The Pipeline Research Council International (PRCI) has published a study on mitigating soil-side corrosion on the bottom plates of aboveground petroleum storage tanks. Corrosion management is a major maintenance focus for operators of these structures.
The research project, Effectiveness of Vapor Corrosion Inhibitors (VCIs) for Corrosion Control on Aboveground Storage Tank Foundations, set out to evaluate three key questions: 1) are VCIs effective in mitigating corrosion to a level comparable to a working cathodic protection (CP) system for tank bottoms, 2) what is the best way to apply and monitor efficacy of VCIs, and, 3) are VCIs compatible with CP?
The results indicate that when applied at vendor-recommended dosage levels, VCI’s can reduce pitting corrosion and have a positive effect on overall surface corrosion. The rigorous data analysis concluded VCI’s are clearly compatible with current CP practice, and that additional field work can optimise the integration of VCI application and CP system design & operation. The three key questions each led to promising results and better understanding of the effectiveness of current practice, such as verifying the use of electrical resistance probes to monitor tank bottom corrosion.
Overall, the project establishes VCI technology improves tank bottom plate corrosion control but does not yet attain the rates specified in NACE SP0193 and SP0169 for demonstrating adequate cathodic protection. Additional work is being proposed that would further define VCI operating and monitoring parameters and lead to a suitable CP criterion. The enhanced capability to mitigate soil-side corrosion carries substantial value to operators from reduced risk of leaks, tank life extension and overall improved asset integrity.
Project Team Lead and Corrosion Technical Committee Chair Len Krissa of Enbridge noted that, “the encouraging results from this research will build confidence for using VCI’s as a supplementary or alternative corrosion control technique, particularly when CP systems have become depleted or inadequate under in-service tank conditions. The research in also providing foundational information and supporting the efforts of the NACE TG543 committee, which is developing a standard practice for External Corrosion Control of On-grade Carbon Steel Storage Tank Bottoms.”
30th July 2018