Inferring highly corroded buried pipeline locations through saturated soil resistivity information

Abstract

Inspection and assessment of ageing buried metallic infrastructure such as pipelines can be costly, especially when soil sampling programs are involved to evaluate large networks and pipe health conditions. In order to reduce these costs through assessment prioritisation at infrastructure locations that are scientifically inferred to be under highly corroded state, advancements in current approaches are necessary. In this study we have investigated the utility of soil resistivity as an index for buried and ageing pipe health status through numerical and field case studies. Numerical study showed that the monotonous relationship between soil resistivity and maximum pit depth that is often considered in literature as linear is actually non-linear. Field study involving in-situ wall thickness measurements of 3 separate water distribution mains (each > 1.5 km in length) at selected excavated locations were compared with the saturated soil resistivity (ρsat) acquired a-prior. The ρsat was found to be highly correlated to the maximum corrosion pit depths observed in-situ. This correspondence is argued to exist provided the saturated soil resistivity displays statistical uniformity along the pipe and the pipes are not under submerged conditions. Locations on the pipe where ρsat < 15 Ω m were found to have corroded relatively more than other locations; in one instant a leaking pipe due to excessive corrosion was also observed. A practical indirect assessment framework was proposed that can be utilised immediately in professional practice.

Keywords

• Underground corrosion
• Soil resistivity
• Condition assessment
• Pipe inspection