As we have discussed before, the PREFERRED pressure/leak testing method is hydrostatic. This is the “rule” for all of the ASME B31 series RAGAGEPs; however, for some odd reason, many businesses believe that pneumatic testing is “easier, cleaner, and cheaper” and will just perform their testing with little to no consideration for using hydrostatic methods. But B31.9, Utility Piping, has some very specific restrictions for using pneumatic testing on “plastic pipe,” and that is what I want to discuss in this article.