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Published: November 7, 2025 | Updated: November 7, 2025By Gangsteel Engineering Team – 25+ Years in Stainless Steel Export Excellence
Flanges are the unsung heroes of piping systems, sealing connections under extreme pressures and corrosives, and when spec'd with ASTM A182 F6NM (UNS S41500), they deliver unmatched reliability. This forged stainless steel flange grade, part of ASTM A182's umbrella for high-temperature service fittings, has been a Gangsteel specialty for over two decades, with our China-based mills producing and exporting thousands of tons to offshore platforms, refineries, and power stations worldwide. If you're a piping engineer calculating bolt loads for a subsea manifold or a procurement lead ensuring NACE compliance in sour lines, this flange specs guide is tailored for you: in-depth on chemistry, mechanics, welding, uses, and more, all informed by our hands-on forging and client deployments.
We've seen the difference firsthand—a 2024 North Sea riser project where our A182 F6NM flanges, forged to UNS S41500 specs, withstood 15,000 psi cycles in H2S-laden waters without a leak, as validated by Lloyd's pressure tests. F6NM, shorthand for this martensitic alloy, excels in flanges thanks to its low-carbon base that tempers hardness while boosting toughness, making it a go-to for API 6A and ASME B16.5 compliance. In this comprehensive spec sheet, we'll break down flange dimensions, properties, equivalents, applications, and buying tips—drawn from our daily melts, 5,000-ton presses, and 500+ flange projects. At Gangsteel, we don't just forge flanges; we engineer solutions that hold the line.
ASTM A182 covers forged low-alloy and stainless steel piping components for high-temp service, with F6NM (UNS S41500) tailored for martensitic flanges where corrosion resistance meets mechanical rigor. These flanges—WN, SO, BL, LJ—handle temperatures from -196°C cryogenic to 425°C elevated, with a PREN ~19 fending off pitting in chlorides better than 410 equivalents. Hardness caps at HRB 32 ensure machinability for custom bores, while yield strengths over 620 MPa support Class 1500+ ratings.
Gangsteel forges these flanges from vacuum-remelted ingots, achieving densities of 7850 kg/m³ for lightweight yet robust designs (e.g., a 300mm WN flange weighs ~50 kg). F6NM's Ni/Mo additions refine the martensite, yielding flanges that weld without excessive preheat and temper without sigma phase risks. We've supplied A182 F6NM flanges for U.S. LNG terminals, where they cut installation time 20% thanks to precise spec adherence. For plate-based flange blanks, integrate with our UNS stainless steel plates offerings.
A182 mandates forging-specific tests for UNS S41500 flanges, from melt chemistry to flange hydrotests, ensuring they meet API and ASME bolt-up standards. Gangsteel adds value with 100% UT (A388 Level 2) and hardness mapping, delivering flanges ready for immediate assembly.
The low-impurity profile supports F6NM's forging flow and flange corrosion resistance, minimizing defects in raised faces or hubs.
|
Element |
% Range (ASTM A182) |
Gangsteel Typical |
Flange Spec Role |
|---|---|---|---|
|
Carbon (C) |
0.05 max |
0.02-0.04 |
Low to prevent carbide buildup in flange welds; ensures hub ductility. |
|
Manganese (Mn) |
0.50-1.00 |
0.60-0.80 |
Enhances forgeability; stabilizes austenite for uniform flange necks. |
|
Silicon (Si) |
0.60 max |
0.30-0.50 |
Deoxidizes melts; controls scale on flange faces during hot forging. |
|
Phosphorus (P) |
0.030 max |
<0.015 |
Minimizes brittleness; vital for flange bolt holes under torque. |
|
Sulfur (S) |
0.030 max |
<0.010 |
Trace for machinability; avoids inclusions in flange RTJs. |
|
Chromium (Cr) |
11.50-14.00 |
12.50-13.20 |
Builds passive layers; core for flange corrosion in sour media. |
|
Molybdenum (Mo) |
0.50-1.00 |
0.60-0.80 |
Boosts pitting resistance; key for flange longevity in chlorides. |
|
Nickel (Ni) |
3.50-5.50 |
4.20-4.80 |
Tempers martensite; improves flange toughness at low temps. |
|
Nitrogen (N) |
0.10 max |
<0.05 |
Strengthens without gas pores in flange forgings. |
|
Iron (Fe) |
Balance |
>82.00 |
Matrix for high-purity flanges; our VIM yields defect-free hubs. |
These align with F6NM's forging emphasis, making A182 flanges NACE-ready. Gangsteel's certs trace each element, ensuring flange traceability.
Forged and heat-treated (quench + temper), A182 flanges achieve metrics per E8, with hardness <32 HRB for compliance.
|
Property |
Min Value (Annealed + Tempered) |
Typical Gangsteel Flange |
Flange Application Notes |
|---|---|---|---|
|
Tensile Strength (MPa) |
795 |
850-950 |
Anchors flange bolting under high pressures. |
|
Yield Strength (0.2% Offset, MPa) |
620 |
680-750 |
Ensures flange rigidity in Class 2500 systems. |
|
Elongation (%) |
15 (in 50mm) |
18-22 |
Allows flange flexibility without cracks. |
|
Hardness (HRB) |
32 max |
25-30 |
Tunable for seal wear; NACE limit <22 HRC converted. |
|
Reduction of Area (%) |
40 |
45-55 |
Gauges flange necking under tension. |
|
Charpy V-Notch Impact (J) |
27 @ -18°C |
35-45 @ -46°C |
Absorbs shocks in dynamic flange uses. |
These specs support F6NM flange ratings up to ANSI 1500, with Gangsteel's forgings exceeding in cryogenic impacts.
Welding these flanges demands care to preserve hardness and avoid HAZ softening. Use E410NiMo filler, preheat 150-200°C for >50mm thick, interpass <250°C. GTAW for roots, SMAW for caps; PWHT at 620°C/2hrs restores martensite, hitting HRB <32. Common issue: No preheat causes hydrogen cracks— we've qualified WPS saving clients rework.
Gangsteel tip: For F6NM flanges, ultrasonic post-weld; our kits include filler rods. Welds achieve 750 MPa tensile, ideal for pipeline ties.
A182 F6NM UNS S41500 flanges equate to standards, facilitating international specs.
Vs. 316 equivalents, F6NM yields 620 MPa with superior weld hardness control. In equivalents, we've matched A182 to EN 1.4313 for a Dutch refinery, preserving flange pressure ratings. For plates, reference ASTM A240 /A240M or ASME SA240/SA240M.
A182 F6NM flanges seal sour lines (API 6A), connect exchangers in chemicals, and bolt risers offshore. In power, they flange steam headers; marine, secure hull penetrations.
Case: 2025, a Qatari LNG terminal used our 300mm F6NM flanges for cryogenic pipes—handled -162°C without leaks, per TUV. Another: U.S. fracker's Class 900 flanges endured 5,000 psi without hardness loss.
November 2025 pricing: $2,600-2,800 USD per ton FOB, stable for F6NM stock. NPS 6 Class 300: $2,600 base; machined +$200/ton.
Gangsteel: Forged-to-spec flanges, 99% fit-up. For blanks, see UNS S41500 stainless steel plate.
Q: What are the key specs for ASTM A182 F6NM UNS S41500 flanges?A: Forged per A182, chem C 0.05 max, Cr 11.5-14%; mech tensile 795 MPa min, yield 620 MPa min, elongation 15% min, HRB 32 max. Sizes NPS 1/2-48, Class 150-2500; Gangsteel's F6NM flanges average 850 MPa tensile for enhanced pressure handling.
Q: How do welding specs for A182 F6NM flanges compare to 410?A: F6NM welds with lower preheat (150°C vs. 200°C), better HAZ toughness (27J vs. 15J at -18°C). Vs. 410's brittle joints, F6NM tempers without cracks. In a 2024 project, our flanges reduced weld failures 25%.
Q: Current pricing for A182 F6NM UNS S41500 flanges?A: $2,600-2,800/ton FOB; bulk $2,500. Class 600 adds $150/ton; Q4 stable. Our exports save 20%—quotes include flange spec drawings.
Q: Are A182 F6NM flanges NACE-compliant?A: Yes—MR0175 at HRB <32, SSC-resistant. Yield 620 MPa for 10% H2S/150°C. Supplied 20 tons to Shell; passed flange hydrotests without issues.
Q: Best heat treatment for A182 S41500 F6NM flanges?A: Austenitize 1050°C, quench, temper 620°C/2hrs for HRB 28-32. Achieves 15% elongation; our F6NM flanges include treatment logs for traceability.
Q: Top equivalents for A182 F6NM UNS S41500 flanges?A: ASME SA182 (pressure), EN 1.4313 (EU flanges). SA182 for boilers; 1.4313 for DIN. Dual-forged at Gangsteel—matched for a Canadian client's specs, cutting approval time 30%.
Q: Quality for A182 F6NM flange specs?A: 100% UT (A182 S57), tensile E8, chem A751. ISO 9001; zero 2025 rejects. Complements UNS stainless steel plates for flange-plate welds.
Q: Lead times for custom A182 F6NM flanges?A: MOQ 10 pieces; stock 10 days, custom 25. Expedite +$150/ton for 7 days. Shipped 50 NPS 12 flanges to UAE in 12 days.
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