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Old 12-16-2008, 01:37 AM   #1
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soldering pipe


I am not a plumber by trade but I have soldered pipe many times and for the first time I cant get the the solder to stick. IT always seems to have a little pin hole when I turn the water on.I was wondering if there is different grades of solder. I know to clean the pipe and the connector good and flux it but I am trying to do something as simple as cap an existing line hot & cold water and it will not hold no matter how good I clean the pipe and cap.I did it 4 times and it leaked everytime.There was paint on the pipe but I made shore it was clean 4 times .I bought the solder at home depot and it has a red label on it and I was wondering if it was a weaker grade of solder.any help would be appreciated.

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Old 12-16-2008, 08:48 AM   #2
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In my opinion this doesn't point to the quality of the solder.

Is there water anywhere near the joint (in the pipes) that you're soldering? If so, small leaks are very likely. To keep water and steam at bay while soldering, take some white bread and ball it up into a dough-ball and stuff a hunk of it a few inches into the pipe to plug it up. The bread will quickly and easily dissolve and come out of the faucet when the water is turned back on.

You may be overheating the joint and melting your flux too much. That'll also cause pinhole leaks, because the solder can't draw into the joint if the flux has boiled out.

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Old 12-16-2008, 10:00 AM   #3
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Quote:
but I am trying to do something as simple as cap an existing line hot & cold water
Ayuh,...

Is this line Open on it's other end When you're doing this,..??

If Not,... I'd think you're causing a rise in it's air pressure,+ it'll Never seal it...
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Old 12-16-2008, 10:29 AM   #4
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If it is a pressure deal, you can solder a threaded adapter on the end then use a threaded cap.
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Old 12-16-2008, 11:08 AM   #5
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Pinholes are usually a sign of water in the line being soldered. The water vaporizes and turns to steam and blows the solder out of the joint.
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Old 12-16-2008, 11:30 AM   #6
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SourMash:

People often assume that the most common cause of bad solder joints is water in the piping or not enough heat, but that's not true.

The most common cause of bad solder joints is that they don't leave an escape route for the air or steam pressure in the piping to escape. When you heat the piping to solder it, then you get both thermal expansion of the air and/or steam generation. If you don't provide a path for the increasing pressure inside the piping to escape OTHER THAN the joint you're trying to solder, then the pressure building up inside the piping will push the hot flux out of the joint, allowing air into that joint.

Soldering flux is nothing more than Petroleum Jelly (sold as "Vaseline") with an acid (or a chemical called zinc chloride added to it to make it acidic at soldering temperatures), and hot Petroleum Jelly will burn if exposed to the torch flame. So, you have a situation where the solder flux gets pushed out of the joint and what's left behind might burn away and expose the bare copper metal to oxygen in the air whereby it will form an oxide film on the copper metal almost instantanesously. Copper oxide is brown in colour, and it's the reason why new pennies and copper pipes are orange and old pennies and copper pipes are brown. That oxide film is slow to form at room temperature, but forms extremely quickly at soldering temperatures. In fact, the reason why soldering flux has the acid or zinc chloride in it is to dissolve the copper oxide inside the joint to expose bare copper. Copper oxide dissolves much more readily in hot acid than the copper metal itself.

WHEREAS, if you supply an alternate path for the pressure inside the pipe to escape, then capillary pressure holds the molten flux inside the joint until the solder starts to melt and the greater affinity of the molten solder to the copper (and hence higher capillary pressure of the molten solder) pushes that molten flux out of the joint. That flux being inside the joint prevents oxygen in the air from contacting the bare copper metal to ensure there is no copper oxide present inside the joint.

PS: You CAN use ordinary Vaseline as soldering flux. It doesn't work well, but it does work. You just have to "Vaseline" the joints immediately after sanding or brushing them to prevent any oxide film from forming on the bare copper metal until you solder the joint.
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Last edited by Nestor_Kelebay; 12-16-2008 at 05:30 PM.
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Old 12-16-2008, 01:59 PM   #7
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are the 2 pipes sticking out of the wall facing you on horizontal...asking because you need the water to drain out of the ones you want to cap.if the pipes are on the vertical they are holding water just below where you are trying to solder.the flame of the torch is heating the water(steam)not the pipe....if so take a paper towel twist it into a pencil shape and put it down the pipe to soak up at least 6" from the soldering area at the top.steel wool the pipe again and sand cloth it to raw copper flux it...clean the caps....flux them and your good to go.any paint in the soldered area will defeat the joint........heat the top of the cap 2" away and hit the joint.
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Old 12-16-2008, 02:30 PM   #8
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Originally Posted by biggles View Post
are the 2 pipes sticking out of the wall facing you on horizontal...asking because you need the water to drain out of the ones you want to cap.if the pipes are on the vertical they are holding water just below where you are trying to solder.the flame of the torch is heating the water(steam)not the pipe....if so take a paper towel twist it into a pencil shape and put it down the pipe to soak up at least 6" from the soldering area at the top.steel wool the pipe again and sand cloth it to raw copper flux it...clean the caps....flux them and your good to go.any paint in the soldered area will defeat the joint........heat the top of the cap 2" away and hit the joint.

So, you're saying that as long as the water level in the piping is far enough below the top of the pipe so that getting the joint hot enough won't be an issue, he should have no trouble soldering that cap on?

I'd like your thoughts and comments on my post immediately before yours.
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Last edited by Nestor_Kelebay; 12-16-2008 at 05:29 PM.
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Old 12-16-2008, 03:27 PM   #9
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You can try to use a turkey baster to remove excess water from the pipe system before you solder so that the solder will stick. Make sure you turn the house water supply off and you should also make sure to use plenty of flux. And remember, solder always runs towards the heat source.

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