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51318-11067-The Performance Effect of Coating Rusty Steel with an Epoxy-Amine Coating

Compares the accelerated corrosion performance of an alkylated phenolic polyamine cured epoxy coating applied to abrasive blasted steel (NACE 1/SSPC-SP5) to the same application on substrates allowed to rust.

Product Number: 51318-11067-SG
Author: Mike O’Donoghue / Vijay Datta / Carl Reed
Publication Date: 2018
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Popular wisdom holds that abrasive blasted steel cleaned to a near-white metal finish (NACE 2/SSPC-SP10) or better provides the optimum performance for coatings applied to the substrate. This is certainly true for inorganic silicate coatings such as zinc silicates where the silicic acid from the binder will covalently bond with metallic iron. For organic coatings, however, in particular epoxy-amine coatings, the mechanism of bonding with metallic iron, other than van der Waals forces, is not known, if it exists at all. On the other hand, the mechanism of epoxy-amine coatings binding to iron oxide is well known, and consists of a strong Lewis acid-base interaction which may result in enhanced coating performance properties. This may indicate that applying an epoxy-amine coating over clean (i.e. without soluble salts) rusty steel could provide better corrosion mitigating performance than that achieved by using clean, white metal blasted steel.

This study compares the accelerated corrosion performance of an alkylated phenolic polyamine cured epoxy (epoxy-phenalkamine) coating applied to abrasive blasted steel prepared to a NACE 1/SSPC-SP5 standard cleanliness and to substrates that have been allowed to rust in a variety of conditions, including varying soluble salt compositions and density. Performance properties evaluated included adhesion loss, scribe creep and cathodic delamination away from the scribe on the epoxy-phenalkamine coating. The mechanism of improved anti-corrosion performance of an epoxy-amine coating over rusty steel is examined in detail.

Key words: rusty steel, epoxy-phenalkamine, bonding mechanism, Lewis acid-base interactions, soluble salt

Popular wisdom holds that abrasive blasted steel cleaned to a near-white metal finish (NACE 2/SSPC-SP10) or better provides the optimum performance for coatings applied to the substrate. This is certainly true for inorganic silicate coatings such as zinc silicates where the silicic acid from the binder will covalently bond with metallic iron. For organic coatings, however, in particular epoxy-amine coatings, the mechanism of bonding with metallic iron, other than van der Waals forces, is not known, if it exists at all. On the other hand, the mechanism of epoxy-amine coatings binding to iron oxide is well known, and consists of a strong Lewis acid-base interaction which may result in enhanced coating performance properties. This may indicate that applying an epoxy-amine coating over clean (i.e. without soluble salts) rusty steel could provide better corrosion mitigating performance than that achieved by using clean, white metal blasted steel.

This study compares the accelerated corrosion performance of an alkylated phenolic polyamine cured epoxy (epoxy-phenalkamine) coating applied to abrasive blasted steel prepared to a NACE 1/SSPC-SP5 standard cleanliness and to substrates that have been allowed to rust in a variety of conditions, including varying soluble salt compositions and density. Performance properties evaluated included adhesion loss, scribe creep and cathodic delamination away from the scribe on the epoxy-phenalkamine coating. The mechanism of improved anti-corrosion performance of an epoxy-amine coating over rusty steel is examined in detail.

Key words: rusty steel, epoxy-phenalkamine, bonding mechanism, Lewis acid-base interactions, soluble salt

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