mostly foam dams / but there is basic things to understand like always vent to an open end and make sure you have lashing wire fitted to pull em out not blue rope . an oxy meter will confirm
they are ok
of course there is ready made systems available but they must be looked after and dont last with daft welders ,punctures ,explosions usual neglect
and dissolving film that usualy detach /dissolve halfway through the root needs good fitters
To understand how good a purge you have, you really need to invest in a purge monitor like a TAG 100 handy purge etc.
It's amazing how long it takes for a purge to get down to 0.01% O2 on bigger pipes. And that's just minimum required on stainless - you need something like 0.001% on titanium.
Always set the purge inlet at the low point and (small) vent at high point, and tape everything up. The joints will pull in O2 unless you do.