ABSTRACT
This chapter focuses on coupon monitoring and on two frequently used on-line corrosion monitors: electric resistance monitors and linear polarization resistance monitors. Coupon monitoring provides long-term performance data on general corrosion and information on localized corrosion. Coupons are small pieces of metals, usually of a rectangular shape, which are inserted in the process stream and removed after a period of time for study. Once corrosion products form, they will be some-what protective; the corrosion rate will drop from the initial rates. The resistance probe must be allowed to corrode for a period of time before accurate corrosion measurements can be made. The change in corrosion rate caused by the reversal in current causes a change in potential of the test electrode when compared to the freely corroding reference electrode. Electric resistance monitors give medium- to long-term data on general corrosion or erosion.
