PHMSA Gas Transmission (GT) Integrity Management
Time: 09/03/2014 02:06 AM

Frequently-Asked Question FAQ #275

FAQ-275: Requirements for reassessments using ILI

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Question: For reassessments using ILI, are verification digs required if the ILI tool does not show any defects/anomalies? The baseline assessment and/or previous reassessment was completed and anomalies were repaired, as needed.

Answer: When using in-line inspection tools for conducting integrity management baseline assessments, § 192.921(a)requires the operator to follow ASME/ANSI B31.8S, section 6.2 for special considerations for the use of in-line inspection tools. The operator must verify that an in-line inspection tool performs within its published specification with respect to detection sensitivity tolerances, classification, sizing accuracy, location accuracy, and requirements for defect assessment. An operator must not assume that results (showing no identified anomalies that exceed the reporting threshold) are reliable until the tool's performance is confirmed by verification digs. Different tools, tool sensors, different analysts, changes in pipe cleanliness or operating parameters, etc., can affect tool performance/results.

49 CFR § 192.933 addresses integrity issues such as inline tool inspections, pressure reductions, and discovery of conditions. Section 192.921(a)(1) states that an operator must follow ASME/ANSI B31.8S, section 6.2 in selecting the appropriate internal inspection tools for the covered segment. ASME/ANSI B31.8S, sections 6.2.6 outlines the screening and examination of the in-line tool results, and states:

"Results of in-line inspection only provides indications of defects, with some characterization of the defect. Screening of this information is required in order to determine the time frame for examination and evaluation.

"Examination consists of a variety of direct inspection techniques, including visual inspection, inspections using NDE equipment, and taking measurements, in order to characterize the defect in confirmatory excavations where anomalies are detected. Once the defect is characterized, the operator must evaluate the defect in order to determine the appropriate mitigation actions."

An operator must have a method to accurately characterize and evaluate in-line tool results. Excavation of selected in-line tool results is a method to determine if the in-line tool including its sensors, other electronics, and evaluation models are properly evaluating the pipeline segment. When an in-line tool has no findings on a pipeline segment, excavation is still an important method of meeting the requirement to verify results. Operators must have in-line tool procedures that include a valid method such as excavation to confirm tool performance within specifications and the accuracy of in-line tool results.

These Frequently Asked Questions (FAQs) are intended to clarify, explain, and promote better understanding of the pipeline integrity management rules. These FAQs are not substantive rules and do not create rights, assign duties, or impose new obligations not outlined in the existing integrity management regulations and standards. Requests for informal interpretations regarding the applicability of one or more of the pipeline integrity management rules to a specific situation may be submitted to PHMSA in accordance with 49 C.F.R. 190.11.
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