E. LeMay established the structural integrity program for the United States Air Force (USAF). Since then, the USAF has been honing the requirements for extending the service life, durability, and safety of aircraft. These requirements have evolved to include Damage Tolerance principles that encompass the design and the management of aircraft with the objective of reducing maintenance burdens and ensure structural integrity for airworthiness, safety, and mission capability. Recently, requirements of some agencies and companies include Holistic Life Structural Integrity Process (HOLSIP) and concepts aimed at improving the early prediction and detection of structural discontinuities that can pose a safety concern. HOLSIP is intended to reduce the inspection & maintenance cycle while identifying prevention and mitigative measures to be employed. This holistic methodology addresses the total life of components and related issues. It is a physics based approach that incorporates the interaction of known possible degradation mechanisms and their potential failure modes. It provides the basis for analytical, experimental and procedural methods to make structural integrity predictions of components from the design, manufacturing, commissioning, maintenance and inspection intervals that would meet the desired level of safety and reliability. Non-destructive evaluation methods are incorporated in this approach as well. As part of continuing to ensure the safety and reliability of pipelines systems, the energy pipeline industry performs periodic risk assessments and maintenance activities and can enhance current integrity management programs by adopting HOLSIP principles and framework. In the early 2000s, pipeline industry associations and government regulators published a risk assessment based process for prioritizing pipeline segments for inspection and remediation. These processes have been formally integrated into an Integrity Management Program (IMP). By incorporating risk assessments and periodic inspections as part of the IMP, energy pipeline operators have achieved great success in removing damage that can pose an immediate or short-term safety concern to the public, environment and piping facilities. However, in-service pipeline failures continue to occur suggesting that the treatment of integrity threats, degradation mechanisms and failure modes is still fragmented. There needs to be a strong sense of wholeness in the approach to managing pipeline integrity. The absence of this can lead to unnecessary inspections and assessments, early pipeline retirements, over conservative assumptions or worse, further in-service accidents. As energy pipelines around the world continue to age and their safe performance is expected to increase, the need for HOLSIP becomes more apparent. This paper provides an overview of the fundamental principles and concepts of a holistic approach developed for maintaining aircraft fleets and how they apply to structural integrity engineering assessments for pipelines. A comparison with the current pipeline integrity management practices and regulations is highlighted.

The application of in-line inspection (ILI) to assess pipelines for various anomalies is standard practice in the pipeline industry. When ILI data identifies the presence of anomalies such as denting or ovalization, current convention is to perform either a depth-based or strain-based assessment to assess the severity. Although a strain-based methodology is generally accepted in the pipeline industry, this approach does not address all of the primary damage mechanisms associated with pipeline dents. Assessment based upon either depth or strain alone may not only provide non-conservative results but also fail to properly rank dents in order of their true severity. A life-cycle assessment approach that considers the damage caused by the dent formation, the stress intensification effect of the dent profile, and the severity of future pressure cycling provides an improved understanding of the probability of failure, allowing for more informed integrity management decision making. Strain-based assessment of dents in pipelines is typically performed by calculating the local curvatures in the dent geometry as measured by ILI. Local strains are then calculated based on these local curvatures. However, this approach does not address that once a dent has been formed, continued pressure cycling at that location is what will ultimately cause a failure. The current strain-based methodology does not account for the severity of the pressure cycling at the dent. A new and innovative methodology has been developed which takes a life-cycle approach to the assessment of pipeline dents. This approach estimates the remaining life of a dent based on fatigue damage accumulation. Finite element analysis (FEA) is used to calculate various stress concentration factors (SCFs) based on the geometry of the dent. These SCFs are used to calculate an equivalent alternating stress for a unit pressure cycle event. Past representative pressure cycling data is gathered using a rainflow counting approach. The amount of damage accumulated during each pressure cycle is calculated using stress or strain based (S-N) fatigue curves; this allows for a damage rate to be calculated based on past operational history. A remaining life can be estimated based on this damage rate and an estimation of the initial fatigue damage accumulated during formation of the dent. This estimation is made based on previous elastic-plastic FEA of various scenarios which simulate the formation and shakedown of a pipeline dent. Case studies which explore the use of different assessment methods to analyze dents will be presented. A comparison of different assessment methodologies will illustrate the improved understanding of the probability of failure of dents based upon the life-cycle assessment.

Hydrogen embrittlement is one of the most severe steel degradation mechanisms. Using hydrogen enhanced decohesion (HEDE) and hydrogen enhanced local plasticity (HELP), we can predict if more hydrogen atoms will accumulate into the plastic zone, enhancing the hydrogen embrittlement and the crack growth rate. In the current study, a relationship has been proposed between operations of pipeline steels and hydrogen accumulation to quantify the effects of hydrogen embrittlement. The study find that hydrogen accumulation rate is proportional to stress intensity and inversely proportional to temperature; hence, higher stress intensity and lower temperature will enhance hydrogen accumulation and crack propagation. Hydrogen potential, diffusivity, hydrostatic stress near the crack tip, and the critical loading frequency have been considered in the new model to predict crack propagation rates in pipeline steels. The predicted values are compared with experimental results of X-65 steel in two near-neutral pH solutions to verify the model. This hydrogen diffusion model helps show former neglected hazard operations such as minor cycles, and offers an easier way to optimize operations that will prolong the life of pipeline steels.

A significant portion of the global energy pipeline infrastructure is constructed with pipe materials manufactured using the Electric Resistance Weld (ERW) process. The longitudinal seam of these ERW pipelines may contain manufacturing flaws and anomalies that can grow over time through pressure cycle fatigue and result in a pipeline integrity failure. These flaws/anomalies can be present in both vintage pipe (generally pre-1970) manufactured using a low frequency ERW process and more modern pipe that is manufactured using a high frequency ERW process. ERW seam anomalies are challenging to detect, discriminate, and size with current In-Line Inspection and In-Ditch NDE inspection technologies, which is driving the industry to better understand current inspection industry performance and to develop new technologies for ERW seam anomaly inspection. Ultrasonic (UT) imaging using inverse wave field extrapolation (IWEX) is an emerging NDE technique that is being applied to improve discrimination and sizing of anomalies in pipelines. This paper will describe the IWEX development, the challenges related to seam weld integrity and assessment and SCC assessment, and results from studies to evaluate performance. Ultrasonic imaging is also compared to the current state-of-the-art techniques such as ultrasonic phased array (PA). A goal of the project is to produce images capable of discriminating cold welds, surface breaking hook cracks, non-surface breaking upturned fiber indications, poor trim, offset plate edges, and anomalies with fatigue cracking. The goal is to size all of the cracks in a SCC colony and produce a three-dimensional map of the area. In mapping these anomalies the sizing needs to be sufficiently accurate to qualify in-line inspection tools used for crack inspection.

A comprehensive study was conducted to investigate the reinforcement of LF-ERW flaws located in a 16-inch × 0.312-inch (406-mm × 7.93-mm), w.t. Grade X52 ethylene pipeline. The study was prompted by an in-service leak that was discovered in an LF-ERW seam during routine maintenance activities. The investigation was subsequently expanded as a result of the discovery of several additional leaks. An initial failure analysis of the leak location was conducted followed by broader material testing, full-scale testing, and metallurgical analysis of the remaining pipe. The use of composite repair systems as a feasible method of LF-ERW seam reinforcement was also examined. As part of this study, testing was also conducted on 8.625-inch × 0.250-inch. (219-mm × 6.35-mm) pipe material having LF-ERW seams. Test results documented the potential for composite repair systems to provide reinforcement to LF-ERW flaws and crack-like defects. Distinct contrasts were observed between the performance of samples with unreinforced and reinforced notches subjected to cyclic pressure and burst tests. Reinforced samples exhibited improvements in pressure cycle life and significantly increased burst pressure capacities as compared to unreinforced samples. The results of this program demonstrate that, when properly designed and installed, composite materials are an effective means for reinforcing LF-ERW long seam weld flaws and other planar defects. The composite repairs served to ensure that cracks neither form nor propagate during aggressive pressure cycling and burst testing. It should be noted that the testing program was specific to the operating and material conditions associated with a particular ethylene pipeline that is the subject of this paper.