My last pipe soldering question for a while

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I finally did the installation I have asked a bunch of questions about. It involved putting some Ts in the main water line.
One of the joints had a tiny leak, maybe a cup an hour. Reheating it, needless to say, didn't help; so I pulled it apart, recleaned, refluxed and resoldered. It is fine now. But I have some questions for future reference.
1) If I had ignored the problem (it would have drained into the sump anyhow) would it have been stable, or would it erode over time? (A couple years ago a friend soldered in my new water heater and one of the joints has a tiny leak; maybe a cup a day. I wrapped a cloth around it and it evaporated faster than it leaked. A year later I put in a pressure regulator and it stopped. Apparently the joint was okay at 55PSI, but leaked at 90PSI.)
2) I have some plastic stretch tape that claims it stops leaks. If I applied it with the water off, would it have stopped the leak; had I not been able to take it apart? If not, would any product?
Thanks
I don't plan on doing anymore plumbing in the new future. Oh, not quite true; I have to replace the kitchen faucet. Hmm.
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One of those things you just never know about. Leaks may stop after time because minerals build up and clog the leak, or corrosion in iron pipes. Me, I'd not sleep at night knowing a pipe is not properly soldered and could get worse while I'm away on vacation.
At work we had a joint not properly soldered in a 2" copper tubing. It never leaked, but the tubing was not properly seated into the elbow. It took about 8 years, but if finally let go one morning. Thousands of gallons of water flowed before it could be shut off.
I'm not familiar with the tape, but I'd not trust it. OK for an emergency, but I'd still fix the pipe properly.
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Edwin Pawlowski wrote:

Never ignore warning signs when they are given to you.
I installed a water softener with all sweat soldered fittings. Apparently I didn't seat one of the fittings all the way, or maybe it was a cold solder joint. The joint never leaked, but it let go one night and fortunately I was home to hear the water gushing out into the garage. Had we been away on vacation, it would have flooded our home.
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What is a cold solder joint? If the solder melts on the pipe and flows in, it must be hot soldered; no?

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toller wrote:

If the solder melts and flows it is hot, the problem is the pipe may not be hot and it may not be properly bonded to the cold pipe. Watch what happens when a drip of solder lands on a cold pipe sometime. It just forms a ball and rolls off. That is why you heat the pipe not the solder and wick the solder into the joint. It will not melt or wick if the pipe\fitting is not hot.
--
Joseph Meehan

26 + 6 = 1 It's Irish Math
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But if it does wick, then it is hot; right? (That is what I meant by melting on the pipe and flowing in.)
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toller wrote:

Not always, but I most of the time anyway.
--
Joseph Meehan

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A cold solder joint means that the copper is coated by the solder, but it never actually combined with it. Usually caused by dirt/oxide on the copper or movement during cooling.
A proper solder joint actually blends the copper and solder together into an alloy.
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Movement during cooling? My understanding is that the solder is either liquid (when it can be moved) or solid (where it can't be moved). The transformation was quick enough that movement was not an issue; at least in small pipe not exposed to high forces. If any of the solder is solid enough to be be damaged by movement, it has already become strong enough to prevent that movement.
Am I misinformed?
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toller wrote:

Yes.
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Yes, you are. The transition from liquid to solid is neither as rapid nor as clear-cut as you think. Alloys generally don't have a crisp melting or freezing point; instead, they liquefy or solidify over a range of several degrees. There is also a range of temperatures below the melting point in which the metal is plastic, that is, easily deformable. If a solder joint is mechanically stressed before the solder has cooled below the plasticity temperature range, it will be considerably weakened and may fail.
-- Regards, Doug Miller (alphageek at milmac dot com)
Nobody ever left footprints in the sands of time by sitting on his butt. And who wants to leave buttprints in the sands of time?
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wrote:

We talking seconds or minutes? I don't think I have ever moved a pipe after soldering, but I have turned the water on a few minutes afterwards. Event hen, since there was a faucet open downstream, there wouldn't have been much force on the joint.
Speaking of which, if the water pressure is 60PSI, does that mean the maximum pressure on the joint is 22 pounds? Would there be less with taps open?
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toller wrote:

Seconds. 1 to 5, maybe.

Nope, 60 psi.

Of course.
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Doug Miller wrote: ...

Correct...it's the "wetted perimeter"...there's a total of (pi*id) in^2 of surface area on the inner wall of the pipe/unit length.
However, as you note there is no portion of the solder joint that is directly exposed to the water except that which fills the annulus between the OD of the pipe and the ID of the fitting...that's a <much> smaller area.
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Not sure... my gut feeling is that it's on the order of twenty or thirty seconds, but I've never timed it. Certainly it's not "minutes", but I don't want to tell you "seconds" and have you think that I mean as little as two or three seconds. I'm sure it's more than that.

You're treading on thin ice IMO. I always allow joints to cool to room temperature before pressurizing them. Allowing water into the joint too soon will produce *very* rapid cooling, which certainly introduces unnecessary mechanical stress on the joint.

Not unless you're talking about some pretty small pipes.
Nominal 3/4" pipe is a bit under 7/8" actual diameter, and hence approximately 2.75" in circumference. The joint is about 3/4" deep, so the total area of the joint is around two square inches. Thus the total force exerted on the area of the joint, at 60 psi, would be around 120 pounds.
Similar calculation for nominal 1/2" pipe gives approximately 50 pounds total force if I did the math right.

Certainly.
-- Regards, Doug Miller (alphageek at milmac dot com)
Nobody ever left footprints in the sands of time by sitting on his butt. And who wants to leave buttprints in the sands of time?
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Doug Miller wrote: ...

...
But the solder joint only "sees" the area of the annular section between the OD of the pipe and the ID of the fitting which I think is what toller's concerned about...
I don't know what design tolerances are but they're certainly no more than roughly 1/32" so for a 3/4" pipe you're talking an area of roughly 7/8"*pi*1/32" < 0.1 in^2.
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It seems to me that the outward force is irrelevant to the joints failure. The force that will cause the joint to fail is perpendicular to the joint. Obviously that force is proportional to the pressure. My sense is that it is, as I said before, that it is PSI*( joint cross section area); but my engineering degree has 30 years of dust on it.
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toller wrote: ...

I thought you were concerned w/ the pressure on the area of solder...
The (static) mechanical force to cause a pipe section lengthwise out the end of the joint is the pressure times the cross-sectional area of whatever the end termination happens to be. Radially exerted forces aren't significant for the joint failure.
Dynamic forces will far exceed static and the strength of a good solder joint will withstand significantly above the static pressure before failing. In fact, I would expect the first point of failure to be the tubing seams or other fittings long before actual joint failure.
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On Thu, 17 Feb 2005 08:58:13 -0600, Duane Bozarth

Depends on which force(s) you're talking about. The force that is exerted in trying to force the joint apart endwise (pulling the pipe out of the fitting) is proportional to the cross-sectional area of the pipe. Since the pipe is probably not actually all the way home against the stops, you'd use the OD of the pipe to calculate this.
The force that's trying to squeeze the solder out from between the pipe and the fitting is proportional to the area of the seam between the pipe and fitting, wich you would calculate by taking the difference between the OD of the pipe, and the ID of the fitting.
The "bursting force" applied to the part of the pipe that's inside the fitting, would be found by multiplying the ID of the pipe by Pii and again by the length inserted, but that last force is pretty much irrelevent, since it's resisted by the pipe-metal itself.
Is all cases, the pressure exerted by the system when everything is still will be dwarfed by the pressures exerted when someone shuts off a fixture somewhere. (This is one of the few things about which a normal gate valve is better than a ball valve. Gate valves close more slowly.)
--Goedjn
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Doug's referring to total outward pressure on that "section" of the plumbing (where the fitting and pipe overlap). Since the pipe and fitting are theoretically bonded by solder, that's the total pressure that the combined assembly is being expected to withstand.
Given that standard copper pipe is rated for 200PSI, and the fitting will add more than 200PSI to that, I don't think toller needs to worry about the plumbing bursting ;-)
That said, since we were actually talking about inadequately seated fittings and "bursting apart", this is the wrong number for Toller. For toller, you have to compute the force being exerted longitudinally, and compare that to the shear strength of the existing solder bond he managed to establish.
The longitudinal force is simply the cross-sectional area of the pipe multiplied by the PSI. The shear strength of the solder joint is a shear strength of solder (whatever that is, in PSI) multiplied by the solder-wetted area (whatever that is).
[Counting dry-solder areas as zero shear strength ;-)]
If the shear strength is less than the longitudinal force, then the joint pops apart.
Further, during water hammer, the longitudinal force can jump _substantially_. So, the solder-wetted area may be high enough for static 60PSI, but when you have several hundred PSI of water hammer pressure spike, you need more wetted area than 60PSI would suggest.
Clearly, there's lots of safety-margin in standard plumbing. Indeed, I believe that a regular endcap would rupture before a properly done full depth solder joint failed.
But if you only managed an average of 1/32" worth of solder round the circumference of the joint, 60PSI is probably enough to blow the joint apart.
[Remembers, not fondly, discovering that the main ABS waste stack on our two story house was seated perhaps only 1/16" of an inch into the elbow under the basement slab. Top end was rigidly held "up" by the house framing. After a few years, building expansion/contraction finally popped the joint apart. Shit fountain. I hate that.]
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.
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