RD&D-Programme 2004 - SKB

Conclusions in RD&D 2001 and its review
SKI pointed out the importance of investigating the joint after FSW in order to establish whether
foreign particles from the tools or oxidation occur. Investigations of the material’s composition
and the occurrence of impurities in the weld joint were also recommended.
Newfound knowledge since RD&D 2001
As a result of development work during the period from March 2003 at the Canister Laboratory,
further experience has been accumulated with full-scale welding by FSW. Thanks to the new
welding machine and the availability of resources for nondestructive testing, it has been possible
to conduct the project under rational forms with regard to both execution and evaluation of
welding trials.
An important milestone has been reached in the development of the encapsulation technology
with the fabrication and sealing of a full-scale canister according to the quality plan. The
constituent components have thus met SKB’s current quality requirements. Furthermore, the
FSW technology has been demonstrated as a welding method for the canister bottom, see
Figure 6-19. No significant discontinuities have been detected in the lid and bottom welds.
Tests have shown that a two millimetre wide gap with a depth of 32 millimetres in the joint line
does not affect the quality of the weld. This shows that the process works with large tolerances
and that it is possible to repair volumetric defects.
The risk of causing defects during welding is elevated during the start sequence. Once the
process is in the parameter window (steady state) and no disturbances occur, no risk of defect
formation has been observed.
Figure 6-19. Start sequence and FSW tool on the way up to the parking position at the bottom
weld.
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