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Buried pipelines, used for transporting liquid and gas, are often subjected to axial pulling forces due to seasonal temperature changes and (or) relative ground movements. The axial pullout force is exerted through soil-pipe interaction, which depends on the pipe material, surrounding soil and pipe-soil interface properties. In this research, axial pullout force on ductile iron pipe buried in sand is first experimentally investigated through development of a new laboratory facility. Based on the test results, simplified methods for predicting the axial forces are discussed. Finite element modelling is then used to investigate the mechanism of soil-pipe interaction and identify the key parameters contributing to the axial pullout force, which could not be measured during the laboratory tests. The constrained dilation of sand near the pipe- soil interface and arching effects due to a different stiffness of the pipe with respect to the soil are found to influence the mobilized axial forces on pipes. Key words: buried pipeline, soil-pipe interaction, axial pullout, full-scale tests, ductile iron pipe, sand. Les canalisations enfouies, utilisees pour le transport de liquides et de gaz, sont souvent soumises a des forces de traction axiales en raison des variations saisonnieres de la temperature ou des mouvements relatifs du sol. La force de traction axiale est exercee par l'interaction sol-tuyau, qui depend du materiau du tuyau, du sol environnant et des proprietes d'interface tuyau-sol. Dans le cadre de cette recherche, la force de traction axiale exercee sur les tuyaux en fonte ductile enfouis dans le sable est d'abord etudiee experimentalement par le developpement d'une nouvelle installation de laboratoire. Sur la base des resultats des essais, des methodes simplifiees de prevision des forces axiales sont discutees. La modelisation des elements finis sert ensuite a etudier le mecanisme de l'interaction sol-tuyau et a determiner les parametres cles qui contribuent a la force de traction axiale, qui n'a pu etre mesuree au cours des essais en laboratoire. La dilatation limitee du sable a proximite de l'interface tuyau-sol et l'effet de voute attribuable a la rigidite differente du tuyau par rapport au sol influent sur les forces axiales mobilisees sur les tuyaux. [Traduit par la Redaction] Mots-cles : canalisation enfouie, interaction sol-tuyau, extraction axiale, essais a grande echelle, tuyau en fonte ductile, sable., Introduction The landslide is a common geohazard that affects the performance of buried pipelines. Most of the pipelines carrying hydrocarbons and water are buried and are sometimes subjected to relative [...]

Municipal water distribution systems in Canada and other countries include a large number of cast iron pipes that were installed almost 50 years ago. For structural integrity assessment of these pipes, the fracture mechanics approach is found to be more effective than the conventional continuum mechanics-based approach. This paper presents the mechanical properties for fracture mechanics-based strength assessment of water mains determined through testing of cast iron pipes exhumed from two cities in Canada. Microstructure analysis is conducted to understand the materials' inherent properties. Uniaxial tensile tests are conducted to determine the stress-strain relations. The influence of the rate of loading on stress-strain behaviour and loading-unloading responses are investigated. A simplified single-edge notch beam test is used to obtain the fracture toughness. Probabilistic distributions of the parameters are provided to account for the uncertainty and variabilities observed in the test results. Key words: cast iron water main, tensile test, single-edge notch beam (SENB) test, micro-structure analysis, fracture mechanics finite element analysis. Les reseaux municipaux de distribution d'eau au Canada et dans d'autres pays comprennent un grand nombre de tuyaux en fonte qui ont ete installes il y a pres de 50 ans. En ce qui concerne l'evaluation de l'integrite structurale de ces tuyaux, l'approche de la mecanique de la rupture est jugee plus efficace que l'approche classique fondee sur la mecanique des milieux continus. Cet article presente les proprietes mecaniques pour l'evaluation de la resistance des conduites principales fondee sur la mecanique de la rupture, determinee par des essais sur des tuyaux en fonte exhumes de deux villes au Canada. L'analyse de la microstructure est effectuee afin de comprendre les proprietes inherentes des materiaux. Des essais de traction uniaxiale sont realises pour determiner les relations contrainte-deformation. L'influence du taux de chargement sur le comportement de contrainte-deformation et les reponses de chargement-dechargement sont etudiees. Un essai simplifie de poutre a encoche a rebord simple (<>) permet d'obtenir la tenacite. Les distributions probabilistes des parametres sont fournies pour tenir compte de l'incertitude et des variabilites observees dans les resultats des essais. [Traduit par la Redaction] Mots-cles: conduite principale d'eau en fonte, essai de traction, essai de poutre a encoche a rebord simple (<< single-edge notch beam test >>), analyse des microstructures, mecanique des fractures, analyse des elements finis., Introduction Cast iron was extensively used as the dominant material for municipal water mains until the middle of the twentieth century. Although cast iron pipes are no longer manufactured or [...]

The strength of pipeline with multiple corrosion patches depends on the number of corrosion patches within an area on the pipe surface, the locations of corrosion patches along the longitudinal and circumferential directions of the pipe. In this paper, the strength and deformation characteristics of corroded pipeline are investigated using finite element analysis. Pipes with different diameters and different depths of corrosion patches are considered. The spacing of the corrosion patches is varied along longitudinal, diagonal, and circumferential directions of the pipes. The study shows that the limiting spacing for interaction of corrosion patches depends predominantly on pipe wall thickness, corrosion depth, and the location of the defects. The diameter of the pipe has some influence on the interaction for large diameter pipes. A new interaction rule for the limiting spacing for interaction is developed for longitudinally spaced corrosion patches. For circumferentially spaced corrosion patches, the ASME recommendation for the limiting spacing is found to be reasonable. Key words: corroded pipe, multiple corrosion patches, burst pressure, longitudinal interaction, circumferential interaction, limiting spacing, interaction rule. La resistance de pipeline presentant de multiples plaques de corrosion depend du nombre de plaques de corrosion dans une zone a la surface de conduite, les emplacements de plaques de corrosion dans les sens longitudinal et circonferentiel de la conduite. Dans le cadre de cette etude, la resistance et les caracteristiques de deformation de pipeline corrode sont examinees au moyen d'analyse par elements finis. On considere les conduites de diametres differents et les differentes profondeurs de plaques de corrosion. On varie l'espacement des plaques de corrosion dans les sens longitudinal, diagonal et circonferentiel des conduites. L'etude montre que l'espacement limite au niveau d'interaction des plaques de corrosion depend principalement de l'epaisseur de paroi de conduite, de la profondeur de corrosion et de l'emplacement des defauts. Le diametre de la conduite a une certaine incidence sur l'interaction dans le cas de conduites de grand diametre. On elabore une nouvelle regle d'espacement limite au niveau d'interaction, et ce, pour des plaques de corrosion longitudinalement espacees. Pour des plaques de corrosion espacees sur la circonference, la recommandation emise par l'ASME pour l'espacement limite s'avere raisonnable. [Traduit par la Redaction] Mots-cles: conduite corrodee, multiples plaques de corrosion, pression d'eclatement, interaction longitudinale, interaction circonferentielle, espacement limite, regle d'interaction., Introduction Pipelines are used for transporting hydrocarbons, municipal water and waste water, and for other industrial applications. The pipes are often exposed to corrosive environments causing wall corrosion. The corrosion [...]

A number of burst pressure models were developed to determine the remaining strength of corroded pipelines. However, no single model has been found to be acceptable for predicting the burst pressure correctly. In this paper, the burst pressure models for corroded pipelines are revisited based on the structures of three existing models. The model parameters are re-evaluated using an optimization (differential evolution) algorithm with a database developed based on finite element (FE) analysis. A series of FE analysis are performed to determine the burst pressures of corroded pipelines with varying pipe diameters, wall thicknesses, corrosion dimensions and material strength grades. The models with new sets of model parameters provide the burst pressure reduction factors that match with the FE results and experimental data better than the existing models. The study reveals that FE analysis along with an optimization algorithm can effectively be used to develop improved models for better fitness-for-service assessment of pipelines. Key words: corroded pipeline, burst pressure model, finite element analysis, optimization, differential evolution, fitness-for-service. Un certain nombre de modeles de pression d'eclatement ont ete developpes afin de determiner la resistance restante de pipelines corrodes. Cependant, aucun modele unique ne s'est avere acceptable pour prevoir correctement la pression d'eclatement. Dans le cadre de cette etude, les modeles de pression d'eclatement pour des pipelines corrodes sont reexamines a la lumiere de structures de trois modeles existants. Les parametres des modeles sont reevalues en utilisant un algorithme d'optimisation (l'evolution differentielle) avec une base de donnees developpee en fonction de l'analyse par elements finis (EF). Une serie d'analyses EF est effectuee pour determiner les pressions d'eclatement de pipelines corrodes ayant differents diametres de tuyaux, epaisseurs de paroi, dimensions de corrosion et niveaux de resistance de materiau. Les modeles avec les nouveaux ensembles de parametres de modele fournissent les facteurs de reduction de pression d'eclatement qui correspondent plus fidelement avec les resultats des EF et les donnees experimentales que les modeles existants. L'etude revele que l'analyse EF de pair avec un algorithme d'optimisation peut efficacement servir au developpement de modeles ameliores aux fins d'une meilleure evaluation de l'aptitude fonctionnelle des pipelines. [Traduit par la Redaction] Mots-cles : pipeline corrode, modele de pression d'eclatement, analyse par elements finis (EF), optimisation, evolution differentielle, aptitude fonctionnelle., Introduction Pipelines are important infrastructure that provide economic means of transporting water, wastewater, oil and gas, and other products. Metal pipes are popularly used for high-pressure applications due to the [...]

A number of water main breaks occur every year in municipalities due to ageing, aggressive environmental conditions and undesirable soil conditions. However, the failure mechanism observed in cast iron water mains is often obscure. Non-uniform soil support conditions resulting from the erosion of the surrounding soil by the water escaping from leaks may induce excessive stresses on the pipe wall. Due to partial erosion of backfill soil or the presence of large rock pieces, the localised point supports on the pipe accentuate the pipe wall stresses further. This research employs three-dimensional finite-element analysis to investigate the effects of non-uniform soil support and the localised point support on the pipe wall stresses. This study results in the development of a better understanding of the mechanism of cast iron water main failure. It is shown that a localised support with a stiffness equivalent to the spring constant of 1500 N/mm may result in the failure of cast iron water mains. [ABSTRACT FROM AUTHOR]

Burst pressure models are used for the fitness-for-purpose assessment of energy pipelines. Existing burst pressure models for corroded pipelines are unable to predict the pipe capacity correctly. In this paper, an improved burst pressure model is developed for corroded pipelines considering the burst pressure of flawless pipes and a reduction factor due to corrosion separately. The equation for the burst pressure of flawless pipe is revised based on the theory of the thick wall cylinder. A new model for the Folias factor is proposed for calculating the reduction factor. The new model for the Folias factor incorporates the depth of corrosion defect, whereas the existing models do not account for the effect of the defect depth. The authors' earlier work revealed that the Folias factor depends on the depth of defect. The proposed burst model reasonably predicts the burst pressures obtained from finite element (FE) analysis conducted in this study and the burst test results available in the published literature. [ABSTRACT FROM AUTHOR]

Codes/standards have been developed to calculate accurately the burst pressure for corroded pipelines. Five burst pressure models are evaluated in this paper using three-dimensional finite-element (FE) analysis. The finite-element models are validated using burst test results available in the literature. The design codes/standards are found to calculate variable burst pressures with respect to the finite-element calculations and the laboratory test results. The variability in the calculated burst pressures is attributed to the use of different flow stresses for the material and different burst pressure reduction factors for the corroded geometry. The Folias factor is considered as the major parameter contributing to the burst pressure reduction factor. Three different equations are currently used to calculate the Folias factor in the design codes that are expressed in terms of l2/(Dt). However, the finite-element evaluation presented here reveals that the Folias factor also depends on other parameters such as the defect depth. [ABSTRACT FROM AUTHOR]