Enameling coating of pipes: Thermal proprieties and corrosion tests

Enamel coating on pipelines can be done in several ways such as the wet process, plasma spray, and electrostatic process. Wet process requires little capital expenses and provides an acceptable finish for industrial applications particularly when the part to be coated is small. Electrostatic process of enamel powder is most promising to coating large pipelines in field conditions. The enamel coating applied by the electrostatic process is very consistent and smooth since each particle is glass only. However, the powder is very fragile until fired and the charge retention is lowered in high humidity conditions. Coupons cut from a full-size steel pipe of low carbon steel using high pressure water jet were coated and enameled by Roesch Inc. and provided to Missouri University of Science and Technology for evaluation. The wet process of enamel slurry was compared with the electrostatic process to demonstrate their performances measured by coating uniformity, surface roughness, and corrosion resistance.