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PRCI Report 190
- Chevron Notch for DWTT Use on High-Toughness Steel
- Report / Survey by Pipeline Research Council International, 09/01/1990
- Publisher: PRCI
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L51622e
Battelle Memorial Institute
Need: This research is aimed at finding a new type of notch that would produce propagation data similar to that produced by the PC DWTT. High-toughness materials and materials that had previously been studied were used assuming that if the new notch worked on these materials it would be satisfactory for lower toughness materials. Several notch modifications were tried and most were no better than the standard pressed notch used in the API specimen.
Benefit: A search for a new type of notch for the standard drop-weight-tear-test (DWTT) specimen has been completed. This new notch specimen is to replace the precracked DWTT specimen which has been shown to predict full-scale behavior but has received-little support from pipe manufacturers. The new notch is a chevron notch causing fracture initiation to occur at a machined point located at mid-wall thickness
and about 0.2 inch below the specimen edge (i.e., at the same depth as the pressed-in notch of the standard DWTT). No precracking or other severe prestraining, which may create strain aging problems, is required to produce the specimen. A good correlation was obtained between the chevron-notched DWTT and the Charpy V-notch specimens for conventionally rolled steels; this correlation effectively ties the chevron notched data to past fracture research data and to published correlations that
describe fracture in terms of Charpy upper-shelf energy. A procedure is included for preparing and conducting the Chevron notched DWTT.
Result: The CN DWTT specimen has been demonstrated to reproduce the capabilities of the standard PN DWTT for conventionally rolled steels. CN DWTT reproduces the transition temperature and provides a statistically close correlation with the CVN upper-shelf E/A. The specimen also reproduces the capabilities of the PC DWTT specimen for a high-toughness, controlled-rolled steel, a material that in previous
testing showed problems of notch blunting and consequently erroneously high impact-energy values. Determining the transition temperature of high-toughness quenched-and-tempered materials has also been a problem; the CN DWTT specimen transition temperature closely agrees with that determined by the PC DWTT. The apparent requirement is that nearly all of the fracture energy measured should be fracture propagation energy, which is what is measured by the CN DWTT specimen. This specimen type should work because initiation takes place at only the point of the
chevron and the material at this point is small in volume and fully restrained.
Battelle Memorial Institute
Need: This research is aimed at finding a new type of notch that would produce propagation data similar to that produced by the PC DWTT. High-toughness materials and materials that had previously been studied were used assuming that if the new notch worked on these materials it would be satisfactory for lower toughness materials. Several notch modifications were tried and most were no better than the standard pressed notch used in the API specimen.
Benefit: A search for a new type of notch for the standard drop-weight-tear-test (DWTT) specimen has been completed. This new notch specimen is to replace the precracked DWTT specimen which has been shown to predict full-scale behavior but has received-little support from pipe manufacturers. The new notch is a chevron notch causing fracture initiation to occur at a machined point located at mid-wall thickness
and about 0.2 inch below the specimen edge (i.e., at the same depth as the pressed-in notch of the standard DWTT). No precracking or other severe prestraining, which may create strain aging problems, is required to produce the specimen. A good correlation was obtained between the chevron-notched DWTT and the Charpy V-notch specimens for conventionally rolled steels; this correlation effectively ties the chevron notched data to past fracture research data and to published correlations that
describe fracture in terms of Charpy upper-shelf energy. A procedure is included for preparing and conducting the Chevron notched DWTT.
Result: The CN DWTT specimen has been demonstrated to reproduce the capabilities of the standard PN DWTT for conventionally rolled steels. CN DWTT reproduces the transition temperature and provides a statistically close correlation with the CVN upper-shelf E/A. The specimen also reproduces the capabilities of the PC DWTT specimen for a high-toughness, controlled-rolled steel, a material that in previous
testing showed problems of notch blunting and consequently erroneously high impact-energy values. Determining the transition temperature of high-toughness quenched-and-tempered materials has also been a problem; the CN DWTT specimen transition temperature closely agrees with that determined by the PC DWTT. The apparent requirement is that nearly all of the fracture energy measured should be fracture propagation energy, which is what is measured by the CN DWTT specimen. This specimen type should work because initiation takes place at only the point of the
chevron and the material at this point is small in volume and fully restrained.
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