Hydrothermal degradation of polybenzimidazole coating

The usefulness of a room-temperature film-forming polybenzimidazole (PBI) resin as a high-temperature anti-corrosion coating for carbon steel in geothermal environments was evaluated. PBI displayed thermal stability at temperatures up to 600 °C. However, when its film was exposed to 300 °C brine, it underwent hydrolysis, which causes the opening and breakage of imidazole rings in the PBI structure, followed by the formation of two hydrolysate derivatives, biphenyl tetra-amine and benzodicarboxylic acid. This shortcoming lowered the film's maximum effectiveness in minimizing the rate of transportation through it of corrosive electrolytes in hydrothermal environments. As a result, the PBI coating film was hydrothermally degraded, and it delaminated from the underlying steel substrates after a 14-day exposure.