Chu, Wu-Yang (University of Science and Technology) | Gao, Biao GuKe-Wei (University of Science and Technology) | Huang, Yi-Zhong (University of Science and Technology) | Xiao, Ji-Mei (University of Science & Technology Beijing)
Weare, Richard (Petrolite Ltd) | Saleh, Marwan (Petrolite Ltd.) | El-Raghy, Saad (Gulf of Suez Petroleum Co.) | Wood, Brian (Gulf of Suez Petroleum Co.) | Abuleil, Hussein (Gulf of Suez Petroleum Co.)
IR Drop coupons are being utilized worldwide to determine the IR Drop in a potential measurement of a buried structure and to determine the effectiveness of cathodic protection on the buried structure. This paper will explain the use of IR Drop Coupons as a test method for determining IR Drop, cathodic protection effectiveness and verify the polarization level of buried structures.
Over the last two decades, the use of buried coupons has been rediscovered as a practical method to determine the level of polarization of a buried structure and to confirm the IR Drop in a potential measurement. Acceptance of IR Drop coupon technology is slowly happening. Research sponsored by Industry and the American Gas Association has utilized IR Drop coupons for several research projects and has helped validate the use of this technology.
To assess the effectiveness of a cathodic protection (CP) system using fixed potential measurements, voltage (IR) drops, other than those across the structure - electrolyte boundary must be considered. This is a key requirement of NACE RPOI 69-96. Several methods are utilized to consider the voltage drop.
· Minimize the distance between the reference electrode and the surface of the structure.
· Measure the potential when the current flow is interrupted (instant-off)
· Measure the formation of polarization or decay of polarization of the structure when the current is energized or interrupted.
· Install buried coupons in the vicinity of the structure to replicate a coating holiday.
All of these methods have their advantages and disadvantages.
· The advantages for buried coupons are as follows:
· IR free potentials may be obtained without interrupting multiple CP power sources.
· IR free potentials maybe obtained on buried structures with direct connected galvanic anodes.
· Depolarization testing maybe performed without de-energizing the CP system.
The major disadvantage of coupons is when comparing existing data to the coupon data their is a possible discrepancy between the structures polarized potential and the coupons polarized potential. The polarized potential of the coupon will not necessarily duplicate the structure polarized potential at the same location. This is due to the coupon representing a holiday of similar size on the pipeline and not actually being located at the holiday location. The structure potential would be representative of the nearest or most influencing holiday, while the coupon potential would be at the coupon, therefore when comparing potentials taken at the same location, there should be some difference.