In-Situ Measurement of Corrosion in Buried Pipelines Using Vertically Measured Pipe-to-Soil Potentials
Application of in-situ corrosion rate measurement technology for buried pipelines
An Southwest Research Institute (SwRI) developed patent-pending (U.S. patent application number 14,161,165) state-of-the-art, in-situ corrosion rate measurement technology for external surfaces of buried pipelines under cathodic protection. The technology is based on pipe-to-soil potentials measured vertically from ground surface near the location of interest on the buried pipeline.
This technology provides several advantages because it does not require any major excavation or interruption in the cathodic protection system circuit. Furthermore, it can measure corrosion rates both at the "holiday" and on coated sections of the pipes. Corrosion rate information at coated pipe sections can be used to quantify quality of the in-service coating.
Device to measure and record pipe-to-soil potential with vertical depth from ground surface
The technology is based on application of the differential form of Ohm’s law
and current-potential distribution in soil due to the cathodic protection system. Using Ohm’s law, the current density (ipipe) at any location on the pipe can be estimated provided the normal component of the gradient of the pipe-to-soil potential [(n · ΔΦ) pipe] at the pipe surface and the soil resistivity (κ) near the pipe are known. While soil resistivity can be readily measured using a commercially available soil-resistivity meter, estimation of (n · ΔΦ) pipe requires vertical measurements and data extrapolation. Data extrapolation is required because pipe-to-soil potential measurements cannot be conducted very close to the pipe surface because of safety concerns related to drilling a hole that could damage the pipeline if it contacts the pipe surface. SwRI designed a pipe-to-soil potential measurement device capable of recording the pipe-to-soil potentials as functions of vertical distance from the ground surface. Because the gradient of the pipe-to-soil potential is needed near the location of interest and the pipe-to-soil potential cannot be measured very close to the pipe surface, extrapolation of measurements is performed to estimate the gradient of the pipe-to-soil potential at the pipe. SwRI developed a numerical algorithm to obtain the pipe-to-soil potential gradient at the pipe surface. The algorithm relies on computer modeling of pipe-to-soil potential distribution for a pipeline under cathodic protection.
corrosion measurement • in-situ measurement of corrosion • buried pipelines • cathodic protection system circuit • Ohm's law • pipe density • corrosion rate information