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TitleEngineering approach for ductile fracture arrest based on CTOA
AuthorXu, SORCID logo; Bassindale, C; Wang, X; Williams, B WORCID logo; Tyson, W RORCID logo; Guan, C
SourceProceedings of the Biennial International Pipeline Conference, IPC; 2022, 1-8 pages,
Alt SeriesNatural Resources Canada, Contribution Series 20230025
PublisherThe American Society of Mechanical Engineers
MeetingInternational Pipeline Conference; Calgary; CA; September 26-30, 2022
Mediapaper; digital; on-line
File formatpdf
Subjectsengineering geology; fractures; pipelines; Steel
ProgramCanmetMATERIALS Joining and Structural Performance
Released2022 12 19
AbstractDuctile fracture propagation control and arrest are important elements in fracture control of pipelines transporting natural gas and other high-vapour-pressure media (e.g., dense-phase carbon dioxide). The most familiar crack arrest methodology, the Battelle Two-Curve Method (BTCM), is based on Charpy absorbed energy, and is well known to under-predict requirements for current high-strength high-toughness steels. Adjustments have been made, either by using correction factors or using absorbed energy from the drop-weight tear test (DWTT), but these remain empirical. The crack-tip opening angle (CTOA) has been proposed for a number of years as a fundamental parameter to characterize propagation toughness in aerospace and pipeline applications. It is convenient for finite element (FE) modelling of fracture in full-scale structures such as pipe. However, early procedures to measure pipe CTOA by a “two-specimen” method have been shown to be unreliable. Moreover, previous CTOA models (PFRAC and PICPRO) produced very different results. Recent work has addressed both shortcomings, including validation of a practical test for determining CTOA of pipe steels (ASTM E3039) and development of reliable FE models for axial crack propagation in pipes. Fracture resistance curves (crack velocity as a function of pressure at constant CTOA) including the effect of backfill have been computed over a wide range of variables. For a given design (pipe geometry, gas pressure and backfill) only tensile properties and CTOA are required to determine conditions for arrest; there are no adjustable constants in the methodology. Results to date are in good agreement with full-scale burst tests (FSBTs) by researchers at TC Energy and at the University of Tokyo, and with Maxey's original treatment of the effect of backfill on fracture velocity at high pressures.
Summary(Plain Language Summary, not published)
This paper pertains to the CanmetMATERIALS Fracture Control of Pipelines project in alignment with NRCan's Materials for Energy under Energy Innovation Program. One of the key project objectives is to develop standards and methodologies for fast ductile fracture control of high-pressure gas transmission pipelines. Ductile fracture propagation control is an essential part of the fracture control plan for gas transmission pipelines, including those transporting CO2 and hydrogen or hydrogen blends. Specification of an appropriate fracture propagation toughness parameter is important for design and materials selection. The purpose of this paper is to present an overview of engineering approach for ductile fracture arrest based on an advanced parameter, crack-tip opening angle (CTOA). All the engineering tools needed to specify CTOA for arrest as a function of steel grade and design parameters using the two-curve approach are now available, at least for gases that undergo single-phase decompression. What is needed now is further finite element (FE) pipe modeling aimed at specific fluids and full-scale validation, i.e. full-scale burst test (FSBT) data for steels that have been characterized by CTOA.

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