Since the introduction of the Drop Weight Tear Tester - DWTT, materials have moved on. In particular, demands for high operating pressures of line-pipes and larger diameters have driven the development of higher strength steels. Forty years ago the work that led to the drop weight tear test was done on X52 steel (360MPa yield strength). Improvements in thermo-mechanical processing has yielded improvements of approximately 10,000psi per decade, to the point where the state of the art is now X100 steels, and the use of X120 steels is being considered.
This development in material technology has placed substantial demands on conventional test techniques and the relevance of some results have been drawn into question.
Since a Drop Weight Tear Tester - DWT tester represents a significant investment both in terms of capital cost and operator training, it is important that any equipment being specified now should have the flexibility and the capacity to cover developments in test methodology and the mechanical properties of materials for the expected service life of the apparatus, ten years or more. To this end, this article examines issues concerning the measurement of fracture toughness of steel, and in particular the use of high capacity instrumented DWT testers.
Drop Weight Tear Tester - DWTT Instrumented
A range of drop weight impact testers for measuring the fracture characteristics and fracture ductility of steel specimens according to the following standards: API recommended practice 5L3, EN 10274, ASTM-E 436 and ‘Pellini’.
DWT40-25 impact energy up to 24,500J requiring a floor-to-ceiling height of 5.5m
(500kg to 1000kg impact mass at 4.5m/s to 7.0m/s impact velocity)
DWT40-42 impact energy up to 40,500J requiring a floor-to-ceiling height of 7.0m
(500kg to 1000kg impact mass at 4.5m/s to 9.0m/s impact velocity)
DWT60-42 impact energy up to 61,500J requiring a floor-to-ceiling height of 7.5m
(1000kg to 1500kg impact mass at 4.5m/s to 9.0m/s impact velocity)
DWT100-42 impact energy up to 103,000J requiring a floor-to-ceiling height of 7.5m (1000kg to 2500kg impact mass at 4.5m/s to 9.0m/s impact velocity)
Available options for the DWTT product Range
|Variable mass system||Improves the range of applicable impact energy. The range improvement varies for the product range.|
|Specimen Cooling Bath||–80ºC to +20ºC, The DWTT cooling bath accommodates up to 14 specimens of 20mm thickness at a time, enabling preconditioning of the specimen at low temperature.|
|Specimen Notcher||The DWTT notcher applies the pressed notch to the specimen according to the following standards:
API recommended practice 5L3, EN 10274, ASTM-E 436.