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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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was carried out by jacking up the tank. The rebottomed tanks were replaced with bitumen foundations as the corrosion pro- tection barrier. Consequent to the failures, a detailed CP survey was carried out for the storage tanks in 2016. The previous CP survey was done in 2008. Both surveys showed very low "instant off " potentials for all the tanks, with an average of –450 mV vs. a copper/copper sulfate (Cu/CuSO 4 ) electrode (CSE). This highlighted that the CP system had failed in its design purpose and there was inadequate protection to the AST bottom plates. 3 As it was not practical to inspect all the tanks, an out-of-ser vice schedule (O OS) was agreed upon by all stakeholders of the plant, with the intention of implementing an online corrosion protection strateg y to extend the service life of the tanks and meet the OOS. The refinery evaluated all possible options, with its feasibility based on a cost/time and success factor. As the ICCP system is placed between the tank bottom and a high-density polyethylene (HDPE) liner, there is no possibility of pro- viding any additional external anodes due to the shielding effect of the plastic sheet. Hence, as there is no direct access to the CP system, any rectification would mean to jack up the tank and have access to the soil. Secondly, it would require a complete redesign of the CP system with hardware changes. In spite of all this, the bottom plate replacement would be required and th ere i s uncer tainty on achie ving pro- tection potentials. Therefore, the refin- er y identified other possible short-term options that would extend the tank life to meet the O OS. The immediate solution adopted was to inject corrosion inhibitors without any disruption to the operations and seal the chime area of the tanks to avoid any further air or moisture ingress. Instantly, th e numb er of tank s was identified based on a consequence-based risk ranking for the implementation of online injection of the VCI and installation of ER probes to evaluate the effectiveness of this technology. The main objective of the project was to extend the service life of the tanks floors, eliminate unplanned shut- downs or emergency incidents, and avoid VAPOR PHASE CORROSION INHIBITORS FIGURE 3 Three-period rolling average corrosion rate (mpy) for sour water tank. FIGURE 4 Typical ER probe installation with grout removed above probe location. TABLE 1. CORROSION RATES AND CALCULATED INHIBITOR EFFECTIVENESS Tank Probe No. Pre-Injection Corrosion Rate (mpy) Post Injection Corrosion Rate (mpy) % Efficiency TK-02 2731 1.09 0.25 77 2732 1.17 0.25 79 2733 1.96 0.27 86 TK-03 2829 1.67 0.28 83 2830 1.60 0.36 78 2831 3.44 0.65 81 2832 2.21 0.28 87 2834 10.29 0.74 93 2835 2.82 0.28 90 2836 1.46 0.28 81 6 JUNE 2018 MATERIALS PERFORMANCE CORTEC SUPPLEMENT TO MP

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