When working with the ASME B31 series for piping installation, many of the requirements are based on the “Category” of the fluid which will be traveling within the pipe. Of course, the higher the hazard, the higher the safety is necessary for your piping circuits. This is NOT my creation, and to be perfectly honest, I am not even sure where it came from (I googled it in an attempt to find its origin), but it seems to be used in many locations by a wide array of businesses so I am posting here for convenience sake. It is by far the best summary of the ASME Categories Services for fluids!