Review: This paper is a collection of opinions about the use of coupons as a tool for monitoring cathodic protection systems. The opinions expressed in this paper are a good summary of the findings and conclusions of several published studies on the subject. However, Didas does not reference these studies.

• The following three advantages of using coupons are very important:

• IR free potentials may be obtained without interrupting multiple CP power sources.

• IR free potentials may be obtained on buried structures with direct connected galvanic anodes.

• Depolarization testing may be performed without de-energizing the CP system.

Only one disadvantage is listed:

• The major disadvantage of coupons is the possible discrepancy between the true structure potentials and the coupon potentials.

Good engineering practice demands that a number of issues be considered when implementing the use of coupons to monitor cathodic protection systems. Didas briefly discusses seven such issues:

• number of coupons

• coating conductance

• coupon material

• method of construction

• surface preparation

• the voltmeter used for the potentials

• coupon placement in relation to any existing anodes

The design considerations listed in this paper are:

• Didas calls for a standard size to duplicate "typical" coating holidays and recommends 100 sq.cm.

• Didas recommends the use of older or aged steel of a grade similar to the structure's steel.

• Didas recommends that coupons manufactured from new steel remain disconnected from the structure and permitted to corrode freely for a period of one or two months.

• Didas recommends that the coupon be placed in backfill material similar to the material surrounding the structure and compacted to a similar density.

• Didas recommends that the coupon be installed at the same depth as the structure and about .33 meters (1 foot) from the structure.

• Didas recommends that the soil access tube be backfilled with well compacted native soil.