Session: 01-02-02: Strategic Risk Reduction

Paper Number: 132232

132232 - Substantiation of Recommended Crack ILI Response, Onshore Pipelines 

Abstract: 

As pipeline crack threat management through in-line inspection has now become standard practice, a normative response to inspection results is being recommended in the API RP1176 refresh. Built upon primarily two data driven PRCI projects, this paper justifies reasonable and prudent response criteria which considers uncertainty, response timing, and growth to next inspection elements. Failure Pressure Ratio (FPR) and depth thresholds are examined from both an historical incident and operator-provided ILI/NDE pair data lens. Criteria which consider tool tolerance have been integrated into the holistic response to address that uncertainty aspect and motivate desirable behaviors. Crack ILI technology advancements and demonstrated performance metrics are reviewed as an integral part of this substantiation. The appropriateness of the 1.39 FPR and 50% depth response thresholds, written into regulations for scheduled metal loss response, are challenged and found to be unsuitable for crack threat management. Burst model performance data in the 50-70% wall thickness range are presented in conjunction with justification of a maximum depth threshold. In addition, the paper presents comprehensive crack reliability analysis for a wide range of pipeline properties, crack morphologies, and operating pressures for liquid pipelines. The reliability analysis compares calculated burst Probability of Failure (PoF) for crack defects, using Monte Carlo Simulation-based model, with calculated deterministic FPR values for the same crack defects. The comparisons will demonstrate appropriate FPR values to achieve acceptable reliability targets and maintain pipeline safety from a risk perspective. While crack management methodologies can vary between gas and liquid operation, the applicability of the recommended crack ILI response was investigated for both commodity categories. [MI1] The intent and philosophy of legacy document STP-PT-011, which focusses on holistic management of axial stress corrosion cracking in gas pipelines through direct assessment methods, was carefully considered and compared to the recommended ILI response criteria. While many elements of STP-PT-011 have no direct corollary to an integrity response to crack ILI data, the intent and philosophy elements of STP-PT-011 were found to be in complete harmony with the findings and recommendations of NDE-4-20.

The paper demonstrates that an incremental increase beyond the recommended values of 1.25 FPR without tool tolerance and 1.1 considered with tool tolerance would not measurably reduce incidents. Crack outlier root causes cannot practically be addressed by an increase in FPR thresholds; other remedial actions are needed. Increasing FPR thresholds beyond 1.25 would divert resources away from resolving cracking incident root causes and is demonstrated as being unsustainable.

 

Presenting Author: Lyndon Lamborn Lamborn Engineering Inc.

Presenting Author Biography: With more than 35 years of experience in fracture, fatigue, structural design, stress and loads analysis, testing, incident investigation, and 6 years as Crack Threat Subject Matter Expert at Enbridge Liquids Pipelines, Lyndon is now a consulting contractor. Lyndon holds a bachelor of science degree in Mechanical Engineering and two Masters degrees: Aeronautical Engineering and Secondary Education, and was employed in the aerospace industry at Boeing for 30 years. Lyndon is a Professional Engineer in the province of Alberta, Canada, holds eight US Patents, and is heavily involved in advancing pipeline integrity science.

Authors:

Lyndon Lamborn Lamborn Engineering Inc.
Cara Macrory RSI Pipeline Solutions
Taylor Shie Shell
Mahmoud Ibrahim Enbridge Liquids Pipelines