While not the most glamorous subject, we have to deal with refrigerant pipe material every day so it’s a good idea to understand the rules associated with its use. As is often the case with rules it’s not always clear what is allowed and what isn’t. Let me explain, with the necessary caveat that code interpretation is 100 percent up to your authority having jurisdiction (AHJ), of course.
In Canada, the rules for refrigerant piping begin in the Canadian Standards Association (CSA) B52 code which is adopted into legislation in some form or another in every province and territory. There actually isn’t that much information in the code related to piping material. A quick search reveals a clause that says simply that any material used in a refrigeration system shall be suitable for that system including when moisture is present. This seems simple but is a fairly complicated requirement if you want to use an unusual material – it would be up to you to prove the compatibility.
There is a bit more information on not allowing magnesium alloys in the presence of halocarbons and not allowing copper with ammonia. There is also a clause that does allow aluminum with ammonia. Straightforward so far.
Continuing on through the B52 code you discover that unless the equipment is exempt from registration because it is covered under other CSA standards and tested by an approved testing laboratory, refrigerant piping must be registered in accordance with CSA B51 and designed and constructed in accordance with American Society of Mechanical Engineers (ASME) B31.5. What does this mean? Well, your piping won’t likely be exempt on the grounds that it is covered by other CSA standards unless it is part of a prefabricated system, so you probably need to worry about CSA B51 and ASME B31.5.
On the materials front, CSA B51 says that the design must be registered and comply with ASME B31.5. Registration means that you have to submit the design to the AHJ for approval. You may be thinking at this point think that I’m talking only about large commercial and industrial applications. Nope, so far everything I’ve written applies to every single refrigeration system, as far as CSA B52 is concerned at least.
ASME B31.5 is a code for pressure piping that applies to refrigeration and heat transfer components. It goes through all the material requirements of piping material (strength tests, impact tests, material types, fabrication, assembly, welding, brazing, etc.…). ASME B31.5 starts off by saying that all materials must conform to a listed specification from ASTM (Formerly the American Society of Testing and Materials).
ASME B31.5 then goes through and describes minimum design pressures, what factors have to be considered in the piping design such as wind loading, impact, seismic, thermal expansion, etc. and then outlines the allowable strength and temperature ratings of different materials with ASTM testing standards. It includes a list of many acceptable materials but does not rule out any material, including non-metallic ones, providing they meet the requirements (in order to figure this out, you will need another huge standard – ASME B31.3 Process Piping). ASME B31.5 is the standard that mechanical engineers use when designing large piping systems, but the content is applicable to all refrigerant piping.
Where does this leave us? Other than a few material compatibility requirements in CSA-B52 code we have to use ASME B31.5 when choosing piping materials. ASME B31.5 is fairly complicated to use but it gives us a lot of options.
Back in CSA B52 there are additional requirements that apply only to ‘unprotected refrigerant piping and tubing’. Conveniently, there is also a definition of what ‘unprotected’ means and basically it is tubing that is not covered by a protective enclosure. I must admit that this section has baffled me for a long time. It requires unprotected hard copper tubing to be ASTM B88 type K or L (Type M, L, K are all copper tubing with increasing wall thickness – M is the thinnest and used mainly in plumbing applications) and then goes on to say that soft tubing must comply with ASTM B280. ATSM B280 covers both hard and soft tubing and is equivalent in thickness to Type L so I’m not sure why the code references two different material standards. The copper that is manufactured to ASTM B280 also has to be cleaned.
In any case, the intent here looks to be that copper that is unprotected must have a specified wall thickness in order to prevent failure due to physical damage (to make things even more confusing, the table of wall thicknesses published in the current edition of CSA B52 is incorrect at least according to the ASTM B280-03 that I have on hand).
Then there is a requirement that copper tubing be brazed and not soldered. While it is certainly industry practice to use brazing all of the time and doing so is usually (but not always) a requirement under ASME B31.5, I don’t understand why it’s in a section relating only to unprotected copper tubing.
So now that I’ve thoroughly confused everyone let’s recap. CSA B52 has a few pipe material requirements but generally the material selection comes down to the requirements in ASME B31.5 which a lot of refrigeration contractors have never seen. A lesson on ASME B31.5 is not something we can do quickly but I would point you in that direction if you are interested in the subject – ASME B31.5 is also the code responsible for a lot of the brazing and welding procedure requirements you may be familiar with, depending on your jurisdiction.
Requirements not well known
So why haven’t we all heard of many of these requirements. The answer is simple and there are three reasons. First, the legislation in most provinces exempts an awful lot of systems. Most provinces don’t even adopt the CSA B52 for systems under three tons. After that, many piping systems under a certain internal volume are exempted from registration, which means that while you are supposed to comply with ASME B31.5, no one actually checks.
Second, there has historically been little to no enforcement in many areas of the CSA B52 code, even when someone is supposed to check. Third, we have worked in an industry that for a long time has had a very simple standard practice. We have copper tubing that is designed and cleaned specifically for refrigerants. This tubing meets ASME B31.5 requirements in most cases and is used almost exclusively on halocarbon systems. In other words we didn’t really need to worry about using other materials.
You have more than likely heard of the high discharge pressures of CO2 refrigerant. It turns out that ACR copper doesn’t meet the high side pressure requirements of many CO2 systems, so we have to use different materials. And we are using a lot of them – stainless steel tubing, stainless steel pipe, copper alloys, etc.
There have also been accidents and failures because designers and contractors used incorrect materials. This isn’t something we’ve had to worry about for a long time and understanding ASME B31.5 and CSA B52 will help make sure we don’t make more mistakes. We are seeing systems with different materials on the high and low sides and sometimes they look the same. Different grades of the same metal can have different pressure ratings and it’s up to us make sure we are using the correct material.