Inflection Point Engineering Calculators

Compressor Anti-Surge Margin Calculator

Centrifugal compressor steady-state surge check. Fits a parabolic surge line Hsurge(Q) = a + bQ + cQ² through three vendor-curve points, computes operating inlet ACFM from process conditions, and returns flow-based surge margin against control-line and trip-line targets per API 617 and CCC anti-surge practice.

Method: Inlet density ρ1 = P1·MW / (Z·10.7316·(T1+459.67)) (lbm/ft³); Qop = W / (ρ1·60) (ACFM). Surge line fit by solving the 3×3 system for parabolic coefficients (a, b, c) such that Hsurge(Qi) = Hi; inversion via the quadratic formula gives Qsurge at Hop. Surge margin %SM = (Qop − Qsurge) / Qop · 100. Control line QCL = Qsurge(1 + mCL/100); trip line QTL = Qsurge(1 + mtrip/100). Validation: c < 0 (surge curve concave down), Qop > Qsurge, and discriminant b²−4c(a−Hop) ≥ 0. References: API 617 (9th Ed.) Axial and Centrifugal Compressors; API 670 Machinery Protection Systems; ASME PTC-10 Compressors and Exhausters; Compressor Controls Corp. (CCC) "Anti-Surge Control: Concepts and Applications" (2016). For axial / high-density service, prefer invariant-coordinate (ACT/ITCC) control schemes over fixed flow margin.

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© 2026 Inflection Point Engineering, LLC. All rights reserved.