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.