ABSTRACT

The corrosion and fouling of steel surfaces are major problems affecting the infrastructure of most industries, especially the oil and gas industries. The application of barrier coatings is one of the most widely used methods for mitigating these metal-loss causing problems. In particular, multifunctional hybrid sol-gel coatings are a very promising alternative to the currently used commercial toxic anticorrosion/antifouling coatings. This study describes the functionalization of a hybrid sol-gel polymeric coating with MOLY(1) or ZAPP(2) corrosion inhibitors and viable endospores of Bacillus licheniformis isolate (B6). The resulting functionalized coatings were applied to S36 grade mild steel substrate and their corrosion protection properties have been evaluated in the lab using electrochemical impedance spectroscopy (EIS) technique as well as scanning electron microscopy and visual observations. The field testing of the anticorrosion and antifouling properties of all coatings was also conducted by the in-situ exposure of the coated panels to seawater at a marine exposure site. Both lab and field testing results of all coated samples indicated that the biotic systems (containing bacterial spores) inhibited corrosion and fouling more than the abiotic (without bacterial spores) ones due to varying adhesion, barrier and antimicrobial properties of these coatings. It revealed also that abiotic and biotic coatings doped with Moly inhibitor have demonstrated excellent corrosion and fouling inhibition properties comparing to ZAPP coatings and the Corro(3) commercial coating.

INTRODUCTION

Steel alloys are widely used in the infrastructures of various industries especially the oil and gas industry. However, these alloys are suffered heavily from corrosion and fouling due to the high temperature and humidity of the environment of the Gulf region.1 One of the most widely reported corrosion mitigation approaches in literature is the use of barrier coatings; like protective hybrid sol-gel coatings.2,3 Hybrid silica materials exhibit a combination of desirable properties of both inorganic (thermal stability, hardness, durability) and polymeric (toughness and flexibility) components within a single network.4-7 A recent sol-gel modification has seen the incorporation of compatible bioactive systems as a unique application in sol-gel corrosion protection and the mechanism of interaction of some microorganisms on metal substrates has the potential for industrial exploitation. Appropriate choice of the precursor chemistry, reaction conditions, and protective bacteria may produce functionalized hybrid sol-gels with reliable aging stability, prolong shelf life and microbiologically-induced corrosion (MIC) inhibition properties.8-10 In the present work, a very hydrophobic organic-inorganic hybrid sol-gel coating has been functionalized with anticorrosive pigments acting in dual positions as pore/crack fillers as well as corrosion inhibitors in the bulk of the coating and their corrosion protection properties for S36 grade mild steel have been evaluated in 3.5 wt% NaCl saline solution. Coating synthesis and functionalization with anticorrosive pigments were followed by a further incorporation, within these protective coatings, of a thermophilic strain of Bacilli bacteria endospores. Both laboratory-based electrochemical impedance studies and field trials were conducted in this study to evaluate the anticorrosion and antifouling properties of these bioactive coatings.

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