A New Consideration on the CVN Test for Arctic Welding Application
By Wesley Wang on Monday, February 24th, 2014
The temperature in Arctic region was reported to be around -60 Celsius degree in the winter. Such a low temperature has a definite impact on steels mechanical properties, especially for the Charpy “V” notch (CVN) impact toughness. The CVN toughness is also an important and popular measure on weld metal toughness. A standard CVN testing specification is ASTM A370. The standard defines CVN samples with a dimension of 10mm x 10mm x 55mm. Currently, most of the CVN toughness testing on steel welds are conducted at a temperature no lower than -40 Celsius degree. The test has been very successfully applied to today’s steel fabrication industry.
For heavy-section steel fabrication, multiple CVN samples extracted from different depths and lateral positions of a weld cross-section. Those samples are tested to acquire a CVN toughness profile on the weld cross-section. This works well for conventional steel design and welding qualification.
As we know, the volume percent of re-heated zone on a CVN sample has a great contribution to the resultant CVN toughness. It actually changes with locations on a weld. Testing CVN samples at different locations only yields localized CVN toughness information. For a very hostile environment, such as the Arctic region, this conventional practice on CVN toughness evaluation deserves the following consideration:
•The actual toughness of a whole weld is an integration of contributions from every spot on a whole weld. The function of the integration is unknown. How large the deviation is between the whole and the individuals? This question directly affects the structure design and welding consumables qualification.
•Due to the configuration difference in different types of groove designs, whether a rendered profile from localized CVN testing results can represent the CVN toughness of the whole weld needs to be confirmed.
To answer the above, a CVN sample design with larger dimensions and more powerful CVN toughness testing equipment should be explored.