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This paper proposes a novel mitigation approach to improve the safety and structural integrity of buried steel transmission pipelines subjected to ground deformation. This method involves altering the boundary condition of buried pipelines with adjacently installed special geomaterial blocks (SGBs) consisting of a set of expanded polystyrene geofoam and polypropylene squared plastic boxes. The proposed SGB allows accommodating ground deformation while significantly reducing the ground-induced forces in the pipe. The mitigation technique is first presented, followed by the experimental test program developed to evaluate the beneficial effects of SGB on the pipe response when subjected to lateral and oblique displacements. Furthermore, a simplified spring-based analytical modeling approach is proposed for predicting the force-displacement response of the pipe–SGB–soil assembly with emphasis on the interaction between the pipe and soil under the new boundary condition. The analytical model is validated using experimental test data. The results of the experimental tests confirm the efficiency of the proposed remediation and feature the relationship between the applied displacement and the force developed in the pipe. Furthermore, it is found that the proposed simplified analytical model can appropriately predict the expected reaction of the pipe equipped with the SGB. [ABSTRACT FROM AUTHOR]

A novel mitigation technique is proposed in this paper to effectively improve the safety and integrity of buried pipelines subjected to ground deformation and to mitigate the detrimental effects of ground deformation on the pipe. This technique involves the installation of special geomaterial blocks (SGBs) adjacent to the pipe. The SGB consisting of multiple layers of hollow plastic boxes placed between layers of high-density expanded polystyrene (EPS) geofoam blocks forms a thick sandwich panel structure, which is oriented such that its orthotropic mechanical property allows the pipe to move laterally without developing significant reactions against the soil. A summary of past mitigation techniques and the method proposed in this study are first presented. Large-scale experimental testing used to assess the beneficial effects of the SGB on the pipe response when subjected to lateral and oblique displacements is then presented, followed by a simplified finite element model proposed to numerically simulate the pipe-SGB-soil interaction under lateral soil displacement. The results confirm that the proposed remediation method can significantly reduce the soil-pipe interaction force. Furthermore, the proposed beam-based numerical model that can be used in engineering design predicts well the lateral load-deformation response of the system. [ABSTRACT FROM AUTHOR]

Mechanical damage in form of dents, cracks, gouges, and scratches are common in pipelines. Sometimes, these damages form in proximity of each other and act as one defect in the pipe wall. The combined defects have been found to be more injurious than individual defects. One of the combined defects in pipeline comprises of a crack in a dent, also known as dent-crack defect. This paper discusses the development of finite element models using extended finite element criterion (XFEM) in Abaqus to predict burst pressure of specimens of API X70 pipeline with restrained and unrestrained concentric dent-crack defects. The models are calibrated and validated using results of full-scale burst tests. The effects of crack length, crack depth, dent depth, and denting pressure on burst pressure are investigated. The results show that restrained dent-crack defects with shallow cracks (depth less than 50% wall thickness) inside dents do not affect pipeline operations at maximum allowable operating pressure if crack lengths are less than 200 mm. Releasing restrained dent-cracks when the pressure is at maximum allowable operating pressure can cause propagation of deep cracks (depth of 50% wall thickness or more) longer than 60 mm. However, only very long cracks (200 mm and higher) propagate to burst the pipe. Cracks of depth less than 20% of wall thickness inside dents formed at zero pressure are not propagated by the maximum allowable operating pressure. Dent-crack defects having dents of depth less than 2% outside diameter of pipe behave as plain cracks if the dents are formed at zero denting pressure but are more injurious than plain cracks if the dents are formed in pressurized pipes. [ABSTRACT FROM AUTHOR]

Wide plate testing has been traditionally applied to evaluate the tensile strain capacity (TSC) of pipelines with girth weld flaws. These wide plate tests cannot incorporate the effect of internal pressure, however, numerical analysis in recent studies showed that the TSC is affected by the level of internal pressure inside the pipeline (Wang et al. 2007, "Strain Based Design of High Strength Pipelines," 17th International Offshore and Polar Engineering Conference (ISOPE), Lisbon, Portugal, Vol. 4, pp. 3186-3193). Moreover, most of the past studies focused on the effect of circumferential flaws on the TSC for pipelines of steel grade X65 or higher. The current Oil and Gas Pipeline System Code CSA Z662-11 provides equations to predict the TSC as a function of geometry and material properties of the pipelines. These equations were based on extensive studies on pipes having grades X65 or higher without considering the effect of internal pressure. This paper investigates the TSC for pipelines obtained using an experimental technique considering the effect of internal pressure and flaw size. Eight full-scale tests of X52 NPS 12 in. pipes with 6.91 mm wall thickness were conducted in order to investigate the effect of circumferential flaws close to a girth weld on the TSC for vintage pipelines subjected to eccentric tensile forces and internal pressure. The tensile strains along the pipe length and on the outer circumference of the pipe were measured using biaxial strain gauges and a digital image correlation (DIC) system. Postfailure macrofractography analysis was used to confirm the original size of the machined flaw and to identify areas of plastic deformation and brittle/ductile fracture surfaces. From the experimental and numerical results, the effect of internal pressure and flaw size on the TSC and the crack mouth opening displacement (CMOD) at failure were investigated and presented. [ABSTRACT FROM AUTHOR]

The material model proposed in Part I (Neupane et al., 2012, "Modeling the Deformation Response of High Strength Steel Pipelines--Part I: Material Characterization to Model the Plastic Anisotropy," ASME J. Appl. Mech., 79, p. 051002) is used to study the defor-mation response of high strength steel. The response of pipes subjected to frost upheaval at a particular point is studied using an assembly of pipe elements, while buckling of pipes is examined using shell elements. The deformation response is obtained using two different material models. The two different material models used were the isotropic hardening material model and the combined kinematic hardening material model. Two sets of material stress-strain data were used for the isotropic hardening material model; data obtained from the longitudinal direction tests and data obtained from the circumferential direction tests. The combined kinematic hardening material model was calibrated to provide an accurate prediction of the stress-strain behavior in both the longitudinal direction and the circumferential direction. The deformation response of a pipe model using the three different material data sets was studied. The sensitivity of the response of pipelines to the choice of a material model and the material data set is studied for the frost upheaval and local buckling. [ABSTRACT FROM AUTHOR]

The design equations for pipelines subjected to both internal pressure and longitudinal loading are based on the isotropic hardening plasticity model. However, high strength steel (HSS) pipelines exhibit plastic anisotropy, which cannot be incorporated in the traditional isotropic hardening plasticity model. The stress strain behaviors of HSS in the longitudinal and the circumferential directions are different. Thus, it would not be desirable to adopt the same design equations based on the isotropic hardening plasticity model for HSS pipelines. The design equations of HSS steel pipelines have to be developed by solving numerical models incorporating a suitable material plasticity constitutive model for the HSS that can deal with the exhibited plastic anisotropy. In this paper, various plasticity models are studied and an appropriate plasticity model is adopted and calibrated to model the plastic anisotropy exhibited by the HSS. [ABSTRACT FROM AUTHOR]

Abstract: The purpose of this work is to describe a numerical procedure that was conducted to examine the effect of internal pressure on the possibility of puncturing and rupturing a high-pressure gas pipeline due to the impact of a falling rock. The mass and the height of the falling object were fixed. The analyses were performed in two parts: first by comparing an initial potential energy of the indenter with the energy needed to dent and possibly puncture the pipeline, then by determining if the resulting puncture would result in unstable crack extension leading to pipeline rupture. Finite element analysis was used to examine various shapes of the indenting surface to assess the effect of contact geometry on the puncture resistance. For cases where puncture is predicted, the dimensions of the hole are compared to the critical pressure to cause rupture, using industry standard methodology. The overall procedure can thus be utilized to determine the critical pressure to avoid a rupture due to a falling rock. By further application of an appropriate safety factor, the safe working pressure for a pipeline excavation can be established. [Copyright &y& Elsevier]

Pipelines exposed to geo-hazards such as moving slopes, discontinuous permafrost, and other ground movements may be subjected to displacement-controlled loading, which may lead to significant plastic strains. This can potentially impact pipeline structural capacity and their leak-tight integrity. Traditional stress-based design methods may become uneconomical in the design of pipelines subjected to large plastic strain. In view of the extensive use of such pipelines, reliable calibration of the tensile strain capacity (TSC) plays a critical role in strain-based design (SBD) methodology. Recent studies were focused mostly on high toughness modern pipelines with limited research performed on lower-grade vintage pipelines. However, the effects of biaxial loading due to internal pressure and bending stresses imposed on pipelines as a result of interactions with geo-hazards were not properly addressed in previous studies. This paper investigates the effect of internal pressure and flaw size on the TSC of X42 welded vintage pipelines using experimental testing. Eight full-scale pressurized four-point bending tests were conducted on 22 inches (558.8 mm) diameter X42 grade welded vintage pipes with D/t ratio of 44 to examine the effect of the influential parameters on the TSC. Biaxial strain gauges and a digital image correlation (DIC) system were major instrumentations used for measuring strain. The results were used to examine the crack growth rate by estimating the crack mouth opening displacement (CMOD) at failure and the effects of internal pressure and flaw size on the TSC. The TSC obtained from the tests were compared with those predicted using TSC predictive models proposed by ExxonMobil and Pipeline Research Council International (PRCI). [ABSTRACT FROM AUTHOR]

This paper presents an investigation of the potential of extended finite element method (XFEM) implemented in Abaqus standard software, with maximum principal strain and fracture energy as damage parameters for analysis of crack propagation and prediction of burst pressure in pipelines. Models of API 5L X60 pipe were calibrated first, using data from single edge notched tension test and then using burst pressures from 3 full scale tests. Both calibrations produced low fracture energy and marginally varied strains as XFEM damage parameters. The models were used to predict burst pressures of pipe specimens having varying sizes of longitudinal cracks that were rectangular in profile and located on the external surface of the pipes. Burst pressures were also predicted using analytical methods and the results compared with tests and XFEM predictions. All analytical methods accurately predicted burst pressures of specimens with shallow crack depth but were inaccurate for deeper cracks. XFEM predictions were satisfactory for all specimens. Although few cracks were analysed, the results show XFEM can be effective for analysis of crack propagation and prediction of burst pressure in pipelines, but investigation using more crack sizes, pipe grades and pipe geometries is recommended for a firm conclusion. • XFEM with maximum principal strain and fracture energy as damage parameters analyses cracks in pipelines. • Damage parameters best estimated by calibration and validation with tests. • Full scale tests, being costly maybe replaced with small scale tests in calibration. • Constraint effects influence values of calibrated parameters of the pipe. • Damage parameters of a pipe vary with size of crack and pipe configuration. [ABSTRACT FROM AUTHOR]