Maximize Flow Capacity on Corroded Liquid Pipelines: A Massive Defect Assessment Methodology Based Upon Hydraulic Simulations and ILI Results

Abstract

Many aging liquid pipeline systems face demands to increase viscosity and/or flow capacity requirements. This paper presents a methodology to assure old pipelines’ up-rating serviceability by means of an optimizing integrity evaluation procedure where metal loss defects, reported by smart pig inspection, are assessed based upon maximum pressure profiles. The referred methodology comprises the following steps: 1. simulate the most severe pressure profiles scenarios for both steady and transient states and define maximum construct pressure envelopes; 2. build up representative equations of the maximum pressures observed at each profile point to steady/transient conditions; 3. assess pipe defects population reported by recent smart pig inspection considering the maximum pressure and the appropriate failure model; 4. determine rehabilitation hydrostatic testing pressures required to validate the new operating conditions; 5. re-assess pipe defects population considering the hydrostatic testing pressures. To illustrate the methodology applications, three case studies are presented, all carried out on pipelines older than 30 years. In order to accomplish the increased required capacity, four additional pump facilities were design and erected. Over thirty thousand metal loss defects (from ILI reported population greater than one million) were effective assessed for hydrostatic testing and operating conditions — considering individual pressure calculation. Regarding operating conditions, repair scenarios were constructed considering rehabilitation for a time interval of 5 years (based on estimated corrosion growth). The hydraulic simulations and the metal loss defect assessment where performed using, respectively, Pipeline STONER Simulator 9.3 and PLANPIG 2.0 software’s. This methodology has been successfully applied by PETROBRAS TRANSPORTE S.A. on revamping of corroded pipelines: despite the cases’ corrosion damage severity and the lack of conservatism on hydrostatic testing modeling, no test break was observed at the two tested lines and the required repairs number was dramatically reduced as compared to the traditional “as good as new” rehabilitation approach.