Gas Transmission Networks and Protection
National Grid Gas Transmission currently have a number of tunnels on their network, approximately 5 to 6 segmental lined tunnels & 100’s pipe crossings in sleeve’s. These are mostly in locations where the NTS Feeder main needs to cross a road, river, railway or challenging geography. CP is provided by Impressed Current and Sacrificial Anode techniques. This works to protect the pipeline by allowing current to flow through the pipeline / to and from the ground bed to ensure that material is not lost in corrosion products.
However NGGT are looking for a method that fine tunes these existing techniques to make them suitable for a flooded tunnel environment.
There are known and managed CP issues on recent tunnel projects further pointing out the need to look at specialist marine type applications where there is a flooded tunnel.
Known challenges surrounding the tunnel exit / entry points / bulk heads of the tunnel; the water chemistry if an impressed current system is used which is a vicious cycle over time; and the challenges in returning to rectify a CP defect.
By utilising Dr Pat Lydon, one of the few CP specialists in the UK who is registered to level 3 with The Institute Of Corrosion (ICORR), National Grid will have access to his vast experience with marine type applications where solutions are complex / novel and have potential to experience saline, brackish and freshwater tunnel fill types.
To investigate options for CP of pipelines within a tunnel and develop a specification based on the most appropriate techniques. This will deliver reduced procurement and construction costs for tunnel CP systems, provide greater integrity for pipeline during its lifecycle and potentially reduce requirement to design.