The stress range equation in ASME B31.3 accounts for which stresses?

• A. Sustained and displacement stress
• B. Thermal stress only
• C. Fatigue stress only
• D. Elastic stress only

Answer: (A)

In ASME B31.3, the stress range used for fatigue is built from two kinds of stresses that vary during a cycle: those from sustained loads (like internal pressure and dead weight) and those from displacement (movement or deformation, such as thermal expansion or contraction that is restrained and creates bending or axial stresses). The combination of these two components gives the full stress range the pipe experiences in a cycle.

Thermal effects are not treated as a separate, standalone category for the fatigue range; they manifest as displacement stresses when the structure expands or contracts and is restrained. Fatigue is not assessed from a single type of stress in isolation, and it’s not limited to purely elastic stresses, but from the overall range produced by the combination of sustained and displacement stresses.

So the stress range equation accounts for sustained stresses and displacement stresses.