Flexible plastic liners are sometimes installed into new and existing oil and gas pipelines toprevent corrosion of the pipe wall. A practical difficulty of this method is that the plasticliners are permeable to gases, which can collect and form an annular space between theliner and the pipe. If the operating pressure in the pipe decreases then the collected gas cancause the liner to collapse and block the pipe.One method for overcoming this problem is to insert vents at intervals along the liner toallow the gas to escape into the pipe during depressurisation. However, there is concernthat this arrangement might lead to excessive corrosion beneath the vent where the pipewall is exposed. The rate of corrosion is expected to be controlled by the vent size butthis principle needs to be confirmed by experiment. The work described in this thesis isaimed at investigating this corrosion by experiment for a range of conditions typical ofoil and gas production.A novel crevice corrosion cell was designed, consisting of an X100 carbon steel plate and asheet of transparent Perspex, separated by a thin gasket. A small hole in the Perspexsimulated a liner vent and allowed carbon dioxide to reach the steel surface. Tests werecarried out in 3.5% NaCl solutions saturated with carbon dioxide at 1 bar partial pressure.Corrosion rates along the length of the annular space were measured using the LinearPolarisation Resistance (LPR) technique on pairs of insulated X100 electrodes set into theplate. The corrosion rates within the annular space have been shown to be small comparedto those in the bulk solution and to diminish rapidly with distance from the vent.Mathematical modelling, based on the transport of carbon dioxide, is described to explainthese findings and support the experimental work. The effectiveness of the LinerVentTM,installed over the vent, in a turbulence pipeline was demonstrated. The benefit of applyingcathodic protection within the annular space was also demonstrated. The results arediscussed in terms of the fundamental corrosion principles and their practical implications
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