Review: This is a report on the effects of stray current from Telluric currents and from DC rail systems. This study does not address questions regarding the validity of using coupons to monitor cathodic protection systems. A basic assumption of this study is that coupons are a viable method to monitor cathodic protection systems in the presence of stray currents. The study was done by staff at British Gas for consumption by British Gas.
In the introduction Greenwood states:
"The use of buried coupons to measure pipe/soil potential is now common: the technique has shown promise as one relatively immune to the effects of varying current."
In view of his basic assumption, the first item in his list of three conclusions is particularly interesting:
- Buried coupons provide the best method available for accurate measurement of pipe/soil potentials on pipelines affected by stray current.
- The effects of transient stray current on cathodic protection of pipelines are negligible if the average stray current is near zero.
- For condition monitoring purposes on pipelines affected by stray current an accurate potential may be obtained at Pearson defects by recording the local potential for a suitable period.
Buried coupons should be used for routine measurements of pipe/soil potential on pipelines affected by stray current.