Can I use pvc pipe for a water heater TPR valve outlet

If you mean coming down out of a T&P valve the answer is yes. http://www.texasinspector.com/Temperature%20and%20Pressure%20Relief%20Valve%20In stallation%20Instructions.pdf

As a rule we use copper but CPVC's acceptable. Good luck, Tom

We also use copper, usually type "M". This pipe has to be sloped and lead to the exterior, terminating 6" above ground.