The use of natural gas as a fuel has been an attractive alternative in both economic and environmental perspectives. Natural gas pipelines show usually low internal corrosion rates. Hydrogen sulfide, carbon dioxide, water and other contaminants are removed to specified limits during processing stage to assure quality and safe use of natural gas to customers. Nevertheless, the presence of contaminants dissolved in condensed water can result in internal corrosion processes (ICP), production losses and equipment damage. In order to assess ICP, the use of corrosion monitoring techniques has been extensively studied and improved. Electrical resistance probes and weight loss coupons have been successfully used, fitted in specific points of the pipelines where corrosion is mostly expected, to monitor corrosion progress. Corrosion rates are expected to be higher in bottom-of-the-line (BOL-six o'clock position) where condensed water flows by gravity. But depending on gas velocity different flow patterns can be encountered and top-of-the-line (TOL-twelve o'clock position) corrosion is also found. When gas velocity is high the flow pattern is usually annular. At very high velocities and low liquid contents, a mist flow can be achieved. The stratified is more common when gas velocities are lower. This work presents the first approach and results of internal corrosion monitoring in a specific Brazilian natural gas pipeline using electrical resistance probes placed at three selected TOL sites of a 357 km length, API 5LX 65 steel, 16" nominal diameter natural gas pipeline .
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