Using lpr to predict underground corrosion of cast iron watermains

LPR testing of soils has been used extensively by a number of water utilities, principally Sydney and Hunter Water, for many years now to determine the condition of buried ferrous watermains. The LPR test itself is a relatively simple, inexpensive test that serves as a substitute for actual exhumation and physical inspection to determine corrosion losses. LPR testing results (and the corresponding pit depth estimates) in combination with proprietary pipe failure algorithms can provide a useful predictive tool in determining the current and future condition of an asset (Nicholas 2009). A number of LPR tests have been developed on soils over the years (Nicholas 2009), but few have gained widespread commercial use, partly due to the difficulty in replicating the results. The author has conducted an extensive review of current approaches to LPR testing of soils, in combination with an extensive program of field exhumations to examine the relationships between short term electrochemical testing and long-term field corrosion. This paper addresses the underlying principles of LPR and examines the scenarios in which the technique appears to be successful and, perhaps more importantly, identifies where LPR does not appear to be successful. The discussion in this paper will focus on the correlations identified by the author through an experimental field program, and consider these in relation to those published by other researchers in this field, notably Hay (1984) and Ferguson (2009). Aside from these attempts within Australia no other authors have attempted to correlate long term corrosion of buried ferrous assets using a very short electrochemical test (i.e. at initial Ecorr stabilisation), and most researchers still advocate the use of extended tests to predict corrosion. The data from this experimental program would suggest that longer-term electrochemical tests are simply unnecessary to provide a meaningful result