Operational Life Estimation of Carbon Steel Heat Exchanger with Cooling Water based on Extreme Value Analysis
Masao Nakahara, Tetsuo Shoji
The operational life of a carbon steel heat exchanger has empirically been determined based upon penetration of pitting corrosion in cooling water environment. In the recent years, approach called “extreme value analysis” has been introduced and been proven to be a useful tool for the purpose of life estimation in corrosible environments. However, the growth rate of pitting and its relation with operation conditions have not been made fully clear yet, which gives limitation of the development of the method for accurate estimation of heat exchanger life.
The experimental data of a series of the extreme value analysis of heat exchangers were collected and were analyzed in this study, with the data mainly collected from heat exchangers with passing water through tube inside.
The time dependence of the location parameter (λ) and of the scale parameter (α) in extreme value analysis were examined at first. As a consequence, it was found that these parameters had similar time dependence and had similar saturated tendency at some years after beginning the operation of the facilities of interest. A multilinear regression analysis was carried out, next, to clear the relations of time dependence, operational conditions and water quality on these parameters. A life estimation equation for heat exchangers was then developed, based on the results of this regression analysis. The effects of operational conditions and water quality on pitting propagation was made clear from these studies and practical application of this approach was emphasized.