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Ductile-Fracture Resistance in X100 Pipeline Welds Measured with CTOA

Published

Author(s)

Elizabeth S. Drexler, Philippe P. Darcis, Christopher N. McCowan, Jeffrey W. Sowards, Joseph D. McColskey, Thomas A. Siewert

Abstract

A test for evaluation of resistance to ductile fracture (crack tip opening angle, CTOA) was found to reveal changes in crack propagation through the strain and strength gradients near weld joints in X100 pipeline steels. This test provides a long ligament for crack propagation data not available in Charpy or drop-weight tear specimens, and is much less expensive than the full-scale burst tests. Modified double cantilever beam (MDCB) specimens were used to evaluate the ductile-fracture resistance of the base metal, welds, and heat-affected zones (HAZ). The thickness of the test section was either 3 mm or 8 mm. Girth welds, perpendicular to the growing crack, and seam welds and their HAZ, parallel with the crack, were tested with a cross-head displacement rate of 0.02 mm/s (with the exception of one girth weld specimen for each thickness, which were tested at 0.002 mm/s). Analysis of the data reveals some general differences, such as changes in CTOA and crack growth rate as the crack moved through the base metal, HAZ, and girth weld material. The values for CTOA were observed to increase and the crack propagation rate decreased as the crack moved through the weld and approached the fusion line. The plastic deformation appears to be strongly influenced by the properties and geometry of the narrow HAZ, the fusion line, and the tougher base material. Consequently, the CTOA of the HAZ associated with the girth weld was larger than that of the seam-weld HAZ. It was not possible to obtain CTOA data for the seam weld with the crack parallel within the weld, because the crack immediately diverted out of the weld material into the HAZ. CTOA values from both girth welds and seam-weld HAZ were smaller than those of the base material. The 8 mm thick specimens consistently produced larger CTOA values than their 3 mm counterparts, introducing the possibility that there may be limitations to CTOA as a material property.
Citation
Welding Journal
Volume
90

Keywords

crack extension, crack propagation, crack tip opening angle, CTOA, HAZ, heat-affected zone, pipeline steels, SMAW, SAW, welds

Citation

Drexler, E. , Darcis, P. , McCowan, C. , Sowards, J. , McColskey, J. and Siewert, T. (2011), Ductile-Fracture Resistance in X100 Pipeline Welds Measured with CTOA, Welding Journal (Accessed June 22, 2024)

Issues

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Created December 1, 2011, Updated February 19, 2017