Assessment of Vented Flexible Liners for Corrosion Protection of Pipelines

A practical difficulty of plastic liners to control internal corrosion is gas permeating and forming an annular space between the liner and pipe.  A decrease in operating pressure can cause the liner to collapse, blocking the pipe.  One solution is to insert vents along the liner, allowing gas to escape into the pipe during depressurisation but there is concern that this would lead to excessive corrosion where the pipe wall is exposed.  This paper investigates the extent of this corrosion and effectiveness of methods of control.
 A novel crevice corrosion cell was designed, comprising plates of X100 carbon steel and Perspex, separated by a thin gasket.  A small hole in the Perspex simulated a liner vent.  Tests were carried out in brines saturated with carbon dioxide at 1 bar pressure.  Corrosion rates in the crevice were measured using the Linear Polarisation Resistance method on pairs of X100 electrodes, set into the plate.
Corrosion rates were shown to diminish rapidly with distance from the vent, particularly when a porous plug was used to restrict mass transport of carbon dioxide. Mathematical modelling was used to explain these findings and the benefits of applying cathodic protection within the crevice will be discussed.