Appendix G: P-T Limit (Brittle Fracture Prevention)

ASME BPVC Section XI (2025) Appendix G — Pressure-Temperature Limit (Brittle Fracture Prevention)

Pressure-Temperature Limit Curve (2K_{Im}+K_{It} \lt K_{Ic})

This tool applies the ASME XI (2025) Appendix G analytical assessment procedure G-2215 for shell and head regions away from discontinuities (Service Levels A/B). For the assumed t/4 flaw (G-2120) it combines the membrane stress intensity factor K_{Im} from internal pressure and the thermal stress intensity factor K_{It} from heatup/cooldown transients, then solves the allowable pressure at each temperature using the criterion 2K_{Im}+K_{It} \lt K_{Ic} to produce the brittle fracture prevention P-T limit curve.

The reference fracture toughness K_{Ic} is indexed two ways:

• the classical reference nil-ductility transition temperature RT_{NDT} (G-2110(a));
• a Master Curve route that converts an ASTM E1921 T_0 into RT_{T0,index} (G-2110(c)).

You set the vessel geometry, flaw orientation (axial or circumferential), the transient (heatup, cooldown or isothermal) and the heatup/cooldown rate. Besides the full curve, the tool reads:

• the allowable pressure and margin at one assessment temperature;
• the minimum hydrotest temperature (RT_{ref}+33°C);
• the LTOP enable temperature.

This is a complete calculation of the G-2215 closed-form procedure, but only a subset of all of Appendix G: it covers the shell remote from discontinuities, so nozzle corners, flange discontinuities and irradiation chemistry models need the matching fuller methods. Results use SI units only.

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