Copper Pipe Joints
Do you braze or solder copper pipe?
First, I would like to start by wishing everyone a Happy New Year! We now have a new code in effect in California, but I am yet to dive into the changes. I hope to get into that subject next month. Our code is based on the 2015 UPC which is amended to become the 2016 CPC that goes into effect January 1, 2017. I haven’t heard about any major changes, but I will investigate. In Los Angeles, we have a new water conservation ordinance, which is a big deal — surely a lot more dramatic than anything new in the code.
Anyway, the other day we were talking in-house about soldering versus brazing. In a project managers’ meeting it was mentioned that our field labor prefers to braze rather than solder large diameter pipes; apparently they’re easier to braze. I pointed out that brazing reduces the pressure rating of the copper joints so you need to be careful when you braze in a tall building. But how much of an effect does it actually have?
Copper tube is divided into two major categories, annealed (soft) and drawn (hard). Within those two categories, there are three different wall thicknesses: Types K, L and M. Type K has the thickest wall and Type M has the thinnest. Most of us specify Type L drawn copper. The thicker the wall thickness, the harder the pipe and the greater the pressure rating. The smaller the pipe diameter the greater the pressure rating. As two extreme examples, Type K drawn tube ¾ inch in diameter has a rating of 1,278 psi. In contrast, four-inch Type M annealed tube has a pressure rating of 251 psi. That’s quite a difference.
Many engineers and field plumbers don’t realize that when you braze copper rather than solder copper joints, you reduce the pressure rating to that of annealed tube. A soldered four-inch Type L joint has a pressure rating of 440 psi. If the plumber in the field decides to braze that joint rather than solder it, the rating will be reduced to 293 psi — the annealed rating. If that joint is at the base of a 50-story tower, the rating will be compromised, since the operating pressure would likely be 300 psi or more. The heat of the brazing process actually anneals (softens) the hard tube, reducing its pressure rating.
I learned another interesting factoid about solder just today. I have used the term 95-5 solder and lead-free solder quite interchangeably for a long time. The term 95-5, of course, is a reference to 95 percent tin and five percent antimony. This is a fairly hard alloy, and I am told it is harder to work with this than lead-free silver solder. Silver solder is a silver/tin/copper-enhanced alloy. It is softer and melts easier than 95-5, making it easier to work with. It is more expensive than 95-5, but the labor savings I’m told pays for the premium several times over.
It is worth noting that when one does braze a joint, a nitrogen purge must be used to prevent black oxidation from forming on the inside of the pipe.
Of course there are alternatives for joining copper tube that go beyond just soldering and brazing. There are mechanical joints such as Victaulic, ProPress and SharkBite to name a few, as well as T-DRILL, a mechanically extruded soldered joint. Let’s look at the pressure rating for each of those.
Copper mechanical couplings such as Victaulic have a pressure rating of 300 psi for all sizes two inches through eight inches for both K and L tube. This means that it is the coupling and not the material that is dictating the pressure rating. For type M tube it starts at 250 psi for two inches tube and decreases as the sizes get larger to 200 psi for the larger sizes. This implies that it is harder for the mechanical couplings to hold the pipe together for the thinner walled material than the thicker walled material.
ProPress, one of several mechanical press joint fitting manufacturers, is rated for 200 psi across the board with sizes up to four inches in diameter. These joints, for those unfamiliar, have a rubber gasket that is pressed onto the coupled pipe to form a firm pressure seal. However, this seal, while strong, is not as strong as that of solder of brazing. But it is an efficient means of assembling pipe and fittings for pressures within its rating. This product may not serve as the right choice for a 300 psi pump discharge line in a high-rise building, but for pressure zones of less than 200 psi, it is a time-efficient means of assembling pipe.
Similar to the mechanical press joint is the push-on barbed joint made by SharkBite and others. These joints are convenient for obvious reasons — no tools are required to put them together (except for cutting of the pipe itself). I had difficulty finding their pressure rating. I assume it is at least the code maximum of 80 psi, and I would suspect that they are rated for at least 125 psi. These fittings are only available in small sizes up to one inch, with “large fittings” for straight runs of 1-1/4-inch. I think it’s safe to say that this is more of a residential product.
For the Nibco version of the push-on fitting, I was able to find more product information. Its push-on fitting is available up to two inches in size and is rated for 200 psi, thus making it fairly versatile for commercial applications. I have not had firsthand experience with this product, but I think it warrants further investigation.
In researching product and installation techniques with the union guys here at my company, what became abundantly clear is that soldering pipe is becoming a bit of a lost art with the younger guys in the field. Between the challenges posed by lead-free solder coupled with the availability of many different mechanical joint options, the focus on soldering has diminished and the practice of the art has reduced. It seems that if a four-inch or six-inch soldered joint is required in the field, the old-timers sometimes have to be brought in to get the job done.
Another point worth mentioning is that here at my company, when we get into larger pipe sizes (above four inches) we often transition to stainless steel for economy sake. Pressure rating is not an issue. If Victaulic (or equal) style couplings are used, the schedule 10 rating is 600 psi for a four-inch pipe or higher depending on the coupling style you chose. If we weld the pipe the pressure rating is higher still. I found it difficult to find an exact pressure rating for schedule 10 stainless steel. The only information readily available in schedule 10 was for austenitic pipe, which would be total overkill for a plumbing application. Standard schedule 40 pipe is rated for 1,531 psi, so the schedule 10 pipe is surely rated for something in between that and the 600 psi coupling rating.
This article went a little further into fittings and materials than originally intended. The real point of this article was to emphasize the fact that copper pipe has a lower pressure rating when it is brazed rather than soldered. So, if you are designing a tall building be sure to factor that in to your material specifications. Consult the Copper Development Association’s literature as required.
Timothy Allinson, P.E., LEED AP, is vice president of Engineering at Murray Co., Mechanical Contractors, in Long Beach, California. He holds a BSME from Tufts University and an MBA from New York University. He is a professional engineer licensed in both mechanical and fire protection engineering in various states, and is a LEED accredited professional. Allinson is a past-president of ASPE, both the New York and Orange County chapters. He can be reached at firstname.lastname@example.org.