Hastelloy C-276 Blind Flanges — UNS N10276 Blind Flange Manufacturer
Tesco Steel & Engineering forges Hastelloy C-276 blind flanges — ASTM B564, UNS N10276, W.Nr. 2.4819 — to ASME B16.5 Class 150–2500 from ½″ to 24″ NB and to ASME B16.47 up to 60″. This is the alloy of last resort — the grade the chemical industry specifies when the stream is mixed, contaminated, cycling or simply unknown. The only mainstream alloy that ranks molybdenum above chromium (15–17% Mo over 14.5–16.5% Cr), with 3–4.5% tungsten behind it: firepower in reducing acids, chromium enough for oxidizing ones, and essential immunity to chloride pitting, crevice attack and SCC — the ladder that started at 316L ends on this page. Wet chlorine, FGD scrubbers, bleach plants, sour wells that exhaust 825 and 625. Defined, predictable duty? We will down-sell you to 904L or Alloy 20 — and say so on the quote. 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.
Hastelloy C-276 · ASTM B564 · UNS N10276W.Nr. 2.4819Mo 15–17% — Ranked Above Cr+ Tungsten 3–4.5%The Alloy of Last ResortChloride Ladder — Final StepNACE MR0175 — Harshest Sour TiersASME B16.5 ½″–24″ · Class 150–2500EN 10204 3.1 / 3.2 · ISO 9001:2015
Hastelloy C-276 Blind Flanges — Specifications at a Glance
What is a Hastelloy C-276 Blind Flange?
The last-resort closure. A solid forged disc of nickel-molybdenum-chromium-tungsten alloy (ASTM B564 / UNS N10276 / W.Nr. 2.4819) with no bore — the grade specified when the environment has beaten everything cheaper. Mo 15–17% ranked above Cr 14.5–16.5%, W 3–4.5% in support: deep resistance in reducing acids, chromium cover for oxidizing media, and essential immunity to chloride pitting, crevice corrosion and SCC. Solution annealed — 690/283 MPa, 40% elongation — extra-low C (≤0.01%) and Si. Dimensions per ASME B16.5 / B16.47 in RF, FF and RTJ facings; EN 10204 3.1 on every lot.
Also searched as: Alloy C-276 blind flange, C276 blind, N10276 blind flange, B564 C-276 blind, 2.4819 blind flange, Ni-Mo-Cr blind flange, FGD blind flange — all refer to the product on this page. See also the sibling Hastelloy C-22 blind flanges, the strength rival Inconel 625, the acid trio 904L / Alloy 20 / 825, the other C-276 types — weld neck, slip-on, spectacle blind — and the facing pages BLRF / BLFF / BLRTJ.
Both Flanks of the Acid War
Environment Class
What Defends
C-276's Answer
Reducing acids — HCl, dilute H2SO4, phosphoric
Molybdenum + tungsten
Mo 15–17% + W 3–4.5% — the deepest standard-alloy reserve
Oxidizing media — ferric, cupric, wet Cl2 chemistry
Chromium
Cr 14.5–16.5% — enough cover for mixed and contaminated streams
Chlorides — pitting, crevice, SCC
Mo + W + nickel base
Essentially immune — the final step of the chloride ladder
Sour service — H2S + chlorides + sulphur
The whole recipe
NACE MR0175 — qualified into the harshest tiers, no ageing complications
The Signature: Molybdenum Above Chromium
The Ration Ends Here
Every grade below rations molybdenum — 316L gets 2%, 904L 4–5%, 254 SMO 6%, 625 9%. C-276 stops rationing: 15–17%, ranked above its own chromium — the only mainstream alloy built that way.
Tungsten, the Heavy Cousin
3.0–4.5% W works alongside Mo in the same defensive chemistry — pushing the pitting resistance number beyond any practical brine, hypochlorite or seawater duty.
The '276' Purification
Carbon ≤0.01%, silicon ≤0.08% — the fix that turned old alloy C into C-276: clean grain boundaries in the as-welded condition, no re-anneal after fabrication welds, no preferential attack beside the seam.
Hastelloy C-276 Chemical Composition (UNS N10276)
Element
Ni
Mo
Cr
Fe
W
Co
Mn
V
Si
C
P
S
Weight %
Balance (~57)
15.0–17.0
14.5–16.5
4.0–7.0
3.0–4.5
≤2.5
≤1.0
≤0.35
≤0.08
≤0.01
≤0.025
≤0.010
Two things to read: molybdenum ranked above chromium with tungsten in support — the reducing-acid signature no other standard grade carries — and the extra-low carbon and silicon that define the '276' purification. Our PMI reads the Mo-Cr-W signature on every piece; a wrong heat cannot leave the works.
Mechanical Properties (Solution Annealed)
Property
ASTM B564 N10276 Requirement
Tensile Strength
≥ 690 MPa (100 ksi)
Yield Strength (0.2%)
≥ 283 MPa (41 ksi) — above the 300-series and 825; the chemistry specialist's honest figure
Elongation
≥ 40% — generous ductility from a single-condition solid-solution alloy
Condition
Solution annealed — non-hardenable, no ageing windows, no hardness ceilings; the certificate is the qualification
Service Span
Cryogenic upward to ~675°C in code work — but its money is spent on chemistry, not heat
Hastelloy C-276 / UNS N10276 Blind Flanges are available in the following specifications:
Material Grade
Hastelloy C-276 — ASTM B564 (UNS N10276), W.Nr. 2.4819; plate B575 and bar B574 appear on mill paperwork, the flange certificate reads B564
Heat Treatment
Solution annealed — furnace records certified; extra-low C/Si guarantee travels on the MTC
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 on the nickel-alloy B16.5 lines
Facings
Raised Face (BLRF), Flat Face (BLFF), Ring Type Joint (BLRTJ) with groove per B16.20
Service Span
Reducing and oxidizing acids, wet chlorine, hypochlorite, chlorides without limit, harshest NACE sour tiers; hot concentrated nitric excluded
Surface Finish
Pickled or natural machined — no paint; segregated alloy handling throughout
Modifications
NPT-tapped test and injection blinds; matching spectacle blinds, spades and bleed rings from the same certified stock
Testing
Tension & chemistry per heat — the Mo, W and low-C/Si windows verified; PMI routine on every piece
Certification
EN 10204 3.1 (standard) / 3.2 witnessed — solution-anneal records included
Why Hastelloy C-276 Blind Flanges Are Specified
The Stream Is Mixed, Cycling or Unknown
Defined duties have cheaper right answers. C-276 is bought for the streams that cross the redox line, carry contamination, or change with every campaign — multi-product reactors, spent-acid recovery, waste-gas cleaning.
The Chloride Escalation Ends
When crevice attack appears under a 6Mo gasket or a chloride problem defeats 625, C-276 is where the ladder stops — pitting and crevice numbers beyond any practical brine, and SCC off the failure map.
The Worst Sour Wells
H2S + chlorides + elemental sulphur at temperature — the combination that exhausts 825 and 625 — is C-276's NACE franchise, with no ageing windows or hardness ceilings to manage.
The Closure Should Match the Vessel
A scrubber or chlorine header built in C-276 deserves a closure with no cheaper sacrificial member — one alloy, one heat, one MTC across the isolation point.
Know the Map
Defined acid duty: 904L / Alloy 20 / 825 — and we will say so. Strength or heat leading: 625. Oxidizing-side chemistry: C-22. Facings: BLRF / BLFF / BLRTJ.
Specification Notes — Getting C-276 Right
Three honest limits.Hot, strongly oxidizing media are not its war: with chromium rationed in favour of molybdenum, hot concentrated nitric acid belongs to high-chromium grades — C-22, or plain stainless, which handles nitric for a fraction of the price. Heat is not where its money goes: code use runs to ~675°C, but oxidation-limited hot duty belongs to 601 and the 800 trio. And the price is real: C-276 is among the most expensive standard flange alloys — a defined, predictable duty usually has a cheaper right answer, and our quotations name it when it does.
How Our Hastelloy C-276 Blind Flanges Are Manufactured
1
Forging — cut billet of the spectro-verified N10276 heat — the Mo and W windows and the extra-low C/Si confirmed — is hot-forged into the solid disc blank with full heat traceability and segregated alloy handling.
2
Solution annealing — the anneal-and-quench that locks the clean solid-solution structure; furnace charts retained against the heat number.
3
Machining & facing — faces, OD, drilling and any NPT taps cut to ASME B16.5 / B16.47; RF serrations, flat face or RTJ groove gauged per B16.20.
4
Testing — tension test and full chemistry against the heat; PMI reads the Mo-Cr-W signature on every piece before it can mix with any other alloy.
5
Finishing — pickled or natural machined finish; marked with standard, grade, size, class and heat number.
6
Certification & packing — EN 10204 3.1 MTC (3.2 witnessed on request) including solution-anneal records; faces protected, palletised or crated sea-worthy — no carbon-steel contact in transit.
Where Hastelloy C-276 Blind Flanges Are Used
Where the escalation stops: FGD scrubbers and absorber trains, chlor-alkali plants and wet chlorine headers, pulp & paper bleach plants, hypochlorite and ClO2 systems, spent and mixed acid recovery, pickling lines, agrochemical and pharma reactors, waste incineration gas cleaning, and the harshest sour oil-and-gas closures. Production below:
Large Blind Flange — Auxiliary Nozzle ClosureHeavy-Section Forged Blind — Machined at Our WorksHastelloy C-276 Flanges — Protected Stock
Hastelloy C-276 Blind Flange Dimensions
Blind dimensions are class-governed — identical across material grades. Full charts:
How to Specify & Order a Hastelloy C-276 Blind Flange
Five elements — and if the duty is defined, tell us: the down-sell check is free:
1
Size & standard — e.g. 6″ NB ASME B16.5, or the B16.47 series for 26″ and above.
2
Pressure class & facing — Class 150–2500; RF, FF or RTJ (with ring number) to match the mating flange.
3
Grade — ASTM B564 UNS N10276 (Hastelloy C-276), solution annealed; W.Nr. 2.4819 where the European designation is required.
4
Service declarations & certification — sour service (NACE MR0175) where applicable; NPT tap size if a test blind; matching spectacle blinds or spades from the same heat if the isolation set is ordered together; PMI or 3.2 witnessing as specified; EN 10204 3.1 — our standard.
A Hastelloy C-276 blind flange is a solid forged disc of nickel-molybdenum-chromium-tungsten alloy — ASTM B564, UNS N10276, W.Nr. 2.4819 — drilled to the standard bolt pattern with no bore, used to close a flanged connection in the most aggressive chemical services in industry. Its chemistry ranks molybdenum above chromium (15.0-17.0% against 14.5-16.5%) with 3.0-4.5% tungsten behind it, which buys firepower against reducing acids, enough chromium for oxidizing ones, and essential immunity to chloride pitting, crevice corrosion and stress corrosion cracking. 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 is C-276 called the alloy of last resort?
Because it is the grade the chemical industry specifies when the environment has already beaten everything cheaper — or cannot be predicted at all. Most corrosion alloys pick a side: stainless and high-chromium grades handle oxidizing media, nickel-molybdenum grades handle reducing media, and each fails on the other side of the line. C-276 holds both flanks — molybdenum and tungsten for the reducing half, chromium for the oxidizing half — and shrugs off the chlorides that dissolve compromise choices. That is why it anchors services where streams are mixed, contaminated, cycling or unknown: FGD scrubbers, waste incineration, spent-acid recovery, multi-product reactors. It costs accordingly, and we will down-sell to 904L, Alloy 20 or 825 whenever the duty is actually defined enough to allow it.
Why does C-276 rank molybdenum above chromium?
It is the only mainstream corrosion alloy that does — 15.0-17.0% molybdenum over 14.5-16.5% chromium, with tungsten at 3.0-4.5% acting as a heavier chemical cousin of Mo. Molybdenum is the element that defends metal in reducing acids (hydrochloric, dilute sulphuric, phosphoric) and jams the chloride pitting mechanism; chromium defends in oxidizing media. Every grade lower on the ladder rations molybdenum — 316L gets 2%, 904L gets 4-5%, 254 SMO gets 6%, 625 gets 9%. C-276 simply stops rationing. The pitting resistance number that results is so high the alloy is treated as immune to chloride pitting and crevice attack in practical seawater and brine service.
What is the chemical composition of Hastelloy C-276 (UNS N10276)?
Nickel balance (about 57%), molybdenum 15.0-17.0%, chromium 14.5-16.5%, iron 4.0-7.0%, tungsten 3.0-4.5%, cobalt ≤2.5%, manganese ≤1.0%, vanadium ≤0.35%, silicon ≤0.08%, carbon ≤0.01%, phosphorus ≤0.025%, sulphur ≤0.010%. Two things to read from it: molybdenum ranked above chromium with tungsten in support — the reducing-acid signature — and the extra-low carbon and silicon that define the '276' purification. Our PMI reads the Mo-Cr-W signature on every piece; a wrong heat cannot leave the works.
What are the mechanical properties of Hastelloy C-276 blind flanges?
In the solution-annealed condition ASTM B564 requires tensile strength 690 MPa (100 ksi) minimum, yield strength 283 MPa (41 ksi) minimum and elongation 40% minimum. Read it as a corrosion specialist's sheet: respectable strength — above the 300-series stainless grades and 825 — with generous ductility, from a single-condition, non-hardenable solid-solution alloy. Where a design needs aged-alloy yield inside a corrosive certificate, the answer is a different family — 625 for strength with seawater, 925 or K-500 for the gamma-prime grades — and C-276 keeps the chemistry crown.
What does the extra-low carbon and silicon in C-276 do?
It is the alloy's founding innovation — the '276' is a purified re-issue of the original alloy C, whose carbon and silicon precipitated at the grain boundaries beside welds and caused preferential attack, forcing a re-anneal after every weld. With carbon held to 0.01% and silicon to 0.08%, C-276 stays clean in the as-welded condition — fabricators can weld it and put it straight into acid service. For a bolted blind flange the story is simpler still: our blinds ship solution annealed with the furnace records certified, and the low-C guarantee travels on the MTC for whatever welding happens elsewhere in the line.
Is Hastelloy C-276 resistant to chloride pitting and SCC?
Essentially immune, and it closes the ladder this site has been climbing. The chloride sequence runs 316L → 317L → duplex → 904L → super duplex → 254 SMO → 625 — each step buying a higher pitting resistance number and a higher critical temperature. C-276 ends the conversation: with 16% molybdenum plus tungsten, its pitting and crevice numbers sit beyond any practical brine, seawater or hypochlorite duty, and its nickel base removes chloride stress corrosion cracking from the failure map entirely. When a chloride problem has defeated a 6Mo grade or shows crevice attack under gaskets at high temperature, C-276 is where the escalation stops.
Hastelloy C-276 or Inconel 625 — how do they divide?
They overlap heavily — both nickel bases with high molybdenum, both essentially chloride-proof — and divide by what leads the specification. 625 (9% Mo plus niobium) brings 414 MPa yield, fatigue strength and high-temperature capability: it is the marine, aerospace and heat-plus-corrosion grade. C-276 (16% Mo plus tungsten) gives up strength — 283 MPa yield — and spends everything on chemistry: it goes deeper in reducing acids, wet chlorine and hypochlorite, and is the standard escalation grade of the chemical process industry. Practical split: seawater plus strength or heat, 625; aggressive or mixed acid chemistry, C-276. Both are stocked here; the service sheet decides.
Hastelloy C-276 or C-22 — which one?
C-22 (UNS N06022) rebalances the same idea toward the oxidizing side: chromium up to around 22%, molybdenum down to 13%, tungsten trimmed. That makes C-22 stronger in oxidizing acids and wet-oxidizing environments and gives it an edge in some hypochlorite and nitric-bearing mixtures, while C-276 keeps the advantage in strongly reducing media — hot hydrochloric, hot dilute sulphuric — thanks to the higher Mo+W. C-276 remains the default of the two: the longest track record, the widest approvals, the deepest stock. Where a specification names C-22, we supply it — see our Hastelloy C-22 blind flange page — and where the buyer may choose, the redox balance of the stream decides.
Is Hastelloy C-276 acceptable for NACE MR0175 sour service?
Yes — solution-annealed C-276 is among the most highly rated corrosion-resistant alloys in NACE MR0175 / ISO 15156, qualified for the harshest sour environments the standard contemplates, essentially without the environmental restrictions that hedge lesser CRAs. In sour oil-and-gas duty it appears where H2S, chlorides and elemental sulphur combine at temperature — the conditions that exhaust 825 and 625 — typically as the closure grade on the worst wells and sour flowlines. Being single-condition and non-hardenable, it carries no ageing-window or hardness-ceiling complications: the solution-annealed certificate is the qualification.
What facings are Hastelloy C-276 blind flanges made with?
All three: raised face (BLRF) — the default — flat face (BLFF) for mating the lined, rubber-coated and FRP systems common in exactly the chlorine and scrubber services C-276 serves, and ring type joint (BLRTJ) for high-pressure sour and acid systems. Each facing has its own page on this site. Gasket selection matters more than usual here: the gasket must not be the corrosion weak point of a joint built around a last-resort alloy — PTFE-based and C-276-wound spiral gaskets are the usual companions. NPT-tapped test and injection blinds are machined and certified at the works.
Where are Hastelloy C-276 blind flanges used?
Flue-gas desulphurisation scrubbers and their absorber trains, chlor-alkali plants and wet chlorine headers, pulp and paper bleach plants, hypochlorite and chlorine dioxide systems, spent and mixed acid recovery, pickling lines, agrochemical and pharmaceutical reactors, waste incineration gas cleaning, and the sour oil-and-gas services that combine H2S, chlorides and sulphur at temperature. C-276 blinds close those systems as isolations, spare-nozzle blanks, spectacle-blind companions and tapped test points — the closure matching the vessel alloy so the joint has no cheaper sacrificial member.
Which standards cover Hastelloy C-276 blind flanges?
The forging standard is ASTM B564 (UNS N10276) — the same solid-solution nickel-alloy forging specification that covers 600, 625, 800 and 825; plate is B575 and bar is B574, which is why those numbers appear on mill paperwork but not on a flange certificate, and A182 does not cover nickel alloys at all. The European designation is W.Nr. 2.4819. Dimensions follow ASME B16.5 for ½"-24" and ASME B16.47 for 26"-60", rated on the nickel-alloy lines. A complete specification reads: 'Blind Flange, RF, 6", ASME B16.5 Class 300, ASTM B564 UNS N10276 (Hastelloy C-276), solution annealed' — and our EN 10204 certificates state it exactly that way.
Can I get C-276 blinds to match a spectacle blind or spade set?
Yes — and in C-276 services the isolation hardware family matters, because scrubber and chlorine systems are maintenance-intensive and isolate often. We manufacture the full set in N10276 from the same certified stock: blind flanges from this page, spectacle blinds and spade-and-spacer sets (see our Hastelloy C-276 spectacle blind page), bleed rings for between-flange draining, and the weld neck, slip-on and threaded C-276 flanges the rest of the line uses. Ordering the set together puts one heat and one MTC across the whole isolation point — which is how the auditors of chlorine plants prefer to find it.
Who manufactures Hastelloy C-276 blind flanges in India?
Tesco Steel & Engineering is an ISO 9001:2015 certified flange manufacturer based in Mumbai, India, forging Hastelloy C-276 / ASTM B564 / UNS N10276 blind flanges from ½" to 24" NB per ASME B16.5 in Classes 150-2500 and to 60" per ASME B16.47 — solution annealed with furnace records certified, pickled, PMI-verified with the Mo-Cr-W signature read on every piece, certified to EN 10204 3.1/3.2 on every lot — in raised face, flat face and ring joint facings, alongside Hastelloy C-22, Inconel 625, Incoloy 825, Alloy 20 and the full nickel-alloy blind range. Exported to more than 50 countries.
