The ANSI/ASME B31G guideline has been useful to pipeline operators in assessing the integrity of corroded line pipe. Because large safety margins have had to be incorporated, the guidelines can be excessively conservative, which in turn can force costly repairs and replacements that may not actually be necessary. On the other hand, because the current guidelines consider only pressure loading and neglect bending and axial compression, they could give nonconservative failure predictions when combined loading exists. Therefore, a study was initiated to develop a theoretically sound methodology for assessing the integrity of corroded line pipe subjected to combined loading. A key step in the successful application of this methodology is the development of a sophisticated three-dimensional finite element procedure that can accurately simulate full-scale pipe tests under conditions of combined loading. This paper describes thirteen full-scale failure tests on artificially corroded pipes subjected to simultaneous internal pressure, bending, and longitudinal compression and presents a detailed account of the finite element analysis procedure that was developed to simulate these tests numerically. Additional finite element analyses that were conducted to investigate the effect of key parameters on failure, and to expand the corroded pipe failure database, are also discussed.
It is commonly believed that bending and other secondary loading will reduce the rupture pressure of a corroded pipe. This paper shows through theory, full-scale tests and finite element analysis (FEA) that this need not be the case in the field where displacement controlled bending and axial loading are induced by differential settlement and axial constraint. Based on this result, a new strain-based rupture prediction model is developed for buried corroded pipes subjected to internal pressure, lateral bending, thermal loading and residual stress. The selection of an appropriate “bulging factor,” the determination of a biaxial strain limit and the treatment of the heat affected zone (HAZ) are also discussed in the paper. The predicted rupture pressures agree well with the full-scale test results.
The Barkhausen noise amplitude was measured under conditions of biaxial stress in steel pipe for the case of a magnetic field noncoaxial with the stress axes. The stress axes for stresses σ1 and σ2 were orthogonal to each other. In particular, σ1 was the axial stress and σ2 was the hoop stress. Various angles were used for the field direction, along with various stress magnitudes, both compressive and tensile. The stress σ2 was always tensile, but σ1 was both compressive and tensile. A model for this biaxial stress situation, based on the Sablik–Jiles magnetomechanical model, was formulated. Using a model for the Barkhausen noise deriving from the Alessandro et al. model, the Barkhausen noise power maximum amplitude was computed for various field angles and stresses σ1 and σ2. The numerical results from this model calculation agreed qualitatively with many features of the experimental results. Thus, one found both numerically and experimentally that with field direction at small angles from the σ1 axis, the Barkhausen noise amplitude increased as the stress σ1 was increased from negative to positive. At large angles (generally greater than 45°), the reverse was true and the Barkhausen noise amplitude decreased as stress σ1 was increased. Also, the curves for the various angles tended to intersect when σ1 was set equal to σ2. Differences between numerical and experimental results are discussed, and suggestions are made for further improvement of the modeling.
Motivated by the inability to accurately address non-pressure related stresses within the framework of current assessment guidelines, a three phase study aimed at the progressive development of a reliable and readily-useable procedure suitable for the analysis of internally pressurized degraded pipes which sustain large settlement and/or axial loads was performed. To ensure accuracy of the resulting procedure, full-scale experiments and finite element numerical simulations of artificially corroded 48-inch (122-cm) diameter X65 pipes subjected to combined loadings were designed to produce upper and lower bound rupture and global buckling failure envelopes for a given set of representative corrosion dimensions. The evaluation model accommodates combined stresses arising from internal pressure, axial bending, and axially compressive loadings to predict operational margins of safety for a pipe containing discrete or multiple metal loss regions guided by failure criteria which considers two critical failure modes: 1) a von Mises type failure criterion for rupture moment capacity determination, and 2) a global buckling failure criterion for identification of the critical moment capacity approximating collapse of the pipe mid-section due to a reduction in bending stiffness attributed in part to ovalization of the cross-section. The new methodology has been incorporated in the personal computer based program SAFE (Shell Analysis Failure Envelope), developed by Southwest Research Institute (SwRI) for the Alyeska Pipeline Service Company. The user-friendly program allows for definition of combined applied stresses and geometry of the degraded region through implementation of field-obtainable pre-or post-excavation measurements, and employs unique features which provide for the examination of pipe sections exhibiting distinct areas of general corrosion, or “patches,” separated both longitudinally and circumferentially, in a single analysis run. This paper outlines the model development and validation with supporting experiments and numerical analyses, and extension of the new procedure through sophisticated numerical techniques embodied in SAFE to actual corrosion profiles and service loadings. Detailed information included in the review are the finite element and SAFE program failure predictions for pipes analyzed with a given set of corrosion dimensions and load magnitudes, and a thorough discussion of the practical application of the SAFE program.
To provide a data base for the confirmation of computational and classical residual strength analyses of corroded pipelines subjected to combined loads, full scale experiments of 48-inch diameter pipe sections with artificial corrosion were conducted. Design of the experiments was guided by the prerequisite of testing pipe sections in full scale such that subsequent corrections for the uniform depth and extent of the degraded region, and D/t ratios were not required. The testing and analysis procedures were progressively developed through three distinct phases of the program: 1) one proof of concept experiment performed on smaller diameter pipe with artificial corrosion subjected to internal pressure and axial bending, 2) five 48-inch diameter pipe tests, each with artificial corrosion, subjected to internal pressure and axial bending, and 3) eight 48-inch diameter pipe tests, each with artificial corrosion subjected to pressure, axial bending, and axial compression. Combined loading on the test specimens followed a predetermined path until failure by either rupture or global buckling occurred, while the elastic-plastic load-deflection and large strain behavior was recorded. The uniform depth, axial length, and circumferential length of the degraded region were selected to represent commonly observed general corrosion dimensions found among in-service pipelines, with the maximum and minimum extents reflecting the typical wall loss characteristics at the girth and seam weld locations. The pipe behavior during the experiments and analyses was ultimately modeled and verified by an elastic-shell model capable of defining failure pressure and curvature for a corroded pipe subjected to combined service loads. This paper presents details on the test procedures, specimen preparation and design, and complex data acquisition techniques utilized in the generation of required global and location response information. In addition, significant experimental results from the program which enabled the development and validation of a new procedure for the assessment of corroded pipes under combined loads are reviewed.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.