Review of GERG study

Reference: The State-of-the-Art of Using Buried Coupons in Cathodic Protection, GERG PC-2 Transport and Storage Cathodic Protection Joint Research Team, 1991.

Review: This paper is a compilation of data collected with a questionnaire sent to European pipeline companies in 1991.

The stated objective of the survey was:

"... a report on the state of the art of the use of buried coupons for cathodic protection measurements and in this way illustrate how buried coupons are being used in managing corrosion control problems."

Reviewer's Note: Although two respondents indicated they were conducting research programs related to the use of coupons for cathodic protection measurements, the information obtained from the questionnaire is merely an indication of how coupons were being used in 1991(precisely the intended purpose of the survey). This report, by itself, does not provide evidence of the validity of using coupons for cathodic protection measurements.

The survey was sent to 49 companies, 29 companies responded, and 14 of the respondents are using a total of 8000 coupons on more than 100,000 kilometers of pipe. Five additional companies indicated that they would start using coupons in 1991. One company has been using coupons for 30 years but most had been using them for less than 10 years.

Several respondents indicated they did not use coupons with internal reference electrodes because leakage of the electrolyte from the coupon was observed.

All respondents use coupons in areas which require special attention as the result of stray currents, AC interference, telluric currents, or other external influences.

There is no standard with respect to coupon size, geometry, orientation. There is no standard with respect to criteria nor interpretation of data collected from the coupons.

Thompson ^[THO2] presents the following good five point summary of the GERG study.

"Most coupons were installed as a tool to monitor IR-drop free polarized potential measurements."

"Many coupons were installed to monitor sites requiring special attention such as stray current (AC and DC) sites and direct connect sacrificial anode locations."

"Many coupon designs incorporated a permanent reference electrode as part of the design; however, most of the problems associated with the use of coupons were related to either the failure of the permanent reference or the contamination of the soil near the coupon by the permanent reference."

"Several of the coupon designs incorporated coupons of different surface areas. The range of surface areas of the coupons was from 1 to 300 cm2."

"The majority of the sites were installed with the coupon facing away from the structure or facing up towards ground level. Many of the installations were cylindrical in nature, i.e., with bare surfaces exposed for 360°."