Thanks for your replies and input so far, some scary pics there !
It's the Tig weld method that's raised the question really but I can see the sense in a spacer when trying to match or disguise the patterns at the joint when using donor damascus tubes.
It's whether there's a problem with the weld heat "unravelling" or weakening the old welds between the iron and steel that got me thinking ?

Rust never sleeps !