Session: Session 6. Pipeline Integrity Management and Risk Assessment
Paper Number: 119011
119011 - Dig Effectiveness and Repair Criteria for Dents in Gas Pipelines
Pipeline dents form from different causes including a third-party damage, backfilling issues, pipe sitting on rocks. US DoT include dent repair and remediation criteria based upon dent depth, dent location (top or bottom side), pressure cycling, strain, and dent interaction with other threats like welds, corrosion, cracks. These criteria are easy to apply, however, they may cause conservative excavations.
Over 80 deformation excavation results were reviewed. The results were compared against In-Line Inspection (ILI) reported values. The results were investigated to focus on trends caused by tool size, deformation dimensions, ILI year, vendor, etc.
The paper is targeted to gas pipelines, but some of the conclusions can be applied to liquid pipelines and facilities.
This paper includes a review of in the ditch excavation results based on ILI data review. This paper describes approaches to evaluate fitness-for-service of dents. ASME B31.8 includes repair criteria for plain dents considering assessment of formation strain is an indication of the potential for cracking. As found results were reviewed and no cracks were found in majority of excavations with high strain.
The depth and strain based dent assessment criteria as required by various government regulations and industry codes have served the pipeline industry as an evaluation method to determine fitness for service. However, this criteria can result in unnecessary excavations. Excavation results are reviewed versus as called to investigate the level of conservatism embedded in critical strain values recommended by ASME B31.8. Megarule Part 2 has a maximum level for dent strain (10%) where engineering critical analysis is not allowed and dent must be repaired. The as found results were compared where this strain level was achieved for any possible crack initiation.
The review results and conclusions will be one source to improve integrity repair decisions and can be used to support modifications of guidelines, standards, or regulatory documents. Information presented will be of interest to pipeline operators, in-line inspection (ILI) companies, integrity management specialists and regulators.
Presenting Author: Mady Mojarad TC Energy
Presenting Author Biography: Mady Mojarad is an Integrity Engineer at TC Energy. She has extensive experience in pipeline and facility integrity management processes, engineering assessments, remaining-life assessments. Mady strives for knowledge-sharing across the industry, promotes a culture of excellence, and promotes strategic thinking.
Dig Effectiveness and Repair Criteria for Dents in Gas Pipelines
Paper Type
Technical Paper Publication