The design factor in ASME B31.8 gas transmission piping is used for?

• A. Wall thickness calculation
• B. Maximum operating pressure determination
• C. Material selection guidance
• D. Pipe routing optimization

Answer: (A)

In ASME B31.8 gas transmission piping, the design factor provides a safety margin that is used when calculating how thick the pipe wall must be to safely carry the design pressure. It works by reducing the allowable stress that can be used in the wall-thickness equation. If the design factor increases, the allowable stress decreases, so the calculation requires a thicker wall to meet the same design pressure. This is why the design factor is tied directly to determining the minimum wall thickness.

It isn’t used to set the operating pressure itself, nor is it the primary driver for material selection or pipe routing. Those aspects are governed by other parts of the design process, while the design factor mainly controls the thickness needed to ensure safe service under the design pressure.