PR-201-153718-R03 Integrity Assessment of DTI Pipelines Using High Resolution NDE in Select Areas
Authors: Bowlin Elizabeth , Agarwal Puneet 
Published: August 2023

Hydrostatic test and In-Line Inspection are the prescribed integrity assessment methods cited in various Codes and Regulations and have been proven to enhance pipeline safety. But a significant number of pipelines across the world remain difficult to inspect and impractical to modify for inspection by the prescribed methods due to physical configurations or operating conditions. This research performs a state of the art (SOTA) analysis of NDE technology readiness considering physical and operational barriers and technology deployment from inside, outside or over pipelines, and the possible role of inspection sampling to conclude pipeline integrity and justify intervals for conversion for piggability or hydrotest. The goal of the research is to propose alternatives to ILI for safe prioritization and scheduling for conversion or replacement and not to replace hydrostatic test or ILI as currently prescribed in Codes and Regulations. The scope of the research is limited to technologies and integrity management concerning metal loss threat.

This report represents the third and final update of prior reports from the two preceding years presenting a compendium of technologies describing technology readiness for state of the art non-destructive evaluation (NDE) technologies intended for low resolution pipeline condition screening and high resolution NDE for deployment at sample locations with capabilities applicable to difficult to inspect pipeline configurations. Integrated cleaning and inspection pigs, smart balls, external deployed ultrasonic, radiographic and magnetometry are pipe wall screening technologies evaluated in the reports. A structured process is proposed for assessing pipeline integrity based on low resolution screening of the full length of a pipeline segment followed by high resolution NDE samples at locations where screening indicates locations of possible wall loss. The process employs extreme value analysis for prediction of maximum metal loss severity across the screened segment. For instances where no metal loss indications reported by screening or from high resolution samples an alternative "compliance approach" is also addressed.

Case studies are presented where PRCI members have deployed some of the technologies referenced in the NDE SOTA phase of the research and implemented the proposed extreme value or the compliance approaches. Validation of fitness for service conclusions based on inspection sampling by comparison with full length high resolution ILI or hydrostatic test are included in some of the case studies. The conclusions of the case studies demonstrate integrity conclusions obtained from the PRCI structured process are conservative and consistent with ILI or hydrostatic test conclusions. Based on the experience from the case studies and the SOTA, a metal loss screening efficiency factor (MLSE) is proposed enabling pipeline operators to understand the general relationship between screening level (sample stratification) and direct examination (inspection sampling) required to provide equivalent understanding of pipe wall condition, limited to metal loss. As mentioned by ASME/API ILI has limitations that need to be considered in its deployment and full discovery of metal loss conditions. Under some conditions (noted by API 1163) ILI predictions can be accepted without any direct examinations or verifications, i.e full length screening (high resolution) and no verification samples. At the other end of the spectrum random sampling can be theoretically deployed as a screening approach but depending on the condition of the pipeline, the high-resolution sample area could be very large to obtain a significant integrity conclusion. This report proposes a comparative scale of effectiveness for SOTA pipe wall screening technologies that offer the operator an expectation of high resolution NDE sample size.

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