Analysis of close interval survey (CIS) profiles is a staple of external corrosion direct
assessment (ECDA) process for underground pipelines. There are multiple possible
combinations of the ON- and OFF-potential profiles that are routinely observed during
the CIS surveys – e.g., the ON-potential changes while the OFF-potential remains flat.
Are certain combinations associated with more likely corrosion? Is it possible to glean
this information from merely looking at the ON/OFF potential shapes making up the CIS
profile? This paper describes the effort to determine whether the CIS profile ‘shapes’ can
act as indicators of conditions that warrant closer attention. The results of statistical
analysis of ILI data superimposed on the CIS profiles are encouraging in that they
support the current industry practices. The primary conclusion from the combined
analyses of the CIS profile shapes and regression analysis linking the metal loss and CIS
and soil characteristics is that certain CIS shapes are more likely to be associated with
corrosion – particularly the familiar ‘dip’ in both ON- and OFF-potentials, especially if
the CP criterion has not been met.