Field Signature Method Electric Fingerprint

This comprises the measurement of the changes in an applied electric field within a pipe spool, caused by the loss of material from the inner wall due to internal corrosion. Field signature methods are commercially available. 

Thin contact pins, typically up to 64 in number, are welded or cemented to the outside of the pipe wall in a configuration that is determined by the position and the pattern of internal corrosion expected. 

Each pin is connected to a data acquisition unit that monitors the potential difference generated between individual pairs of pins as a consequence of the application of an external current between two auxiliary pins spanning the measurement pin configuration. 

Using appropriate software the change in the fingerprint coefficient with time for each pair of pins enables a graphical representation of the corrosion pattern to be developed with quantitative estimates of the loss in wall thickness across the area covered by the pin array. 

The technique has the advantage that it measures the actual corrosion taking place within the process system, regardless of process fluid type and with a high degree of sensitivity, without the need for access fittings, intrusive probes, and retrieval operations. Removal of the spool pieee for confirmation of the pattern and extent of corrosion being indieated is reeommended. This wiU normally have to coincide with a plant shut-down. 

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