These metal coupons are inserted in to test loops which are connected to the water mains. Water from the main is diverted through the test loop where it comes in contact with the metal coupons. Each metal coupon has been precisely weighed by the manufactured prior to installation. After 3 months the coupons are removed and returned to the manufacturer. There, the coupons are processed and weighed again.
Any weight loss is recorded and used to calculate a corrosion rate in mils per year.
A weight gain indicates scale is being deposited on the interior of the distribution system. Several test loops located in various areas throughout the distribution system are maintained by laboratory staff as part of our corrosion control study. Laboratory staff also use a corrosion meter to check the corrosion rates in the distribution system on a weekly basis. This meter measures the instantaneous corrosion rate using a technique called Linear Polarization Resistance. Corrosion monitoring also provides data that can be used with other data to estimate the lifetime of plant equipment.