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Zhou H.,Center for Reliable Energy Systems | Liu M.,Center for Reliable Energy Systems | Wang Y.-Y.,Center for Reliable Energy Systems | D'Eletto D.,National Grid U.S.
Proceedings of the Biennial International Pipeline Conference, IPC | Year: 2014

Horizontal directional drilling (HDD) is a trenchless technique which has been frequently used to install underground pipelines due to its minimal impact on surrounding areas. In some circumstances, pneumatic hammers (or pipe rammers) are needed to assist HDD pullback. The repeated impacts from the hammer can free a stuck pipeline during HDD pull back and facilitate the HDD installation. However, the operation of the hammer may plastically deform the pipe and/or induce fatigue flaw growth in girth welds which can negatively affect the integrity of the installed pipeline. Compared with the relatively large number of studies and guidelines on HDD, there are few studies on the application of the pneumatic hammer for the pull-back assistance. This paper describes the key considerations for using the pneumatic hammer in the HDD pull-back. The topic covered in the paper includes: (1) identification of key issues for integrity assessment; (2) realistic estimation of impact loads; (3) assessment of potential integrity threats; and (4) operation monitoring and documentation. Copyright © 2014 by ASME.

Martens M.,TransCanada | Chen Y.,Center for Reliable Energy Systems | Liu M.,Center for Reliable Energy Systems
Proceedings of the Biennial International Pipeline Conference, IPC | Year: 2014

Back-beveled transition welds for joining unequal wall thickness are often used in gas and oil transmission pipelines, as recommended in the pipeline codes and standards, such as CSA Z662, ASME B31.8, and ASME 31.4. However, one North American pipeline operator has successively utilized a counterbore-tapered design for transition of unequal wall thicknesses for over 30 years. The design philosophy of the counterbore-tapered joint is to reduce the stress concentrations in the heat affected zone, facilitate the welding of unequal wall thickness and NDT while achieving better quality, reliability, and productivity. By conducting a comparative finite element analysis of the two joint designs, the present study evaluated the pressure containment capacities, the stress concentration factors, the stress intensity factors, and the limit loads of plastic collapses for both the counterbore-tapered and the back-beveled designs. The effect of a key design parameter, the counterbore length, on the integrity of the counterbore design was also examined. The results of the comparative analysis showed that compared to the back-beveled joint, when the pipe materials of unequal wall thickness have the same strength, the counterbore-tapered joint has the same pressure containment capacity as the back-beveled joint. The back-bevel design offers lower stress concentration factor, lower stress intensity factor, and higher limit load of plastic collapse than the back- beveled design. Copyright © 2014 by ASME.

Wang Y.-Y.,Center for Reliable Energy Systems | Liu M.,Center for Reliable Energy Systems
Journal of Pipeline Engineering | Year: 2014

STRAIN-BASED DESIGN and assessment (SBDA) focuses on potential failures driven by high longitudinal strains. Pipeline failures driven by longitudinal stresses or strains are relatively rare events in comparison to failures driven by hoop stresses. Longitudinal strains are often associated with ground movement or other unusual upsetting events. SBDA is performed by comparing strain demand with strain capacity. Strain demand may be obtained from direct measurement or pipe-soil interaction models. Strain capacity is typically estimated using suitable models supported by experimental test data. There are gaps between the present approaches to SBDA and field conditions under which SBDA is applied. For instance, linepipes are delivered with a range of tensile properties.Welds are produced by a variety of processes with a range of tensile and toughness properties. Pipe dimensions, mechanical properties, and soil conditions affect both strain demand and strain capacity. The overall process of SBDA is introduced first. It can be seen that conditions assumed in models can be quite different from those in actual field applications. For instance, there can be considerable variations in the tensile strength of linepipes.The potential impact of strength variations on the measured/reported strain demand and strain capacity is described.The overall approaches to SBDA with appropriate consideration of actual field conditions are suggested. Some unresolved issues related to SBDA are described, particularly in the context of characteristics of modern linepipes.

Liu M.,Center for Reliable Energy Systems | Zhang F.,Center for Reliable Energy Systems | Kotian K.,Center for Reliable Energy Systems | Nanney S.,U.S. Department of Transportation
Proceedings of the Biennial International Pipeline Conference, IPC | Year: 2014

Local buckling generated by excessive bending and/or longitudinal compression is one of the main threats to pipeline integrity. The resistance to local buckling is usually measured by compressive strain capacity (CSC). Extensive work has been performed on the CSC of pipes through both experiments and numerical modeling. Many CSC models have been developed to compute the CSC. The comparison of the existing CSC models often shows (1) large differences in recognized input parameters and their applicable ranges, (2) large differences in computed CSC, especially for pressurized conditions, (3) large differences in recommended safety factors; and (4) inconsistent trends on model conservatism. Refined compressive strain models were developed recently. The development involves comprehensive review of existing CSC models, selecting modeling processes that represent field conditions, sensitivity studies on parameters affecting the CSC, and the model evaluation against experimental data. In this paper, the refined compressive strain models and the key improvement to the modeling processes are summarized. Copyright © 2014 by ASME.

Wang Y.-Y.,Center for Reliable Energy Systems | Chen Y.,Center for Reliable Energy Systems | Salama M.,ConocoPhillips
Proceedings of the Biennial International Pipeline Conference, IPC | Year: 2014

In order to optimize cost and performance of high pressure gas pipelines by reducing the wall thickness, pipeline companies are considering the use of higher grade (X70 or above) steels or a composite pipe of thin steel liner and fiber wrap. The use of high strength steels and thinner pipes can result in challenges when the pipe is installed in areas imposing high strain demand such as discontinuous permafrost regions. For high strength steels, the difficulty of ensuring the strength overmatching of the weld metal and the potential softening of the heat affected zone (HAZ) can result in gross strain concentration in the weld region and thus reduce the strain capacity of the pipeline in the presence of weld defects. Also, a thinner pipe has lower strain capacity than a thicker pipe for the weld defect of the same dimensions. One of the economical and effective ways of mitigating the possibility of gross strain concentration and increasing the strain capacity of a weld region containing weld defects is through the use of appropriate weld profiles. For instance, adding a smooth and wide layer of weld reinforcement (termed weld overbuild) can increase the effective strength of the weld. The effectiveness of the weld overbuild in improving the tensile strain capacity of girth welds is evaluated using the Level 4a approach of the PRCI-CRES tensile strain models. The crack-driving force is obtained through finite element analysis (FEA) of welds with planar weld and HAZ flaws of various sizes. It was demonstrated that weld overbuild with appropriate dimensions is an effective method to increase the tensile strain capacity (TSC) of girth welds which may have limited TSC without the overbuild. The role of weld profiles in girth weld integrity is discussed from the perspectives of historical evidence and more recent analysis and experimental tests. Copyright © 2014 by ASME.

Wang Y.-Y.,Center for Reliable Energy Systems | Kotian K.,Center for Reliable Energy Systems | Rapp S.,Spectra Energy Transmission
Proceedings of the Biennial International Pipeline Conference, IPC | Year: 2014

High levels of high-low misalignment in pipeline girth welds have been identified as one of the possible contributing factors to some of the recent pre-service hydrostatic test failures or subsequent service failures. However, pipeline service experience indicates that nominally defect-free girth welds with high levels of misalignment and proper weld profiles can provide satisfactory long-term service. In this paper, recent analytical and experimental work aimed at understanding the impact of high-low misalignment in girth welds is described. In nominally defect-free welds, the performance of the welds is found to be predominantly determined by the misalignment ratio, weld strength mismatch ratio, and the weld profile. Iso-load-capacity relations are developed through finite element analysis (FEA) to capture the interdependence of those key parameters. The analysis procedure is validated by cross-weld tensile testing of girth welds with various levels of misalignment and weld strength mismatch. The effects of the circumferential extent of misalignment, alternatively termed local misalignment, are also analyzed. The effects of misalignment in girth weld with planar flaws are examined in the context of the tensile strain capacity. The analytical and experimental evidence indicate that the absolute level of misalignment is not a sole indicator of girth weld performance. Weld transition profile, pipe wall thickness, and weld strength mismatch all play an important role. With proper weld profiles, minimal or small reduction of load capacity is observed even at very high levels of misalignment. Work is continuing to further examine the effects of high-low misalignment with a goal of making practical recommendations to be included in codes and standards. Copyright © 2014 by ASME.

Narayanan B.K.,Lincoln Electrical Company | Brady N.,Lincoln Electrical Company | Wang Y.-Y.,Center for Reliable Energy Systems | Ogborn J.,Lincoln Electrical Company
Proceedings of the Biennial International Pipeline Conference, IPC | Year: 2010

Ferritic weld metal was deposited with gas shielded flux cored arc welding (FCAW-G) process. The nitrogen level in the deposited weld metal varies typically between 20 to100 ppm. Nitrogen is a fast diffusing solute element that is known to cause strain ageing affecting both strength and toughness. Weld metal was produced with intentional additions of two strong nitride formers, titanium and vanadium. All-weld metal tensile samples were subjected to varying levels of strain, aged at 170°C for 20 minutes and reloaded to failure. Both the yield and tensile strength increased with increase in pre-strain confirming the presence of strain ageing. The strain hardening rate is also seen to change with strain ageing. There is also a corresponding decrease in the uniform elongation with increase in nitrogen and prestrain. The effect of strain ageing treatment on weld metal toughness was also evaluated. A nominal 2%-3% strain was imposed on the weld metal by straining it in the direction of welding and Charpy V-Notch toughness of the weld was measured. The ductile to brittle transition temperature (DBTT) of the weld metal was estimated by measuring the percent shear and the weld metal toughness at different temperatures. The DBTT of the weld metal is seen to shift slightly to higher temperatures with increase in pre-strain. However there was a dramatic drop in the upper shelf energy and a consistent decrease in the average toughness of the weld metal at all temperatures. The as-welded and reheat microstructure of the weld metal was characterized using optical and electron microscopy techniques. The possible implications of strain ageing on pipeline girth weld procedure qualification and inservice integrity are discussed. Copyright © 2010 by ASME.

Liu M.,Center for Reliable Energy Systems | Wang Y.-Y.,Center for Reliable Energy Systems | Rapp S.,Spectra Energy Transmission
Proceedings of the Biennial International Pipeline Conference, IPC | Year: 2012

For large diameter spiral pipes, there can be one skelp-end weld (SEW) in every 5-7 joints of pipes. The industry acceptance of SEWs is uneven although API 5L permits SEWs in finished pipes. A joint industry project (JIP) [1] was formed to develop uniformly acceptable inspection and test plans (ITPs) for SEWs. The development was conducted through two parallel processes: (1) fitness-for-service analysis of the SEWs under a variety of loading conditions expected in their life time and (2) consensus building based on the best practice and quality control protocols. This paper details the fitness-for-service analysis of SEWs. A companion paper provides a summary of the recommended ITPs developed in the JIP [2]. In the fitness-for-service analysis, the SEWs were subjected to a variety of loading conditions covering construction, commissioning, and normal service with and without internal pressure. For in-service loading, both static and cyclic loading was considered. The extensive fitness-for-service analysis demonstrated that there is no inherent integrity risk associated with the SEWs when these welds are manufactured, tested, and inspected using generally accepted quality control measures applied to helical seam welds. Additional inspection and quality control for coil end properties and T-joints are recommended in the companion paper. Copyright © 2012 by ASME.

Zhang F.,Brown University | Zhang F.,Center for Reliable Energy Systems | Bower A.F.,Brown University | Curtin W.A.,Brown University
Acta Materialia | Year: 2012

Three-dimensional finite element simulations are used to investigate the role of serrated flow on the strain at the onset of necking in a cylindrical uniaxial tension specimen. The material is idealized using a modified form of the McCormick constitutive equation, which has an additional material parameter that allows the rate of transient aging to be varied without affecting its steady-state response. Stability calculations and direct simulations show that, if the transient response is sufficiently slow, serrated flow can be suppressed, even though the material has negative steady-state strain rate sensitivity. This result is then used to determine the effect of suppressing serrated flow on the strain to localization. We find that negative steady-state sensitivity significantly reduces the strain required to initiate necking failure in a tensile specimen. However, the strain to failure is largely unaffected by the transient response of the material, and suppressing the serrated flow in particular has a negligible effect on the localization strain. We conclude that, while both serrated flow and reduced ductility are observed in materials with negative rate sensitivity, the reduction in ductility is not a direct consequence of serrated flow. © 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Zhang F.,Center for Reliable Energy Systems | Wang Y.-Y.,Center for Reliable Energy Systems
Proceedings of the International Conference on Offshore Mechanics and Arctic Engineering - OMAE | Year: 2014

The propagation of seismic waves introduces strains in buried pipelines. Considerable amount of work was performed in 1970's and early 1980's in this subject area. A good representative of such work is the model developed by Shinozuka and Koike in 1979. The analytical models developed during this period are still the major tools in assessing the influence of seismic waves on buried pipelines. The foundations of these models are the assumptions and some simplified soil and pipe interaction models available at the time. In 1984 a spring model representing the interaction between soil and buried pipes was introduced by American Society of Civil Engineers (ASCE) in Guidelines for the Seismic Design of Oil and Gas Pipeline Systems. An improved version of the ASCE model was later published in Guidelines for the Design of Buried Steel Pipe by American Lifelines Alliance in 2001. Since then, the spring model has become one of the most widely used models by various industries and has been incorporated into commercial software, such as AutoPIPE®. Most of the soil properties in fields are represented by the parameters of the ASCE soil-spring model. However, it is inconvenient to assess the influence of seismic waves on pipelines with soil properties described by parameters of the ASCE model. There are differences between the ASCE soil-spring model and the soil-pipe interactions in the seismic wave analysis model. In this paper the foundation of Shinozuka and Koike model is first reviewed. The model is then revised to accommodate the ASCE soil-spring model. Some unnecessary assumptions in the Shinozuka and Koike model are removed to make the model more generally applicable to various field conditions. Finally, the revised model is verified by finite element analysis under several typical pipeline field conditions, including straight segments and segments with bends and tees. Copyright © 2014 by ASME.

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