PR-201-153718-R02 Integrity Assessment of DTI Pipelines Using High Resolution NDE
Authors: Bowlin Elizabeth , Agarwal Puneet , Dotson Rhett 
Published: August 2023

This is a new revision of the Year 2 work.

The NDE-3-2 project seeks to advance the state of the art for integrity assessment of difficult to inspect pipelines by proposing guidance for application of alternate inspection approaches other than hydrostatic test, in-line inspection and ECDA/ICDA currently prescribed by Code and Regulations. The hydrostatic test and in-line inspection methods for integrity assessment have in common the concept that the full length of the pipeline is assessed. Many pipelines exhibit configuration and operational issues that preclude integrity assessment by the prescribed methods. The ECDA/ICDA structured processes employ evaluation of protective barriers followed by deployment of a small sample of high resolution wall thickness measurements. The NDE-3-2 study proposes a new structured process that evaluates low resolution NDE data of the pipe wall for the full length of the pipeline followed by statistically significant numbers of high resolution wall thickness measurements to predict the condition of the pipeline relative to the fitness for service criterion of corroded pipe such as prescribed in ASME B31G. While conventional ILI inspections or hydrotest rely on full coverage as the basis for evaluating the integrity of a pipeline segment, this structured process would seek to use partial inspections at discrete locations and then use Extreme Value Analysis to estimate the integrity of pipeline segments. The objective is not to provide guidance to replace ILI or hydrostatic testing but rather to offer an alternative for the purposes of gathering data to justify the safe prioritization of piggability conversion or pipeline replacement of difficult to inspect pipelines for both onshore and subsea.

This report documents the current state-of-the-art for corrosion location NDE, selection models, and Extreme Value Analysis (EVA) Methodologies for deployment in a structured process as an Alternative to In-Line Inspection of difficult to inspect pipelines. The research on NDE screening technologies addressed in this report reviews technologies identified in the Year 1 work that can be used to screen the condition of pipe wall along its full length as well as existing location selection models such as employed by Direct Assessment Methodologies. This report leverages extensive research that has been conducted on existing Extreme Value Analysis Methodologies from multiple sources and applications including metal corrosion (HOIS, HSE), pipeline corrosion, metocean criteria, wind loading, and multiple textbooks.

Multiple case studies are summarized in this report that demonstrate the use of the Partial Inspection Integrity Assessment process utilizing EVA on segments of a pipeline compared to results from full length integrity assessments (either ILI or hydrotest). This report also documents a full Extreme Value Analysis using a demonstration case study and then compares the EVA results with the wall thickness measurements from a full length integrity assessment as a validation example. Ultimately, it is the goal of NDE-3-2 to identify more case studies that might serve as demonstrations.

The report also identifies gaps that currently exist and the work that must be completed to develop a complete validated structured process required to deploy the technologies for integrity assessment of difficult to inspect pipelines. The research also aims to compare predictions of remaining life using statistical approaches applied to the partial inspection data with remaining life obtained from conventional integrity assessment using ILI or hydrostatic test.