Duplex F51 (UNS S31803) Flange: 50% ferrite and 50% austenite, combining stress corrosion resistance (Ferrite) and toughness (Austenite).
HT PIPE offers Duplex F51 (UNS S31803) Flange according to ASTM A182. Types: WN Flange, LWN Flange, SO Flange, SW Flange, Blind Flange, Plate Flange, Threaded Flange, Lap Joint Flange, Orifice Flange, Spectacle blind flange, rings, forgings, disc, shaft sleeve
ASTM A182 F51 Flange Specification:
Standard: ASME B16. 5, ASME B16.47, DIN, EN, BS, JIS
Size: 1/2"-48", DN6-DN400
Class: 150#,300#,400#,600#,900#,1500#,2500#
ASTM A182 F51 Flange Chemical Composition
| Grade |
UNS |
C≤ |
Mn≤ |
P≤ |
S≤ |
Si≤ |
Ni |
Cr |
Mo |
N |
Cu |
| F51 |
S31803 |
0.03 |
2.00 |
0.03 |
0.02 |
1.00 |
4.5–6.5 |
21.0–23.0 |
2.5–3.5 |
0.08-0.20 |
- |
High Cr + Mo + N: improves F51 pitting resistance (PREN = Cr% + 3.3Mo% + 16N% ≥ 33), resistance to seawater, resistance to acidic media H₂S/CO₂ (a key requirement in oil and gas fields).
Ultra-low carbon (C≤0.03%): inhibits intergranular corrosion and ensures weld integrity.
ASTM A182 F51 Flange Mechanical Properties
| Mechanical properties |
Tensile, min, ksi[MPa] |
Yield, min, ksi[MPa] |
Elongation, %(min) |
| F51/S31803 |
90 [620] |
65 [450] |
25 |
Tensile strength twice than 316L Stainless steel.
A182 Duplex F51 Flange Heat treatment
Solid solution treatment:
Temperatures 1020-1100°C, followed by rapid quenching (water quenching or air quenching at a rate of ≥ 50°C/sec) to below 260°C. Special attention should be paid to avoid staying in the temperature range 600-1000 ℃ to avoid σ-phase precipitation leading to embrittlement.
Forging process control:
Initial forging temperature ≤1150℃, final forging temperature 1000~1050℃, forging ratio ≥3:1 (to avoid overheating leading to impact work decrease).
Duplex F51 is suitable for Arctic oil and gas platform pipeline system, chemical plant desulfurization, subsea system, etc. Although the price of F51 is about 1/3 more expensive than 316L, from the point of view of maintenance and usage time, F51 is more cost-effective!
