PR-218-063505-R03 Safe Inspection Procedures for Dent and Gouge Damage

Recommendations are often made that the operating pressure of a pipeline be reduced prior to investigating suspected mechanical damage in the field, due to the unknown severity of the dam-age. The ensuing question is: knowing only what can be inferred from in-line inspection and the characteristics of the pipeline, what is the appropriate amount of pressure reduction? A common recommendation is to lower the operating pressure to 80% of a recent high pressure level. Oper-ators may question whether the same pressure reduction is necessary or adequate for all pipelines, e.g. different Location Classes, and all modes of damage, e.g. rock-induced damage as opposed to encroachment damage. With some operations, pressure reduction by an arbitrary proportion is impractical or very costly.

Two levels of assessment are provided: a conservative "Level 1" assessment relying mainly on qualitative information and requiring no calculation, and a "Level 2" assessment that is consider-ably more involved but which could justify a smaller pressure reduction (or even no pressure re-duction). The choice of assessment level will depend on the information available to the operator, as well as on the degree of conservatism the operator desires to invoke.

This report presents procedures for determining whether or not a pressure reduction is needed to assure safety of maintenance personnel before excavating and examining plain dents or dent-with-gouge defects on pipelines based on information obtained from in-line inspection (ILI) data. The procedures also allow for calculating the amount of pressure reduction that is needed.