ASTM A182 F347 Weld Neck Flanges — Niobium-Stabilized SS 347 & 347H
Tesco Steel & Engineering forges ASTM A182 F347 weld neck flanges in stainless steel 347 — UNS S34700, Werkstoff Nr. 1.4550, the niobium-stabilized 18Cr-11Ni austenitic — from 1/2″ NB to 56″ NB, in ASME B16.5 Class 150–2500 and European PN patterns. Niobium locks the carbon into stable carbides, carrying the grade through the 425–816 °C sensitization zone and — decisively for refineries — defeating the polythionic acid cracking that strikes sensitized stainless at every shutdown. The high-carbon creep grade F347H (S34709) is forged alongside, with dual-certified 347/347H heats covering both callouts — mating A312 TP347/TP347H pipe. Supplied with IBR, PMI and EN 10204 3.1/3.2 on request. ISO 9001:2015, made in Mumbai, India — exported worldwide.
A182 F347 · UNS S34700 · 1.4550
Nb-Stabilized · 10×C Min
Polythionic Acid Resistant
F347H Creep Grade · Dual-Cert
1/2″ – 56″ NB
Class 150 – 2500 · PN 2.5 – 400
ISO 9001:2015 · Exported Worldwide
ASTM A182 F347/347H Weld Neck Flange — Stainless Steel 347 (UNS S34700), Technical Specifications
What is an ASTM A182 F347 Weld Neck Flange?
ASTM A182 F347 is the forged-flange grade of stainless steel 347 (UNS S34700 / 1.4550) — classic 18Cr-11Ni austenitic chemistry with a niobium (columbium) addition of at least 10×C. The niobium ties carbon into stable carbides before chromium can, so the grade works through the 425–816 °C sensitization zone and resists polythionic acid stress corrosion — the shutdown-time cracking that ruins ordinary stainless in sulphur-bearing refinery service. An F347 weld neck flange pairs that metallurgy with a long tapered hub butt-welded to the pipe, bore matched to schedule, joint fully radiographable.
Against its titanium-stabilized sibling 321, niobium holds three quiet advantages: it survives the welding arc (so a true matching 347 filler exists), it is not burned off surfaces in hot oxidation, and it delivers slightly better creep strength — which is why refinery and boiler specifications lean 347. For sustained creep-range pressure design, the high-carbon F347H (UNS S34709) carries the certified ASME time-dependent stresses; our heats are typically dual-certifiable 347/347H.
The stabilized family splits by enemy: 321 owns exhaust and hot-air tradition, 316Ti adds molybdenum for corrosive chemistry, and 347 owns the refinery — hydroprocessing, FCC and reformer units specify it by name.
Also searched as: SS 347 weld neck flange, UNS S34700 flange, 1.4550 flange, 347 WNRF flange, SA182 F347 flange, 347H flange, F347H weld neck flange, UNS S34709 flange — all covered on this page; dual-certified 347/347H stock serves both.
Chemical Composition of ASTM A182 F347
| C | Mn | Si | P | S | Cr | Cb | Ni |
|---|
| 0.080 max | 2.00 max | 1.00 max | 0.045 max | 0.030 max | 17.00-20.00 | 10xC – 1.10 | 9.00-13.00 |
Values in weight %. The niobium (columbium) requirement — 10×C minimum to 1.10% max — is the grade's defining feature, locking every carbon atom into stable NbC. The H variant (347H / S34709) runs carbon at 0.04–0.10% with niobium at 8×C minimum, buying certified creep strength.
Mechanical Properties of ASTM A182 F347
| Tensile Strength, MPa | Yield Strength, Min, MPa | Elongation % min. | Hardness Rockwell HRB | Hardness Brinell HB |
|---|
| 515 | 205 | 30 | 92 max | 201 max |
Minimums per ASTM A182. The niobium carbides give 347 slightly better elevated-temperature strength than its titanium-stabilized sibling — the margin visible in the ASME allowable stress tables. The solution-annealed condition is documented on every certificate.
Equivalent Grades of ASTM A182 F347
| Standard | Werkstoff Nr. | UNS | JIS | GOST | EN |
|---|
| SS 347 | 1.4550 | S34700 | SUS 347 | 08Ch18N12B | X6CrNiNb18-10 |
The high-carbon creep variant is 347H / UNS S34709, dual-certifiable with standard 347. System partners: A312 TP347/TP347H pipe, A403 WP347 fittings and A240 347 plate. Stabilized siblings: 321/321H (Ti) and 316Ti.
ASTM A182 F347 Weld Neck Flange Specifications
| ASTM A182 347 Weld Neck Flanges are available in the following specifications: |
|---|
| Size | 1/2"NB to 56"NB |
| Class | 150#, 300#, 400#, 600#, 900#, 1500#, 2500# |
| Sch (Schedule) | XS, XXS, STD & Schedule 20, 40, 80, 160 |
| Pressure Ratings | PN 2.5 - PN 400 |
| Standards | ASME B16.5, ASME B16.47, EN 1092-1 Type 11, DIN 2631–2635, BS 4504 |
| Condition | Solution Annealed; niobium-stabilized (Cb ≥ 10×C); dual-certifiable 347/347H |
| Other Services | Pickling & passivation on ASTM A182 347 Weld Neck Flanges
Sand Blasting on ASTM A182 347 Weld Neck Flanges
Shot Peening on ASTM A182 347 Weld Neck Flanges
IGC (ASTM A262), PMI & IBR Form III-C certification
Project-specific marking, wrapping & export packing |
Why 347 is the Refinery's Stabilized Stainless
Polythionic Acid Immunity
Sulphide scale + air + moisture at shutdowns cracks sensitized stainless intergranularly; 347's grain boundaries never lose their chromium, so there is nothing to attack — the property NACE SP0170 practice is built around.
A True Matching Filler
Niobium survives the welding arc, so E347/ER347 delivers a stabilized weld metal — base, HAZ and weld all one pedigree. 321 has to borrow this filler.
Better Creep Margin
NbC carbides give 347 slightly higher elevated-temperature strength than 321 — and the H variant carries full code-listed creep stresses above 525 °C.
Dual-Certified 347/347H
Heats melted into the 0.04–0.08% carbon overlap certify to both grades — one flange covers specifications written around either.
Refinery Paperwork Ready
IBR Form III-C, 3.2 witness, PMI, IGC A262 — the documentation hydroprocessing and FCC projects specify, delivered with the flange.
Welding 347 — The Stabilized Grade With Its Own Filler
347 welds with standard austenitic practice — moderate heat input, no preheat, no PWHT — and holds a distinction among stabilized grades: matching E347/ER347 filler. Niobium transfers cleanly across the arc where titanium cannot, so base metal, heat-affected zone and weld metal all carry the same stabilized chemistry — the completeness fabricators want on critical refinery hot systems. On heavy sections, control heat input to limit hot-cracking risk in fully austenitic weld pools.
Creep-range note: for sustained pressure duty above ~525 °C — superheater headers, hot reactor piping — specify F347H: its 0.04–0.10% carbon carries the certified ASME creep stresses that standard 347's chemistry cannot. Our dual-certified stock usually satisfies both callouts.
Where ASTM A182 F347 Weld Neck Flanges Are Used
Refining leads: hydroprocessing reactors and piping, FCC units, catalytic reformers and furnace outlet systems — the services that specify 347 by name for polythionic-acid protection. Boiler superheater auxiliaries follow in the H variant, then chemical plant hot sections, expansion bellows and high-temperature exchangers. Our machined weld neck production below:
ASTM A182 F347 Weld Neck Flanges — Machined Production Stock
ASTM A182 F347 Weld Neck Flange Dimensions
F347 weld neck flanges share their dimensions with every other material in the same class — OD, thickness, hub, bore, bolt circle and bolting per the standard tables. Full ASME B16.5 charts:
European PN dimensions are published on the EN 1092-1 Type 11, DIN 2631–2635 and BS 4504 pages.
Price List & How to Order
Stainless pricing tracks nickel and niobium plus the certification scope, so we quote live with a stated validity rather than publish a static list. To get a firm quotation, usually within 24 hours:
1
List your requirement — size (NB), class or PN, standard (ASME B16.5 / B16.47 / EN / DIN / BS), grade (F347 — or F347H / dual-certified 347/347H for creep-range design), pipe schedule or bore, and quantity.
2
Add the certification scope — IBR Form III-C, 3.2 witness, PMI, IGC A262 or project specifications.
ASTM A182 F347 Weld Neck Flanges — Frequently Asked Questions
What is an ASTM A182 F347 weld neck flange?
It is a weld neck flange forged from ASTM A182 grade F347 — niobium-stabilized stainless steel 347, UNS S34700 / 1.4550. Niobium (columbium) ties up carbon as stable carbides, so the grade works through the 425 to 816 °C sensitization zone and resists the polythionic acid attack that strikes refinery stainless at shutdowns. The long tapered hub is butt-welded to the pipe with the bore matched to the pipe schedule, giving a radiographable, fatigue-resistant joint in the refinery industry's stabilized stainless of choice.
What is the difference between 347 and 321 stainless steel?
Both are stabilized against sensitization; the stabilizer differs. 321 uses titanium, 347 uses niobium — and niobium holds three practical advantages: it survives the welding arc (so matching 347 filler exists, where 321 must borrow it), it is not lost from surfaces during high-temperature oxidation, and it gives slightly better creep strength. The price is a modest premium. Refineries and boiler codes lean 347; exhaust and aerospace tradition leans 321. We forge both families.
What is the difference between F347 and F347H flanges?
Carbon, and the code credit it buys. Standard 347 allows carbon to 0.08% with niobium at 10 times carbon; 347H (UNS S34709) requires carbon at 0.04 to 0.10% with the stabilization ratio adjusted to 8×C minimum, giving it the certified creep and stress-rupture strength ASME codes list above about 525 °C. For sustained pressure duty in the creep range — superheater headers, hot refinery piping — specify F347H; dual-certified 347/347H heats cover both callouts on one certificate.
What is polythionic acid stress corrosion cracking and why does 347 resist it?
In refinery units, sulphide scale on stainless surfaces reacts with air and moisture at shutdowns to form polythionic acids, which attack sensitized grain boundaries and crack ordinary stainless intergranularly — a failure that appears exactly when the unit is opened for maintenance. Because niobium has already locked up the carbon, 347's grain boundaries never lose their chromium, so there is nothing for the acid to exploit. That immunity, formalized in NACE SP0170 practice, is why hydroprocessing and FCC units specify 347 by name.
What temperature range can F347 flanges be used in?
The grade's home is 425 to 816 °C — the sensitization zone it was engineered to survive — with oxidation resistance in intermittent service to about 870 °C and full austenitic toughness down to cryogenic temperatures. For sustained creep-range pressure design above about 525 °C, the code points to the high-carbon 347H variant, which carries certified time-dependent allowable stresses.
What are the equivalent designations for A182 F347?
SS 347 in general usage; UNS S34700; Werkstoff Nr. 1.4550 (EN X6CrNiNb18-10); JIS SUS 347; and GOST 08Ch18N12B. The high-carbon variant is 347H / UNS S34709. System partners share the chemistry: A312 TP347 and TP347H pipe, A403 WP347 butt-weld fittings and A240 347 plate. An enquiry in any of these designations is quoted as the same material.
What is the chemical composition of ASTM A182 F347?
Per ASTM A182: carbon 0.080% max, manganese 2.00% max, silicon 1.00% max, phosphorus 0.045% max, sulphur 0.030% max, chromium 17.00 to 20.00%, niobium (columbium) at ten times the carbon content up to 1.10% max, and nickel 9.00 to 13.00%. The niobium requirement is the grade's defining feature — enough to lock every carbon atom into stable NbC carbides. For 347H, carbon runs 0.04 to 0.10% with niobium at 8×C minimum.
What are the mechanical properties of A182 F347 flanges?
Minimum tensile strength 515 MPa (75 ksi), minimum yield strength 205 MPa (30 ksi) and minimum elongation 30%, with hardness typically limited to 92 HRB / 201 HB. The solution-annealed condition is documented on every certificate, and the niobium carbides give 347 slightly better elevated-temperature strength than its titanium-stabilized sibling — the margin that shows up in the ASME allowable stress tables.
Which pipe grades do F347 weld neck flanges mate with?
ASTM A312 TP347 seamless and welded pipe is the standard partner — TP347H for creep-range systems — with A403 WP347 butt-weld fittings completing the system. The weld neck bore is machined to the pipe schedule you state, so the bore runs flush through the joint and the bevel arrives ready for a matched-chemistry butt weld.
How are 347 flanges welded to pipe?
With matching E347 / ER347 filler and standard austenitic practice — moderate heat input, no preheat, no PWHT. Unlike titanium, niobium transfers cleanly across the welding arc, so 347 is the one stabilized grade with a true matching consumable: base metal, heat-affected zone and weld metal all carry the same stabilized pedigree. That completeness is a quiet reason fabricators prefer it on critical hot systems.
Why do refineries specify 347 stainless steel?
Because refinery hot service combines everything the grade was built for: operating temperatures in the sensitization zone, sulphur chemistry that primes polythionic acid attack at every shutdown, and long campaigns that demand creep-rated material in the H variant. Hydroprocessing reactors and piping, FCC units, catalytic reformers and furnace outlet systems specify 347 and 347H by name — often with NACE SP0170 shutdown-protection practice built around the material's immunity.
Are F347 flanges suitable for IBR (boiler) applications?
Yes — boiler superheater and hot steam auxiliaries suit the grade, with 347H the code-correct choice for creep-range pressure parts, and we supply flanges with IBR Form III-C certification for Indian boiler regulation scope on request. State the IBR requirement in the enquiry so the heat, testing and documentation are aligned from the start.
What testing and certification do you supply with F347 flanges?
Every lot ships with EN 10204 3.1 mill test certificates covering chemical analysis — including niobium and the stabilization ratio — mechanical properties and the solution-anneal record, with 3.2 certification witnessed by Lloyd's, DNV, BV or TÜV on request. We also offer intergranular corrosion testing to ASTM A262, PMI verification, IBR Form III-C and hydrostatic or hardness testing to project specifications, with full heat-number traceability.
Where are ASTM A182 F347 weld neck flanges used?
Refinery hydroprocessing and FCC units above all — the grade's home industry — plus catalytic reformers, furnace outlet piping, boiler superheater auxiliaries, chemical plant hot sections, expansion bellows and high-temperature exchangers. Wherever hot service meets sulphur chemistry or the specification says polythionic acid protection, 347 and its H variant are the engineered answer.
What sizes and standards do you manufacture F347 weld neck flanges in?
From 1/2 inch NB to 56 inch NB: ASME B16.5 Class 150 to 2500 up to 24 inch, ASME B16.47 above, and European PN 2.5 to PN 400 patterns to EN 1092-1 Type 11, DIN and BS 4504. Raised face is standard, ring joint for high-class refinery service on request — the machined weld necks photographed on this page are our own production — and every bore is machined to the mating pipe schedule from Sch 10 through XXS.
Do you keep A182 F347 weld neck flanges in stock? What is the lead time?
Common refinery sizes in Class 150, 300 and 600 rotate through regular production, with popular items often available from stock. Larger diameters, higher classes, F347H and witness-tested lots are forged to order, typically in 3 to 5 weeks. Prices track nickel and niobium, so quotations carry a validity period — send the size list and we confirm the stock position the same day.
What information should I include in an F347 flange enquiry?
Six things: size (NB), pressure class or PN rating, dimensional standard (ASME B16.5, B16.47 or EN/DIN/BS), grade (F347 — or F347H / dual-certified 347/347H if the design sits in the creep range), pipe schedule or bore, and quantity. Add any certification scope — IBR Form III-C, 3.2 witness, PMI, IGC A262 — since refinery paperwork is usually specification-driven. With these details we return a firm quotation, usually within 24 hours.
Do you export ASTM A182 F347 flanges outside India?
Yes. Tesco Steel & Engineering is an ISO 9001:2015 certified manufacturer based in Mumbai, and F347 flanges ship to refinery, petrochemical and power projects across the Middle East, Europe, Africa, Southeast Asia and the Americas. Flanges travel pickled, face-protected and seaworthy-packed, with full heat-number and test traceability.
