What is indicated by the notation '3-inch, 150#' on an isometric drawing?

• A. 3-inch thickness, 150 psi
• B. 3-inch length, 150 pounds
• C. 3-inch diameter, 150# Flange
• D. 3-inch radius, 150 foot-lbs

Answer: (C)

In piping isometrics, a notation like "3-inch, 150#" communicates two key facts about a flange: the size and the pressure rating. The 3-inch part is the nominal pipe size the flange fits, meaning the flange is sized for a 3-inch pipe. The 150# part is the flange’s pressure-class rating (Class 150), which defines the maximum working pressure the flange is designed to handle, according to standard tables. This pairing identifies the component as a flange suitable for a 3-inch line with a Class 150 rating. It’s not describing thickness, length, or a radius, and the 150# designation isn’t a direct psi value but a standard pressure class used with corresponding bolt patterns and dimensions.