PR-015-153602-R01 Vapor Corrosion Inhibitors Effectiveness for Tank Bottom Plate Corrosion Control

Soil side corrosion of the above ground storage tanks bottoms is a major challenge for the midstream operators owning tanks farms. In North America subcontinent, a large fraction of tanks are installed with an active cathodic protection (CP) system to protect the tank bottom from corrosion. However, CP systems could fail, and sometime even with the CP system, corrosion can occur. In addition, several tanks without CP system could experience elevated corrosion including pitting corrosion. Vapor corrosion inhibitors (VCIs) are being promoted as alternative corrosion control measures in addition to the CP. This study was conducted to determine whether the VCIs are effective in mitigating corrosion to a level comparable to a working CP for tank bottoms, what is the best way to monitor efficacy of VCIs, and whether the VCIs compatible with CP or not. Extensive amount of laboratory scale and limited field testing was conducted. Both laboratory and field data were rigorously analyzed. It was found that the VCIs are effective in mitigating corrosion when vendor specific recommended dosages are used, and the electrical-resistance based corrosion rate monitoring technique does show the effect of VCIs. Regarding VCI and CP compatibility, VCIs indirectly affect the CP as exposure of tank bottom steel to VCIs change its native potential which in turn changes the CP current demand. Overall, VCIs were found to be a viable alternative corrosion control measure.