In an isometric drawing, the notation '3-inch, 150#' most likely describes which feature?

• A. A 3-inch length and 150 weight
• B. A 3-inch thickness and 150 psi
• C. A 3-inch diameter flange with a 150# rating
• D. A 3-inch radius and 150 bolts

Answer: (C)

In piping isometrics, the shorthand “3-inch, 150#” tells you the flange size and its pressure class. The 3-inch part is the flange’s nominal diameter, and the 150# denotes a Class 150 pressure rating. This rating, from ASME standards, defines the maximum allowable working pressure for that flange size and material at standard conditions. It isn’t about weight, psi, bolts, or a radius. So the notation describes a flange with 3-inch diameter and Class 150 rating.