Developing design schemes for underground pipelines with out-of-spec axial curvature using ILI data

Abstract

WHEN CONDUCTING IN-LINE INSPECTIONS (ILIs) of trunk pipelines, pipe sections may be found with curvature exceeding the values required by specifications. An out-of-spec bend in pipe sections leads to the pipeline operating in conditions of increased stress-strain state, which does not comply with regulatory requirements. Where sections with out-of-spec curvature are found, repair works are carried out in order to return them to a state which complies with specifications. The priority shall be given to a method which does not involve cutting into the pipeline. In order to develop the project of the pipeline repair and to predict the stress-strain state during repairs and in subsequent operation, it is necessary to create design schemes which take into account the actual operating conditions of the pipeline, data from ILI, and the reasons why out-of-spec curvature formed at the section. In this article, an algorithm is proposed for the development of design schemes which describe the actual curvature of pipeline sections before repair, while repair works are carried out, and after they are finished. The methodology is based on a set of design scheme parameters, which allow a combination to be obtained, including both the design curvature and the actual pipeline section curvature according to ILI data. Design schemes for various situations where an out-of-spec curvature has formed were developed using actual data from ILI.