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Further new interpretations of the corrosion of ferrous metals in soils

Paper Number: 23
Author/s: R E Melchers, R B Petersen & T Wells
Organisation: Centre for Infrastructure Performance and Reliability, The University of Newcastle, Australia


The long-term corrosion of steels and cast irons in various types of soil, without cathodic protection, remains of much interest to certain applications, most notably the remaining viability of internally cement lined cast iron water pipes used extensively in water supply networks in many major cities. Some of the existing pipes date back more than 130 years and are still in good condition whilst others, much younger have failed or are showing signs of severe external corrosion. The most extensive data base for corrosion of ferrous objects in soils is the US NBS data base (Romanoff 1957) but efforts to make sense of the data and thus to produce models to predict likely corrosion have proved elusive. Earlier (Melchers and Petersen 20XXX) it was shown that the compaction properties of the backfill soil immediately adjacent to the metal, and in particular the size of the likely air voids, was related to the severity of localized corrosion observed and that this was related to the type of soil used as backfill. The present paper used additional data for the average annual precipitation, or time of wetness as best as can be estimated, to show that these are related to the severity of localized corrosion but that this can be demonstrated only for individual soil types. Failure to differentiate soil types is considered responsible for the failure of previous efforts to relate time of wetness to corrosion. The results allow explanation for the generally higher rate of corrosion of cast iron water pipes in cities such as Sydney and Newcastle compared with many places in the UK where they were used already in the 1850s.