For corrosion inhibitor assessment, usually people don’t calculate the corrosion rate, or MPY.
Usually we get the inhibiting efficiency, that is a percentage. For example, with blank solution without adding inhibitor, we get a i0. If inhibitor 1 is added, we get i1.
If inhibitor #2 is added we get i2.
We calculate the percentage:
(i0-i1) / i0 x100%
Similarly for inhibitor #2
(i0-i2) / i0 x 100%
If you need MPY, you will need to calculate according to below formula: