Tesco Steel & Engineering forges ASTM A182 F11 weld neck flanges in 1.25% chromium, 0.5% molybdenum alloy steel — UNS K11597, Werkstoff Nr. 1.7335 (13CrMo44), supplied as Class 2 — from 1/2″ NB to 56″ NB, in ASME B16.5 Class 150–2500 and European PN patterns. The workhorse chrome-moly of power generation: creep strength for boiler and steam-header service to ~560 °C, mating A335 P11 pipe through boilers, HRSG modules and turbine piping. Normalized & tempered, hardness-controlled 143–207 HB, with IBR, NACE MR0175, PMI and EN 10204 3.1/3.2 on request. ISO 9001:2015, made in Mumbai, India — exported worldwide.
A182 F11 Cl2 · UNS K11597 · 1.73351.25Cr – 0.5Mo Power Grade1/2″ – 56″ NBClass 150 – 2500 · PN 2.5 – 400Steam Service to ~560 °CIBR · NACE · PMI · 3.1/3.2ISO 9001:2015 · Exported Worldwide
ASTM A182 F11 is the 1.25Cr-0.5Mo alloy steel forging grade (UNS K11597) — the workhorse chrome-moly of power generation, supplied as Class 2 unless a spec says otherwise. An F11 weld neck flange pairs that chemistry with the strongest flange design: a long tapered hub butt-welded to the pipe, bore matched to the pipe schedule, joint fully radiographable — carrying creep strength for steam service to ~560 °C.
The chemistry splits the work: molybdenum resists creep, letting the joint carry pressure for decades at temperatures where carbon steel slowly stretches, while the modest 1.25% chromium adds oxidation margin and resistance to hydrogen attack at boiler conditions. That balance — enough alloy to serve, little enough to stay affordable and weldable — is why F11 is the highest-volume alloy flange grade in power construction, running with A335 P11 pipe and A234 WP11 fittings.
On the chrome-moly ladder, F11 hands over to F22 (2.25Cr-1Mo) for hotter headers and hydrogen service, and to F91 for supercritical creep duty; when sulphur drives the corrosion allowance, F5 and F9 take the refinery path. We forge every rung in-house.
Also searched as: A182 F11 Cl2 WNRF flange, SA182 F11 weld neck flange, 1.25Cr-0.5Mo flange, 13CrMo44 flange, UNS K11597 flange, alloy steel F11 flange — all refer to the product on this page.
Chemical Composition of ASTM A182 F11 CL2
C
Mn
P
S
Si
Cr
Mo
0.10-0.20
0.30-0.80
0.040 max
0.040 max
0.50 - 1.00
1.00-1.50
0.44-0.65
Values in weight %, for Class 2. Note the carbon window — a floor as well as a ceiling — which underwrites the Class 2 strength level, while the modest chromium keeps F11 the most weldable of the chrome-moly family.
Mechanical Properties of ASTM A182 F11 CL2
Tensile Strength, MPa [ksi]
Yield Strength, Min, MPa [ksi]
Elongation % min.
Reduction of Area % min.
Hardness HB
485 [70]
275 [40]
20
30
143-207
Class 2 minimums — the industry default. Class 1 (415/205 MPa) and Class 3 (515/310 MPa) are supplied against specification. The hardness band certifies the normalize-and-temper heat treatment, keeps welds sound, and holds the flange under NACE limits where sour service applies.
Equivalent Grades of ASTM A182 F11
Standard
Werkstoff Nr.
UNS
DIN
Alloy F11
1.7335
UNS K11597
13CrMo44
The same 1.25Cr-0.5Mo chemistry runs through the whole piping system: A335 P11 seamless pipe, A234 WP11 butt-weld fittings and A217 WC6 castings. An enquiry in any of these designations is quoted as the same material.
ASTM A182 F11 Weld Neck Flange Specifications
ASTM A182 F11 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
Grade / Strength Class
A182 F11 Class 2 standard; Class 1 and Class 3 on request
Other Services
Hot Dip Galvanized (GI) ASTM A182 F11 Weld Neck Flanges Sand Blasting on ASTM A182 F11 Weld Neck Flanges Shot Peening on ASTM A182 F11 Weld Neck Flanges Epoxy Coating on ASTM A182 F11 Weld Neck Flanges FBE Coating on ASTM A182 F11 Weld Neck Flanges
Why F11 for Power-Plant Flanged Joints
The Power-Plant Workhorse
Enough molybdenum for creep duty to ~560 °C, little enough alloy to stay affordable — the highest-volume alloy flange grade in power construction worldwide.
Mildest Chrome-Moly to Weld
E8018-B2 consumables, moderate preheat, standard PWHT — the friendliest welding rules on the ladder, proven across thousands of boiler joints.
Hydrogen-Attack Margin
The 1.25% chromium resists the hydrogen attack that limits carbon steel at boiler pressures and temperatures — insurance written into the chemistry.
One Chemistry, Whole System
F11 flanges, A335 P11 pipe, WP11 fittings — matched chemistry and matched procedures from economiser to header.
IBR & Code Ready
IBR Form III-C for Indian boiler work, EN 10204 3.1/3.2, PMI and hardness surveys — the paperwork arrives as complete as the flange.
Welding F11 — What the Grade Demands
F11 is the mildest chrome-moly to weld, but it still hardens in the heat-affected zone if the thermal rules are ignored. Sound joints use matching 1.25Cr-0.5Mo consumables (E8018-B2 / ER80S-B2), preheat around 150–200 °C, and PWHT at roughly 620–720 °C where the governing code requires it — which, above thin-wall exemption limits, is most of the time in boiler work.
Plan the PWHT. ASME B31.1/B31.3 and the boiler codes invoke post-weld heat treatment for the 1.25Cr class beyond modest thicknesses — cheap insurance on joints that will spend decades in creep service.
Where ASTM A182 F11 Weld Neck Flanges Are Used
Power generation is home ground: boiler steam circuits, main and reheat steam headers, HRSG module piping, turbine drains, extraction and feedwater systems — every joint that runs hotter than carbon steel's comfort zone but below the F22/F91 threshold. Refinery and petrochemical services at moderate temperature use F11 for the same economics. Below ~425 °C, A105 saves money; above F11's range or in hydrogen service, F22 and F91 continue the ladder.
Production, Stock & Packing
F11 is our highest-volume alloy grade: certified 1.25Cr-0.5Mo blanks are forged, normalized and tempered, hardness-surveyed and PMI-verified, then CNC-turned with the bore matched to your pipe schedule and the weld end bevelled to 37.5°. The photographs below are our alloy steel production — black-coated flanges in yard stock and lined packing:
F11 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:
F11 pricing follows the alloy steel market plus heat-treatment and certification scope, so we quote live rather than publish a static list — and as our highest-volume alloy grade, it ships fastest of the chrome-moly family. 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 and class (F11 Cl1 / Cl2 / Cl3), pipe schedule or bore, and quantity.
It is a weld neck flange forged from ASTM A182 grade F11 — the 1.25% chromium, 0.5% molybdenum alloy steel (UNS K11597), supplied as Class 2 unless specified otherwise. 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 workhorse chrome-moly grade of power generation — boilers, steam headers and turbine piping running hotter than carbon steel can serve.
What is the difference between F11 Class 1, Class 2 and Class 3?
Strength level, set by carbon content and heat treatment. Class 1 (lower carbon) offers 415 MPa tensile / 205 MPa yield minimums; Class 2 — the industry default and what we supply unless told otherwise — offers 485 / 275 MPa; Class 3 raises the bar to 515 / 310 MPa. Chemistry is otherwise the same 1.25Cr-0.5Mo family. State the class in your enquiry and the certificate documents it.
What temperature can F11 flanges handle?
F11 serves creep-range steam duty to around 560 °C, with design stresses per the ASME rating tables. Below about 425 °C, carbon steel A105 is usually the economical choice; above F11's range, F22 (2.25Cr-1Mo) and then F91 take over. The grade's molybdenum resists creep, and its modest chromium adds oxidation margin plus resistance to hydrogen attack at boiler conditions.
How does F11 compare with F22?
F22 carries roughly double the chromium (2.25%) and molybdenum (1%), buying higher creep strength and better hydrogen-attack resistance — the step power plants take for hotter headers and hydroprocessing units for high-pressure hydrogen service. F11 remains the value grade for the broad middle of steam temperatures, which is why it is the highest-volume alloy flange in power construction. We forge both, plus every other rung of the ladder.
When would I use F5 or F9 instead of F11?
When sulphur, not just temperature, drives the corrosion allowance. F11's 1.25% chromium is creep-oriented; it offers little defence against hot sulphidation in refinery streams. F5 (5Cr) and F9 (9Cr) trade a little economy for chromium that resists hot H2S attack. Rule of thumb: clean steam — F11 or F22; sour hot hydrocarbons — F5 or F9.
What are the equivalent designations for A182 F11?
UNS K11597; Werkstoff Nr. 1.7335; and the DIN designation 13CrMo44 (13CrMo4-5 in current EN numbering). Its system partners share the chemistry: A335 P11 seamless pipe, A234 WP11 butt-weld fittings and A217 WC6 castings. An enquiry in any of these designations is quoted as the same material.
What is the chemical composition of ASTM A182 F11?
For Class 2: carbon 0.10 to 0.20%, manganese 0.30 to 0.80%, phosphorus 0.040% max, sulphur 0.040% max, silicon 0.50 to 1.00%, chromium 1.00 to 1.50% and molybdenum 0.44 to 0.65%. The deliberate carbon window — a floor as well as a ceiling — underwrites the Class 2 strength level, while the modest chromium keeps the grade readily weldable compared with the higher-alloy rungs.
What are the mechanical properties of A182 F11 flanges?
For Class 2: minimum tensile strength 485 MPa (70 ksi), minimum yield strength 275 MPa (40 ksi), minimum elongation 20%, minimum reduction of area 30%, and hardness controlled within 143 to 207 HB. The hardness band — floor and ceiling — confirms correct heat treatment, keeps the flange weldable, and holds it under sour-service limits where NACE applies.
Which pipe grade do F11 weld neck flanges mate with?
ASTM A335 P11 — the 1.25Cr-0.5Mo seamless alloy pipe that shares F11's chemistry — with A234 WP11 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 F11 flanges welded to pipe?
With matching 1.25Cr-0.5Mo consumables — E8018-B2 electrodes or ER80S-B2 wire — preheat around 150 to 200 °C, controlled interpass temperature, and post-weld heat treatment at roughly 620 to 720 °C as the governing code requires (mandatory above modest thicknesses for this P-number). F11 is the mildest of the chrome-molys to weld, but it still hardens in the heat-affected zone if the thermal rules are ignored.
Is PWHT required for F11 flange welds?
In most practical cases, yes. ASME B31.1 and B31.3 require post-weld heat treatment for the 1.25Cr class above thin-wall exemption limits, and boiler codes almost always invoke it. PWHT tempers the hardened heat-affected zone and relieves residual stress — cheap insurance on joints that will spend decades in creep service. Plan it into the construction sequence from the start.
Do you supply F11 flanges with IBR certification?
Yes. For Indian boiler and power plant work we supply F11 weld neck flanges with IBR Form III-C documentation under the Indian Boiler Regulations, alongside the EN 10204 3.1 or 3.2 material certificate. State the IBR requirement in your enquiry so the inspection and countersigning are scheduled into production.
Where are ASTM A182 F11 weld neck flanges used?
Power generation above all: boiler steam circuits, main and reheat steam headers, HRSG module piping, turbine drains and feedwater systems — plus refinery and petrochemical services at moderate temperatures where a little chromium and molybdenum extend life beyond carbon steel. F11 is the highest-volume alloy flange grade in power construction worldwide.
What sizes and standards do you manufacture F11 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 service on request, and every bore is machined to the mating pipe schedule from Sch 20 through XXS.
What testing and certification do you supply with F11 flanges?
Every lot ships with EN 10204 3.1 mill test certificates covering chemical analysis, mechanical properties, heat treatment condition and hardness, with 3.2 certification witnessed by Lloyd's, DNV, BV or TÜV on request. PMI verifies the chromium and molybdenum on the actual flange, hardness surveys support NACE MR0175 compliance, and IBR documentation is available for boiler work — with full heat-number traceability throughout.
Do you keep A182 F11 weld neck flanges in stock? What is the lead time?
F11 is our highest-volume alloy grade: common power-plant sizes in Class 150, 300, 600 and 900 are regularly available from stock or short production runs — the yard photographs on this page are real F11-family production. Larger diameters, Class 1500/2500 and IBR-witnessed lots are forged to order, typically in 3 to 5 weeks. Send your list for a firm delivery commitment.
What information should I include in an F11 flange enquiry?
Six things: size (NB), pressure class or PN rating, dimensional standard (ASME B16.5, B16.47 or EN/DIN/BS), grade and class (F11 Cl1, Cl2 or Cl3), pipe schedule or bore, and quantity. Add any extras — IBR, NACE, PMI, 3.2 certification, RTJ facing. With these details we return a firm quotation, usually within 24 hours.
Do you export ASTM A182 F11 flanges outside India?
Yes. Tesco Steel & Engineering is an ISO 9001:2015 certified manufacturer based in Mumbai, and F11 weld neck flanges ship steadily to power projects, EPC contractors and stockists across the Middle East, Europe, Africa, Southeast Asia and the Americas. Flanges travel face-protected in lined packing — as photographed on this page — with full heat-number and heat-treatment traceability.
