API Standards Quick Reference

Common API, ASME, and industry standards referenced in refining and petrochemical design. Grouped by issuing body; search to locate a specific standard or topic.

API Standards

Standard	Title	Scope	Key Sections	Common Mistakes	When You Need This
API 520 Part I	Sizing, Selection, and Installation of Pressure-Relieving Devices — Sizing	Equations for sizing PSVs for gas, vapor, steam, liquid, and two-phase relief. Covers critical and subcritical flow.	Part I Sec 4 (gas/vapor), Sec 5 (steam), Sec 6 (liquid), Sec 7 (two-phase), Annex D (worked examples).	Using gas equation for liquid service; forgetting back-pressure correction Kb for balanced bellows; not accounting for two-phase flashing; using wrong Kd (0.975 gas vs 0.65 liquid).	Any time you size a new PSV or re-rate an existing one.
API 520 Part II	Sizing, Selection, and Installation — Installation	Installation practices: inlet piping, outlet piping, reaction forces, testing requirements.	Sec 4 (inlet loss < 3% of set pressure), Sec 5 (outlet piping), Sec 7 (reaction forces).	Inlet pressure drop > 3% causing chatter; outlet piping imposing excessive back-pressure; not checking reaction force on elbow.	PSV installation design and piping layout review.
API 521	Pressure-Relieving and Depressuring Systems	Identifies relief scenarios, calculates relief loads, sizes flare/vent systems. API 521 Table 1 = scenario checklist.	Sec 4 (relief scenarios), Sec 5 (disposal systems), Table 1 (scenario matrix), Annex A-D.	Missing relief scenarios (tube rupture in HX, reflux failure); underestimating fire case heat input; not accounting for two-phase flow in flare headers.	Building a relief scenario matrix, sizing a flare system, designing depressuring.
API 526	Flanged Steel Pressure-Relief Valves	Standardized dimensions and capacities for flanged PSVs. Defines orifice letter designations D through T.	Table 1 (effective orifice areas), Table 2 (inlet/outlet flange sizes by orifice and pressure class).	Specifying non-standard orifice sizes; mismatch between required area and selected orifice letter; wrong inlet/outlet rating.	Selecting a PSV orifice size after API 520 sizing. Specifying PSVs on datasheets.
API 560	Fired Heaters for General Refinery Service	Design, fabrication, inspection, testing of process fired heaters. Covers radiant and convection sections.	Sec 5 (design), Sec 6 (tube design), Sec 7 (materials), Sec 8 (fabrication), Annex A (radiant section method).	Under-specifying excess air (typical 15-20%); not checking tube metal temperature limits; ignoring convection section fouling factor.	Specifying or reviewing a fired heater design package.
API 610	Centrifugal Pumps for Petroleum, Petrochemical and Natural Gas Industries	Minimum requirements for centrifugal pumps in refinery/petrochemical service. Classifies pump types (OH1-OH5, BB1-BB5, VS1-VS7).	Sec 6 (design), Sec 7 (accessories), Annex H (pump types), Annex I (datasheets).	Not specifying pump type per Table 1; insufficient NPSH margin; wrong material class for service; missing minimum flow bypass.	Purchasing or specifying any centrifugal pump for hydrocarbon or chemical service.
API 617	Axial and Centrifugal Compressors and Expander-Compressors	Design requirements for centrifugal and axial compressors in refinery/gas processing service.	Sec 4 (centrifugal design), Sec 5 (axial design), Sec 6 (accessories), Annex C (vibration).	Not specifying surge margin; incomplete string test requirements; missing lateral/torsional analysis; wrong seal selection for gas composition.	Any centrifugal or axial compressor purchase or re-rate.
API 650	Welded Tanks for Oil Storage	Design, fabrication, erection of above-ground welded steel tanks. Covers shell, bottom, roof, appurtenances.	Sec 5 (design), Annex C (external pressure), Annex E (seismic), Annex F (internal floating roof).	Not checking wind/vacuum loads; missing anchor bolt design for seismic; wrong annular plate thickness; ignoring settlement.	New tank design, tank modification, or fitness-for-service evaluation.
API 660	Shell-and-Tube Heat Exchangers	Minimum requirements for S&T HXs per TEMA. Covers thermal design, mechanical design, fabrication, materials.	Sec 5 (design), Sec 6 (materials), Sec 7 (fabrication), Annex F (datasheets).	Wrong TEMA class (R vs C vs B); inadequate fouling factors; missing vibration check on tube bundle; wrong tubesheet thickness.	Specifying or reviewing any shell-and-tube heat exchanger.
API 661	Air-Cooled Heat Exchangers	Design and construction of air-cooled HXs (fin-fan coolers). Covers tube bundle, headers, fans, structure.	Sec 5 (thermal design), Sec 6 (mechanical), Sec 7 (fans), Sec 8 (structure).	Undersizing for high ambient; wrong fin pitch for fouling service; inadequate winterization; missing louver/recirculation for pour point.	Any fin-fan cooler specification or review.
API 662	Plate Heat Exchangers	Requirements for plate-and-frame, brazed plate, and welded plate HXs.	Sec 4 (design), Sec 5 (materials), Sec 6 (fabrication and testing).	Wrong gasket material for service; exceeding plate pressure limits; not checking thermal fatigue for cycling service.	Plate HX specification for light-duty or utility service.
API 2000	Venting Atmospheric and Low-Pressure Storage Tanks	Sizing tank vents for normal and emergency conditions. Thermal breathing, liquid movement, fire exposure.	Sec 4 (normal venting), Sec 5 (emergency venting), Annex A (thermal breathing calcs).	Using only thermal breathing and ignoring liquid movement inbreathing; not sizing emergency vent for full fire case; wrong tank insulation credit.	Sizing vent valves or conservation vents on atmospheric tanks.

ASME Standards

Standard	Title	Scope	Key Sections	Common Mistakes	When You Need This
ASME B31.3	Process Piping	Design, materials, fabrication, examination, testing of process piping. The primary piping code for refineries and chemical plants.	Ch II (design, stress limits), Ch III (materials), Ch V (fabrication), Ch VI (examination), Para 323.2.2 (special services: H2, lethal, severe cyclic).	Wrong SIF for branch connections; not checking sustained + displacement stresses separately; missing spring hanger for thermal expansion; wrong corrosion allowance in stress calc.	Any process piping design or stress analysis. Mandatory for refinery/chemical piping.
ASME VIII Div 1	Boiler and Pressure Vessel Code — Div 1	Rules for construction of pressure vessels. Covers design, materials, fabrication, inspection, testing.	UG-27 (cylindrical shells), UG-32 (formed heads), UG-34 (flat heads), UG-37 (nozzle reinforcement), UW (welding), UCS (carbon steel), UHA (high alloy).	Wrong joint efficiency for RT extent; not including corrosion allowance before calculating thickness; missing nozzle reinforcement check; wrong MDMT (minimum design metal temperature).	Designing any pressure vessel or checking an existing one.
ASME B16.5	Pipe Flanges and Flanged Fittings	P-T ratings for standard flanges NPS 1/2 through NPS 24, Classes 150-2500. The flange rating bible.	Table 2 (ratings by material group and class), Table III (flange dimensions).	Using 150# flange above its rating at temperature; wrong material group assignment; not checking gasket seating stress.	Selecting flange class for any piped connection. Checking P-T rating adequacy.
ASME B16.34	Valves — Flanged, Threaded, and Welding End	P-T ratings for valves. Similar to B16.5 but covers additional sizes and special class ratings.	Table 2 (standard class ratings), Table 3 (special class ratings).	Assuming valve rating = flange rating (not always true for body/trim); not checking reduced port vs full port; ignoring trim material compatibility.	Valve specification and rating verification.

Other Standards

Standard	Title	Scope	Key Sections	Common Mistakes	When You Need This
NFPA 70 (NEC)	National Electrical Code	Electrical installation safety requirements. Covers wiring methods, equipment, special occupancies.	Art 310 (conductors), Art 430 (motors), Art 500-506 (hazardous locations), Art 700 (emergency systems).	Undersized conductors for continuous loads (125% rule); wrong conduit fill calculation; missing GFCI/AFCI where required; wrong hazloc classification for equipment.	Any electrical design or installation in the US.
NFPA 497	Classification of Flammable Liquids, Gases, or Vapors and of Hazardous (Classified) Locations	Guidance for area classification (Class I, Div 1/2 or Zone 0/1/2). Maps release sources to classified areas.	Ch 5 (general principles), Ch 6 (petroleum refineries), Ch 7 (chemical plants), Annex (example diagrams).	Classifying too conservatively (expensive) or too loosely (unsafe); not considering heavier-than-air gases pooling at grade; missing indoor ventilation assessment.	Area classification studies for new units or MOC reviews.
IEC 61511	Functional Safety — Safety Instrumented Systems for Process Industries	Requirements for SIS lifecycle: from hazard analysis through SIL determination, design, validation, operations.	Part 1 Sec 9 (SRS), Sec 11 (SIS design), Sec 12 (SIS integration), Sec 16 (maintenance/operations).	Not performing SIL verification after SIL determination; wrong PFD calculation for voted architectures; incomplete proof test coverage; missing bypass management procedure.	Any SIS design, SIL assessment, or functional safety audit.
ISA 84	Safety Instrumented Systems for the Process Industry	US adoption of IEC 61511. Essentially the same technical content with ISA numbering.	Same sections as IEC 61511 — ISA 84.00.01 = IEC 61511-1.	Same as IEC 61511. Additionally: not aligning with OSHA PSM requirements for IPLs; confusion between ISA 84 and ISA 84.01 (old standard).	SIS work in US jurisdiction. Often referenced alongside IEC 61511.
ISA 5.1	Instrumentation Symbols and Identification	Standard P&ID symbology. Defines instrument tag numbering, bubble symbols, line types, functional identification letters.	Sec 4 (identification letters), Sec 5 (tag numbers), Sec 6 (symbols), Table 1 (first letter / succeeding letters).	Inconsistent use of modifier letters (e.g., D vs DI vs DIC); non-standard line types for signal types; missing SIS designation on safety instruments; tag number format drift across project.	Creating or reviewing any P&ID. Establishing project instrument tagging conventions.

Source: API_Standards_Quick_Reference_v1.xlsx

© 2026 Inflection Point Engineering, LLC. All rights reserved. The content of this page — including calculation methods, reference data, written analysis, interactive tools, and source code — is the intellectual property of Inflection Point Engineering, LLC and is protected under applicable copyright, trademark, and trade secret laws. Unauthorized reproduction, redistribution, modification, or derivative use in whole or in part is prohibited without prior written consent.

Disclaimer. This material is provided for informational and educational purposes only and does not constitute professional engineering advice. Calculations, reference data, and methodologies are based on published standards and accepted engineering practice but are not a substitute for engineering judgment, site-specific analysis, or review by a licensed Professional Engineer. Inflection Point Engineering, LLC makes no warranties, express or implied, regarding the accuracy, completeness, or fitness for a particular purpose of any content presented here, and shall not be liable for any direct, indirect, incidental, or consequential damages arising from its use. Users assume all risk associated with applying this content to real-world design, operations, or decisions.