Examples of mathematical modelling of long term general corrosion of structural steels in sea water

Recent progress has been made in developing a mathematical and probabilistic model for general corrosion of structural steels exposed to sea water immersion corrosion. It is based on corrosion science principles, with early corrosion controlled by oxygen concentration limitations that eventually evolve to anaerobic bacterial controlled corrosion behaviour. The model has been calibrated to extensive literature data and original field tests. Herein, three different sets of corrosion field data, for Halong Bay in Vietnam, for an offshore oil platform site and for three coastal sites along the China coast are examined for compatibility with the model. It is shown that all the data are consistent with the model provided allowance is made for the season of the first immersion, the effect of sea water velocity and the possibility of nutrient pollution. In its most general form, the model is probabilistic to allow for natural variability owing to unrecorded (and perhaps unrecordable) influences. The data considered herein are sufficient for comparing with the expected value of the model but not for considering statistical variability. Finally, the model provides plausible explanations for differences in observed corrosion at different sites, considered by others to be due to the action of hard marine fouling.