Anti-Corrosive Paint for Steel Structure

Author: Ir. Dr. Justin LAI Woon Fatt | 29 October, 2022

INTRODUCTION

Steel is an irreplaceable material in the construction industry due to its excellent combination of strength and workability. It is used for beams, columns, roof trusses, gutters, etc. Besides buildings and infrastructures, steel is also used extensively in the manufacture of machines, weapons, and vehicles. However, steel is prone to corrosion if left unprotected, especially in chloride-laden environments.

Anti-corrosive paint is generally defined as a paint formulated with a corrosive-resistant pigment, and a chemical and moisture-resistant binder that can protect a steel component from corrosion. This type of paint forms a physical insulating barrier layer to prevent direct contact between the steel and its environment outside, thus preventing the occurrence and progression of corrosion.

COMPOSITION OF ANTI-CORROSIVE PAINT

Anti-corrosive paint consists of three major components:

1. Corrosion resistant pigments
   Some examples of corrosion-resistant pigments are zinc dust, lead chromate, zinc chromate, and red lead. Zinc dust is a zinc material in the form of a powder that imparts corrosion inhibiting properties. It is widely used to manufacture anti-corrosive paint. Due to the low solubility of zinc dust in the water, it can be applied on sea vessels and ships, offshore rigs, containers, and bridges. Red lead or lead (II, IV) Oxide is well known for its high adhesion and coverage, and long-term inhibiting action in combating corrosion. However, it has been phased out of use in many countries due to its toxic nature [1].
2. Binder
   Binders are the film-forming components of paint that determine its physical and chemical properties. Binders used in anti-corrosive paint are classified into two types: thermoset and thermoplastic. The difference between these two classes is that thermoset coating differs chemically from paint in a can, and it is not affected by solvents once cured. In thermoplastic coating, the dry film and wet paint differ only in solvent and are chemically identical [2]. Linseed oil, which is derived from flax seed, is frequently used as a binder in anti-corrosive paint.
3. Solvent
   The solvent acts as a binder dissolver in anti-corrosive paint. It helps to reduce the viscosity of the paint to a level that is suitable for the various methods of application. For instance, brush, roller, conventional spray, airless spray, etc. After application, the solvent evaporates and plays no further part in the final paint film [3]. An example of solvent for anti-corrosive paint is thinner.

TYPES OF ANTI-CORROSIVE PAINT

Some of the anti-corrosive paints are [4]:

1. Fluoropolymer paint
   Fluoropolymer is a combination of high-performance resins and fluoropolymer lubricants. It can be used in environments with very high/ low temperatures. Besides having high resistance to corrosion and chemical, it has some degree of electrical resistance as well. This combination of traits makes it suitable for various types of fasteners.
2. Epoxy paint
   Epoxy is a popular industrial coating made from epoxide resin and a polyamine hardener (catalyst). Some examples of epoxy paints include coal tar epoxy, amine epoxy, and polyamide epoxy. Epoxy paint is highly durable and corrosion resistant. As a result, it can be used to protect water transmission pipelines, steel pipes, and fittings in the oil and gas industry, and concrete reinforcing rebar in the construction industry from corrosion.
3. Inorganic zinc paint
   Inorganic zinc paint is a type of paint with large amounts of zinc metallic dust mixed with a binder. It is effective against weathering and salt attacks, making it ideal for steel protection, especially in marine atmospheric environments. Inorganic zinc is compatible with a wide assortment of topcoats such as epoxies, phenolics, and silicones, thus further enhancing its corrosion protection.