Significance of the Drop-Weight Tear Test and Charpy V-Notch Impact Test Results

Abstract

The results of extensive research on piping and pressure vessels of plain carbon and low-alloy materials is providing an understanding of the significance of impact test results in terms of the full-scale fracture initiation and propagation characteristics. The impact tests employed in the research work were the Charpy V-notch impact test and the drop-weight tear test (DWTT). The impact tests have been correlated with full-size cylindrical vessel tests in which the initiation and propagation characteristics have been determined under controlled conditions. The results of the research indicate that, for the materials studied, the impact test fracture appearances relate to the structural fracture appearance with certain limitations. Specifically, the DWTT when conducted on material of the same thickness as the structure will predict directly the fracture propagation transition temperature. The Charpy V-notch test fracture appearance can be correlated to the structural fracture propagation transition temperature but is offset generally on the temperature scale because of the difference in thickness between the Charpy specimen and the structure. Correlations have been attempted between Charpy or DWTT energies and the fracture initiation characteristics determined from full-scale cylindrical vessel experiments. These correlations to date between the plane stress-stress intensity factor Kc and the plateau impact energies have exhibited considerable scatter, and no consistent trends are indicated. Also, correlations were attempted between the impact energies and the fracture propagation behavior, but no consistent relationship was found.

Evaluation of energy parameters of fracture during drop weight tear tests based on the analysis of the geometry of the specimens

“…Secondly, "the complex nature of the formation of the specimen fracture type does not allow it to be interpreted as a criterion for the material toughness and confirms the doubt about the legality of using the fracture type as a quantitative criterion for assessing the crack resistance of welded pipes and other structures" [6]. Even the authors of this type of test, who initially discovered a correlation between fractures after testing of pipes and plate specimens [7], were not able to establish a clear correlation between the parts of fibrous fracture in the destroyed pipes and in the specimens, when they have tested another series of pipes [8]. Thirdly, it is not rational that such technically difficult test gives so little information about the processes that occur in the material during deformation and fracture.…”

Effect of microstructure on drop weight tear properties and inverse fracture occurring in hammer impacted region of high toughness X70 pipeline steels

“…Drop weight tear test (DWTT) uses specimens as thick as actual pipeline steels in order to predict fracture propagation transition temperature of the pipeline, unlike Charpy V-notch (CVN) impact test. [1][2][3][4][5] This testing method was developed by Battelle Memorial Institute of USA in the mid 1960s. As the toughness of pipeline steels has been increasing, the American Petroleum Institute (API) specified that the standard pressed notch (PN) DWTT which was originally developed by Battelle should be used for low toughness steels, while the chevron notched DWTT should be used for high toughness steels.…”