Thomasjl - I know that cracking due to expansion/contraction can be an issue for soft soldered connections on low pressure steam, but I'm not aware of any particular problem in relatively low temp water systems like domestic hot water or hydronic heating. Do you have some specific instances of cracking failure due to expansion and contraction in these systems that we should be aware of?
TBP
It has nothing to do with the temperature, or at least not directly. It’s the mechanical working of the expansion and contraction that does the damage. I haven’t seen it happen it the field. I am just an engineer who does what a specification says. This spec appears trustworthy to me.
Thomasjl
YOU SAID:
"I am just an engineer who does what a specification says. This spec appears trustworthy to me."
Do you actually do the brazing or just write it down on a drawing or work sheet because thats what someone told you you should always do. What spec is that.. I would like to know.
Is it a specification your company developed or what?
Soft soldered CU has been used for what 50 years or so the only change I am aware of is the elimination of LEAD in the solder. I know that other sealing methodes are coming on the market but these methodes need to be proven out over time.
No! thermal expansion/contraction are not the causation of leaks in the domestic hot water systems its just poor workmanship of the joint. Have you ever seen a bad brazed joint? Well they leak too!!!
Thomasjl - I figured the "delta-T part" was inherent in the discussion when I wrote "...do you some specific instances of cracking due to thermal expansion...". Sorry.
It is not necessary to braze copper piping joints in commercial hot water heating service. If someone is regularly getting leaks on soft soldered joints for hot water heating, then the issue is workmanship, not the method or material. Compressed air systems are another story - I see soft soldered copper joints in those regularly. I just shake my head, and ask the plant people what they figure is going to happen if there's ever a fire.
Pennpoint,
This is not regarding a hot water supply system, which is normally soldered, but a heating system. A heating system is both hotter and temperature changes more often. I would not recommend CU piping anyway, but that is not Blutforts question. My concern is regarding the strength or behaviour of the joints over time. Neither the designer nor the guy who actually does the soldering is aware of that. Sometimes points are written in specifications as result of feedback from the field due to bad experiences. Just as easy those points remain in a spec while the state of the art has changed. I am not sure whether that is the case here. I think it is called the “yield strength(?)”which is weaker from soft solder rather than the brazing.
To answer your direct question, I believe there is a very good reason why a hot (180 oF) water system (I have to assume copper pipe, since you fail to identify the conduit) should not be brazed instead of soldered: It is not required and is a gross over-kill.
I've soldered my own and others' water systems in retrofits and new homes. As an old boilermaker working my way through college I learned the advantage of being an engineer instead of a welder: if you use your head instead of your rods, you burn up less energy and wind up with a better system.
I'm surprised that all the Mechanical Engineers on this thread have not asked what the type of piping is, what flux(es) are being used, what solder alloy is being discussed, and the merits of brazing over soft solder (1.5% Silver, min.). Nor has the difference between soft solder, hard solder, and brazing been discussed.
For a hot water system operating at less than 100 psig and 200 oF, using a 100% copper pipe with copper/brass/bronze fittings I fail to see the value of any debate on the subject. I've soldered these joints and have personally gone back after over 40 years to find them still working without a leak in their history. I've also soldered Stainless Steel, Sch 10S pipe for sanitary applications without any problem. Have I been doing something wrong over the past 50 years?
I've always reserved brazing for steel and cast iron applications (over 450 oC fusiondefines brazing). I've soldered in both hot (under 200 oF) and cryogenic (under -100 oF) applications in the field with constant success. The copper/solder joint just gets tougher and stronger as the temperature decreases. I prefer silver solder (what the purists call "hard solder") and maintain that it is the long-term, leak-free joint of choice with experienced welders/solderers. Of course, I'm assuming the application is being done by an experienced, knowledgeable and clean solderer, and not some sloppy dude. All good and professional soldering should be done under almost surgical conditions - if the application is to be taken seriously.
For some background on engineered solder information, I recommend the following website.
Bravo! Very good answer. As I read down the post I was asking the same questions you did! Good job of putting everything straight. My hat is off to you!
Thank you all for the responses. The discussion and resources mentioned are excellent. The firm that I work in mainly deals in refrigeration and our equipment and technicians are "tooled" for brazing. The occasional project tht we have that is Hot Water based takes forever. Having observed the piping techniques, I'm estimating that I could shave 20-33% off the piping time by having them braze instead of solder. The speed loss comes from the fluxing and cleaning of the copper prior to soldering. They aren't doing that prior to brazing.
It never occured to me that people who don't normally work with little low pressure/temperature hot water heating systems would not know that soldering or brazing copper pipe & fittings was the issue at hand. If you're talking "soldered joints" regarding one of these little systems, it's copper pipe. And more often than not, run by the same guys who did the plumbing, using the same materials/tools/methods. (Note that this is not always a GOOD thing, as while the actual pipe fitting and techniques are the same, there are some significant differences in the layouts. Many hot water heating systems function poorly because the differences are not understood, or addressed.)
Little Hot Water Heating Systems:
- Pre WWII systems were screwed sch 40 steel with 125 cast iron or 150 malleable iron screwed fittings.
- Post WWII, copper piping with soldered joints became the norm.
- Copper is still extensively used, but plastic tubing with an oxygen barrier (PEX) is becoming more common. Joints in copper systems are now often made with ProPress (or equivalent). This method is displacing soldering for both hot water heating and plumbing, because the the huge labour savings.
Residential/small commercial domestic hot & cold water piping, and hot water heating system piping have pretty much always used very similar (often identical) pipe and fittings.
