Tesco Steel & Engineering forges ASTM A182 F304L blind flanges — UNS S30403, the weld-safe member of the 304 family — to ASME B16.5 Class 150–2500 from ½″ to 24″ NB and to ASME B16.47 up to 60″. With carbon capped at 0.030%, weld zones cannot sensitize — the property that made 304L the default of welded corrosive-process piping worldwide — while the widened 8–13% nickel keeps the austenite (and the cryogenic capability) intact. The trade is honest: gentler mechanicals than F304, answered in practice by F304/F304L dual-certification; sustained hot duty belongs to F304H, chlorides to F316L. Facings: BLRF, BLFF or BLRTJ. Every lot with EN 10204 3.1/3.2 MTC. ISO 9001:2015, made in Mumbai, India — exported to 50+ countries.
ASTM A182 F304L · UNS S30403 · EN 1.4307Low Carbon ≤0.030% · Sensitization-ProofCryogenic Capable · No DBTTF304/F304L Dual-CertificationASME B16.5 ½″–24″ · Class 150–2500RF · FF · RTJ FacingsEN 10204 3.1 / 3.2 · ISO 9001:2015
ASTM A182 F304L Blind Flange — Specifications at a Glance
What is an ASTM A182 F304L Blind Flange?
The weld-safe stainless closure. A solid forged disc of low-carbon austenitic 304L (UNS S30403) with no bore, closing pipes, valves and nozzles in welded corrosive-process systems. Carbon ≤0.030% means heat-affected zones cannot sensitize — welds stay as corrosion-resistant as parent metal — and the widened Ni 8–13% keeps the structure austenitic: tough to cryogenic temperatures, capped near 425 °C hot. Tensile ≥485 MPa, yield ≥170 MPa; commonly F304/F304L dual-certified. Dimensions per ASME B16.5 / B16.47 in RF, FF and RTJ facings; EN 10204 3.1 certified.
Also searched as: SS 304L blind flange, 304L blind, S30403 blind, SA-182 F304L blind (the ASME boiler-code twin), 1.4307 / X2CrNi18-9 blind (the EN equivalent), F304/F304L dual-cert blind — all refer to the product on this page. See also the stainless steel hub, the F304L slip on flanges, siblings F304 / F304H / F316L blind flanges, and the facing pages BLRF / BLFF / BLRTJ.
The Weld-Safety Story — Removing the Ammunition
Every weld drags nearby metal through the 425–815 °C sensitization range, where plain 304's carbon precipitates as chromium carbides and primes the heat-affected zone for intergranular corrosion. The L grade's answer is subtraction:
Too Little Carbon to Matter
Below 0.030% there is not enough carbon to precipitate consequentially — welded joints stay as corrosion-resistant as parent metal, without post-weld annealing.
Nickel Widened on Purpose
Carbon is also an austenite stabiliser, so its removal is compensated: nickel runs to 13.0% where F304 stops at 11.0 — the "typo" on the datasheet that is actually the design.
The Honest Price Is Strength
Tensile drops to 485 MPa and yield to 170 — the family's gentlest numbers, with the L grades in their own, slightly lower rating group. Dual-certification is the standard answer.
Dual certification bridges the everyday middle: modern melts hold carbon below 0.030% while meeting F304's strength, so one forging certifies as both — weld-safe like an L, rateable like a standard grade. The H corner stands alone: its carbon minimum cannot coexist with the L cap.
F304L Chemical Composition (UNS S30403)
Element
C
Si
Mn
P
S
Cr
Ni
Weight %
≤0.030
≤1.00
≤2.00
≤0.045
≤0.030
18.0–20.0
8.0–13.0
Two bold columns carry the design: carbon suppressed, nickel extended. No molybdenum — chloride duty belongs to 316L — and no other change from the 18-8 baseline.
Mechanical Properties & The Service Span
Property
ASTM A182 F304L Requirement
Tensile Strength
≥ 485 MPa (70 ksi)
Yield Strength (0.2%)
≥ 170 MPa (25 ksi)
Elongation
≥ 30%
Reduction of Area
≥ 50%
Hardness
No A182 limit — typically soft as annealed
Condition
Solution annealed — mandatory
Service Span
Cryogenic (LNG, LN2) to ~425 °C continuous — sustained hotter duty passes to F304H
Rate against the right line. The L grades sit in their own, slightly lower group of the B16.5 stainless tables — a joint being class-checked at its limit should be checked against the L-grade line, not standard 304's. Where the margin matters, order F304/F304L dual-certified: the forging then meets the higher strength while keeping the low carbon — both worlds on one certificate.
ASTM A182 F304L Blind Flanges are available in the following specifications:
Material Grade
ASTM A182 F304L (UNS S30403); F304/F304L dual-certification standard where the melt qualifies; EN 1.4307 to order
Heat Treatment
Solution annealed — mandatory; condition stated on certificate
Size
1/2"NB to 24"NB per ASME B16.5; 26"–60" per ASME B16.47; EN 1092-1 to order
Class
150#, 300#, 400#, 600#, 900#, 1500#, 2500# — rated per the L-grade stainless lines
Facings
Raised Face (BLRF), Flat Face (BLFF), Ring Type Joint (BLRTJ) with groove per B16.20
Service Span
Cryogenic to ~425 °C continuous — sensitization-proof at welds throughout
Surface Finish
Pickled & passivated or natural machined — no paint; segregated stainless handling throughout
Modifications
NPT-tapped centre (hydrotest / vent / drain / gauge), lifting provisions — machined & certified at the works
Testing
Tension & chemistry per heat; PMI routine; IGC (ASTM A262) and other corrosion tests where specified
Certification
EN 10204 3.1 (standard) / 3.2 witnessed — dual F304/F304L designation on request
Why F304L Blind Flanges Are Specified
Sensitization-Proof by Chemistry
No post-weld anneal, no HAZ worry, no intergranular surprise years later — the corrosion resistance survives fabrication because the ammunition was never loaded.
The Welded-System Standard
Most stainless process piping is welded and corrosive-wetted — which is why line classes default to 304L, and why the closure follows the line.
Cryogenic Capability Retained
The stabilised austenite keeps the family's no-transition toughness — the same L-grade blind serves the cold box and the process header.
Dual-Cert Practicality
F304/F304L on one certificate: weld-safe like an L, rateable like a standard grade — one stock for both paperwork worlds.
Three details buyers miss.Check ratings against the L line: the L grades carry a slightly lower rating group — at a marginal class check, dual-certified material closes the gap. Not a hot grade: above ~425 °C sustained, the missing carbon is missing creep strength — that duty belongs to F304H, and no dual-cert can bridge it. Chlorides still bite: low carbon fixes welds, not pitting — salt-bearing duty steps to 316L or duplex exactly as it does for standard 304.
How Our F304L Blind Flanges Are Manufactured
1
Forging — cut billet of the spectro-verified S30403 heat — carbon confirmed below 0.030% — is hot-forged into the solid disc blank with full heat traceability and segregated stainless handling.
2
Solution anneal — restoring the uniform austenite the grade's corrosion resistance depends on; furnace charts retained against the heat number.
3
Machining & facing — faces, OD and drilling to ASME B16.5 / B16.47; RF serrations, flat face or RTJ groove gauged per B16.20; NPT taps machined where ordered.
4
Testing — tension test and chemistry against the heat; PMI on every piece; intergranular-corrosion (ASTM A262) and other tests where specified.
5
Pickling & passivation — the restored chromium-oxide skin and hygienic finish, with marking of standard, grade (dual F304/F304L where certified), size, class and heat number.
6
Certification & packing — EN 10204 3.1 MTC (3.2 witnessed on request); faces protected, palletised or crated sea-worthy — no carbon-steel contact in transit.
Where F304L Blind Flanges Are Used
Wherever welded stainless meets corrosive duty: chemical and pharmaceutical process piping, food and beverage plants, water and wastewater treatment, pulp and paper, and cryogenic gas systems. Production below:
Machined Flanges — Off the CNC Line at Our WorksLarge Stainless Blind Flange — Machined Face Detail
F304L Blind Flange Dimensions
Blind dimensions are class-governed — identical across material grades. Full charts:
An ASTM A182 F304L blind flange is a solid forged disc of low-carbon austenitic stainless steel — UNS S30403, the weld-safe member of the 304 family — drilled to the standard bolt pattern with no bore, used to close pipes, valves and vessel nozzles in welded corrosive-process systems: chemical and pharmaceutical plants, water treatment, and cryogenic service. Carbon is capped at 0.030% so heat-affected zones cannot sensitize. Dimensions follow ASME B16.5 from ½ inch to 24 inch and ASME B16.47 beyond, in raised face, flat face and ring joint facings.
Why does the L grade exist?
Because welding is where plain 304 gets hurt. Every weld drags nearby metal through the 425-815°C sensitization range, and plain 304's carbon precipitates there as chromium carbides — priming the heat-affected zone for intergranular corrosion. The L grade removes the ammunition: with carbon below 0.030% there is too little to precipitate consequentially, so welded joints stay as corrosion-resistant as the parent metal. That single property made 304L the default of welded corrosive-process piping worldwide.
What does F304L give up for its weld safety?
Strength — honestly and measurably. Carbon is an austenite strengthener, so the L grade's minimums drop to 485 MPa tensile and 170 MPa yield against F304's 515/205, and the flange rating tables place the L grades in a slightly lower group. For a class-governed blind the practical impact is modest, but a joint being class-checked at its limit should be checked against the L-grade line, not the standard one — or ordered as F304/F304L dual-certified, which meets the higher strength while keeping the low carbon.
Why is F304L's nickel range wider than F304's?
Deliberate compensation. Carbon is a powerful austenite stabiliser, and removing it risks the structure drifting toward ferrite; the specification answers by letting nickel — the other stabiliser — run to 13.0% where F304 stops at 11.0%. It looks like a typo on a datasheet and is anything but: the widened window is how the L grade keeps the fully austenitic structure that gives the family its toughness and cryogenic capability.
F304, F304L or F304H — which one?
By carbon, which is to say by duty. F304 (≤0.08%) is the general-purpose default. F304L (≤0.030%) is the welded-corrosion-duty choice — this page's grade, and the one specified whenever field welds meet corrosive service. F304H (0.04-0.10%, minimum enforced) is the sustained-hot-service choice, melted to order for creep duty. Most modern melts satisfy both F304 and F304L, so dual-certified forgings are the practical standard for the everyday middle. Our F304 and F304H blind flange pages cover the other corners.
What does F304/F304L dual certification mean?
One forging satisfying both specifications on one certificate — carbon low enough for L, strength high enough for standard 304. The practical bonus runs in both directions: the dual-cert forging is weld-safe like an L grade and rateable like a standard grade, so it serves line classes written around either designation from one stock. Most of our austenitic production qualifies; state the requirement on the enquiry and the certificate reads accordingly.
What are the mechanical properties of F304L blind flanges?
Tensile strength 485 MPa (70 ksi) minimum, yield strength 170 MPa (25 ksi) minimum, elongation 30% minimum and reduction of area 50% minimum, in the solution-annealed condition — A182 specifies no hardness limit. These are the family's gentlest numbers, the deliberate price of the low carbon; dual-certified material meets standard 304's 515/205 while keeping the L chemistry. As across the austenitics, the toughness is the unadvertised asset: ductile to cryogenic temperatures with no impact-test question.
What temperature range does an F304L blind flange cover?
Cryogenic — LNG, liquid nitrogen — up to roughly 425°C continuous. The low end it owns outright: no ductile-brittle transition, no impact testing, the standard answer of cold-box and cryogenic piping. The hot end is where it steps aside: above ~425°C sustained, the missing carbon means missing creep strength, and the duty passes to F304H. Between those bounds — the whole world of ambient and warm corrosive process — is exactly where 304L lives.
A blind flange isn't welded — why specify L at all?
Fair question, honestly answered: the forged blind itself never sees a welding arc, so sensitization is not its personal risk. The L specification earns its place at system level — one material of construction across pipe, fittings and flanges keeps certificates, welding procedures and future modifications simple; the blind may later be replaced by a welded spool at the same joint; and mixed 304/304L systems invite substitution errors. When the line class says 304L, the closure says 304L — uniformity is the cheap insurance.
When should F316L be used instead of F304L?
When chlorides enter the picture. 316L adds 2-3% molybdenum to the same low-carbon logic, buying measurably better pitting and crevice resistance in salt-bearing water, coastal atmospheres and mild brine. 304L remains the economical weld-safe default for fresh water, food-adjacent chemistry and general process duty. Our F316L blind flange page covers that side; serious chlorides jump past both to duplex.
What facings are F304L blind flanges made with?
All three: raised face (BLRF) — the process-industry default — flat face (BLFF) for mating GRP and lined systems, and ring type joint (BLRTJ) for high-pressure duty, the ring chosen softer than the groove. Each facing has its own page on this site. The forging is common to all three; the mating flange governs the choice, and for RTJ the ring number follows from size and class.
Can F304L blind flanges be tapped for testing or instruments?
Yes — fill, vent, drain, gauge and injection taps are machined into the centre of the blind at the works and certified with the flange. Austenitic stainless work-hardens as it machines, so works tooling beats field drilling; the tap arrives ready to plug with the solution anneal undisturbed. State the NPT size on the enquiry.
Where are F304L blind flanges used?
Wherever welded stainless systems carry corrosive duty: chemical and pharmaceutical process piping, food and beverage plants, water and wastewater treatment, pulp and paper, and cryogenic gas systems — the L grade's home since welded corrosion duty is most of what stainless piping does. F304L blinds serve the usual closure duties — isolations, future connections, tapped test blinds — with the pickled, paint-free finish hygienic industries expect.
Which standards cover F304L blind flanges?
The material standard is ASTM A182 grade F304L (UNS S30403), with ASME SA-182 as its boiler-code twin and EN 1.4307 / X2CrNi18-9 as the European equivalent; dimensions follow ASME B16.5 for ½"-24" and ASME B16.47 for 26"-60", with the L grades carrying their own rating group in the stainless tables. A complete specification reads: 'Blind Flange, RF, 4", ASME B16.5 Class 150, ASTM A182 F304L (or F304/F304L dual)' — and our EN 10204 certificates state it exactly that way.
Who manufactures ASTM A182 F304L blind flanges in India?
Tesco Steel & Engineering is an ISO 9001:2015 certified flange manufacturer based in Mumbai, India, forging ASTM A182 F304L / UNS S30403 blind flanges from ½" to 24" NB per ASME B16.5 in Classes 150-2500 and to 60" per ASME B16.47 — solution annealed, pickled and passivated, PMI-verified, F304/F304L dual-certified where required, certified to EN 10204 3.1/3.2 on every lot — in raised face, flat face and ring joint facings, alongside F304, F304H, F316/F316L, duplex and nickel-alloy blinds. Exported to more than 50 countries.
