A reinterpretation of the Romanoff NBS data for corrosion of steels in soils

Data published in the 1957 Romanoff National Bureau of Standards report for the corrosion of steels buried in soils for up to 17 years are re-interpreted using the bi-modal model for corrosion in wet environments. The relevant soil properties are those of the backfill, not those of the undisturbed soil at the depth of the steel samples. Using estimated backfill properties shows that stiff clays, calcareous foams and gravelly barns corrosion transitioned from Mode 1 to Mode 2 after 4-8 years, following severe corrosion and deep pitting. For most other backfill soils, the transition occurred later and corrosion was less severe. These differences are attributed to the relative influence of differential aeration and localised corrosion caused by air-voids at the soil-metal interface. The declining rate of corrosion in the later part of Mode 2 is attributed to backfill consolidation decreasing the diffusion of oxygen and possibly also of moisture.