Controlled area record · non-normative arithmetic

Documented Pressure-Relief Area Comparison Worksheet

Compare one required effective discharge area from an approved governing calculation with one compatible certified candidate area. The two values must describe the same relief case, fluid regime, coefficient basis and unit.

no sizing formulano default coefficientsno API letter tableno compliance verdict

This worksheet does not size or select a pressure-relief device. It does not establish the relieving load, choose an API/ISO/ASME equation, determine allowable overpressure, calculate back-pressure or viscosity corrections, certify capacity, or verify inlet/outlet installation.

Controlled comparison record

Enter areas only after a competent calculation and a certified manufacturer record have established a compatible basis.

Shared effective-area unitChanging the unit clears both areas and the result; this worksheet performs no hidden unit conversion.

Required effective discharge area AreqPositive area copied from the approved governing calculation.

Certified candidate effective area AcertPositive compatible area from the controlled valve certificate/catalog/type-test record.

Manufacturer, model and orifice/designation

Required-area calculation report, ID and revision

Governing code/standard, exact edition, addenda and jurisdiction

Sizing equation, clause/table and licensed-source reference

Relieving scenario, required load and load-derivation revision

Fluid composition, phase and flow model

Relieving inlet state and upstream-loss record

Back-pressure, discharge configuration and correction record

Discharge/capacity and combination-correction coefficients

Certified area/capacity source and revision

Installation, inlet/outlet and certification boundary

Comparison record ID and intended decision boundary

Required compatibility confirmation Areq came from the approved governing method for the recorded credible scenario and required relieving load; it was not calculated by this page. Acert is a certified effective discharge area or capacity-derived area on the same basis, not merely a nominal bore, seat diameter or geometric opening. The unit, fluid regime, inlet state, pressure convention, coefficient set, corrections, valve configuration and certification basis are compatible and no factor is missing or applied twice. I will not use this arithmetic comparison as a sizing, selection, installation, certification, PASS/FAIL or code-compliance decision without independent competent review.

Arithmetic comparison result

Candidate-to-required area ratio Q = Acert/Areq

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Dimensionless arithmetic only; not a code acceptance ratio.

Arithmetic area utilization U = Areq/Acert

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Not a certified capacity utilization or compliance value.

Signed area difference Acert − Areq

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Relative area difference (Acert − Areq)/Areq

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Pure arithmetic; no allowance,capacity margin or certified tolerance is inferred.

No selection verdict is produced. A larger recorded area does not prove adequate certified capacity,stable operation,acceptable blowdown,compatible valve construction or compliant installation.

Formula and model boundary

For positive compatible effective areas expressed in one shared unit:

Q = Acert/Areq · U = Areq/Acert = 1/Q · ΔA = Acert−Areq · δ = (Acert−Areq)/Areq

Q, U and δ are dimensionless; ΔA retains the selected area unit. These identities do not establish a relief load, discharge capacity or regulatory acceptance criterion.

Why the former sizing formulas and presets were removed

The previous page combined gas/vapour and steam, assumed fixed discharge coefficients, invented a generic back-pressure factor, used a fixed 10% overpressure and treated water density as universal. It did not control critical versus subcritical flow, phase behaviour, certified coefficient basis, inlet losses, built-up and superimposed back pressure, viscosity/two-phase behaviour, installation or jurisdiction. Those omissions can change a required area materially and cannot be repaired by relabelling one simplified equation.

API 520 Part I and the relevant ISO 4126 parts are controlled standards with application-specific procedures and data. Their closed equations, coefficients and tables are not reproduced or inferred here. A competent engineer with the licensed governing documents and manufacturer data must produce Areq and verify Acert.

Exact numerical checks

Входове	Q	U	ΔA	δ
Areq=100 mm²; Acert=120 mm²	1.2	83.3333333333%	20 mm²	20%
Areq=0.5 in²; Acert=0.75 in²	1.5	66.6666666667%	0.25 in²	50%

Official source status and classification

Източник	Current public status inspected	Use on this page
API Standard 520 Part I	10th edition, published 2020-10-28; official API title is sizing and selection of pressure-relieving devices in refineries	Scope/lifecycle only. No formula or coefficient is copied.
API Standard 526	8th edition, published 2023-08-14; flanged steel pressure-relief valves	No built-in orifice-letter table. Use the controlled current standard and manufacturer record.
ISO 4126-1:2013 + Amd 1:2016	Edition 3, published and confirmed in 2025	The official abstract calls Part 1 a product standard and says it is not applicable to applications of safety valves.
ISO 4126-7:2013 + Amd 1:2016	Edition 2, published and confirmed in 2025	Common data for Parts 1–6; licensed content is required for technical use.
ISO 4126-9:2008	Edition 1, published and confirmed in 2026	Application/installation of safety devices for static pressure equipment; its public scope assumes single-phase discharge and points two-phase conditions to ISO 4126-10.

API 520 Part I official announcement · API official standards plan · ISO 4126-1 official card · ISO 4126-7 official card · ISO 4126-9 official card

Accessed: 15 July 2026. Licensed-source boundary: NEEDS_LICENSED_SOURCE for every sizing equation, coefficient, correction, allowable-overpressure rule, standardized orifice table and acceptance criterion. None was guessed from a search snippet or another online calculator.

Independent engineering and manufacturer review required. Verify the credible overpressure scenarios and required load, governing code and jurisdiction, fluid phase/properties, relieving pressure and temperature, inlet loss, back pressure, reaction forces, discharge disposal, valve stability, materials, certification, set-pressure tolerances, capacity certification and installation before any safety decision.