Corrosion and inhibition process of carbon steel in LiBr-H2O solution

Lithium bromide (LiBr)-H2O triple-effect absorption chillers are supposed to have a much higher carbon steel corrosion rate under high temperature than double-effect ones. Although the annual corrosion rate was investigated in our previous study, a simple extrapolation with experimental data for a short period of time can cause very significant errors because the corrosion process becomes quite complicated if a corrosion inhibitor exists in the solution. Therefore, in this study, corrosion and inhibition characteristics over time have been investigated for carbon steel specimens in LiBr-H2O solution under the optimal operation conditions of double- and triple-effect absorption chillers. Pyrex tube ampoules containing a carbon steel specimen and the 63 % LiBr-H2O solution with a corrosion inhibitor (lithium molybdate, Li2MoO4) were prepared and placed in a high-temperature oven at 150 °C and 200 °C, which are typical operation temperatures of double- and triple-effect absorption chillers, respectively. After various exposure times (25–4000 hours), the ampoules were opened and analyzed using three methods: Analysis of mass loss, solution analysis, and microscopic image analysis. Results indicated that the passive films were formed not linearly with time but rapidly at the beginning. Moreover, the concentration of the corrosion inhibitor (Li2MoO4) should be maintained above 100 ppm for stable passive films. To explain the experimental data, a model with three stages of corrosion and inhibition process was proposed. The present study is expected to give important information for the development of triple-effect absorption chillers.