Various aspects of the mechanism of C02 corrosion are reviewed, together with a discussion about the validity of a number of simplifications which can be used with models for predicting the corrosion rate. A "worst case" rate can often be predicted. To this end a number of parameters has been identified, the
influence of which has to be accounted for. The effects of protective corrosion product layers and of dissolved corrosion product on pH needs to be included in the prediction. More quantitative information about the effect of flowpattern and flowrate is needed. For wet gas pipelines, the prediction of the effect of injection of glycol as a measure against corrosion is of special interest. Predictive models consisting of a system of rules and equations can be conveniently developed in computer spreadsheets.
The aggressiveness of the atmospheric environment can be assessed by measurement of climatic and pollution factors, or by determination of the corrosion rates of metals and coatings. The latter is a low cost technique which has traditionally been employed at single isolated sites with different types of environments. This approach does not, however, adequately portray the levels of corrosivity across a city or region which can vary by an order of magnitude. A technique has been devised at the Commonwealth Scientific and Industrial Research Organization (CSIRO) in which specimens are exposed across a grid of contiguous sites and the results computer contoured to generate corrosivity maps. A new method of h hyperbolic interpolation of the data has been developed to model corrosivity approaching the coastline. The paper presents results from surveys around an industrial point source of S02, conducted over two different periods. The technique of corrosivity mapping was demonstrated to be a sensitive indicator of localized zones of enhanced corrosion, and the two maps reflected changed conditions in the plant's operation in the two periods. The paper also discusses corrosion mapping in countries other than Australia and examines the costs of such exercises and the potential savings they can provide.