Reasons for the negative corrosion inhibition rate
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In a batch of over 10 corrosion inhibitors tested under static conditions (using X66 test plates, with a concentration of 100 ppm and a temperature of 30–40 degrees), none were able to achieve a corrosion inhibition rate of 70%. What’s more absurd is that negative corrosion inhibition rates were observed; out of 8 samples, 6 had negative values, with the highest one reaching almost -300%. This means that adding a corrosion inhibitor actually accelerates corrosion. Although there is no data available, these corrosion inhibitors are nothing more than things like imidazolines and quaternary ammonium salts – so how can such absurd values arise? The water sample used is oil field wastewater, with a high sulfur content as well as carbon dioxide; its mineralization degree is over 100,000. What is the principle behind this? Why does this happen?
The corrosion inhibition rate generally refers to the ratio of the corrosion rate of a metal under certain environmental conditions to its corrosion rate after the addition of a corrosion inhibitor. When the corrosion inhibitor fails to achieve the expected effect of suppressing corrosion, the corrosion inhibition rate may take on a negative value. This is because the inhibitor does not perform as intended; instead, it accelerates the rate of metal corrosion, resulting in a corrosion inhibition rate that is less than 1 or even negative. Furthermore, factors such as the concentration of the corrosion inhibitor, the method of addition, and environmental conditions all affect the value of the corrosion inhibition rate. -
Is it because the corrosivity of water is too high, and the concentration of the corrosion inhibitor added is insufficient?
When conducting corrosion inhibition tests, a blank sample must also be used. If the water has strong corrosive properties, the blank sample will suffer severe corrosion as well; and in principle, even if the amount of corrosion inhibitor used is insufficient, its effect should still be better than that of the blank sample. Moreover, the addition level has reached 100 ppm, which is a significant amount and meets the requirements of the latest industry standards; generally speaking, there will be no situation where the addition amount is insufficient.