Expert ForumsCorrosion

Topic: Re: Will operating at elevated temperature lower the recommended maximum working pressure?

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As you implied by your question, operating at elevated temperature will lower the recommended maximum working pressure. I checked the website of a manufacturer of CPVC piping and their 3-inch schedule 80 pipe has a recommended working pressure of 370 psi at 73 degrees F just like yours. Since the pressure ratings given are for water, non-shock, at 73 degrees F, a de-rating factor has to be applied to the working pressure rating when operating at elevated temperatures. For this manufacturer of CPVC pipe, the de-rating factor is between 0.25 and 0.20 for a temperature of 85 degrees C. Being conservative and multiplying 370 psi by the de-rating factor of 0.2 gives a new maximum working pressure of 74 psi at 85 degrees C. This is less than the pressure of 100 psi you asked about. Of course, the answer may be different for something other than water.  I suggest you contact the manufacturer of your CPVC piping for help answering this question for your specific situation.