Why Are There so Many More Failures with CPVC Pipe Compared with PEX?

CPVC and PEX are both ductile. CPVC is rigid while PEX is flexible.  A key difference between PEX and CPVC is that PEX is highly crystalline and therefore is inherently resistant to hydrocarbon chemicals. CPVC, on the other hand, is incompatible with most hydrocarbon chemicals. Since hydrocarbon chemicals are everywhere, the most common cause of failure of CPVC is exposure to incompatible hydrocarbon chemicals while PEX is compatible with virtually all hydrocarbon chemicals. It is the combination the inherent chemical resistance of PEX with its extremely high ductility and flexibility that makes PEX a more reliable plumbing product than CPVC.

The only advantage the CPVC has over PEX is that it is easily joined using solvent cementing. However, solvent cementing is actually not as simple as some people think. There are certain rules that must be followed to make reliable solvent cemented joints. If these basic rules are not followed, the results can be disastrous!  The rules are described in all CPVC pipe manufacturer’s installation manuals as well as in several ASTM standards including ASTM D2855, D2846, and F645.

The Basic Rules for Make Reliable CPVC Joints Include:

  1. Square cutting pipe ends.
  2. Beveling or chamfering of the sharp outside edge from the end of the pipe.
  3. Removal of burrs created on the end of the pipe while saw cutting the pipe.
  4. Using the right size dauber to apply the cement.
  5. Adding a thick layer of cement to the end of the pipe.
  6. Adding a medium coat of cement to the inside of the socket.
  7. Adding a second thick layer of cement to the end of the pipe.
  8. Complete insertion of the pipe into the socket until the pipe bottoms out.
  9. Rotation of the pipe ¼ turn after insertion into the socket.
  10. Holding the pipe in place, after insertion and rotation, until the cement cures enough to keep the pipe from backing itself out of the socket.

Our experience has taught us that there are many installers that do not follow these basic rules. In fact, we have interviewed some pipe installers who started installing CPVC piping systems with no formal training believing that the process is so simple that it is virtually impossible to screw up.