Sources of galvanic corrosion can show up in subtle or unexpected ways. For example, a common mistake is to install a copper corrosion coupon up stream of a carbon steel coupon in a corrosion coupon rack. When the copper corrosion coupon corrodes, copper ions dissolve into the water and can plate on the steel coupon, galvanic attack will then accelerate corrosion of the steel coupon. This can lead to significantly higher steel corrosion rates.
In systems where corrosion coupons of various metals are in use, such as in a coupon rack, special care should be taken to ensure the coupons are installed in order of nobility.