Trepanning is the process of creating a hole through the centre of a solid bar, where a portion of the metal is removed as a smaller solid bar, rather than just removing the entire hole as swarf. This process can be much quicker, but also retains a solid bar removed from the hole which may be used to produce further components and is therefore of more value than swarf.
A note of caution regarding the smaller solid bar removed from the original bar during trepanning is the validity of the original mill test certificate. The diameter of the removed bar is obviously much less, and the test piece location from the original solid bar also means that the reported mechanical properties are not representative. One way to work around this is to re-solution anneal and re-test the removed bar to ensure consistency.
The nuclear industry frequently relies on trepanned core materials because they can be easily tested for critical performance and safety specifications and considerations plus, they can be archived for later evaluation.
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