A Synthesized Approach to Pressure Reduction for Investigating Mechanical Damage

It is often recommended 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 damage. The primary 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? Secondarily, operators also question whether the same pressure reduction is necessary for all pipelines, e.g. different Location Classes, and all modes of damage, e.g. rock-induced damage as opposed to encroachment damage. Two levels of assessment are provided: a conservative “Level 1” assessment relying on mainly qualitative information and requiring no calculation, and a “Level 2” assessment that is considerably more involved but which could justify a smaller pressure reduction in response to the damage. 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.