What’s The Difference Between PVC And CPVC?

In the world of polymer science, a single, seemingly small change in a polymer’s molecular structure can have a huge impact on how a material behaves in the real world — and on the products you make from that material. Polymer “kissing cousins” PVC and CPVC illustrate this concept brilliantly.

pvc

PVC (polyvinyl chloride) has been around since the late 19th century, but didn’t have widespread use until after World War II. Today, its strength, durability, relatively low cost, and easy utility make it a top choice for plumbing and drainage applications. If you’ve ever passed a construction site — commercial or residential — you almost certainly have seen multiple choices of PVC pipes being used for plumbing or ductwork. However, as great as it is, PVC can only handle fluids up to around 140°F.

Enter PVC’s cousin, chlorinated polyvinyl chloride (CPVC). Both PVC and CPVC are essentially the same molecule, with one simple, yet significant difference — during the manufacturing process, the use of a free radical chlorination reaction boosts the chlorine content of CPVC. The chlorine content is increased from 57% to as high as 74%. That simple alteration affects how CPVC behaves in real-world applications.

The most significant difference is CPVC’s improved heat resistance. It can handle fluids up to about 200°F — making it a better choice than PVC, for hot-water plumbing. If you pipe water that is too hot through PVC pipes, they could melt, crack and leak — leaving you with a literal hot mess!

However, CPVC has a big vulnerability, one that it shares with PVC — it is susceptible to environmental stress cracking (ESC) by phthalates, such as diisononyl phthalate (DINP). DINP is a plasticizer commonly used to make PVC more flexible, and its use allows us to have vinyl car seats (Oh yay!), super-thin electrical cable insulation, and rust-resistant car bumpers. It’s also commonly used in sealants — and therein can lie a problem.

Recently, a client asked us to help them understand why a CPVC pipe had failed. We suspected a caulk containing DINP had been in contact with the pipe.

We conducted an environmental stress cracking experiment. We inserted a large metal ball bearing inside a piece of pipe to create significant hoop stress, applied a drop of DINP to the exterior of the pipe (over the location of the ball), and then videotaped the pipe for 15 hours.

The experiment perfectly illustrated a vulnerability that PVC and CPVC have in common. You can see the test results here — where we compressed the 15 hours to a 90-second video. This visual is eye opening! 

http://www.ppfahome.org/pvc/historypvc.aspx

18 Comments


  1. Very professional article with good info.
    CPVC however has one serious drawback to PVC – too much chlorine (74% vs 57%) which is environmentally bad – if ESC occurs with CPVC piping, a lot more chlorine enters the environment, really bad if water is being carried.

    Reply

    1. Hi Tony,

      Thanks for reading out post and also leaving feedback! You raise a great point for consideration. We hope you continue reading & interacting with our blog.

      Best wishes,

      Caitlyn

      Polymer Solutions

      Reply

    2. ESC does not cause either CPVC or PVC to dehydrochlorinate. The chlorine remains bound in the polymer even after the pipe cracks and fails.

      Reply

  2. But, if DINP is a plasticizer, shouldn’t it make CPVC more flexible and, therefore, deform rather than crack?

    Reply

    1. Great questions, Jav!

      Basically, the plasticizer in the right concentration and blended with the polymer, when the polymer is made into a product, creates a flexible product.
      When a stiff plastic product is made, and then the plasticizer is added later, it “lubricates” between polymer chains, allowing them to detangle. This reduces the load carrying capacity of the plastic and a crack develops. This is why ESC always requires a chemical agent AND stress. One or the other alone can never cause an ESC failure.

      I hope that information is helpful to you! Please let me know if you have follow up questions.

      Best wishes,

      Caitlyn
      Polymer Solutions

      Reply

  3. I agree with Tony Mack a lot of damage can be done with CPVC

    Reply

  4. Hi,

    This is a great article. I’d like to do some testing myself. I wonder if you could share what caulk contains DINP please.

    Pretty amazing what a drop of stuff can do.

    Thanks,
    Chris

    Reply

  5. Best Article for this subject according PVC Pipe and this type pipe very best uses in construction and other field.

    Reply

    1. Hi Jayesh,

      Thanks for reading our blog and leaving feedback!

      Stay curious,
      Ashlyn
      Polymer Solutions

      Reply

  6. Good to see this helpful information here, Thanks for sharing with us….This is great….

    Reply

  7. How about cements?
    Specifically may CPVC cement be safely used on PVC piping?

    Reply

    1. Hi Bill,
      Great question! You are welcome to email info@polymersolutions.com to discuss your question in more detail.
      Best wishes,
      Amanda, PSI Blog Team

      Reply

  8. Very nice article. Thank you for sharing this.

    Reply

  9. Hi. Which tests can be performed to distinguish CPVC from PVC if I don’t have the specs? Thermal properties?

    Reply

    1. Hi Bejie,
      Great question! You are welcome to email info@polymersolutions.com to discuss your question in more detail.
      Best wishes,
      Amanda, PSI Blog Team

      Reply

  10. very informative article.Good to see this helpful information here, Thanks for sharing with us….This is great.

    Reply

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