CO2 Corrosion Resistance of Steel Cord Reinforced Thermoplastic Materials for Flexible Pipe Systems

Steel cord reinforced thermoplastic (SC-RTP) tape is a composite material consisting of parallel steel cords embedded in a thermoplastic matrix.  SC-RTP tape was developed for reinforcing flexible thermoplastic pipes and makes them resistant to high pressures. SC-RTP tape combines the high tensile strength of steel cords with corrosion resistance and easy processability.

High pressure pipes can be obtained by wrapping them with layers of SC-RTP tape. Pipe liner and the thermoplastic tape material protect the steel cord from direct contact with corrosives.  Corrosion of the steel cord can occur when molecules permeate through the polymer. Steel cords inside the polymer tape are further protected from corrosion by a sacrificial zinc coating. This study focuses on corrosion processes caused by CO₂ and water. SC-RTP tape samples were exposed to a humid CO₂ environment for up to 3 years. The corrosion rate was determined by measuring the decrease of metallic (non-oxidized) zinc in the sacrificial coating. The small corrosion rate can be attributed to several factors: low permeation rate through the polymer matrix, limited space between steel cord filaments, and the formation of a passive zinc carbonate layer. This passivation layer was characterized with x-ray photoelectron spectroscopy and scanning electron microscopy.