A crack is a crack. In metal the atomic force holding the metal...

A crack is a crack. In metal the atomic force holding the metal atoms together the EMF holds the electrons in place but being metal these outer electrons can jump across to other atoms and its parting leaves a hole that is immediately filled with another electron from another atom to satisfy the EMF electron swapping. this massive swapping goes on at scale, called the covalent bonding. the greater the swapping the more flexible the metal. Stretching between atoms is allowed but if the gap gets to far the bond is broken and you have a crack which cannot be joined again unless you fuse it. Yes you can fill this crack to seal the gap and a vacuum would be maintained but CVM sensor pads seal of the whole area been measured so not a problem kept nice and clean. Size of crack detected depends on the sensor pads sensitivity, check Roach Sandia Labs, they have that info. Under that sensitivity yes it would not be detected but you will find CVM sensitivity is very small and a crack at that length is not deemed a problem. The CVM vacuum gally gaps are so small the sensors can actually measure the crack growth rate. Rest assured it will detect a crack before you could actually see it. No crack can maintain a vacuum.