ASME B31J

Covers — determination of stress intensification factors (SIF), flexibility factors, and sustained/other stress indices for metallic piping components (elbows, tees, branch connections, reducers, etc.), including a test method to develop factors for components not tabulated.

Does NOT cover (exclusions) — the following are governed elsewhere:

• The stress-analysis rules and allowable stresses that use these factors → ASME B31.1 / B31.3.
• Component dimensions/ratings → ASME B16.9 / B16.5, etc.
• Fatigue design curves for vessels → ASME BPVC Section VIII Div 2.

B31J supplies the SIF/flexibility factors; the piping code applies them within its stress-analysis rules.

B31J provides factors and methods:

• Stress Intensification Factors — test-based SIFs for standard components by geometry.
• Flexibility Factors — factors quantifying component flexibility for the analysis model.
• Sustained-Stress Indices — indices for sustained-load evaluation.
• Test Method — a standardized fatigue-test procedure to derive SIFs for non-tabulated components.

ASME B31J is the consolidated, test-based source for the stress intensification factors (SIF) and flexibility factors used in piping flexibility and stress analysis. These factors tell a pipe-stress model how much each fitting amplifies bending stress and how flexible it is — central to evaluating thermal-expansion and sustained stresses.

It supersedes the older Appendix D values, which were sometimes over- or under-conservative, with more accurate factors, and it provides a standardized fatigue-test method to develop SIFs for non-standard components. B31.1 and B31.3 reference B31J for improved-accuracy analysis.

Engineering Note: Use the current B31J factors rather than legacy Appendix D values where the code permits — an inaccurate SIF distorts the whole flexibility analysis, either hiding a real overstress or forcing unnecessary loops and supports.