Materials Performance

DEC 2018

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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24 DECEMBER 2018 W W W.MATERIALSPERFORMANCE.COM CATHODIC & ANODIC PROTECTION T Volatile corrosion inhibitors (VCIs) and cathodic protection (CP) are applied jointly to effectively mitigate corrosion in both the electrolytic and vapor- phase exposures on the soil-side of tank bottoms. The electrochemical characteristics of available VCI prod- ucts vary widely, and all are not mutu- ally compatible with CP when applied jointly. Three VCI products were investigated. One enhanced cathodic polarization while substantially reduc- ing CP current requirement, another caused anodic polarization with little effect on CP current requirement, and a third had no polarization effects while increasing the CP current require- ment—demonstrating the need to con€rm VCI compatibility before joint application with CP. There is a growing trend to supplement cathodic protection (CP) with volatile cor- rosion inhi bitors ( VC Is) b en eath tank f loors to specifically address vapor-phase corrosion and enhance overall protection of tank bottom plates against soil-side cor- rosion. The objective of this experimental work is to expand on the study done by Pynn and Abed 1 and investigate mutual compatibility and interactions of three dif- ferent VCIs and CP when applied jointly on an oxygen concentration corrosion macro- cell setup. Effect of Volatile Corrosion Inhibitors on Cathodic Protection KHALIL M. ABED, Cortec Middle-East, Dubai, United Arab Emirates CALVIN R. PYNN, Prydwen International, Inc., Collingwood, Ontario, Canada Effective control of soil-side corrosion on aboveground storage tank bottoms dur- ing the complete life cycle of the tank is critical, both operationally and environ- mentally. Different foundation construc- tion methods and corrosion protection techniques have been implemented over the last several decades in attempts to con- trol soil-side corrosion, including the use of asphalt pad , bituminous sand , CP, and coatings. Despite these measures, field experience and inspection activities indi- cate that soil-side tank floor corrosion per- sists in some cases. 2-3 Underside sur faces of tank bottom plates are typically exposed to a combina- tion of electrolytic and vapor-phase corro- sive environments. While CP can be an effective corrosion mitigation technique w h ere th ere i s an electroly tic contact between the tank bottom surface and the underlying soil, it is ineffective in a vapor- phase environment. Air gaps or where there is intermittent moisture in the soil contact- ing the tank bottom surface are typical examples of vapor -phase environments under a tank f loor. Published technical articles have discussed the practical limita- tions of the different protection methods, including CP systems, that are ineffective in providing protection in air gap areas or where cathodic current is shielded. 2,4 Th ere are se veral studies and f ield applications that confirmed and/or rec- ommended the use of VCIs as a potential solution for this chronic industrial prob-

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