The effect of atmospheric precipitation on the corrosion of ferrous metals buried in soils

Data from the US NBS study for corrosion of buried objects are employed to show that average annual atmospheric precipitation directly influences corrosion of ferrous objects buried in various soils. This is attributed to the softness of precipitation waters and their delivery of oxygen. Also, as surrogate for time of wetness at the buried object within the soil, atmospheric precipitation has a clearer effect on corrosion loss and localised corrosion than does ground surface time of wetness. The relationship and the amount of corrosion also depend on soil type, a matter not previously considered. The results allow an explanation for the generally higher rate of corrosion of cast iron water pipes in cities such as Sydney with mainly clay-loam soil backfill and high precipitation compared with many locations in the UK with much lower annual average precipitation.