PSA 2.2 — The B31.3 Code Stress Equations
Your model reports 137 MPa at an elbow . Pass or fail? Trick question — it depends on which check the 137 belongs to. The same pipe sits three different exams, each with its own equation, its own allowable, and its own idea of failure:
S_L = √[ (|Sa| + Sb)² + (2·St)² ] Sa = Ia·Fa/Ap ≈ P·D/4t + axial weight terms (axial: pressure thrust + Fax) Sb = √[(Ii·Mi)² + (Io·Mo)²] / Z (sustained bending, sustained SIFs I) St = It·Mt / (2Z) (torsion) Use t̄ = nominal − corrosion/erosion for sustained section properties. The pressure term is…
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