breaking a weld

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Is it possible to break a weld by reheating it?  I  have a water valve for a sprinkler system needs to be connected into an copper elbow with threads.   There's no other way to get this back on unless I break the weld or cut it off.   Any advise is greatly appreciated.
Reply:Is this a weld in a steel pipe?  BTW, where in Michigan?www.urkafarms.com
Reply:Both are copper.  Detroit Metro....Novi.
Reply:muells,You talking about a solder joint?  Solder joints are a piece of cake to undo.  You'll probably bugger up the fitting as they're so thin and it takes a bit of twisting to get them apart.Can you better describe exactly what you're doing?
Reply:There's a copper elbow with threads going into the water valve. On the other side of the elbow is where the elbow is soldered onto the copper pipe which goes into the ground to the sprinker system.   If I apply enough heat to that,  I have map gas,  will I be able to get that apart?   Thanks for your interest.  Look forward to your reply....
Reply:If it isnt full of water heat it up and twist it apart.  Once the solder is melted it will lose all its strength and come right apart.www.urkafarms.com
Reply:Thanks.   Will let you all know how it turns out.  I'm also hoping to resodder this piece when I get the new water valve on and assuming this will not be a problem.
Reply:muells,What Sberry said is dead on.  If there's water in the system anywhere near that joint, you'll not get the solder to melt.
Reply:muells;Resoldering it may be a problem.Solder fittings are designed with a close fit, and if you dont get all the solder off the parts they simply wont go back together once the solder has cooled.Getting the solder off the pipe may be as simple as wiping it with a damp cloth while it is still hot. Getting it out of the inside of the elbow is more of a challenge.The only practical way is to use a reamer the same size as the O.D. of the pipe. Most plumbers would simply use a new elbow, its not worth the time and effort. .I'm not very clever,But I can lift heavy things.
Reply:Correcton in my earlier statement.    The pipe is copper...obvious,   the valve is made of brass.  The copper slips into the brass fitting on the valve.     The map gas heated it quite quickly and I was able to break the weld and pull it off with minimal twisting.   Lucky me,  it came off quite clean.  I let cool and wiped it off with a rag,   re-soldered it back on and was in business.   No leaks!!!    Thanks for the advise from all.  Saved a service call.    Wouldn't mind doing this for a living!
Reply:cool, it's awesome when something works right. What trade are you in??, You are welcome to stick around!!StangnetShop Full Of Stuff. Joey
Reply:Muells you wouldn't want to do it for a living very long. Those things don't break when its nice outside on a sunny day, they freeze at 10 o'clock at night when the wind is blowing and its 25 degrees outside, then the next morning when it starts warming up they bust and nobody knows about it for a couple of hours (now the ground is real muddy under the break). Then you have to go out and swimn in and fix them. DavidDavid
Reply:I was thinking the same thing,,, they aint always that easy.www.urkafarms.com