API 579-1 (2021) Part 9, §9.4.3.2 — FAD Level 2 fracture assessment, 5 crack geometries
Answers whether a cracked component can stay in service. It runs the complete 12-step Level 2 failure assessment diagram (FAD) procedure from API 579-1/ASME FFS-1 (2021) Part 9, §9.4.3.2 for five crack geometries:
It plots the assessment point (L_r^P, K_r) and gives a verdict against the Option 1 FAD curve f(L_r) (Eq. 9.22).
The fracture ratio is K_r=(K_I^P+\Phi K_I^{SR})/K_{mat} (Eq. 9.18): the primary stress intensity factor K_I^P comes from the Annex 9B solution for the chosen geometry, the secondary K_I^{SR} from the residual stress, the plasticity interaction factor \Phi scales the secondary part (a multiplicative factor, unlike the additive \rho used in BS 7910), and K_{mat} is the fracture toughness you enter. The load ratio is L_r^P=\sigma_{ref}^P/\sigma_{ys} from the Annex 9C reference stress. The cut-off is L_{r,max}=\sigma_f/\sigma_{ys}^r when strain hardening is known, or a conservative L_{r,max}=1.0 when it is not.
Loads are internal pressure for cylinders or primary membrane plus bending for plates, with optional uniform welding residual stress. The effective yield \sigma_{ys}^r=\sigma_{ys}+69 MPa (no PWHT, Annex 9D Eq. 9D.1) is used only for the cut-off, not for the Irwin plastic-zone correction. Cracks are checked at the deepest (\varphi=90^\circ) and surface (\varphi=0^\circ) points, and the worse one governs. The engine has been checked against API 579-2 Example Problem 9.5.
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