Improving the Quality of ECDA Indirect Inspection Data

ABSTRACT

The quality of the indirect inspection data is a critical factor in conducting a successful ECDA. It is therefore essential to increase the accuracy of the field data collection, to improve the data processing and to effectively present the results. This paper describes several challenges faced during this continuous improvement process.

Techniques for obtaining accurate field data for assessing the risk of AC corrosion are reviewed.

Data processing considerations are presented in the context of a case of third-party damage. The implications for similar DCVG indications on the same line are discussed, and a mechanism for these “apparent” DCVG indications is presented.

A new format for displaying the data is also presented, allowing a better visual co-ordination between the indications and the site features, as well as allowing immediate assessment of the proposed locations for direct examinations in terms of access and other challenges.

INTRODUCTION

The quality of the indirect inspection data is a critical factor in conducting a successful ECDA. Decisions made based on false indications can result in high cost excavations at the wrong locations, while missed severe indications can result in an immediate threat to pipeline integrity.

It is therefore essential to increase the accuracy of the field data collection, to improve the data processing and to effectively present the results.

This paper describes several challenges faced during this continuous improvement process.

ASSESSING THE RISK OF AC CORROSION DURING THE ECDA PROCESS

An ECDA process was conducted in 2005 on a NPS8 gas pipeline in southern Ontario. The pipeline parallels HVAC power lines for almost its entire length. With increased awareness in the industry regarding the risk of AC corrosion, the standard ECDA procedure was extended to include AC corrosion (ACC) indications.

The soil resistivity was measured at the test posts using the 4-pin Wenner method. The survey results are shown in Table 1.

AC induced voltages were measured to near earth at the test posts. The data were used in conjunction with the soil resistivity data to calculate the AC current density on a circular holiday having a critical surface area⁽¹⁾ of 1 cm²:

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