You are absolutely correct; fortunately I just misspoke rather than misunderstood; I meant fitting in all contexts.
Interestingly, my OP referred to the first soldering of the joint failing. When I pulled it apart there was no solder on the top of the fitting; yet it was bright and the scratches from the brush were still visible. The pipe on the other hand was completely covered with solder. All I can figure is that I didn't put enough flux on it, but even if I didn't, shouldn't enough flux have rubbed off from pipe to have worked? Apparently not. Anyhow, I started using twice as much flux.
If you want to be perfectly anal about it, the best way is to heat the fitting, and then apply solder to the _pipe_, on the other side of the joint, and not touch the solder to the edge of the fitting until it starts to flow against the pipe.
What this does is force you to be applying solder against the coolest part of the joint. Once _that_ is up to temperature, you're guaranteed that the rest of the joint is up to temperature.
It matters more to pros, because they're often using acetylene or MAP torches, which heat the joint much faster than the gentle roasting of a propane torch, and temperature differences can be rather high.
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?
I can remember once when I put in a water heater using CPVC and turned the water back on. Everything was looking good when a little drop formed under a fitting. I touched it and it gave way. I had totally missed that fitting, no cleaner no solvent. :-)
You should apply heat only to the fitting; the pipe will get hot enough anyway through contact with the fitting. If the pipe is heated directly, it can expand far enough to prevent sufficient solder from flowing into the joint, producing a weak joint.
-- 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?
Could be worse... this guy I used to know re-plumbed his kitchen, and didn't even *know* he was supposed to cement the pipes into the fittings. I heard the story from his wife; I guess there was quite a fountain in the crawlspace when he turned the pressure back on...
-- 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?
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?
If you are referring to very thin teflon tape (which has no adhesive), then it's for sealing threaded joints. Unscrew, apply to the thread then screw up the connection. In the old days, plumbers used sisal for the same purpose.
It is black, slightly adhesive, tape called SealWrap Repair tape. It feels similar to electrical tape, except that you stretch it out as you apply it. I have had it sitting in my basement for 2 years without using it, so yesterday I decided to see what it would do. I taped up a 1.5" PVC pipe joint. After 15 minutes, with one end clamped in a vice, it was very difficult to pull apart. Not as strong as gluing it, but it would certainly hold a drain together. I don't know what it would do on a supply line leak. Maybe I will try that next.
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 smaller area.
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
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.
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.)
A few opinions on sweating pipes, I do this for a living. Even went to school for it. Use the hottest torch you can get, my favorite for soft solder is a Turbo Torch using Mapp gas. Then use the hottest part of the flame, in this case about 1/2" past the inner cone. You will do less damage to the surrounding area with a hot torch. Get in there get it hot and get out. Clean everything including the solder. Apply a paste flux sparingly to the outside of the pipe, first 1/8" inside of the fitting, and a little on the solder. Secure the pipe to avoid movement. Rule of thumb, with normal 1/8" solder you will use the same length of solder as the circumference of the pipe. Make a bend in the solder at that point. Protect any heat sensitive parts with wet rags. Preheat the pipe concentrating at edge of the fitting and keep the torch moving. When the pipe is hot enough to melt the solder move the torch on too the fitting. That is the big secret, solder will flow towards the heat. This is especially important on vertical joints. Practice on some scrap pipe, with a little technique you can literally pump solder uphill through the joint and into the inside of the pipe. I test all my soft joints at 200 psi and my silver (solder) braze ones at 400 psi, I don't have leaks. Dave
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.]
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.
Try this experiment: solder a pipe joint while rotating the fittings. The joint edges won't be shiny, and there's an extremely good chance it will leak under pressure.
Solder tends to harden via crystalization. If moved during the critical period, the crystals will literally rotate, and the final solidification will be filled with voids, and be much weaker.
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