The worst are the water valves with corrugated hoses permanently attached, from the 80s. Pure junk. If you have those, replace ASAP.

Technically, your water valve doesn’t need to be welded. It needs to be soldered. Easy enough to do with a blowtorch, some flux, and some solder, but you need to get the water co to shut off the water to the house since you can’t solder a squirting pipe.

You can also get a freezing kit that creates an ice plug in the pipe further from where you will solder.

As far as the valve in future, close and open it once every month or so. That keeps deposits from building up and jamming it open or making it leak.