Oct 2009
Gas Transmission
Development of AC OHL survey system and evaluation of ER probes
Oct 2009
Feb 2014
National Grid Gas Transmission
Peter Martin
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Network Innovation Allowance
Gas Transmission Networks
Alternating currents are induced onto pipelines running parallel with high voltage transmission lines. AC electrified railways give rise to combined risks to both the safety of personnel working on these lines and also through significant AC corrosion problems on that pipeline. Induced AC voltage and AC current density measurements can be made at any point on the pipeline to determine likely risk of AC corrosion. At present these measurements are only made at test posts and so little is known about the levels of AC interference between test posts. This means that potential significant corrosion causes may be missed. CIPS (Close Intervals Protection Surveys), which currently only addresses DC potential, are carried out between test posts but these will not show AC-driven problems. At present, although AC corrosion has been documented (through-wall failures have been recorded and corrosion rates as high as 1.4 mm/yr calculated) in the UK, mainland Europe and North America, there do not seem to be many solutions available or widely used for over line AC surveys.

It is believed that the capability to perform over line surveys collecting induced AC voltage, DC on/off potentials and AC current density measurements would give the most beneficial means of detecting areas of AC corrosion risk. There is therefore a requirement to establish a suitable device that can be used to perform these surveys along with a process for its operation.

The project therefore will deliver a specific piece of new equipment for use on the gas transmission network.

The desired result is that the project deliver a suitable over line AC survey system, that when implemented, will enable the improved detection and assessment of AC-induced corrosion in gas pipelines, thereby reducing the likelihood of leakage or failure though this particular corrosion process.

Development of a suitable device that can be used to perform AC corrosion survey and a system/process for its operation across the National Transmission System.