Corrosion and Flame Retardant Polymer Coatings for Oilfield Applications
Authors: Dsouza Nandika Anne , Seifollah Nasr , Ganpule Parag 
Published: May 2011

Ethylene vinyl acetate copolymer (EVA) was mixed with ceramic nanoplatelets to make a nanocomposite material. A brabender was used to prepare these nanocomposite materials. These nanocomposite materials were then used as a coating on steel coupons for corrosion resistance testing. The EVA nanocomposites were coated on the steel surface using a compression molding machine at 150 °C. The steel coupons were first polished using a sand paper. The EVA nanocomposites were dried in the oven for a day before being used. The thickness of the coating is around 0.5 to 1 mm.

Electrochemical potentiodynamic test was used to find out the polarization resistance and thus the corrosion rate of these coated steel samples. 0.1N H2SO4 was used as the corrosive fluid in the potentiostatic cell. Mechanical testing such as tensile test and Hardness test were performed to find out the mechanical properties of the nanocomposite materials Flammability of the samples was done using the flammability UL-94 system to determine the burning characteristics of the polymer material. The results show a substantial increase in mechanical properties together with corrosion and flame resistance.

Introduction

Corrosion has been one of the most studied industrial problems for many years. (Fontana, 1986; Asmatulu, 2007) It mostly occurs on metals and alloys as well as polymers, woods and ceramics due to materials interaction with seawater, humid environment, acid rains, emissions, pollutants, chemical by-products and industrial waste, as well as sunlight (combined UV radiation and heat). Interfaces at grain boundaries and interfacial cracks, and between two dissimilar materials are vulnerable sides for corrosion attack. Impurities, surface morphology and lattice imperfection in material structures can also enhance the corrosion rate.

Corrosion usually begins at the surface and decreases the lifetime of materials used regularly in aircraft and spacecraft, land and sea transportation vehicles, infrastructure and electronic and computer devices. As a result of the corrosion on material surfaces, these materials can lose their mechanical, physical and chemical properties as well as their appearances. Because of the corrosion formation on materials, it is estimated that more than 5% of an industrialized nation's gross national product (GNP) is spent for corrosion prevention, replacement of corroded parts, maintenance and environmental protections. This corresponds to nearly a $280 billion cost to the U.S. economy per year in 2001.

Protective coatings are probably the most widely accepted approach for corrosion control. Therefore, a thin film coating is frequently utilized for the purpose of metal surface protection against corrosion attack. Representative organic thin film coating materials, such as polyurethane, polyamide, polyester, PVC, acrylics, alkyds and epoxies play a crucial role as a protective layer by delaying the transition of corrosive species, such as chlorine and hydroxyl ions, water, oxygen, pollutants and pigments, which have affinity to react with the material surface. In other words, the protective coating impedes the interactions between anodic and cathodic sites at the coating metal interface partly by limiting penetration of electrolytes through the metal surface. Otherwise, materials under the coating films can be dissolved as oxide or other compounds in aqueous media due to the chemical or electrochemical reactions. It has been shown that corrosion mitigation effectiveness is also related to the high polarization and coating resistances, low capacitance can be achieved by these organic films on the surface. Due to the environmental effects, coating materials also undergo physical, chemical and physicochemical deterioration. Such degradation of polymeric materials can develop in the form of swelling by water absorption, dissolution, cross-linking, oxidation and color changes due to the heat, radiation, acid rain, oxidative chemistry and other factors. The combined effects of such degradation can be also seen on the organic coatings.