A common method of determining corrosion rates is by using corrosion coupons, which are uniform sized, pre-weighed strips of metal. Corrosion coupons representative of system metals are inserted into a coupon rack installed on the system to be checked.

Normally, system water is allowed to circulate over the corrosion coupons for about 30 - 90 days. The coupons are then removed and returned to a lab where they are cleaned and re-weighed. From this weight loss and the dimensions of the coupon, a corrosion rate in mils/year (mpy) is determined. 1.0 mil/year translates into 1/1000th of an inch of metal loss per year. To convert corrosion rates expressed in millimeter/year (mm/y), a common metric measurement, to mpy, multiply mm/y times 39.4.

Reprinted with Permission from Chem-Aqua