Session: 05-04-01 Fittings and Testing Methods

Paper Number: 86988

86988 - Engineering Assessment and Integrity Management of Substandard In-Line Isolation Fittings 

In-line isolation fittings used in TC Energy systems typically include a split tee assembly, flange, completion plug and bolt-up hardware, and often form part of an in-line isolation train plugging system during maintenance projects. In early 2019, TC Energy was notified that flanges supplied with some of the in-line isolation fittings from a vendor might be potentially problematic and fail to meet required mechanical properties. Metallurgical testing indicated that multiple flanges did not meet ultimate tensile strength or notch toughness requirements, and experienced significant embrittlement, with the lowest CVN measured at 3J. Some of these flanges are currently installed in TC Energy systems. To assess fitness‑for‑service of these flanges and to achieve a safe and cost-effective solution, TC Energy completed an innovative and comprehensive engineering assessment using a characteristic flange with hypothetical worst-case cracks and crack-like flaws. The assessment includes 1) High fidelity finite element analysis (FEA) based on laser scanned geometry, 2) Numerical linear-elastic and FEA‑based elastic–plastic fracture mechanics calculations, 3) Low temperature (-46°C) instrumented pressure testing of flanges up to doubled maximum operating pressure (MOP) with EDM notches at high‑stress locations determined by FEA, 4) Non‑destructive examination (NDE) before and after a pressure test, and 5) Destructive post-pressure test material testing. Both the analysis and testing indicate localized variation of material properties and demonstrate that the flange does not experience any form of brittle fracture, even at low temperature and with worst‑case cracks or crack-like flaws at stress concentration locations. At doubled MOP level, high plastic strain and formation of ductile cracking was predicted by the analysis and recorded in testing, without causing burst of the flange. A reliability-based evaluation established on the engineering assessment of the characteristic flange demonstrated that the installed in-line isolation fitting flanges are, in fact, fit for service with reasonable safety margin. The engineering assessment analysis methods, testing setup, results and findings are summarized in this paper.

Presenting Author: Ken Zhang TC Energy

Presenting Author Biography: Ken obtained his PhD degree in materials and mechanical engineering from Queen’s University. He worked as a consulting engineer for multiple years before joined TC Energy as a Senior Integrity Stress Engineer in 2019. His background comprises fracture mechanics, metallurgical engineering, and pipeline integrity, design and stress analysis. He has extensive experience in stress- and strain-based design, integrity management, and design of pipelines, pipeline stations, and terminals. Ken is a registered Professional Engineer in the Province of Alberta and has authored multiple refereed journal articles in the fields of pipeline, materials and nuclear physics.