It's a little tricky to be sure without knowing an awful lot more about the wider context, but I think it ought to go something like this. BTW, is the original FR a bit suspect? I'm surprised to see the FR word 'raccord' alongside the (usually) EN word 'union'.

Right, so it seems to be that these are going to be TIG welded into palce (so they're clearly not push-on hose connectors).

The slightly hysterical use of both 'raccord' and 'union' makes me think that these may be specifically in-line joiners — just the sort of thing you might use when you have cut into a pipe (découpe) and then want to join it back up again.

Note that they are not referred to as '3-way' connectors, but 3-piece ones — unless the FR is in fact dodgy, this suggests to me that these fittings consist of three components that fit together in some way; compression-type fittings, for example, will have a main body + 2 nuts to tighten; however, of course these are not the same as they are welded ones!

Do note, however, that my description is based on general plumbing fittings; I don't know if there may be some more specialist terminology in this laboratory-type situation.