Pipeline protection and extension of internal coating life

Abstract

Coal tar products have been extensively used to coat the internal surface of steel pipelines and penstocks in hydro-electric power systems, to provide corrosion protection and favourable hydraulic performance characteristics. These coatings have demonstrated excellent corrosion performance in most situations. In some applications, significant weaknesses in the linings have been manifest when these coatings have been exposed to high temperatures due to out of service conditions during construction or later in the service life. Embrittlement of the coating caused by loss of volatile components causes failure of the coating when later exposed to temperature variation. Experiments on sections of pipe have shown the crown of the pipe to reach temperatures of 30°C above ambient in direct exposure to sunlight on typical Tasmanian summer days (20-30°C ambient temperature). Service plans for the pipelines need to take this into account. In addition, externally applied heat reflective coatings have been shown to significantly reduce the maximum crown temperature.