F304
General austenitic
Common for general stainless piping, equipment nozzles and utility service in moderate environments.
Product form hub · Flanges
Stainless Steel Flanges
Specify stainless steel flanges by material grade, nominal pipe size, pressure class, flange type, facing, dimensional standard and bore requirement. Use the selection and size references below to turn a general flange request into a clear purchasing specification.
ASTM A182 F304 / F304L / F316 / F316L
ASME B16.5 / B16.47 dimensional routes
Weld neck, slip-on, blind, threaded & socket weld
Forged stainless flange · product visual
Common gradesF304 / F304L / F316 / F316L
ASME B16.5 rangeNPS 1/2 through NPS 24
Common classes150 / 300 / 600 / 900 / 1500
Build the specification
01Choose material grade
02Set NPS / DN
03Choose pressure class
04Choose flange type
05Confirm facing / bore
06Send RFQ
Product overview
What to define before buying stainless steel flanges
A flange purchase is controlled by more than alloy grade. The mating piping system, dimensional standard, nominal size, pressure class, flange style, facing and bore all need to match the intended joint.
MaterialF304 / F304L
Common forged austenitic stainless grades for general corrosion-resistant piping and equipment connections.
MaterialF316 / F316L
Frequently selected where chloride exposure or more demanding corrosion resistance is expected.
ConnectionWN / SO / BL / SW / TH / LJ
Choose the flange style from welding method, piping design, dismantling needs and project specification.
RatingSize + Class + Facing
Pressure class is part of a complete standard-based rating system and must be paired with material and temperature.
M03 · Grade selection
Choose the flange material from service and piping requirements
For ASTM A182 stainless flanges, the F-grade designation is normally stated on the purchase order. Material selection should follow corrosion exposure, design temperature, welding requirements and the governing piping specification.
F304L
Low-carbon weld route
Often preferred when welded fabrication is important and a low-carbon 304 composition is specified.
F316
Higher corrosion resistance
Frequently considered for chemical, marine-adjacent and chloride-bearing environments.
F316L
Corrosion + welding route
A common choice where improved chloride resistance and extensive welding are both relevant.
M04 · Technical data
Common stainless steel flange size and class reference
ASME flange dimensions are controlled by nominal pipe size and pressure class rather than by one universal outside diameter. Use the ranges below to choose the correct dimensional route before checking the exact standard table for the ordered flange type.
| Nominal size route | Common class range | Common flange types | Typical material route | Buying note |
|---|---|---|---|---|
| NPS 1/2–2 | 150 / 300 / 600 / 900 / 1500 / 2500 | WN / SO / BL / SW / TH / LJ | ASTM A182 F304/F304L/F316/F316L | Small-bore process and utility piping; confirm bore and facing |
| NPS 2 1/2–12 | 150 / 300 / 400 / 600 / 900 / 1500 / 2500 | WN / SO / BL / TH / LJ | ASTM A182 stainless forged flange route | Class 2500 coverage is limited to NPS 1/2–12 under B16.5 |
| NPS 14–24 | 150 / 300 / 400 / 600 / 900 / 1500 | WN / SO / BL / LJ | ASTM A182 stainless grades as specified | ASME B16.5 covers dimensional requirements through NPS 24 |
| NPS 26–60 | 75 / 150 / 300 / 400 / 600 / 900 | Large-diameter WN / BL and project-specified types | Forged / plate route as permitted by the governing standard | Large-diameter flange work moves to ASME B16.47 |
| DN / EN projects | PN designation rather than ASME Class | Type and facing per project standard | Stainless grade per EN/project specification | Do not mix ASME Class dimensions with PN flange systems |
Reference only: exact outside diameter, thickness, bolt circle, bolt holes, bore and facing dimensions depend on size, class, flange type and standard edition.
M05 · Dimensions and connection
Define the flange type, facing and bore
A complete flange description should make it possible to identify the mating geometry without guessing. State nominal size, class, flange type, facing, bore and any special finish or machining requirement.
Flange type
- Weld neck (WN)
- Slip-on (SO)
- Blind (BL)
- Socket weld (SW)
- Threaded (TH) or lap joint (LJ)
Facing / joint
- Raised face (RF)
- Flat face (FF)
- Ring-type joint (RTJ) where specified
- Gasket surface finish per project requirement
- Confirm compatibility with the mating flange
Bore & delivery
- Bore to match pipe schedule for weld neck flanges
- Nominal pipe size / DN
- Pressure class / PN system
- Marking and material traceability
- Required inspection or material documents
M06 · Selection guide
Match the flange style to the piping job
Weld neck for demanding pipingCommon where a butt-welded connection and a smooth stress transition into the pipe are preferred. Specify bore to suit the pipe wall / schedule.
Slip-on for simpler fabricationOften used where installation simplicity is valuable and the piping specification permits the slip-on joint design.
Blind for line isolationUsed to close a piping end, nozzle or branch. Class, facing, material and bolt pattern must match the mating flange system.
316L for chloride exposureF316L is commonly considered before F304L where chloride exposure is more demanding, but the actual service environment still controls alloy selection.
Worked example
Example of a clear stainless steel flange specification
A useful RFQ states the material, flange standard, nominal size, class, type, facing and pipe-bore requirement in one line.
Example only
This is a normal purchasing example, not a live-stock claim. Final dimensions and ratings must follow the project piping specification and the applicable standard edition.
ProductStainless steel weld neck flange
MaterialASTM A182 F316L
Dimensional standardASME B16.5
Size / classNPS 4 · Class 150
FacingRaised face (RF)
BoreTo suit the specified 4 in pipe schedule
Order requirementState quantity, destination, required material documents and any special inspection in the RFQ
M08 · Applications
Where stainless steel flanges are commonly used
Process piping
Flanged joints for chemical, process, utility and plant piping where dismantling and standard bolting are required.
Equipment nozzles
Connections between vessels, pumps, heat exchangers, filters and associated stainless piping.
Water treatment
Corrosion-resistant piping connections in water, wastewater and treatment equipment systems.
Food & beverage plants
Utility and process equipment connections where ASME-type flanged piping is specified rather than sanitary clamp fittings.
Marine / coastal service
316 / 316L flange grades are commonly considered where chloride exposure is more demanding.
Maintenance & isolation
Blind flanges and removable flanged joints support inspection, cleaning, line modification and equipment replacement.
Important limitation: ASME pressure class is not a stand-alone maximum-pressure value. Allowable pressure depends on material group and temperature, and the complete flange joint also depends on bolts, gasket, facing, piping design and assembly. Use the project-approved pressure-temperature rating tables rather than treating “Class 150” or “Class 300” as a fixed pressure number.
M10 · Standards
Standards and purchasing references
Use the project-approved edition on the purchase specification. Standard numbers below are plain-text technical references only and do not link to external websites.
Forged or rolled alloy and stainless steel pipe flanges, forged fittings, valves and parts for high-temperature service.
Pressure-temperature ratings, materials, dimensions, tolerances, marking and testing for pipe flanges and flanged fittings through NPS 24.
Large-diameter steel flange dimensional and rating requirements for NPS 26 through NPS 60.
M11 · FAQ
Stainless steel flanges FAQ
What information is needed to order a stainless steel flange?
State material grade, dimensional standard, nominal pipe size, pressure class or PN, flange type, facing, bore / pipe schedule where applicable, quantity and any inspection or document requirement.
What is the difference between weld neck and slip-on flanges?
A weld neck flange uses a tapered hub and butt-welded neck connection to the pipe. A slip-on flange slides over the pipe and is welded in place. The project piping specification should determine which joint is permitted.
Which stainless grades are common for flanges?
ASTM A182 F304, F304L, F316 and F316L are common austenitic stainless flange grades. Duplex and other alloy grades are also available under applicable specifications when service conditions require them.
What does Class 150 or Class 300 mean?
It is an ASME rating-class designation, not a direct psi value. The actual allowable pressure changes with material group and temperature, so the applicable pressure-temperature rating table must be used.
What facing should I specify?
Raised face is common in ASME piping, while flat face or ring-type joint may be specified for other joint designs. The facing must match the mating flange, gasket design and piping specification.
Product details
What flange buyers usually verify visually
These three areas are ready for your own flange photos. Replace only the background images later; the page structure and copy can stay unchanged.
Flange type & hubWeld neck, slip-on, blind or other connection geometry
Facing & bolt patternRF / FF / RTJ face, bolt holes, marking and machined surface
Marking & packingGrade, size, class, heat traceability and protected packing
Flange resources
Continue from specification to purchase
M13 · Technical reference
Reference basis for this stainless steel flange guide
The page uses current ASTM A182 material scope, current ASME B16.5 and B16.47 dimensional ranges, and normal commercial flange purchasing practice. Exact dimensions, ratings, availability, inspection and certification must be confirmed for the actual project.
M14 · RFQ
Request a technical quote
For a faster flange review, include the material grade, standard, NPS / DN, class / PN, flange type, facing, bore or pipe schedule where applicable, quantity, destination and required documents.
- Material grade / specification
- NPS / DN and pressure class / PN
- Flange type and facing
- Bore / pipe schedule for weld neck flanges
- Quantity, destination and inspection / document requirements