During my “lost years” early in my college days (i.e. before I discovered firefighting and OSH) I built swimming pools during the summers. That job required a lot of piping work, which I got pretty good at, at least I thought I had until I got into my first Chlorine (Cl2) process as a safety engineer. Now words mean a lot and when dealing with Cl2, DETAILS MATTER, so when I was learning about our Cl2 process I was exposed to “solvent welded CPVC joints”. At first, I was sure I was being “punked” by the engineering and maintenance team as I had never heard this phrase in all my years of joining PVC piping together. We always used the word “glue” when we were joining our water pipes together, but folks there is a BIG difference between “glue” and “solvent welded”. When it comes to Cl2 piping, many processes will use PVC or CPVC piping for their vacuum water systems. This was another big surprise for me, as I was used to seeing metal Cl2 piping. So now I was for sure I was being “punked”… we are going to put a HAZMAT that some even consider “lethal service” in a plastic pipe that is “solvent welded”… yeah right, now where’s the hidden camera! But this is reality, let me explain:
The Chlorine Institutes Pamphlet 6, Table 9.2 does permit PVC and CPVC piping to be used for “Cl2 gas ONLY” piping. And with these piping specs, the Pamphlet states that the “solvent cemented socket joints” be used to join these pipes.
Although both PVC and CPVC are allowed, there is a critical difference between CPVC and PVC – their MAXIMUM OPERATING TEMPERATURES!
CPVC can handle temperatures up to 200°F, while PVC is limited to less than 140°F. Above their max temperatures, they will begin to soften, increasing the risk of joints and pipes failing, and therefore, failing of our primary containment system. Keep in mind, ambient 140°F is not hard to achieve in certain parts of the country (or world) in poorly ventilated spaces. We most certainly do not want our PVC piping anywhere near a hear source! We also must consider the temperature of the water/process liquids being used in these pipes.
When I was building my swimming pools I had been trained to prep the pipe with a “primer” and then to “glue” the pipe fittings. Simple terms for a simple man doing a simple water pipe job! But in reality, the “primer” and the “cement” were doing something altogether different than cleaning and gluing! Because there is a difference in the material’s chemical composition, CPVC and PVC pipes and fittings, along with their solvents and bonding agents, CAN NOT be used interchangeably. There are also different solvent types of cement required based on the pipe’s size and intended application, so we MUST be sure you’re using the correct agent for the correct application.
CPVC solvent types of cement must meet ASTM F493 specifications, and PVC solvent types of cement must meet ASTM D2564 specifications. And our QA/QC piping installation specs and inspections MUST include this BIG DETAIL to ensure the proper primers, solvent types of cement, and bonding agents have been used on the Cl2 piping.
But did you know that when we use the correct primer we are doing a heck of a lot more than “cleaning” the piping before we glue it. The primer is actually a very strong solvent and it is breaking down the piping, sort of the way welding melts the metal piping. When we then apply the “cement” the primer and cement are “solvent welding” the two pieces of plastic pipe and when they are done the two pieces of plastic are fused as one. With all of this said, most of my plants used the colored primer so as to be sure they can see any primer that erroneously got onto parts of the pipe that is NOT needed. This primer can WEAKEN the pipe walls if we leave it on the pipe where it is NOT necessary. So CLEANLINESS is critical to our Cl2 piping!
PLEASE NOTE that “solvent welded” connections are required for Schedule 40 and thinner piping. Schedule 80 and 120 can be threaded – Schedule 40 can NOT be threaded!