bluuebunny/crossref_metadata_2025 huggingface dataset:
Morphology and Dynamics of a Premixed Hydrogen-Methane-Air Jet Flame in Hot Vitiated Turbulent Crossflow
Authors: Solana-Pérez R. , Miniero L. , Shcherbanev S. , Bothien M. , Noiray N.
Published: January 2021

The effect of hydrogen enrichment of a premixed hydrogen-methane-air jet in hot vitiated crossflow was studied at atmospheric condition. The hot turbulent vitiated crossflow is generated by a symmetric array of 4 × 4 jet flames burning a lean mixture of natural gas and air in fully premixed condition at equivalence ratio φcf = 0.7 and total thermal power of 50 kW. This crossflow is then used to ignite the premixed perpendicular jet of hydrogen-methane-air at ambient temperature. Three jet parameters are varied to study the effect of hydrogen addition on the flame morphology and stabilization mechanism: the hydrogen mass fraction of the H2/CH4 fuel blend (ξ = 0 – 100%), the jet equivalence ratio (φ = 0.8 – 2.0) and the jet-to-crossflow momentum ratio (J = 3 – 12). High-speed hydroxyl (OH) chemiluminescence is used to obtain the time-resolved imaging of the reactive jet and to compute its time averaged morphology. OH planar laser induced fluorescence (OH-PLIF) is used to acquire OH concentration fields at the jet center plane. The jet morphology is analyzed by considering its mean trajectory, extracted from the experimental data and fitted with empirical correlations available from the literature. New correlations are proposed for the flame length, width and center of gravity as function of the hydrogen content. It is shown that with increasing hydrogen fraction, the flame is shortened and more compact, and it stabilizes close to the jet root. Another finding of this work is the reattachment of the flame at the base of the windward jet shear layer when hydrogen fraction is increased. Robust flame anchoring is observed for H2 mass fractions of the CH4/H2 fuel blend that exceed 50%. Moreover, it is shown using instantaneous OH-PLIF images that for these conditions of increasing hydrogen concentration, the windward shear layer features larger-scale coherent structures that govern the aerodynamics of the reactive premixed jet in turbulent vitiated crossflow.
Comparison of Two Methods for the Sensitivity Analysis of a One-Dimensional Cooling Flow Network of a High-Pressure-Turbine Blade
Authors: Fiedler Barbara , Muller Yannick , Voigt Matthias , Mailach Ronald
Published: January 2021

Efficient cooling of the thermally extremely loaded high-pressure-turbine blades and vanes is required to ensure acceptable service life. The development of cooling systems is a high-dimensional problem, since it includes multiple design parameters. The integration of stochastic methods into the design phase contributes to a better understanding of the complex interaction between the design parameters and the system behavior and thus helps designing more efficient cooling systems. Therefore, the present study compares two stochastic methods, the Elementary-Effect method by Morris and the Coefficient-of-Importance, for the quantification of the sensitivity of the cooling flow to geometric variations using a 1D flow network of a high-pressure-turbine blade. As test case a multipass cooling system with rib-roughened walls is investigated. To achieve geometrically meaningful variations a new parametrization, called Harmonic-Spline-Deformation, is developed and first time presented in the paper at hand. The parametrization proves to be universally applicable to the components of a cooling system and facilitates the interpretation of the physical relationships between variables and resulting system behavior. For a sufficiently large population size, both methods show good agreement in quantifying the importance of design parameters regarding their effect on the cooling flow. The Coefficient-of-Importance, however, proves to be more stable against a decreasing population size and more robust against defects in the population.
Research on Prediction of NOx Emission Performance of Marine Gas Turbine Under Variable Operating Conditions
Authors: Li Jian , Wang Zhitao , Li Tielei , Li Shuying
Published: January 2021

With the global warming, many countries pay more attention to environmental pollution. The NOx emissions has become an important index when gas turbine designed. This paper provides a method for predicting NOx emissions of marine gas turbine under variable operating conditions. Firstly build the 3-D model of combustor. The characteristic regions of combustor were divided according to the reaction principle. Then build the chemical reactor network (CRN) models of different characteristic regions. According to the NOx emissions of several specific operating points simulated by computational fluid dynamics (CFD), fit the relation between residence time and operating conditions by Newton interpolation in the CRN models. Then the prediction model of NOx emissions of gas turbine was established by using neural network. The NOx emissions under 0.7∼1.0 working conditions and 0.019∼0.023 fuel-air ratios can be predicted efficiently.
An Exploration of a New Type of Guide Vanes for Thermoacoustic Bi-Directional Turbine
Authors: Liu Dongdong , Chen Yanyan , Dai Wei , Luo Ercang
Published: January 2021

As a new method of acoustic-to-electric conversion, bidirectional impulse turbine shows great potential for the development of economic and large scale thermoacoustic generators. In this paper, experimental and numerical studies on conventional bi-directional turbine with fixed guide vanes are investigated. A test rig for turbine operating in acoustic oscillating flow has been built. The fundamental output characteristics of the turbine are analyzed in oscillating flow. The maximum turbine efficiency is 38% (with 4000 rpm rotating speed, 853 W output shaft power and 1 flow coefficient). Additionally, enlightened by the bi-directional turbine with self-pitching guide vanes, a new structure of turbine is proposed. The guide vanes of the turbine are divided into two layers: the upper guide vanes and the lower guide vanes. When the turbine blade was rotating, the main flow is expected to flow through the lower guide vanes at the blade inlet and upper guide vanes at the blade outlet. So fluid energy loss could be reduced and efficiency could be improved. Compared with the bi-directional turbine with self-pitching guide vanes, the new structure shows in paper is simpler and more reliable. Different upper guide vanes angles and inclined angles of the nose cone are studied under steady flow. The results show that the maximum efficiency obtained is 31%, which is still lower than that of the conventional turbine. This means the fluid loss in the turbine may not be effectively reduced after the structure change and more optimizations need to be carried out for higher efficiency.
Electrified Aircraft Propulsion Systems: Gas Turbine Control Considerations for the Mitigation of Potential Failure Modes and Hazards
Authors: Simon Donald L. , Connolly Joseph W.
Published: January 2021

This paper provides a high-level review of the potential failure modes and hazards to which electrified aircraft propulsion (EAP) systems are susceptible, along with potential gas turbine control-based strategies to assist in the mitigation of those failures. To introduce the types of failures that an EAP system may experience, a generic EAP system is considered, consisting of gas turbine engines, mechanical drives, electric machines, power electronics and distribution systems, energy storage devices, and motor driven propulsors. The functionality provided by each of these EAP subsystems is discussed, along with their potential failure modes, and possible strategies for mitigating those failures. To further illustrate the role of gas turbine controls in mitigating EAP failure modes, an example based on a simulated EAP concept aircraft proposed by NASA is given. The effects of failures are discussed, along with turbomachinery control strategies, including reversionary control modes, and control limit logic.
Assessment of Surface Roughness Effects on Micro Axial Turbines
Authors: Gamil Abdelaziz A. A. , Nikolaidis Theoklis , Teixeira Joao A. , Madani S. H. , Izadi Ali
Published: January 2021

Surface roughness significantly affects the aerodynamics and heat transfer within micro-scale turbine stages. It results in a considerable increment in the blade profile loss and leads consequently to sizeable performance reductions. The provision of low roughness surfaces in micro gas turbine stages presents challenges on account of the small (mm scale) sizes, manufacturing complexity and associated costs. The axial turbine investigated in this study is fitted to Samad Power’s TwinGen domestic micro combined heat and power unit. The micro gas turbine has a compressor pressure ratio of 3, 1200K turbine inlet temperature and a rotational speed of 170,000 rpm. This paper presents a numerical assessment of the effects of varying the surface roughness on the performance and heat transfer of the micro turbine. The surface roughness was uniformly distributed on the NGV and rotor blades. The results showed that increasing the surface roughness from 3 microns to 6, 20, and 100 microns resulted in a reduction in stage total efficiency of 0.8%, 4% and 12% respectively as well as a comparable decrease in output power (0.7%, 3.6%, and 11% respectively). The turbine temperature was also observed to be very sensitive to surface roughness and a temperature increase of some 5% at the rotor hub and over 4% increment in the blade tip surface was observed for 100 microns when compared to the 3 microns surface roughness case. The findings of this paper highlight the adverse effects of the surface roughness on the micro-turbine performance and temperature distribution as well as the importance of careful consideration of wall roughness during the design and manufacturing stages.
Estimating Toughness for LF and DC Welded ERW Seams
Authors: Kiefner John , Rosenfeld Michael , Veloo Peter , Rovella Troy
Published: January 2021

ERW pipe materials, particularly those manufactured prior to 1970, have exhibited higher rates of failures from seam manufacturing defects than other types of pipe materials. Typically, the seam bond line regions of low-frequency (LF) and direct-current (DC) welded ERW pipe materials exhibit poor resistance to manufacturing defects. The toughness of the bond line region is difficult to determine, and it is likely to vary from one piece of pipe to another.

Pipeline operators must address the risk of ERW seam failures as part of their integrity management plans, but it is unlikely that they will know the toughness levels in the seams of their pipelines comprised of such materials. To avoid having to know the toughness levels in the seams, a pipeline operator can utilize a hydrostatic test to verify the integrity of a vintage ERW pipeline, but there are disadvantages the main one being that the pipeline must be taken out of service. Most likely an operator will choose to use an ILI crack tool to locate ERW seam anomalies to avoid having to take the pipeline out of service. Even if the seam defects can be located, correctly sized, and classified, however, the operator may have no idea of the effective toughness that is the key to deciding whether or not a given crack has to be excavated and repaired.

Presented herein are two options for improving the effectiveness of an ILI integrity assessment of a pipeline with low toughness ERW seams.

• Option 1 involves assuming a conservative level of toughness. Some such levels are available in the publicly available documents. Data from a large database of ERW seam failures are used to show the effectiveness of a fixed level of toughness at identifying critical defects while minimizing unnecessary digs.

• Option 2 consists of first: back-calculating the toughness levels associated with the known crack sizes and failure pressures of the defects in the database of ERW seam failures, and second: calculating the probability that each type of defect would have been correctly identified at a particular level of confidence using a particular level of toughness.

Using either of these options, a pipeline operator can improve the effectiveness of an ILI-crack-tool integrity assessment of a pipeline comprised of LF or DC welded ERW seams by reducing the number of unnecessary excavations while still being able to find the critical defects with an acceptable level of confidence.
Assessing Soil Corrosivity for Buried Structural Steel
Authors: Beauregard Yannick , Mah Andrea
Published: January 2021

Corrosion of steel structures in soils has been a topic of industrial research for many decades. The research has shown that the corrosivity of a soil is highly variable and a function of numerous interconnected parameters including soil resistivity, moisture content and pH. Despite the complexity of the soil environment, methods to evaluate soil corrosivity, guidelines for corrosion control during the design phase and lifetime of a structure have been developed. By applying this understanding, an opportunity exists to optimize the corrosion protection and capital expenses for new projects associated with corrosion protection of buried structural steel components. For instance, for new projects, e.g., identifying regions of low corrosivity where coatings are not required could lead to cost savings without compromising the integrity of the structure. However, within the industry, there is no universally accepted method to guide such decisions.

This paper is intended to address this issue by presenting a literature review and a case study on the topic. The literature review identifies the factors that influence the corrosion of buried steel structures, the range of corrosion rates observed on buried steel structures and quantitative and qualitative methods for assessing soil corrosivity. In the desktop case study, industry standards identified during the literature review (AASHTO R27-01, DIN50929-3:2018, ANSI/AWWA C105/A21.5 and Eurocode 3-5) are applied to applied to evaluate the soil corrosivity at three meter station sites in Alberta. The results are compared and recommendations for implementation are discussed. DIN 50929-3 stands out among the standards as it provides conservative estimates based on the most comprehensive data set and unlike the other standards, it assesses soil corrosivity both qualitatively and quantitatively.
Repair and Reinforcement of Blunt Defects on Pipeline Bends Using Composite Materials
Authors: Hill Paul , Swankie Troy , Bood Robert , Mihsein Dina
Published: January 2021

Previous research on the use of composite repair systems has focused on the repair of damage to straight sections. This paper reports verification testing completed on composite repairs for pipeline bends to support development of a safe and consistent approach that ensures an equal level of performance is maintained over the entire system.

A series of finite element analyses were completed that considered the effects of bend size (diameter and wall thickness), material grade, bend radius and angle. From this work 90° , 1.5D, 12” NB, X52 bends were selected for test. The objective was to demonstrate restoration of the fatigue life of the pipe to acceptable levels rather than just considering burst pressure. Defects equal to 0.5 times the diameter axially and 0.25 times the diameter radially were machined into the intrados of the bend (the location of highest hoop stress). Wall losses of 20% and 80% were replicated. Bounding repair thicknesses were tested to confirm performance was predictable.

Aggressive cyclic pressure ranges of 125Nmm−2 and 90mm−2 were applied to the repaired defects, with the lower stress range loaded for a larger number of cycles. A successful test was defined as one which exceeded the target number of cycles by a factor of 10 AND for which there was no visual sign of repair degradation. The number of load cycles was selected to ensure the repaired lines satisfied the slope of the S-N curve for pristine pipe, confirming the approach maintained the required margin of safety applicable to the rest of the system.

A design method is proposed that addresses weaknesses in the methods given in ISO 24817 and ASME PCC-2 Article 401. It is proposed that this be adopted by the standards for repairs to high pressure gas transmission pipelines to ensure equality of performance with undamaged sections.
Effects of Niobium on Microstructure and Hardness of Base Plate and Coarse Grained HAZ of High Strength X70 Grade UOE Linepipe Steel
Authors: Kizu Taro , Sakai Ryutaro , Imoto Hiroshi , Endo Shigeru , Barbaro Frank
Published: January 2021

The present study systematically evaluated base plates and Coarse Grained Heat Affected Zone (CGHAZ) properties of linepipe steels by using the controlled addition of increasing levels of niobium in a low carbon steel for comparison with other alloying combinations of Mn, Ni, Mo and V using laboratory melts and processed under simulated production conditions. The effects of niobium and other alloying elements on the mechanical properties and microstructural development, have been quantified with the intention of maintaining constant CGHAZ hardness in order that specific compositional effects can be directly compared. Characteristics of martensite and austenite (M-A) constituents in terms of size, shape and chemical composition has also been assessed.

It is demonstrated that niobium additions up to 0.1 mass% in a low carbon steel design provide opportunities to improve pipeline mechanical properties, service performance and safety. For the CGHAZ, austenite grain size was limited as the niobium content increased. Weld HAZ microstructures were relatively similar with little influence of niobium content on MA character, although the hardness was noted to increase with increasing niobium content, which would be beneficial to ensure adequate resistance to weld zone softening.

Bainite and small volume fractions of MA (nearly equal 2%) was a characteristic feature of CGHAZ of the materials having constant CGHAZ hardness, irrespective of chemical compositions examined. Other MA characteristics, such as size and cementite fraction, were also very similar among the steels.
Does Open Cut Pipeline Installation Affect the Geomorphology of Rivers?
Authors: Smith Sheldon , Enes Shannon , Metcalfe Jackie , Guthrie Rick , Dubeau Chuck
Published: January 2021

Open cut has traditionally been the preferred method of pipeline installation traversing watercourses. It is well understood and accepted that open cut excavation of the channel bed and banks during construction causes temporary disturbance to watercourse and aquatic habitat. Horizontal directional drilling, direct push and other subsurface installation methods can potentially avoid channel bed and bank disturbance but may have unique environmental effects such as frac-outs of drilling fluid. Although highly dependent on site conditions, open cut crossings are generally less costly than comparable subsurface installation methods.

When a pipeline is installed in an open cut, the pipe is typically installed on a gravel or sand bed, laid in place, surrounded by a sand pack and surrounding soils placed back in the cut in a manner that attempts to replicate the soil lithology, horizons and native compaction of the cut. It has long been thought that this sediment and soil disturbance and backfilling has the potential create a zone of geomorphological weakness at the cut where soil and sediment become dissimilar to the surrounding channel bed and banks and can result in the acceleration of bed scour, bank erosion, widening and slope instability. In this paper we examine the longer-term effects of open cut pipeline installations on the geomorphic characteristics of watercourses.

Over the course of four years of field investigation, nearly 750 pipeline watercrossings throughout Ontario were visited and assessed for geomorphic stability and depth of cover. The fluvial geomorphology of Ontario is diverse and ranging from alluvial, sinuous, unconfined, low gradient watercourses in the southwest to karst-influenced morphologies in eastern Ontario and often greater slope, confined and bedrock dominated watercourses in the north. By examining the field-based geomorphological characteristics of pipeline watercourse crossings in Ontario installed by open cut and crossing a wide range of fluvial geomorphological types we will explore and draw empirically-based conclusions on whether open cuts do in fact affect the long term geomorphological conditions of the watercourse.
Leak Rate Testing of a Natural Pipeline Defect
Authors: Andrews Robert M. , Short Joe
Published: January 2021

If a stable through wall defect (leak) were to occur in a pipeline, the leak rate is an important factor for both safety and environmental assessments, and also to determine the performance requirements for a leak detection system. For a “large” leak, an assessment can be based on simple idealization as an orifice, but for narrow crack like defects this is not appropriate. The flow through a crack is dependent on factors such as the surface roughness and the crack opening. These issues have been extensively studied for nuclear pipework where the fluid is either pressurized water, steam or CO2, and guidance is given in Annex F of BS 7910. However, there is little published work for pipeline geometries and single phase liquids such as refined hydrocarbons.

This paper presents the results of experiments measuring the leak rates through a tight axial through wall crack in a NPS 8 refined products pipeline. Leak rate measurements were made using water (for safety reasons) over a range of pressures. The data were fitted to a model for leakage through a tight crack that takes account of interaction of asperities in surface roughness. The fitted equation was then adjusted to take account of the different density and viscosity of the pipeline products. It was concluded that the model was able to give a good prediction of the measured leak rates and that the adjustments for the product properties were small.
Pipeline Depth of Cover: Can You Demonstrate Compliance?
Authors: Finley Daniel , Daniel Simon , Ogden Paul
Published: January 2021

Third-party interference is widely documented as being a major cause of damage to buried pipelines. In addition to routine surveillance, maintaining a minimum depth of cover is recognized as a key means of mitigation against third-party interference. We know that the depth of cover over pipelines can change with time. Changes in depth of cover can also be an indication of thermal upheaval, frost heave or ground movement. Current techniques available for measuring depth of cover on buried pipes require significant effort to produce a high-resolution survey for an entire pipeline.

A UK Innovation project completed with National Grid Gas Transmission in 2017 successfully demonstrated a methodology for estimating pipeline depth of cover by combining ground elevation data with high-resolution inertial measurement unit (IMU) data collected during in-line inspection.

Since the end of the project, ROSEN has completed a further eight pipeline depth of cover inspections, with a total length exceeding 400 kilometers and including a range of pipe diameters.
Investigation Four-Phase Multi-Component Flow Techniques in Horizontal and Sub-Sea Pipelines
Authors: Odan Mohamed
Published: January 2021

Offshore drilling projects can be as complex as they are costly, and many problems can arise during the drilling and extraction of sub-sea pipelines petroleum, including environmental issues. The oil and gas industry relies on multi-phase, multi-component flow techniques to transport substances such as gas, oil and water through horizontal and sub-sea pipelines. Artic and offshore drill sites can be particularly challenging due to hydrate formation in the transport horizontal and sub-sea pipelines. This study investigates the feasibility of using a four-phase, four-fluid flow Multi-Component through horizontal pipelines to move a four-phase multi-component flow (oil, gas, water, and sand particles) through submerged pipelines. In order to accurately gauge the multi-component mixtures’ hydro- and thermo-dynamic properties, fluid equilibrium and phase-behavior models are constructed. As well, to examine various interrelated factors such as momentum, mass and heat transfer occurring between pipelines walls and flow, a series of equations are developed.

In the present study, the effect of temperature and pressure on multi-phase flows in horizontal and sub-sea pipelines is investigated. As well, models of flow patterns and pressure drops are created specifically for horizontal and sub-sea pipeline environments. Note that the terms “Four-Phase and Multi-Component flow” are used interchangeably in this study. And Create pressure drops and flow behavior models of multi-phase flows for horizontal and sub-sea pipelines.

Furthermore, multi-phase flows may occur in any one of the following combinations: liquid-gas, liquid-gas-solid, liquid-liquid-gas-solid, An example of a, liquid-liquid-gas-solid flow is four immiscible fluids and component (e.g., water, oil, gas, and solid), immiscible liquids being those which do not form a homogeneous mixture when added together. In terms of practical applications of multi-phase and multi-component flows, water injected into an oil pipelines helps to decreases both the pressure gradient and flow resistance.
A Pressure Reduction to Prevent a Time-Delayed Failure in a Damaged Pipeline
Authors: Cosham Andrew , Leis Brian N. , Roovers Paul , Zarèa Mures , Linton Valerie
Published: January 2021

A time-delayed failure due to stress-activated creep (cold-creep) is a failure that occurs under a constant load and with no growth due corrosion, fatigue or some other environmentally assisted time-dependent degradation mechanism. A time-delayed failure is prevented by reducing the pressure.

ASME B31.4 and B31.8 recommend a 20 percent reduction, to 80 percent of the pressure at the time of damage or discovery. T/PM/P/11 Management Procedure for Inspection, assessment and repair of damaged (non-leaking) steel pipelines, an internal procedure used by National Grid, specifies a 15 percent reduction. The guidance in ASME B31.4 and B31.8, and in T/PM/P/11, is directly or indirectly based on the results of tests on the long term stability of defects conducted by the Battelle Memorial Institute and British Gas Corporation in the 1960s and 70s. The line pipe steels were Grades X52 or X60, and the full-size equivalent Charpy V-notch impact energy (where reported) did not exceed 35 J. The tests indicated that the threshold for a time-delayed failure was approximately 85–95% SAPF (straightaway-pressure-to-failure).

The strength and toughness of line pipe steels has significantly increased over the decades due to developments in steel-making and processing. The question then is whether an empirical threshold based on tests on lower strength and lower toughness steels is applicable to higher strength and higher toughness steels.

In the Tripartite Project, the Australian Pipelines and Gas Association (APGA), the European Pipeline Research Group (EPRG) and the Pipeline Research Council International (PRCI) collaborated in conducting full-scale six step-load-hold tests on higher strength and higher toughness steels. Companion papers present the other aspects of this multi-year project.

An empirical threshold for a time-delayed failure is estimated using the results of the six step-load-hold tests. That estimate is also informed by the other published small and full-scale tests (on lower strength and lower toughness steels). The Ductile Flaw Growth Model is used to infer the effect of strength and toughness on the threshold for a time-delayed failure.

A 15 percent pressure reduction, to 85 percent of the pressure at the time of damage (or of the maximum pressure that has occurred since the time of damage), is considered to be sufficient to prevent a time-delayed failure due to stress-activated creep in lower and higher toughness, in lower and higher strength, and in older and newer line pipe steels.
Earthquake in Papua New Guinea Results in New Concept for Securing Pipelines in Ridgeline Right-of-Way: The Micropile Contiguous Wall
Authors: Ladenhauf Christoph , Remmert Frank , Prager Christoph , Birthwright Rhyssheffer , Cushing Daniel
Published: January 2021

On February 25 (UTC), 2018, the project, a combine of wellpads, gathering lines, transport pipelines and its facilities, sustained a Mw7.5 earthquake, and ca. 300 aftershocks, epicentered directly under the key facilities. Around 150 km of high-pressure gas and condensate pipelines were affected. A number of design and construction decisions protected the pipelines, and prevented serious damage. However, the earthquake disturbed several sections of the pipeline Right-of-Way (ROW), which subsequently required intervention and stabilization. The challenges associated with re-occupying the remotely-situated, mountainous and disturbed ROW, and safely installing stabilization structures, led to the development of a new pipeline stabilization concept: the contiguous Micropile-Wall system.

The concept, leveraging tools and techniques from the tunneling industry, and practices from the Alpine region, consists of 139.7 mm micro piles, installed in 3 m joints, in rows along either side of the pipeline. Once installed, opposing rows of these micropiles are attached to each other at ground level with steel tendons. This new concept can be installed using light equipment with minimal vibration and ground disturbance. It is designed to sustain significant earthquake loads, does not retain groundwater, and is resistant to corrosion and third-party damage. This concept was developed and selected in order to repair parts of the damaged ROW and ensure pipe integrity. Future deterioration of the adjacent slopes was taken into account, but slope stabilization for several dozens of landslides was not looked into, as this would have been too large an effort considering the remoteness of the terrain, climatic conditions, safety considerations and other constraints.
Reliability-Based Crack Threat Assessment and Management
Authors: Yan Jason , Zhang Shenwei , Kariyawasam Shahani , Lu Dongliang , Matchim Tammie
Published: January 2021

Crack or crack-like anomaly is one of the major threats to the safety and structural integrity of oil and gas transmission pipelines. The crack threat is usually managed by hydrostatic test or regular in-line inspection (ILI). For a given crack ILI pipeline tally, operators need to identify critical anomalies, determine appropriate response time, and whether pressure restriction (derate) is required. Traditionally, a deterministic approach is used to determine the mitigation plan based on characteristic values of pipe properties, conservative crack sizing and crack growth rate, and further considering a minimum required safety factor.

This study introduces a reliability-based approach to make the mitigation decision with full details. The annual probability of failure (POF) is evaluated for each reported crack anomaly by Monte Carlo simulation technique considering all the uncertainties associated with pipe geometry, material properties, crack size measurement, and assessment model error explicitly. Both environmental and cyclic fatigue load driven crack growth are considered following API RP 1176. A reliability-based mitigation threshold is proposed and calibrated against the deterministic minimum required safety factor for maintaining the system to a consistent safety level.

Two case studies were conducted to demonstrate the advantages of the reliability-based assessment approach in this paper. Case Study #1 considers an NPS 20 transmission gas pipeline with more than 2000 ILI reported crack anomalies. Compared to the deterministic approach using conservative characteristic values, the reliability-based approach can reduce the number of required mitigation activities significantly without compromising safety. Case Study #2 assumes a severe crack defect on an NPS 34 liquid pipeline to demonstrate the impact of fatigue driven crack growth on POF. The POF of crack anomalies can be compared and combined with other threats, e.g. external corrosion, to evaluate the quantitative risk throughout pipeline systems. The proposed framework in this study could be used by operators to improve the crack assessment programs.
Comparison of Non-Destructive Examination Techniques for Crack Inspection
Authors: Aulin Axel , Shahzad Khurram , MacKenzie Robert , Bott Steven
Published: January 2021

Effective and efficient crack management programs for liquids pipelines require consistent, high quality non-destructive examination (NDE) to allow validation of crack in-line inspection (ILI) results. Enbridge leveraged multiple NDE techniques on a 26-inch flash-welded pipe as part of a crack management program. This line is challenging to inspect given the presence of irregular geometry of the weld. In addition, the majority of the flaws are located on the internal surface, so buffing to obtain accurate measurements in the ditch is not possible. As such, to ensure a robust validation of crack ILI performance on the line, phased array ultrasonic testing (PAUT), time-of-flight diffraction (TOFD), and a full matrix capture (FMC) technology were all used as part of the validation dig program.

PAUT and FMC were used on most of the flaws characterized as part of the dig program providing a relatively large data set for further analysis. Encoded scans on the flash welded long seam weld were collected in the ditch and additional analyses were performed off-site to characterize and size the flaws. Buff-sizing where possible and coupon cutouts were selected and completed to assist with providing an additional source of truth. Secondary review of results by an NDE specialist improved the quality of the results and identified locations for rescanning due to data quality concerns. Physical defect examinations completed after destructive testing of sample coupon cutouts were utilized to generate a correlation between the actual defect size from fracture surface observation and the field measurements using various NDE methods.

This paper will review the findings from the program, including quality-related learnings implemented into standard NDE procedures as well as comparisons of detection and sizing from each methodology. Finally, a summary of the benefits and limitations of each technique based on the experience from a challenging inspection program will be summarized.
Comparison of Buried Pipeline Crossing Assessments Using API RP 1102, Analytical Method and Finite Element Approach
Authors: Joshi Nikhil , Ghosh Pritha , Brewer Jonathan , Matta Lawrence
Published: January 2021

API RP 1102 provides a method to calculate stresses in buried pipelines due to surface loads resulting from the encroachment of roads and railroads. The API RP 1102 approach is commonly used in the industry, and widely available software allows for quick and easy implementation. However, the approach has several limitations on when it can be used, one of which is that it is limited to pipelines crossing as near to 90° (perpendicular crossing) as practicable. In no case can the crossing be less than 30° . In this paper, the stresses in the buried pipeline under standard highway vehicular loading calculated using the API RP 1102 method are compared with the results of two other methods; an analytical method that accounts for longitudinal and circumferential through wall bending effects, and the finite element method.

The benefit of the alternate analytical method is that it is not subject to the limitations of API RP 1102 on crossing alignment or depth. However, this method is still subject to the limitation that the pipeline is straight and at a uniform depth. The fact that it is analytical in nature allows for rapid assessment of a number of pipes and load configurations.

The finite element analysis using a 3D soil box approach offers the greatest flexibility in that pipes with bends or appurtenances can be assessed. However, this approach is time consuming and difficult to apply to multiple loading scenarios.

Pipeline crossings between 0° (parallel) and 90° (perpendicular) are evaluated in the assessment reported here, even though these are beyond the scope of API RP 1102. A comparison across the three methods will provide a means to evaluate the level of conservatism, if any, in the API RP 1102 calculation for crossing between 30° and 90° . It also provides a rationale to evaluate whether the API RP 1102 calculation can potentially be extended for 0° (parallel) crossings.
A Prudent Approach to Evaluate Dig Effectiveness
Authors: Schartner Aaron , Woo Aaron , Puri Dushyant , Kariyawasam Shahani
Published: January 2021

Pipeline operators analyze in-line inspection (ILI) reported features to determine if excavation is required to investigate a feature through direct examination in the ditch. Pipeline excavations require considerable resources and planning. In addition, excavations may cause disturbance to the land owner or cause varying impacts to the operation of the pipeline. Therefore, it is important to ensure that the excavation decisions are made effectively. While operators do review the key performance indicators on how the integrity programs are performing, currently there is no established definition or measure in the pipeline industry to evaluate the effectiveness of a dig program. Defining and measuring dig effectiveness would allow pipeline operators to identify areas to focus on, such as further research and development, opportunities for improvement, and potential optimization of the ILI-based corrosion management program, while maintaining safety and reliability.

This paper presents a method developed by TC Energy to measure dig effectiveness to evaluate the ILI-based corrosion management program. Effectiveness of digs depends on many aspects of the corrosion management program. First, a definition of dig effectiveness that reflects the objectives of the ILI program needs to be established. The method was developed using inhouse historical dig data for external corrosion features that required mitigation based on analysis of ILI data. The focus of the study included the probabilistic evaluation of excavations to baseline what can be expected in a dig program and have a process to evaluate factors that may affect dig effectiveness. The field measurements of digs completed for corrosion driven leak and rupture threats were gathered and analyzed to evaluate the effectiveness of different dig populations and to determine what bounds should be placed to monitor dig effectiveness. The advantages of measuring dig effectiveness using field results as opposed to other metrics such as repair ratio was also demonstrated in this paper. Examples of understanding areas of improvement by using the dig effectiveness are discussed.

Pipeline operators have the potential to incorporate the methodology presented in this paper in the integrity management program to enhance safety and identify areas of focus with the goal of increasing the effectiveness of the corrosion management program.
Third-Party Damage Monitoring: Internal Fiber Optic Installation on a Transmission Pipeline Using a Pig, a Disengagement System and a Pack-Off Hanger
Authors: Meena Carly , Gulewicz Neil , Kennedy Carl , Collis Tim
Published: January 2021

The risk associated with third-party damage to transmission pipelines in areas of urban development is high. Distributed monitoring is a modern technique that uses fiber optic cables as sensors to continuously monitor pipeline parameters such as acoustics, vibration, strain and temperature. The fiber optic system notifies the operator in real-time of ongoing events allowing decisions to be made to prevent external interference or quickly address an incident that has already occurred.

Traditional methods used to install distributed monitoring systems on pipelines have limitations and are not feasible for all transmission pipelines. For instance, it can be both challenging and expensive to trench in fiber optics in developed areas and other installation techniques require the pipeline to be temporarily taken out of service. SaskEnergy Incorporated’s transmission line subsidiary, TransGas Limited partnered with a Canadian pipeline monitoring service provider to install fiber optics inside of a natural gas transmission pipeline using a pig, steel capillary tubing and a pack-off hanger. A disengagement system was incorporated to release the fiber optics after the desired monitoring distance was reached.

It was decided to perform the pilot project on a newly constructed NPS 6 natural gas transmission pipeline located in Humboldt, Saskatchewan. Nitrogen was used as a medium to simulate an in-service pipeline in order to reduce the risks associated with the first attempt of the project designs. The fiber optics were inserted into steel capillary tubing and connected to a disengagement system located at the back of a pig. A pack-off hanger was used to maintain pipeline pressure during and after the installation was completed. The spool holding the steel capillary tubing was stopped once the maximum monitoring distance was reached and the differential pressure activated the disengagement system located at the back of the pig. The pig continued to the receive location and the fiber optics remained in the pipeline for continuous monitoring. The deployment was successful and the fiber optics will remain in the pipeline for a one (1) year monitoring period.

The primary limitation to this pilot project was the strength of the steel capillary tubing. The steel capillary tubing’s ultimate tensile strength would have to be higher to accommodate a pipeline with a larger outside diameter, multiple bends, large changes in wall thickness or large elevation changes. In addition, the steel capillary tubing must be removed from the pipeline in order to perform pigging activities.
Preventing Girth Weld Failure in Pipelines: Measurement of Loads and Application of Assessment Methods
Authors: Young Andy , Andrews Robert M.
Published: January 2021

Pipeline failures from circumferential cracking at girth welds continues to affect large diameter oil and gas transmission lines, even for modern lines constructed this century. The key factors that contribute to the failure at girth welds are the dimensions of defects present, the material properties of the pipe and weldments, and the presence of loading that drives crack growth. The mechanisms of failure are well understood, but identifying and measuring the contributing factors can be a challenge. Locating girth welds that are subject to elevated loads will enable operators to focus on sections with an increased threat of failure.

In this paper, we consider each of the key factors, how these are identified and defined, and the uncertainties in the measurement process. Specific attention is applied to the presence and quantification of loads and how these influence the potential for failure. This includes sources of active external loading due to ground movement, for example, or loads generated in the pipeline from the construction process. Loads can also be quantified by measuring bending strain from inline inspection inertial measurement units. A more complete picture of pipeline loading can be established by integrating a structural analysis that accounts for the direction of pipeline movement and the presence of axial loads. The relationship between assessing pipeline integrity from ground movement — typically with strainbased methods — and establishing whether the defect can survive the load is explored. The relative contribution of bending and axial loads in the failure of defects is considered. The outcome of the study will assist pipeline operators in prioritising actions that enable the quantification of the all the key parameters. The resultant analysis will provide guidance on the girth welds that have an increased risk of failure and this will enable protective actions to be defined and scheduled accordingly.
Characterizing Corrosion Defects With Apparent High Growth Rates on Transmission Pipelines
Authors: Dessein Thomas , Ayton Brent , Sera Travis
Published: January 2021

Consecutive in-line inspections of transmission pipelines enable a comparison between the inspection results to characterize corrosion growth. Despite the high levels of in-line inspection tool accuracy and detection capabilities, corrosion defects with low calculated burst capacities may be detected on a subsequent inspection that were not reported in a previous inspection. These newly reported defects can pose a substantial challenge as the apparent growth rates between inspections of these defects can potentially drive unnecessary repair digs. This paper characterizes the contributing factors that can explain these phenomena, including:

• Typical corrosion growth rates and their associated statistical frequency

• The diminishing detection capability of inspection tools for smaller defects

• The inspection tool minimum reporting threshold

• The measurement accuracy of inspection tools.

A statistical analysis was developed to quantify this interacting set of factors using Monte Carlo simulations that work retrospectively, covering a range of observed measured defect depths and then simulating the processes that could lead to newly reported defects being un-matched in a previous inspection.

This analysis can be used to quantify the likelihood that a defect of a specific measured size would have been unreported in an earlier inspection due only to the performance characteristics of the inspection tool, and not as a result of defect growth that initiated since the time of the previous inspection. A set of case studies covering a range of pipeline inspection intervals ranging from 2 to 10 years are presented to demonstrate how this approach can be used to quantify appropriate growth rates that may be applied to these un-matched defects when assessing the remaining life or predicted probability of failure.
Power Spectral Density Analysis of Pipeline Pressures for Probabilistic Assessment
Authors: Rosenfeld M. J. , Zand Benjamin , Steiner Adam
Published: January 2021

Pipeline pressure-cycle fatigue analysis is typically performed by analyzing pressure data in the amplitude domain and then calculating incremental fatigue crack growth in accordance with the Paris Law. Alternatively, the stochastic pressure history is converted to an equivalent number of uniform-amplitude cycles using a cumulative damage rule. The fatigue life may then be estimated by integration of the Paris Law. This second approach is computationally less involved and therefore lends itself to a probabilistic analysis because of the large number of iterations necessary with techniques such as Monte Carlo analysis.

However, studies have shown that for a broadband stochastic signal, applying linear cumulative damage can introduce large errors. The presence and magnitude of error cannot be easily determined by inspection of the pressure signal.

This paper describes the analysis of the pipeline pressure signal in the frequency domain to determine the power spectral density. The result can be used to estimate correction factors to the estimated linear cumulative damage fraction. The corrections may then be applied with a simplified integration of the Paris Law in closed form to improve both accuracy and speed for probabilistic assessment. The computation time for a probabilistic assessment may potentially be reduced by a significant factor.