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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 [...]

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]