Mechanism for debonding of internal pipeline lining in de-aerated environments

For water injection pipelines used in the offshore industry and for steel and cast iron water supply pipelines in the water supply industry internal linings of polymer materials or cement have been and are being used in an attempt to reduce the internal corrosion of the pipeline. One common, medium term failure mechanism is the debonding of the liner from the steel or cast iron. The life of liners often has been found to be lower than expected where the liner was applied after earlier service and some corrosion of the bare pipeline, despite best efforts in surface cleaning and preparation prior to application of the liner. Some reasons based on experience have been given for the debonding process. The present paper proposes a mechanism for the initiation of the debonding process based on corrosion theory for the special case of very low oxygen availability. It shows that even if the liner is in good condition without pinholes or other defects and still is providing a high degree of diffusion protection against aggressive species in the water debonding of the liner in a pipeline can still occur. In particular, the theoretical reasons are given to show that under certain conditions debonding can initiate without the build-up of substantial oxidation products under the liner.