cathodic protection corrosion Coupon

External Cathodic Protection Coupon

Evidence that cathodic protection is working can be obtained by using coupons of the same metal as that of the protected structure. These coupons, electrically connected to the protected structure.

The coupons should be placed where they receive the same exposure to cathodic protection current as the structure receives; then, after a known exposure time, they are removed and weighed. Corrosion rate is the weight loss per time.External CP coupons can also be used to monitor cathodic protection criteria.

This is particularly useful on well-coated structures where few coating holidays exist. The coupon serves as a surrogate holiday and polarizes to the same structure potential.

Advantages of using CP coupons are that IR-drop-free potentials can be obtained without interrupting multiple power sources, structure-to-reference potentials can be measured on structures with direct-connected galvanic anodes, and depolarization tests can be conducted on the structure without de-energizing the CP system.

 

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