User Question
How are temperature cycles considered in fatigue analysis in AutoPIPE Vessel?
Explanation
In AutoPIPE Vessel, temperature cycles are not treated as independent fatigue load cycles.
Based on verified behavior:
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- Fatigue analysis explicitly accounts for pressure cycles
- Temperature is used only to determine temperature‑dependent material properties, such as elastic modulus
- Changes in mean temperature (Tmean) may influence fatigue results indirectly by modifying material properties.
- Thermal stress range due to ΔT is not calculated separately and is not added as an independent fatigue stress range
Code Interpretation
ASME Section VIII Division 2, Part 5 states that fatigue stress range should include:
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- Mechanical stress range (e.g., pressure)
- Thermal stress range due to temperature variation
However, in the current implementation of AutoPIPE Vessel:
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- Only the mechanical (pressure‑induced) stress range is directly evaluated
- Thermal effects are reflected through material properties, not through explicit thermal stress cycling
Recommended User Practice
When evaluating fatigue with temperature variations:
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- Define temperature correctly so that material properties are evaluated at the appropriate operating condition
- Define fatigue pressure cycles and number of cycles accurately
- If significant thermal stresses are expected, users should:
- Perform a separate thermal stress evaluation, or
- Apply engineering judgment when assessing fatigue acceptability
See Also