Effect of Corrosion Inhibitor Used in Surface Treatment on the Anticorrosive Performance of an Epoxy Paint System

Jorge Felipe Ramos Pontes,Marcos Martins De Sá,Alberto Pires Ordine,Elber Vidigal Bendinelli,Cristina Da Costa Amorim

doi:10.4236/msa.2016.710049

Abstract

The mechanism of corrosion is mainly sustained by an electrochemical process, in which anodic and cathodic reactions take place, keeping their kinetics alive by electrons and ions fluxes. Several specific conditions can accelerate corrosion processes. When studying anticorrosive coatings, one of them is the contamination of metallic surface by soluble salts prior to coating, leading to premature failure of the paint system due to corrosion between the metallic surface and the coating. So the surface preparation step prior to coating is a procedure of great importance to the coating anticorrosive performance. The aim of this step is to clean the surface by removing visible and non-visible contaminants. Usually, wet abrasive blasting methods are the most efficient ones to achieve the latter objective, because they may clean the surface, create a surface roughness and also remove the non-visible contaminants, as they use water as a media. On the other hand, evaporation of water after blasting may create flash rust and to avoid this, it is common to use corrosion inhibitors in the water of wet blasting methods. In this paper, the use of sodium tetraborate (borax) as a corrosion inhibitor in wet abrasive blasting is discussed. Electrochemical measurements and mass loss tests show that a borax content of 1% in a saline solution has the best inhibitory action over carbon steel and zinc surfaces, allowing postponing for the painting step some time. However, residual borax left on the surface generated blistering and corrosion under coating, during accelerated corrosion test in a humidity condensation chamber. Electrochemical impedance spectroscopy confirmed that borax accelerated the permeation of water through the coating, downgrading the anticorrosive performance of the paint system.

Highlights

The electrochemical mechanism of corrosion is the main one to explain most of the corrosion processes
Concerning surface preparation methods, wet abrasive blasting is already used in the maintenance of buried feet of the Brazilian transmission line towers [4] and is a promising option to be applied in the maintenance of galvanized steel structures from the above ground part of the transmission line towers
When borax concentration was equal to 1%, the reduction of the corrosion rate was considerable and of approximately 45% compared with 3.5% NaCl solution without inhibitor

Summary

Introduction

The electrochemical mechanism of corrosion is the main one to explain most of the corrosion processes. It is known that the performance of a paint system depends on the degree of surface cleaning prior to coating [2]. A good cleaning process able to remove visible and non-visible contaminants, generating an adequate roughness profile, prior to coating, is the key to success of the anticorrosive performance of any paint system [3]. Concerning surface preparation methods, wet abrasive blasting is already used in the maintenance of buried feet of the Brazilian transmission line towers [4] and is a promising option to be applied in the maintenance of galvanized steel structures from the above ground part of the transmission line towers. The wet abrasive blasting gives the benefit of removing non-visible contaminants, such as soluble salts, known to damage the anticorrosive performance of paint systems if left in the metallic surface prior to coating [3]. Wet blasting methods may cause flash rust [5]-[7]

Methods

Results

Conclusion