Materials Performance

JUN 2019

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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46 JUNE 2019 W W W.MATERIALSPERFORMANCE.COM CM CORROSION MANAGEMENT I Determination of the likelihood of internal corrosion in unpiggable dry gas transmission pipelines is a signifi- cant problem. Dry gas internal corro- sion direct assessment (DG-ICDA) facilitates accurate determination of the most probable locations for inter- nal corrosion to occur. This article describes a case study where internal corrosion was identified by the appli- cation of the DG-ICDA process. Mul- tiphase flow modeling was performed for the full range of operating condi- tions. Utilizing the results of flow mod- eling, coupled with a detailed under- standing of the current and historical operations of the pipeline system, sites for direct examination were suc- cessfully identified and excavated. Int er n al c or ro si on , i f n ot m an a ged ef fectively, can threaten the safety and reliability of steel pipelines, and loss of reliability could cripple the energy-supply- ing pipeline infrastructure. Although gas entering transmission pipelines passes through gas dehydration treatment facili- ties, located upstream of the pipeline, which removes water necessary for corro- sion, there have been reports of internal corrosion due to water holdup in pipelines carrying nominally dry natural gas. 1 One mechanism for water to enter an in-service pipeline are short system upsets that allow the carr yover of significant amounts of water. Since many pipelines are not pigga- ble, inline inspection tools cannot be used to assess the internal condition of the pipeline. For unpiggable pipelines, f low modeling can be used to predict locations where water can accumulate when it enters the pipeline and cause internal corrosion. A process to identify areas of water accumulation in a normally dry gas trans- mission pipeline using an analytical f low modeling technique, as part of the dry gas internal corrosion direct assessment (DG- ICDA), 2 is presented here. The various steps in DG-ICDA, details of flow modeling, and the basis of predicting the locations of water holdup are discussed. Case Study and Assessment Procedure Internal corrosion was suspected due to possible water intrusion of an unpiggable, 0.91-m (36-in) diameter dry gas transmis- sion pipeline installed in 1978 within a high- consequence area (HCA) in Franklin, Loui- siana, USA. DG-ICDA was performed on a 2.1-km (1.3-mi) long segment of the 0.91-m diameter pipeline. The assessment was per- formed in compliance with NACE SP0206, 2 "Internal Corrosion Direct Assessment Methodology for Pipelines Carrying Nor- mally Dry Natural Gas." The four steps of the DG-ICDA process are described as follows. Step 1—Preassessment Preassessment involves gathering infor- mation related to the physical characteris- tics as well as the current and historical Flow Modeling to Predict Internal Corrosion in Gas Transmission Pipelines Aj A y Ar A kere, M A rl A ne r odriguez, A nd l A rry r A nkin, Corrpro Companies, Inc., Houston, Texas, USA

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