Characterization of corrosive agents in polyurethane foams for thermal insulation of pipelines

Thermal insulated pipelines consists of a pipe, an optional anticorrosive coating, covered by rigid polyurethane (PU) foam and an outer casing made of high-density polyethylene (HDPE). In this paper, a methodology to investigate corrosion under thermal insulation and the compatibility between the polyurethane foams and anticorrosive coatings was developed. It consists of chemical, electrochemical and mass loss tests in aqueous extracts of the foams. The aqueous extracts were prepared according to an adaptation of ASTM C871 standard, taking into account the temperature range commonly employed in pipes operations of heavy petroleum derivatives. The chemical analysis of the extracts included pH, conductivity, phosphate, chloride and fluoride contents. Mass loss, electrochemical impedance and linear polarization were accomplished in autoclave. The influence of temperature, flame retardant and blowing agent was considered on the generation of corrosive agents. It was verified that the content of chloride in the foams is a very important parameter that must be controlled. Still in this paper, the compatibility of polyurethane foams with anticorrosive coatings is preliminary evaluated. The results show that investments on a proper coating selection are essential to guarantee good performance.