Imaging techniques using full matrix capture (FMC) ultrasonic NDE are well suited for in-service examination of electric resistance welded (ERW) pipe seams. We have been involved in developing an imagine technique since 2013 and presented results from Phase I at IPC in 2016 showing the system capable of detecting seam weld and SCC flaws and determining their orientation. The advantages over other methods such as phased array (PA) is the ability to image the flaw surface in addition to the flaw tip and corners where the flaw intersects the pipeline surface. This improves the ability to determine flaw orientation for discrimination of different types or crack-like features. The system produces UT images by overlaying multiple modes using reflections off the ID and OD pipe surface for ultrasonic illumination of the weld area from different directions. Using multiple modes produces a reflection off features regardless of flaw orientation from at least one of the modes. A complementary mode can then be used to size each feature by detecting the tips or ends of the feature from lower amplitude diffraction signals. Phase I used a model which assumed a cylindrical pipe shape. Real world use of this technique found limitations when pipe deviated from the assumed cylindrical shape such as severe offset plate edges, flat spots which can be the result of poor crimping adjacent the seam weld, or thickening of the seam caused by post weld heat treatment. In Phase II a need for reduced sizing error led to improved calibration and more advanced processing. To compensate for the non-perfect nature of real pipe, a new adaptive IWEX technique was developed to improve focusing and alignment of the various modes using the actual geometry to construct better focusing laws. First the OD and ID surfaces are imaged and the resulting surfaces are used to construct focusing laws which adapt to changes in the OD and ID surfaces. Results are better aligned UT images with the ability to image complex flaws with changes in orientation, and the ability to discriminate complex flaws from multiple small flaws in the pipe. Results show improvements in pipe with the greatest improvements in pipe with the largest deviations from a cylindrical shape.

Pacific Gas and Electric Company owns and operates an extensive network of over 10,700 km (6,700 miles) of gas transmission pipelines, much of which is under 16″ diameter and operates at less than 27.5 bar (400 psig), making them difficult to inspect with free swimming in-line inspection (ILI) tools. Additionally, many piggable pipeline sections are multi-diameter and have numerous 1.5D fittings, some of these in back to back configuration, requiring tools that are not currently available. Following several failed attempts to inspect PG&E’s 12″ × 16″ pipelines in 2015 using existing ILI tools, and after working to modify a 12″ × 18″ tool for lower pressure service in 2016, PG&E and ROSEN decided to collaboratively develop new, specially designed, 12″ × 16″ geometry and axial MFL tools. The goal of this project was to develop tools that could meet both the PG&E pipeline passage requirements and allow for an acceptable speed profile. The need to inspect a total of 16 pipeline sections in the long-term ILI Upgrade Plan, in this size range, justified the investment in these new tools. The service provider embarked on a new ILI tool design process including design, manufacturing, fabrication and testing at their facilities in Germany. Through this process, a number of unique ILI tool design features to lower tool drag and improve ease of collapsibility were implemented, resulting in a tool that far exceeds existing industry capabilities. To confirm the tools’ capabilities before their first use in a live gas transmission pipeline, pump testing in water, as well as in compressed air, was performed. In late 2017, using these tools, PG&E inspected two previously unpiggable 12″ × 16″ low-pressure pipelines successfully. In this paper, the process of developing these tools will be discussed. The test program will be reviewed comparing findings under controlled conditions in water and compressed air with pig run behavior in the live pipelines. The analysis also provides an assessment of the operating conditions that are deemed necessary for the inspection tool to gather a good quality data set.

A significant amount of effort has been expended in the area of advancing pipeline dent remaining life assessment methods beginning in the late 1980s and extending to the current day. Initial research efforts were primarily empirical in nature while more recent research efforts have incorporated finite element modelling. Coupled with advancements in assessment techniques, the capabilities of advanced in-line inspection (ILI) tools have increased to a point where they can provide consistent, reliable information that is suitable for dent assessments. As a result of these advancements in assessment models and ILI tools, operators can now perform remaining life assessments using ILI data, and a multitude of remaining life assessment models are available, including solutions from the European Pipeline Research Group (EPRG), Pipeline Research Council International (PRCI), American Petroleum Institute (API), and finite-element based approaches. In addition to these remaining life assessments, many operators routinely perform strain-based assessments based on guidance from ASME B31.8. To date, there have been few studies comparing the various assessment methods on large numbers of dents, and as a result, significant questions persist as to the conservatism inherent in each method. In addition, the EPRG and PRCI methods are largely based on full-scale testing and finite-element models performed with idealized indenter shapes while actual pipeline dents typically exhibit complex shapes and interactions between multiple dents. Each model also has limitations and advantages that are discussed in this paper, such as ease of use and how pipeline geometry and weld association are considered. This paper provides a robust comparison of selected dent assessment methodologies on 220 actual dents from a 24-inch pipeline with depths ranging from 0.6–4.5% OD, and 32 dents from a 30-inch line with depths ranging from 1–2.5% OD. The assessment includes both top and bottom of line dents and investigates the influence of restraint on remaining life. The results presented in the paper are based on high-resolution ILI caliper data collected during two in-line inspections. Furthermore, the paper provides statistical comparisons between strain and remaining life methodologies and also between the various remaining life assessments. The paper also provides a comparison of the restraint parameter from the PRCI model with calculated stress concentration factors from finite-element models. The paper provides a first of its kind comparison of the various methods and discusses how the work may be extended to other pipe diameters and wall thicknesses.

In the last 10 years, technical and economical efforts have been made to improve pipeline integrity management. Those efforts focus on developing “searching tools”, capable of identifying pipe mechanical damage due to slow landslides. We identified two main tools: geohazard mapping and inline inspection (OCP is using caliper with inertial navigation system INS). The INS system generates a substantial amount of information about pipe’s geometry and deformation, reported as pitch, yaw and distance cover for each run. Since the caliper has been used for years, the pipeline’s path of evolution over the years is already available. The INS data was merged with pipeline field inspections to develop an assessment tool based on Machine Learning Technology. This tool was applied to the complete path of the pipeline, analyzing each girth weld, thus obtaining a so called “criticality level” for each weld. Two models were evaluated, which differ on the size of the vicinity considered for each girth weld: 250m and 500m. The highest precision model was found with 250m, which already has allowed improvements in field inspections. This paper will describe this technique, capable of improving OCP’s pipeline integrity management.

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.

Current regulations for prediction and management of potential delayed failures from existing pipeline dents rely primarily on depth and conservative assumptions related to threat interactions, which have shown limited correlation with industry failures. Such miscorrelation can lead to challenges in managing effectiveness and efficiency of pipeline integrity programs. Leading integrity techniques that entail detailed assessment of complex dent features rely on the use of finite element analysis, which tends to be inefficient for managing large pipeline systems due to prohibitively complex modeling and analysis procedures. While efforts are underway to improve dent assessment models across the industry, these often require significant detailed information that might not be available to operators; moreover, they suffer scattered model error which makes them susceptible to unclear levels of conservatism (or non-conservatism). Nevertheless, most techniques/models are deterministic in nature and neglect the effect of both aleatory and epistemic uncertainties. Operators typically utilize conservative assumptions based on subject matter experts’ opinions when planning mitigation programs in order to account for different types of uncertainties associated with the problem. This leads to inefficient dig programs (associated with significant costs) while potentially leaving dents on the pipeline which cannot be quantitatively risk assessed using current approaches. To address these concerns, the problem calls for a dent assessment framework that balances accuracy with the ability to assess dent and threat integration features at a system-wide level with available information in a practical timeframe that aligns with other integrity programs. This paper expands upon the authors’ previously published work regarding a fully quantitative reliability-based methodology for the assessment of dents interacting with stress risers. The proposed semi-quantitative reliability model leverages a strain-based limit state for plain dents (including uncertainty) with semi-quantitative factors used to account for complex geometry, stress riser interactions, and operating conditions. These factors are calibrated to reliability results from more detailed analysis and/or field findings in order to provide a simple, conservative, analytical-based ranking tool which can be used to identify features that may require more detailed assessment prior to mitigation. Initial validation results are provided alongside areas for continued development. The proposed model provides sufficient flexibility to allow it to be tailored/calibrated to reflect specific operator’s experience. The model allows for a consistent analysis of all types of dent features in a pipeline system in a short period of time to support prioritization of features while providing a base-level likelihood assessment to support calculation of risk. This novel development supports a dent management framework which includes multiple levels of analysis, using both deterministic and probabilistic techniques, to manage the threat of dents associated with stress risers across a pipeline system.

The concept of the digital twin dates all the way back to the 1950’s when NASA, GE and other industrial manufacturers started creating abstract digital models of equipment to model their performance in simulations and maintain a record of the asset throughout its life span [1]. Over the years more and more industries have adopted the digital twin paradigm to improve traceability, maintenance, and analytics allowing for improved sustainment of the asset or equipment while reducing various risks identified during life cycle management. It has been found that collectively, the digital twin concept improves the overall net present value of an asset. The oil and gas industry has slowly been adopting the digital twin paradigm of asset life cycle management over the past two decades with the focus on facilities. Recently, field trials were completed to test and evaluate workflows and sensor platforms for the creation of a digital twin for pipelines. The trials resulted in highly accurate pipeline centerlines, weld locations, Depth to Cover (DoC) and ditch geometry capture in digital formats. This paper describes the methodologies used, and the results of an actual construction field trial with a comparison to traditional data collection methods for these attributes. The value of creating a pipeline digital twin during pipeline construction in near-real-time is discussed with an emphasis on the potential benefits to life cycle management and pipeline integrity.

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.

Axial ductile fracture propagation and arrest in high energy pipelines has been studied since the early 1970’s with the development of the empirical Battelle Two-Curve (BTC) model. Numerous empirical corrections on the backfill, gas decompression models, and fracture toughness have been proposed over the past decades. While this approach has worked in most cases, the dynamic interaction between the decompression of the fluid in the vicinity of the crack tip and the behaviour of the pipe material as it opens to form flaps behind the crack has been very difficult to solve from a more fundamental approach. The effects of the pressure distribution on the flap inner surface making up the crack-driving force which drives the crack propagation speed has been suggested in the past, but due to intensive computational effort required, it was never realized. The present paper attempts to tackle this problem by employing an iterative solution procedure where the gas pressure field in the vicinity of the crack tip is accurately solved for by computational fluid dynamics (CFD) for a given flap geometry determined from a dynamic FEA model to render a new flap geometry. In this model a cohesive-zone element at the crack tip is employed as a representation of the material toughness parameter. The final outcome is the determination of the cohesive energy in the FEA (as a representation of the material toughness parameter) to match the measured fracture propagation speed for the specific case. A case study was taken from full-scale rupture test data from one of the pipe joints from the Japanese Gas Association (JGA) unbackfilled pipe burst test data conducted in 2004 on the 762 mm O.D., 17.5 mm wall thickness, Gr. 555 MPa (API 5L X80) pipe.

In this paper, the effect of inertia on the steady-state velocity of a propagating crack in a modern high toughness pipeline steel was investigated. The line pipe steel examined in this work was an American Petroleum Institute (API) Standard X70 steel. A tensile plate model, simplified from the geometry of a pipe, was studied using the finite element code ABAQUS 6.14-2. The cohesive zone model (CZM) was used to simulate crack propagation. The CZM parameters were calibrated based on matching the crack tip opening angle (CTOA) measured from a drop-weight tear test (DWTT) finite element model to the experimental CTOA of the material. The CZM parameters were then applied to the tensile plate model. The effect of inertia on the steady-state crack velocity was systematically assessed by altering the density of the material used with the plate model. To isolate the influence of inertia, the effect of strain rate on the fracture process and material plasticity was neglected. The results of this study demonstrate that the steady-state crack velocity was affected by the density of the material. The steady-state crack velocity was reduced with increasing mass density, as demonstrated by the effect of backfill. Furthermore, it was shown that the CTOA extracted from the CZ model was not affected by the density of the model.

Economic and environmental incentives encourage operators to maintain pipeline operation during repair and maintenance procedures including hot-tap branch fitting installation onto pipelines. Welding onto a liquid-filled pipeline induces accelerated cooling of the weld and heat affected zone (HAZ), increasing the propensity for cracking. In-service welding codes and due diligence requires that several key factors be considered during the design of an in-service welding procedure specification for its intended purpose. The level of restraint (LoR) imposed by the geometry, material, or dimensional differences of the branch compared to the run pipe has also been shown to be a significant contributor to cracking. Finite element analysis (FEA) was utilized to investigate the geometric effects of an in-service weld procedure to approximate the LoR of hot-tap branch installation. The LoR was quantified and compared by simulating multi-pass weld sequences on two configurations: a branch-on-pipe (BoP) configuration of various dimensions and a configuration using perpendicular plates (PP) that has been used as an alternative to the branch-on-pipe configuration. The highest LoR, as measured by transverse tensile stress at the fillet weld toe, was the branch-on-pipe configuration with the largest branch wall thickness, the smallest branch diameter, the largest run pipe diameter, and the largest run pipe wall thickness. FEA modeling revealed that the PP configuration has lower LoR, thus it is not recommended to use for simulating in-service branch weld procedures.

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).

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.

Pipeline operators’ utmost priority is to achieve high safety measures during the lifecycle of pipelines including effective management of integrity threats during excavation and repair processes. A single incident pertaining to a mechanical damage in a gas pipeline has been reported previously which resulted in one fatality and one injury during investigation. Some operators have reported leaking cracks while investigating rock induced dents. Excavation under full operating pressure can lead to changes in boundary conditions and unexpected loads, resulting in failure, injuries, or fatalities. In the meantime, lowering operating pressure during excavation can have a significant impact on production and operational availability. The situation poses two conflicting objectives; namely, maximizing safety and maximizing operational availability. Current pipeline regulations require that operators have to ensure safe working conditions by depressurizing the line to a level that will not cause a failure during the repair process. However, there are no detailed guidelines on how an operator should determine a safe excavation pressure (SEP) level, which could lead to engineering judgment and subjectivity in determining such safety level. While the pipeline industry relies on well-defined fitness for purpose analyses for threats such as crack and corrosion, there is a gap in defining a fitness for purpose for dents and dents associated with stress riser features in order to set an SEP. Stress and strain based assessment of dents can be used in this matter; however, it requires advanced techniques to account for geometric and material nonlinearity. Additionally, loading and unloading scenarios during excavation (e.g. removal of indenter, overburden pressure, etc.) drive a change in the boundary conditions of the pipe that could lead to leakage. Nevertheless, crack initiation or presence within a dent should be considered, which requires the incorporation of crack geometry and application of fracture mechanics in assessing a safe excavation pressure. Recently, there have been advancements in stress and strain based finite element analysis (FEA) of dents coupled with structural reliability analysis that can be utilized to assess SEP. This paper presents a reliability-based approach to determine a safe excavation pressure for dented liquid pipelines. The approach employs nonlinear FEA to model dents interacting with crack features coupled with uncertainties associated with pipe properties and in-line-inspection information. A fracture mechanics-based limit state is formulated to estimate the probability of failure of dents associated with cracks at different levels of operating pressure during excavation. The application of the developed approach is demonstrated through examples within limited scope. Recommended enhancements and future developments of the proposed approach are also discussed.

Pipeline in-line-inspections (ILI) are used to assess and track the integrity of pipelines, aiding in identifying a variety of features such as: metal loss, dents, out-of-roundness, cracks, etc. The presence of these features can negatively affect the operation, integrity, and remaining life of a pipeline. Proper interpretation of the impacts these features may have on a pipeline are crucial to maintaining the integrity of a pipeline. Several codes and publications exist to assess the severity of these features under known operating conditions, either through empirical formulations or more detailed analysis, in order to aid the operator in determining a corrective action plan. These empirical formulations are generally applicable to assess a singular defect but require a more detailed assessment to evaluate combined defects (i.e. dent in a bend). These detailed assessments typically require a higher level numerical simulation, such as Finite Element Analysis (FEA). This detailed FEA can be quite costly and time consuming to evaluate each set of combined features in a given ILI run. Thus, engineering judgement is critical in determining a worst-case scenario of a given feature set in order to prioritize assessment and corrective action. This study aims to assess dent features (many associated with metal loss) occurring in a pipe bend to determine a worst-case scenario for prioritization of a given feature listing. FEA was used to simulate a field bend of a given radius and angle in order to account for residual stresses in the pipe bend. A rigid indenter was used to form a dent of the approximate length, width, and depth from the ILI data. Separate models were evaluated considering the dent occurring in the intrados, extrados, and neutral axis of the pipe bend to evaluate the worst-case scenario for further assessment. The resulting stresses in the pipe bend-dent geometry, under proper loading were compared to the same dent scenario in a straight pipe segment to develop a stress concentration factor (SCF). This SCF was used in the API 579-1/ASME FFS-1 Fitness for Service (API 579) [1] methodology to determine the impact on the remaining life of the combined features.

Standard pipe corrosion assessments are based on simplifying assumptions with respect to corrosion geometry and focus on pressure based loading. Moreover, when corrosion patches traverse girth welds, validity criteria to their assessment become impractically vague. The integrity of girth welds is additionally influenced by axial stresses, which may act in combination with hoop stress resulting from pressure. In an attempt to address these issues, the authors conducted a detailed assessment on a significant, highly irregular corrosion patch traversing a 12″ natural gas pipeline girth weld. The investigation comprises a full scale uniaxial tensile test and supporting detailed finite element (FE) analyses. Hereby, the model mesh adopts detailed geometrical characteristics resulting from a surface profile scan obtained from stereoscopic digital image correlation. The numerical model is validated based on the uniaxial tensile test, in the sense that plastic collapse and highly complex strain distributions are successfully reproduced. Finally, the FE model is used to explore axial tensile failure in presence of internal pressure.

In this paper, three-dimensional finite element models are developed to simulate full-scale burst tests of corroded pipes containing multiple naturally occurring corrosion anomalies. Both the von Mises and Tresca yield criteria and associated flow rules are employed in finite element analysis (FEA). For the Tresca criterion, the corresponding constitutive model subroutine is developed and incorporated in the FEA. The accuracy of FEA is investigated by comparing the burst pressures observed in the tests and corresponding burst pressures predicted using FEA. The implications of using the von Mises and Tresca criteria for the accuracy of the predicted burst pressure are investigated. Sensitivity analyses are also carried out to investigate the impact on the predicted burst pressure due to the mesh density in the corroded region, characterization of the geometry of the corrosion cluster and different types of element (e.g. solid and shell elements) used in FEA. The results suggest that the Tresca criterion always underestimates the burst pressure and the von Mises yield criterion predicts the burst pressure accurately. This study demonstrates the feasibility of using high-fidelity FEA and the Tresca yield criterion to simulate full-scale burst tests of corroded pipes and therefore establish a large database of burst pressure capacities of corroded pipes that can be used to develop an accurate, practical burst pressure capacity model amenable to the pipeline integrity management practice.

Pipeline integrity management commonly leverages nondestructive inspection of pipeline defects via inline inspection (ILI) and assessment of the resultant data. Key parameters for dent analysis include the feature geometry measured by caliper tools and the presence/severity of any interacting features (such as cracks or areas of corrosion) which can be measured with a variety of technologies (such as magnetic flux leakage or ultrasonic tools). Dent profile measurements can be especially susceptible to noise due to the measurement techniques employed, signal quality, and overall tool performance. Analytical methods for strain assessment of dents can employ curve/surface fitting techniques to estimate the curvature and calculate the strain of the dent based on the fitted curve/surface. Noise in the measured profile can result in local areas of high perceived strain, which could lead to misinterpretation of a dent’s true severity, especially when using automated or purely analytical assessment methods. A deterministic strain-based approach for evaluating the severity of dented pipelines has been presented previously which leverages multi-dimensional B-spline functions to more accurately apply the non-mandatory ASME B31.8 equations for dent assessment. The approach presented previously requires relatively smooth dent profile information to minimize the effects of signal noise. While low pass filters can effectively eliminate noise in the signal, they may also lead to loss of accuracy (e.g. excessive smoothing can reduce the depth and sharpness of a measured dent’s profile). This paper discusses how low pass filters can be optimally used to smooth the raw ILI signals to allow for analytical representation of the dent shape without underestimating its severity. The conclusion of this venture is a detailed workflow for the analytical assessment of dented pipelines for the rapid characterization of the severity of deformation in pipelines with limited computational demand. This type of assessment allows for initial ranking and assessment of large and complex pipeline systems to select features requiring more detailed assessment or mitigation.

Pipeline dents lead to changes in the stress/strain state of the pipe body, making it more susceptible to integrity concerns. This susceptibility is especially prevalent in cases where additional stress risers such as crack and/or corrosion features interact with the dented region. While some guidance is available in codes, regulations, and industry best practices, there is substantial room for innovation and improvement to ensure pipeline safety. Existing explicit models are primarily based on experimental correlations and historical findings using simple parameters such as dent depth and location on the pipeline. Moreover, these models are subjected to a substantial uncertainty in both accuracy and precision. This paper presents a state-of-the-art methodology for analyzing dents and dents associated with stress risers through the use of finite element method (FEM) as a mechanical model and reliability analysis to address uncertainties associated with input variables. FEM is used to model the full geometry of dents and any interacting stress risers reported by inline inspection (ILI) to be incorporated into calculations of the internal stresses/strains within the feature. Theoretically, FEM and reliability analysis can be integrated through reliability-based stochastic finite element methodologies due to the absence of closed form mechanical models of dented pipes. However, these methodologies are computationally prohibitive and not suited/designed for frequent integrity analysis. This study aims at further advancing such integration by combining FEM with reliability science to account for pipe properties and measurement uncertainties in order to determine the probability of failure under different operating conditions using surrogate models. This provides the opportunity to more accurately assess the risk posed by ILI reported dent features. Herein, surrogate models refer to the response surface method (RSM) which is considered as a valuable tool for obtaining insight into the behavior of structural random systems at low computational costs. The proposed approach was applied focusing on a plain dent, a dent interacting with a corrosion feature, and a dent interacting with a crack feature. First Order Reliability Method (FORM) is used to evaluate the probability of failure/reliability using the resulting RSM non-linear limit states for each dent feature.