Appendix Y: Crack Growth Rate Curves

ASME BPVC Section XI (2025) Appendix Y — Crack Growth Rate Curves

Crack Growth Rate Curves (da/dN, da/dt)

In the latest ASME XI 2025 edition, the crack growth rate curves previously scattered across several appendices have been consolidated into Appendix Y. This calculator estimates the crack growth rate of reactor components for three mechanisms:

• corrosion fatigue (da/dN);
• stress corrosion cracking (SCC, da/dt);
• irradiation-assisted stress corrosion cracking (IASCC, da/dt).

It covers three material families using separate formula branches:

• austenitic stainless steel (Y-2000);
• ferritic steel (Y-3000);
• nickel-based alloys (Y-4000).

You pick the material, the water environment (air, BWR NWC/HWC, PWR primary or non-reactor) and the temperature, then enter the driving force: \Delta K with stress ratio R for fatigue, and static K_{max} for SCC. The fatigue rate combines a temperature factor S_T, an R-ratio factor S_R and an environment factor S_{ENV}; setting \Delta K=0 or K_{max}=0 skips that branch.

Scope and limits:

• SI units only (no U.S. Customary units);
• does not apply to Type 321 stainless steel or dissimilar-metal welds;
• the IASCC dose is limited to 47.5 dpa.

Sections that the standard still marks "in course of preparation" are not filled in by guesswork.

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