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Oil and gas pipelines transport millions of dollars of products every day making the optimization of their long-term maintenance strategies an essential target for practitioners. Thus, this paper aims to optimize the maintenance plan of such pipelines by maximizing their lifetime average condition with the minimum possible cost. This is achieved in three steps: (1) developing a life-cycle cost model for such pipelines to determine their net present value (NPV) based on the different rehabilitation actions applied throughout their lifetime; (2) establishing a strategy to determine the condition index of such pipelines before and after any rehabilitation action applied throughout their lifetime; and (3) formulating the optimization model and applying the elitist non-dominated sorting genetic algorithm (NSGA-II) to determine the optimum maintenance plans for such pipelines. The optimization model is applied to a real-life case study to demonstrate its applicability. Key words: oil and gas pipelines, optimization, NSGA-II, life-cycle cost, condition index. Les oleoducs et gazoducs transportent des millions de dollars en produits chaque jour, faisant de sorte que l'optimisation des strategies d'entretien a long terme de ceux-ci soit une cible essentielle pour les praticiens. Ainsi, cette etude vise a optimiser le plan d'entretien de ces pipelines en maximisant leur etat moyen a vie au cout minimum possible. Cela se fait en trois etapes : (i) elaborer un modele de cout du cycle de vie pour ces pipelines afin de determiner leur valeur actualisee nette (VAN) en fonction des differentes mesures de rehabilitation appliquees tout au long de leur duree de vie; (ii) etablir une strategie pour determiner l'indice d'etat de ces pipelines avant et apres toute mesure de rehabilitation mise en oeuvre au cours de leur duree de vie; et (iii) formuler le modele d'optimisation et appliquer l'algorithme genetique NSGA-II (<< non-dominated sorting algorithm II >>) afin de determiner les plans d'entretien optimaux de ces pipelines. Le modele d'optimisation est utilise dans le cadre d'une etude de cas reelle pour demontrer son applicabilite. Mots-cles : oleoducs et gazoducs, optimisation, NSGA-II (<< non-dominated sorting algorithm II >>), cout du cycle de vie, indice d'etat., Introduction Pipelines are considered the safest and the most efficient way to transport oil and gas products (Kennedy 1993). However, their failure can cause significant social, environmental, and financial consequences. [...]

The 2013 report card of America's infrastructure has scored the condition of oil and gas pipelines as D+ which means that such pipelines are in a relatively poor condition. More than 10,000 failures have been recorded in the US. These failures have resulted in environmental, health and property damages. Therefore, there is a definite need to give more attention to the maintenance of oil and gas pipelines. This paper develops a comprehensive model for the maintenance planning of oil and gas pipelines. The model selects rehabilitation/repair alternatives for oil and gas pipelines based on their condition during their service life. These alternatives are then used to calculate the cash flow throughout the service life of these infrastructures. The model, which uses Monte Carlo simulation and fuzzy approach to address the uncertainties in the estimation of the maintenance operation costs and the economic parameters, calculates the Equivalent Uniform Annual Worth of the identified alternatives. The optimum maintenance programmes consist of the alternatives that have the lowest life cycle cost of oil and gas pipelines. The model is expected to support pipeline operators in the maintenance decision-making process of oil and gas pipelines. [ABSTRACT FROM PUBLISHER]

Even though they are safe and economical transportation means of gas and oil products around the world, pipelines can be subject to failure and degradation generating hazardous consequences and irreparable environmental damages. Therefore, gas and oil pipelines need to be effectively monitored and assessed for optimal and safe operation. Many models have been developed in the last decade to predict pipeline failures and conditions. However, most of these models used corrosion features as the sole factor to assess the condition of pipelines. Therefore, the objective of this paper was to develop a condition assessment model of oil and gas pipelines that considers several factors besides corrosion. The proposed model, which uses both analytic network process and Monte Carlo simulation, considers the uncertainty of the factors affecting pipeline condition and the interdependency relationships between them. The performance of the model was tested on an existing offshore gas pipeline in Qatar and was found to be satisfactory. The model will help pipeline operators to assess the condition of oil and gas pipelines and hence prioritise their inspections and rehabilitation requirements. [ABSTRACT FROM AUTHOR]