Clustering of corrosion pit depths for buried cast iron pipes

Predicting long-term corrosion of metal alloys in physical infrastructure

“…63 Moreover, observations show that neighbouring pits may coalesce to form almost uniform depth depressions (sometimes noted by experimentalists as 'broad pits' 71 that then provide a new surface for new pitting to occur. This leads to a stepped pattern of metal penetration, as observed in detail for mild steels, 63 and also reported for cast iron 72 and most recently for 6060 Aluminium alloy exposed to seawater. 73 These recent observations have been facilitated with the availability of surface scanners that permit the measurement of many pit depths, to an agreed base level, instead of the laborious process of measuring each pit depth independently to an uncertain base level.…”

Empirical models for long-term localised corrosion of cast iron pipes buried in soils

“…There were also several quite isolated pits, of complex topography, up to about 25 7). Pitting at similar locations has been observed for pipes in other locations [19]. The conditions for their formation and development almost certainly are the same as for pitting along the bottom of the pipes, that is, the presence of air-voids and water for the initial pit depth development and, subsequently, long periods of availability of free water.…”

“…This used the technique of exhuming pipes carefully with a small mechanical excavator or by hand operations, grit blasting the pipes in situ and then measuring the depth of the deepest pits or areas of localised corrosion that could be observed on the exposed pipe. For the latter cases, the surface of the exposed pipe surface was scanned using a Crea-form® scanner and the depth of the deepest pits extracted from the data [19]. Verification checks using a simple pit depth gauge also were employed.…”

“…The soil classifications for the backfill surrounding the pipe at each site were determined, in most cases, by experienced field engineers. For some sites detailed soil chemical properties were obtained, as previously reported [19]. These properties are not employed herein since, as noted above, in the near-stagnant conditions at the soil–metal interface, soil and soil water chemical properties have little or no influence on the severity of longer term pitting corrosion [6,12].…”

Development of long-term localised corrosion of cast iron pipes in backfill soils based on time of wetness

“…However, field observations shown that the pitting process may repeat after formation of plateaus from the lateral growth of pits that have reached their nominal maximum depth [33]. This has been observed for pitting development in cast iron pipes after many years exposure [34]. The depth that develops after many years exposure depends to some extent on the type of soil.…”