Well... we gotta leak.

Pro Press.

Most of our copper work is in 2-4" and we never sweat anymore unless a property specifically wants it. You need a lot of heat for 4", so we would typically do two torches at once, one on each side. There are fancy round pipe torches, but we never had those.

Without re-soldering it, I would silver braze right over it. As long as you're not going to burn anything next to it, its the fastest, easiest fix here. Mad Dog

Cut it out and propress. You wont regret it. When you get done your gonna wonder why you didn't propress it to start.

And yes, i have taken plenty of sweat fittings apart, cleaned them, and resoldered successfully. But i wouldn't do it anymore because of propress. Propress is just to simple. The problem with large size sweat fittings is sometimes the interference fit is a little to large to hold the solder. If not properly aligned the gap is larger on one side than the other. Tinning definitely helps but its and added process the adds labor. Add that all up and a propress fitting doesn't seem that expensive anymore. Priced right and the customer is paying for it anyway.

Good luck

What the blazes is 4" copper used for? Water supply for the whole town?

This is a callback, correct? You're already in the Red. A 4 inch Press Tool and fittings are big bucks. If you want out of there, for the cost 3 or 4 sticks of Silver Solder and some acetylene, you can move on. Mad Dog

at 4" cast iron probably will not scale enough to restrict the flow so that is also an option.

Oe time I had to solder over some joints on 4" copper in a year old hotel! It was the got piping and I think the expansion/ contraction caused the leaks.

I used a rosebud tip but with oxygen/ acetylene, which heated very quickly.

But if you have the press equipment or can borrow the large jaw fro a wholesaler, go that route and be done quickly.

If you soldered it first, don't braze it; brazing over soldered joints can open up a whole new can of worms. So, pick your poison. Solder it where it leaks, and solder the entire joint again, or pro-press it.

One thing I have done in the past after soldering a large joint is to take my smallest turbo torch tip and cap the joint off so it looks factory done. It can look clean and without any runs, and if done right, will show a visually smooth finished joint. One other thing, do not touch all of your other joints. They should be fine.

Yeah. I have brazed over solder joints as well with no issue

A can of worms, you ask? It stinks, as a can of worms does.

Sorry, lol, if this metaphor shows my age. I also have brazed over a solder joint, but not one this large of a diameter, and not one with water in it, as this 4" pipe will surely have some residual water in it, which can surely cause a problem.

@Tom_133 If you do not have the room to propress this repair, try soldering first. If that doesn't work propress the thing and walk away. At this point, only you can measure the difficulty in terms of time and cost. It's like what my doctor might ask. "On a scale of one to ten, how would you rate the pain?"

I also like the comment from @Steve Minnich above.

Well, if you can get the water out on a large 4" fitting…go for it.

What's great about Silver-Brazing is that its so plastic in its molten state that you can bridge large gaps and holes. When you are done Silver-Brazing a joint, it is very obvious, visually, if you have a joint that is not going to leak unlike soft solder where you may have a tiny pinhole leak that is naked to the eye. Mad Dog