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Ensuring the Accuracy of Indirect Inspections Data in the ECDA Process

Published: 20100314 by NACE International
Author(s): Sorin Segall
Co-Author(s): Robert Gummow - Corrosion Service Company, John Shore - Union Gas Limited, Rod Reid - Union Gas Limited

The quality of the indirect inspection data is a critical factor in conducting a successful ECDA program. New NACE standards (SP0207-20071 and TM 0109-092), improved instrumentation, experience sharing, and extensive training during the last several years, has resulted in a significant improvement in the accuracy of the survey data.

This paper covers a number of lessons learned by dealing with less-known sources of measurement error, during six years of ECDA application on more than 50 gas pipelines in Ontario.
Topics addressed include a discussion of errors;

  • generated by rectifying elements in current interrupters,
  • caused by the influence of remote rectifiers,
  • introduced by local changes in soil resistivity during the DC Voltage Gradient Survey, and
  • produced by transient currents during the Close Interval Potential Survey.