The use of polymer liners to prevent internal corrosion in pipelines transporting hydrocarbon products is limited to date, however the application is of interest to the pipeline industry for various reasons. The cost effectiveness of polymer lined pipelines when compared to corrosion resistant alloys (CRA), in addition to a simpler pipeline fabrication process and more immediate material availability, should make polymer lining an automatic choice. But whilst some pipelines transporting hydrocarbons have been polymer lined, the technology is not yet base case in all instances.
The phenomenon of liner collapse dominates industry thinking about polymer lining in hydrocarbon service. The risk of liner collapse has been fully mitigated in water injection and potential failures due to this condition are categorised as low risk. The condition is associated with the permeation of small particles through the liner material whilst under pressure. Gas is considered to accumulate in the annulus whilst the pipeline is operating at pressure. This pressure is eventually in equilibrium on both sides of the liner during normal service. However, when the pipeline operating pressure is reduced, the gas in the annulus expands and may cause the liner to collapse. There have been several JIP’s set up to examine this condition and to seek a way of mitigating the risks to the point where a polymer lined pipeline can be considered as reliable and low risk as one constructed of CRA. To achieve this status, a way of managing the annular gas has to be proven.
Swagelining Limited has proprietary technology aimed at meeting this challenge. The LinerVent™ is designed to balance the pressure on both sides of the liner by allowing any gas accumulated in the annulus to flow through the LinerVent™ back into the main bore of the pipeline. This concept was established and tested successfully in a joint industry 26 week multiphase trial confirming no elevated levels of corrosion or liner collapse. The simplicity of the concept lies in the fact that the pipeline pressure envelope remains intact with no requirement to evacuate gas from the pipeline system. The LinerVent™ effectively balances pressures on either side of the liner inside the pipeline.
Whilst further testing is required to progress the LinerVent™, high performance polymer materials are available that are proven in sour service within flexible pipeline systems. The concept of using these materials as a liner is accepted within the industry. Testing with Swagelining™ technology aimed at proving material properties within the process have shown promising results and more testing is underway - see Swagelining™ Research and Development.
More details on the report The use of Engineering Polymers for Internal Corrosion Protection of Hydrocarbon Pipelines are available by clicking this link.