• Sauvant-Moynot, Valérie
• Kittel, Jean
• Lefebvre, Xavier

Abstract

Three-layer polyolefin coatings are being used classically for external pipeline protection in the oil and gas industries over years although cathodic protection is also applied. They are supposed to provide efficient and sustainable corrosion protection to the pipe steel over 20 years service or more, including exposition to humidity and temperature (cycling conditions). However, the permeability of polyolefin topcoat to water is not negligible and thus does not prevent water ingress into sub-layers after a few months service. Then soaked water in the vicinity to the steel pipe conveying hot effluents possibly induces hydrolysis of the epoxy primer layer and interfacial bonds to metal. This could raise questions over the long term corrosion control. Therefore, the inspection of the water ingress and the investigation of the long-term barrier properties of primer and adhesives layers when exposed to water are mandatory. This paper examines the use of Electrochemical Impedance Spectroscopy (EIS) to monitor durability and anticorrosion properties of three-layer coatings while exposed to water at 60 °C (maximum service temperature). The objective was to investigate the water ingress within a bilayer coating with respect to sublayer thickness. EIS was used to characterise the water uptake but also the long term barrier properties of coatings on industrial tubes. In complement, gravimetry measurements were also performed during ageing on FBE primer coated panels cut from industrially coated tubes to determine the water uptake kinetics using classical destructive techniques. Degradation mechanisms of 3LPO and potentiality of EIS technique are discussed in the paper.

Topics

• corrosion
• steel
• permeability
• electrochemical-induced impedance spectroscopy
• aging
• durability
• interfacial