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51318-10992-AST Corrosion Control and Monitoring with VCI Applications

Conclusions: (1) vapor corrosion inhibitors (VCIs) can control corrosion on steel materials in contact with AST tank bottom backfill. (2) Efficiency of VCIs is affected by salt contamination or impurities in the backfill. (3) Corrosion of small areas of steel are not indicative of corrosion AST tank bottoms. (4) A path forward.

Product Number: 51318-10992-SG
Author: James A. Ellor P.E. / Elisabeth Kuespert
Publication Date: 2018
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Corrosion control of above ground storage tank (AST) tank bottoms remains critical over the life of a tank. A primary form of corrosion control has been the application of cathodic protection (CP). Over time, these systems can fail or reach the end of their design lives. In recent years, vapor corrosion inhibitors (VCI) have been recommended to ensure continued protection of tank bottoms. VCIs have been added as an aqueous slurry mixture under tank bottoms as part of a retrofit of corrosion control systems.

Regulations require monitoring of the efficacy of the corrosion control method. For VCI applications under ASTs, the most common monitoring form has been the use of electrical resistance (ER) probes. ER probes indicate local corrosion action via self‐corrosion that decreases the cross‐sectional area of exposed metal. In AST applications, concerns have been raised as to the long‐term accuracy and relevance of ER probes. The present research indicates that VCIs can indeed control corrosion on steel materials in contact with AST tank bottom backfill materials; however, the efficiency of the VCIs is affected by the presence of salt contamination or impurities (e.g., clay) in the backfill. The research also showed that corrosion of small areas of steel, be it an ER probe or a steel coupon, buried in the sand backfill are not indicative of the range of corrosion that may occur on an AST tank bottom. The research suggests a path forward.

Corrosion control of above ground storage tank (AST) tank bottoms remains critical over the life of a tank. A primary form of corrosion control has been the application of cathodic protection (CP). Over time, these systems can fail or reach the end of their design lives. In recent years, vapor corrosion inhibitors (VCI) have been recommended to ensure continued protection of tank bottoms. VCIs have been added as an aqueous slurry mixture under tank bottoms as part of a retrofit of corrosion control systems.

Regulations require monitoring of the efficacy of the corrosion control method. For VCI applications under ASTs, the most common monitoring form has been the use of electrical resistance (ER) probes. ER probes indicate local corrosion action via self‐corrosion that decreases the cross‐sectional area of exposed metal. In AST applications, concerns have been raised as to the long‐term accuracy and relevance of ER probes. The present research indicates that VCIs can indeed control corrosion on steel materials in contact with AST tank bottom backfill materials; however, the efficiency of the VCIs is affected by the presence of salt contamination or impurities (e.g., clay) in the backfill. The research also showed that corrosion of small areas of steel, be it an ER probe or a steel coupon, buried in the sand backfill are not indicative of the range of corrosion that may occur on an AST tank bottom. The research suggests a path forward.

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