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darsunt 07-02-2009 11:44 AM

Heat safety during copper pipe soldering?
A while back I watched a contractor replace a broken shutoff valve. The welds were about 6 inches from the stucco wall, the ball valve being installed, and a pvc sprinkler line attached to the pipe. Needless to say, I was concerned about fire, a damaged ball valve, and a melted pvc line. Things turned out okay though ( I think)

Since the copper at the joint needs to be around 800F to melt the solder, how hot does the pipe get 6 inches away from the weld? And how easy is it to damage a valve if the weld is fairly close? I'm looking at a lot of cramped situations in future copper welds I might attempt.

For example, I'm looking at a frozen shutoff valve just inches from the wall. I'm thinking it best to just bust out the wall (or two) for safety's sake.


adpanko 07-02-2009 01:50 PM

There are special heat shields that can be used behind pipe/joint when you solder so the effects of the torch against the wall (or whatever is back there) behind the joint won't set the wall on fire. Any plumbing supply place or big home store will sell them. They're maybe about $10, and it is a black nondescript looking cloth, about a foot square. You can blast the thing directly with the torch and it won't catch on fire. It still gets very hot from the torch, but it disperses the heat across the cloth, instead of leaving a highly concentrated flame hitting directly on the wall. And you should always have a fire extinguisher, or at least a pot of water, around when you solder.

When soldering on shut off valves, yes, you want to minimize potential damage to the valve from heat. For ball valves, I don't think there are any internal parts that could be messed up from a normal solder job. But some, if not all, gate valves have a rubber washer in them that presses down tight into the body of the valve to seal it off when you shut the valve. Those washers can possibly melt from the heat of a solder torch. So when you solder on those types of valves, make sure you open the valve before soldering to get that washer away from the body of the valve.

darsunt 07-02-2009 04:19 PM

How much heat is transmitted by the copper pipe itself, or does it dissipate quickly? I have some concern if the pipe itself is hot, touching wood or paper behind the wall.

Although from what I've seen, maybe that isn't a serious problem?

adpanko 07-03-2009 10:04 AM

The pipes still get real hot even within a foot of the solder joint. It gets hot enough that you'll burn your hand if you try to hold it within a foot or so. But I don't think that is enough heat to set walls or framing on fire. You obviously shouldn't pile up loose twigs and paper around the pipe, but I don't think you have to worry about the heat along the pipe setting things on fire. It is the direct heat/flame of the torch that you need to be concerned about, which is why you should always have that flame protector behind it when working in a tight space.

majakdragon 07-03-2009 12:23 PM

Not much worry unless the flame hits the surface. I have used cheap methods, such as wet rags wrapped around a pipe and even used the heat putty that "sucks up" the heat and prevents it from traveling down the pipe. With valves, you need to know if the inside contains plastic that could be damaged when soldering. This is usually marked on a tag on the valve when you buy it.

Marlin 07-04-2009 08:47 AM


Originally Posted by adpanko (Post 296260)
For ball valves, I don't think there are any internal parts that could be messed up from a normal solder job.

Trust me on this. You can mess up a ball valve soldering. Been there, done that, got yelled at for it.

breid 07-04-2009 07:00 PM

why not get a male pipe adapter, then use a threaded ball value. breid

darsunt 07-06-2009 10:16 PM

Yes, the first foot of the pipe gets VERY hot. It stays pretty cool past that, though.

Copper pipe soldering repairs must be a pain. Almost every needed repair I'm looking at is in awfully cramped areas.

kenmac 07-07-2009 07:55 AM

I will sometimes use a product such as this

darsunt 08-14-2011 12:48 AM

I did a solder job on water heater supply lines in cramped space. Job went okay but I burned myself with damn dripping solder because I had no other position to do it in (didn't want to wear gloves because I couldn't grip things right).
I may try another solder job on a valve near stucco. Use a wet towel and spray bottle, maybe some other products mentioned here. From what you guys said, and what I've seen, it should be safe.

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