Unfortunately, the code is not as clear as I would like, and I do get a lot of pushback when I encounter high-expansion fluids in hazardous-materials piping. I deal with a lot of liquids that are Highly Toxic, Flammable, and some that are both, which also have a high coefficient of expansion. So, in this article, I hope to explain why B31.3 requires HRVs on some piping and why the code actually requires it.
Let’s first review the requirement: (emphasis by me)