- ASME B16.5-2025 covers pipe flanges and flanged fittings from NPS 1/2 through NPS 24, with Class 2500 flanges covered through NPS 12.
- The standard covers pressure-temperature ratings, materials, dimensions, tolerances, marking, testing, bolting, gaskets and flange-joint requirements.
- For safety valves, ASME B16.5 confirms inlet and outlet flange compatibility; it does not calculate required relieving capacity or PSV orifice area.
- Flange class must be checked together with material group and actual temperature. A class designation alone does not confirm service suitability.
››› ASME B16.5 Overview
ASME B16.5 connects safety valve selection with real piping and equipment flange requirements
After the required safety valve capacity is calculated, the valve still has to fit the plant. ASME B16.5 helps engineers specify flange dimensions, pressure class, facing, material compatibility and pressure-temperature rating for the valve inlet and outlet connections.
For safety valve procurement, B16.5 is most useful when the RFQ already includes set pressure, relieving temperature, valve type, API orifice or certified capacity, piping class, flange facing, gasket type and installation envelope. It does not replace API 520 sizing, API 521 relief scenario review or ASME pressure equipment code requirements.
What this page helps you confirm
- How ASME B16.5 flange dimensions affect safety valve inlet and outlet connection selection.
- Why flange class must be checked with material group and relieving temperature.
- Which flange data should be included in a safety valve RFQ or replacement enquiry.
- How B16.5 relates to API 526 flanged PSVs, ASME pressure equipment and piping codes.
- What installation and documentation mistakes commonly delay EPC and maintenance projects.
››› What ASME B16.5 Defines
ASME B16.5 is a flange standard used to confirm connection compatibility, dimensions and pressure-temperature ratings
ASME B16.5 is not a safety valve sizing standard. In safety valve projects, it is used to define the flange interface between the valve and the piping or equipment nozzle. The valve must still be sized and selected using the applicable relief code, project specification and manufacturer certified capacity.
01
NPS Size Range and Flanged Fittings
ASME B16.5 is used for pipe flanges and flanged fittings within the standard scope. For safety valve RFQs, the inlet and outlet NPS sizes should match the piping specification, API 526 configuration or equipment nozzle requirement.
02
Pressure Class and Pressure-Temperature Rating
Flange class alone is not the full rating. The allowable pressure depends on material group and temperature. The safety valve flange rating should be checked at operating and relieving temperature, especially for steam, thermal oil, cryogenic, hydrogen and high-temperature process service.
03
Flange Dimensions, Bolt Pattern and Thickness
ASME B16.5 dimensions help confirm bolt circle, bolt hole quantity and diameter, flange outside diameter, thickness, raised face dimensions and fitting compatibility. These details are critical for replacement valves, skid fabrication and field installation.
04
Flange Facing and Gasket Selection
Raised face, ring type joint, flat face and gasket requirements should be specified clearly. A mismatch between valve facing and piping facing can cause leakage, installation delay or gasket failure under relief load.
05
Materials, Marking and Testing
Flange material and marking should be traceable to the project piping class and pressure-temperature rating. Material certificates, markings and inspection requirements should be aligned before manufacturing and shipment.
06
Limits of B16.5 in Safety Valve Projects
B16.5 does not calculate PSV orifice area, certified capacity, accumulation, back pressure or relief case. It should be used together with API 520, API 521, API 526, ASME pressure equipment requirements and project specifications.
››› Sizing to Flange Selection Workflow
How API sizing, ASME code basis and ASME B16.5 flange details work together
A safety valve can be sized correctly but still fail procurement review if the flange class, facing, material group, bolt pattern, pressure-temperature rating or installation dimension is wrong. Use this workflow before issuing a purchase order.
Step 1
Define the protected equipment and relief case
Confirm MAWP, set pressure, medium, relieving temperature, required capacity, relief scenario and applicable ASME / API / ISO / EN code basis before choosing the final valve configuration.
Step 2
Size the safety valve and select the valve type
Use sizing data to confirm required area, certified capacity, valve type, back pressure limits and service requirements before finalizing the flanged connection.
Step 3
Confirm ASME B16.5 inlet and outlet flanges
Check NPS, Class, facing, material group, pressure-temperature rating, gasket, bolting and piping class for both inlet and outlet flanges.
Step 4
Specify tests, drawings and documents
Add GA drawing, flange standard, pressure class, facing, MTC, hydrostatic test, seat tightness test, calibration report, nameplate and inspection requirements to the RFQ.
››› Procurement Matrix
ASME B16.5 flange data matrix for safety valve RFQs
| Flange Data | Why It Matters | What to Specify | Risk if Missing |
|---|---|---|---|
| Inlet NPS and outlet NPS | Confirms valve-to-piping fit and API 526 configuration. | Example: 3 in × 4 in, 4 in × 6 in, 6 in × 8 in. | Valve cannot be installed or requires field modification. |
| Flange class | Defines pressure rating basis with material and temperature. | Class 150, 300, 600, 900, 1500 or 2500 as required. | Under-rated connection or rejected inspection package. |
| Facing type | Determines gasket selection and sealing compatibility. | RF, RTJ, FF or project-specific facing. | Leakage, gasket mismatch or installation delay. |
| Material group | Controls pressure-temperature rating and corrosion suitability. | Carbon steel, stainless steel, alloy steel or project material code. | Wrong rating at temperature or document rejection. |
| Pressure-temperature rating | Confirms flange can handle relieving condition. | Check against set pressure, relieving pressure and relieving temperature. | Flange class appears correct but is not suitable at temperature. |
| Gasket and bolting | Supports joint integrity under pressure, temperature and media. | Gasket type, bolt material, nut material and coating if required. | Joint leakage or site procurement delay. |
| Standard edition and documents | Avoids conflict between buyer, EPC and supplier requirements. | ASME B16.5 edition, drawings, MTC, inspection and marking requirements. | Ambiguous RFQ, rework or inspection hold. |
››› Where ASME B16.5 Is Used
Common safety valve applications requiring ASME B16.5 flange checks
ASME B16.5 is commonly used when safety valves connect to ASME / ANSI class piping, pressure vessels, skid packages or replacement valve installations. The flange data should be confirmed before final layout, fabrication and procurement.
Pressure Vessel Safety Valves
Pressure vessels, separators, receivers, autoclaves and process equipment where inlet flange rating must match the equipment nozzle.
Oil & Gas and Petrochemical Units
Hydrocarbon vessels, flare-connected PSVs, separators, columns, heat exchangers and process skids using ASME class flanges.
Chemical Processing and Corrosive Service
Reactors, storage vessels, dosing skids and corrosive media where flange material, gasket and facing must match the piping class.
Steam, Boiler and High Temperature Service
Steam headers, boiler auxiliary systems, superheated steam and high-temperature relief where pressure-temperature rating must be checked.
Cryogenic and Low Temperature Service
LNG, LOX, nitrogen and low-temperature systems where flange material toughness, gasket choice and cold installation clearance matter.
Replacement and Maintenance Projects
Existing valves where centerline, flange size, facing and bolt pattern must match the installed piping without field rework.
››› Related Standards
Standards normally used with ASME B16.5 flange selection
ASME B16.5 should be used with the project sizing, relief scenario, pressure vessel, piping and valve testing standards. The exact combination depends on equipment type, industry, country, medium and owner specification.
››› Document Package
Typical ASME B16.5 flange document package
- Technical datasheet with tag, model, valve type, inlet size, outlet size, flange class and facing.
- General arrangement drawing showing face-to-face / center-to-face dimensions, weight, flange orientation and maintenance envelope.
- Material certificates for valve body, bonnet, nozzle, disc, flange-connected pressure parts, bolting and trim where required.
- Pressure-temperature rating confirmation for the selected body material and flange class.
- Set pressure calibration certificate, hydrostatic test report and seat tightness test report where required.
- Gasket, bolting, flange finish and connection standard notes for site installation.
- Nameplate data, tag list, inspection witness records and spare parts list where required.
››› RFQ Checklist
Information to send for an ASME B16.5 flanged safety valve quote
A complete RFQ should include both process relief data and mechanical flange data. This allows the supplier to confirm certified capacity, connection compatibility, pressure-temperature rating and installation fit before manufacturing.
- Protected equipment, tag number, MAWP / design pressure and applicable code.
- Medium, phase, molecular weight, special hazards and corrosion or cleanliness requirements.
- Set pressure, operating pressure, relieving pressure, relieving temperature and required capacity.
- Valve type, API orifice if calculated, certified capacity requirement and back pressure condition.
- Inlet and outlet NPS, ASME flange class, facing type and piping class.
- Material group, body material, trim material, gasket, bolting and low-temperature or high-temperature requirement.
- Installation constraints: existing nozzle, skid dimensions, discharge orientation, outlet support and maintenance access.
- Required documents: GA drawing, MTC, sizing report, calibration, pressure test, seat tightness, marking and inspection records.
››› Common Errors
Common ASME B16.5 flange selection mistakes
Most flange-related safety valve mistakes come from treating the connection as a simple size match. Pressure class, material group, facing, temperature, gasket, bolting and installation envelope must be checked together.
Using flange class without checking temperature
Class 300 or Class 600 does not by itself prove suitability. The flange pressure-temperature rating depends on material group and temperature.
Mixing ASME and EN / DIN flange systems
ASME B16.5 flanges are not automatically interchangeable with EN 1092-1 PN flanges. Bolt patterns, dimensions and ratings can differ.
Selecting by inlet size only
Safety valve capacity depends on orifice and certified capacity, not only inlet flange size. The outlet size and discharge system also need review.
Ignoring facing, gasket and bolting
RF, RTJ or FF facing, gasket material and bolting must match the piping class and service condition.
Using B16.5 as a sizing standard
B16.5 does not size a safety valve. API 520, ISO 4126 or project-required sizing methods should be used for relieving capacity.
Forgetting large diameter flange limits
Large flanges above the B16.5 scope may require ASME B16.47 or a project-specific flange standard rather than B16.5.
››› Related Standards & Engineering Pages
Continue your ASME B16.5 flange and safety valve review
Use these pages to complete the full workflow from relief case to sizing, flanged valve configuration, pressure-temperature rating, seat testing and final RFQ documentation.
API 526 Flanged Safety Valves
Open this related resource to confirm standardized flanged PSV dimensions, orifice designation, pressure class and procurement details.
API 520 Safety Valve Sizing
Open this related resource to calculate required relieving area, capacity, set pressure and sizing basis before flange selection.
API 521 Pressure Relief Systems
Open this related resource to define relief scenarios, fire case, flare header and system-level discharge requirements.
ASME Safety Valve Standards
Open this related resource to review ASME boiler, pressure vessel, piping and flange references used in valve projects.
Pressure-Temperature Ratings
Open this related resource to review how material and temperature affect flange and valve pressure limits.
API 527 Seat Tightness Test
Open this related resource to review leakage acceptance, test reports and seat tightness documentation.
Spring Loaded Safety Valves
Open this related product page for standard spring-loaded safety valves with flanged connection options.
Pilot Operated Safety Valves
Open this related product page for pilot operated safety valves in high pressure and selected high back pressure service.
High Back Pressure Service
Open this related application page for valves discharging to flare headers, scrubbers or closed relief systems.
››› FAQ
ASME B16.5 Flange Dimensions FAQ
Short answers for common engineering and procurement questions related to ASME B16.5 flanges and flanged safety valve connections.
What is ASME B16.5 used for in safety valve projects?
ASME B16.5 is used to define pipe flange and flanged fitting requirements such as dimensions, pressure-temperature ratings, materials, tolerances, marking and testing. In safety valve projects, it helps confirm inlet and outlet flange compatibility with piping and equipment nozzles.
Is ASME B16.5 a safety valve sizing standard?
No. ASME B16.5 does not calculate safety valve capacity or orifice area. API 520, ISO 4126 or project-required sizing methods are used for sizing, while B16.5 is used for flange connection requirements.
What flange data should be included in a safety valve RFQ?
A safety valve RFQ should include inlet and outlet NPS, flange class, facing type, material, pressure-temperature requirement, gasket and bolting notes, piping class, standard edition and required inspection documents.
SHOP-FLOOR VERIFICATION
From Code Requirement to Shop-Floor Verification
Standards define technical requirements, but purchase-order compliance depends on design, materials, inspection scope and recorded test results. This actual ZOBAI photograph documents finished-machined flanged valve bodies. It is facility evidence, not a substitute for project-specific certificates or an agreed inspection and test plan.
Does flange class alone confirm the safety valve connection rating?
No. Flange class must be checked with material group and temperature. A flange that appears suitable at ambient temperature may not be suitable at the relieving temperature.
Can ASME B16.5 flanges be connected to EN or DIN PN flanges?
They should not be assumed interchangeable. ASME B16.5 and EN / DIN PN flange systems can have different dimensions, bolt patterns, pressure ratings and facing requirements. Compatibility must be confirmed by engineering review.
What standard is used for flanges larger than the ASME B16.5 scope?
Large diameter steel flanges may require ASME B16.47 or another project-specified flange standard instead of ASME B16.5. The project piping specification should define the correct standard.