Mitigating Measures Against an Internally Corroded High Pressure Pipeline Affected by Microbiologically Induced Corrosion and Settling of Free Water - A Case Study

Internal corrosion in a 14 inch (35 cm) high pressure pipeline, used for transporting heavy oil with up to 30% water was detected, after an in-line inspection with magnetic flux technology. The internal corrosion is affected by settling of water in the pipe in combination with the presence of high concentrations (10⁸ colonies/mL) of sulfate reducing bacteria (SRB) in the transporting medium. Mitigating measures were taken by starting with a chemical treatment program consisting of biocide and corrosion inhibitor injection on fluid entering the pipeline. Internal corrosion monitoring was intensified with weekly corrosion probes measurements in addition to corrosion coupon measurements every 6 months. SRB counts were obtained on a regular basis to monitor the effectiveness of the biocide treatment. Internal corrosion rate readings showed a decreasing trend from medium/high (1-10 mpy), to low (<1 mpy (0.0254 mm/y)) and the SRB count dropped significantly to 10³ colonies/mL. In a pipeline environment with high water cut, low velocity and high SRB count (> 10⁶ colonies/mL), internal corrosion can be mitigated by using a combined biocide and corrosion inhibitor chemical treatment and regular pigging of the line. In-line inspection is needed to determine actual pipeline status.