Fracture Toughness Characterization of High-Pressure Pipe Girth Welds Using Single-Edge Tension SE(T) Specimens

Published

August 1, 2014

Author(s)

Enrico Lucon, Timothy S. Weeks, James Gianetto, W. R. Tyson, D. Y. Park

Abstract

The safety and reliability of large-diameter pipelines for the transport of fluid hydrocarbons is being improved by the development of high-strength steels, advanced weld technologies and strain-based design (SBD) methodologies. Strain-based design imposes a limit on the applied strains rather than the applied stresses in the design condition. For high pressure pipelines, SBD requires an assured strength overmatch for the weld metal as compared to the base material, in order to avoid strain localization in the weldment during service. CANMET and NIST have collaborated in a research project sponsored by US DOT-PHMSA (US Department of Transportation - Pipeline and Hazardous Materials Safety Administration) and PRCI (Pipeline Research Council International), aimed at characterizing the mechanical properties of single-torch and dual-torch girth welds from X100 pipes. This paper presents fracture toughness tests of weld and heat affected zone (HAZ) materials of X100 pipes from low-constraint (Single-Edge Tension, SE(T)) and high-constraint (Single-Edge Bend, SE(B)) specimen configurations. Published studies show that low constraint geometries such as SE(T) or shallow notched SE(B) specimens represent a better match for the constraint conditions of surface-breaking circumferential cracks in pipes during service. However, the SE(T) geometry is not included in any of the most widely used elastic-plastic fracture mechanics (EPFM) test standards. A procedure has been developed for performing and analyzing SE(T) toughness tests using a single-specimen technique, which includes formulas for calculating J-integral and CTOD, as well as estimating crack size using rotation-corrected elastic unloading compliance. It appears that the SE(T) methodology is mature enough to be considered for inclusion in future revisions of EPFM standards such as ASTM E1820 and ISO 12135.

Citation

Materials Performance and Characterization

Pub Type

Journals

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Keywords

Pipelines, high-strength steels, strain-based design, crack-tip constraint, X100, SE(T) specimen, SE(B) specimen, unloading compliance

Citation

Lucon, E. , Weeks, T. , Gianetto, J. , Tyson, W. and Park, D. (2014), Fracture Toughness Characterization of High-Pressure Pipe Girth Welds Using Single-Edge Tension SE(T) Specimens, Materials Performance and Characterization, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=914682 (Accessed December 13, 2024)