Alloy Steel Flanges
Complete guide to alloy steel (chrome-molybdenum) flanges for elevated temperature service. Specifications for power generation, petrochemical, and extreme temperature applications.
Alloy Steel Grades
Chrome-molybdenum steel alloys provide exceptional strength at elevated temperatures.
ASTM A182 F11
Composition:
1.00-1.50% Cr, 0.44-0.65% Mo (nominal 1.25Cr-0.5Mo)
Temperature Range:
Up to ~900°F continuous service (1.25Cr-0.5Mo)
Yield Strength:
30-45 ksi depending on class (Class 1: 30 ksi, Class 2: 40 ksi, Class 3: 45 ksi per ASTM A182)
Applications:
Steam piping, superheater connections, elevated temp service
ASTM A182 F22
Composition:
2.00-2.50% Cr, 0.87-1.13% Mo (nominal 2.25Cr-1Mo)
Temperature Range:
Room to 1050°F
Yield Strength:
30-75 ksi depending on class (Class 1: 30 ksi, Class 3: 45 ksi, Class 4: 60 ksi, Class 5: 75 ksi per ASTM A182)
Applications:
Power generation, steam systems, critical high-temp service
ASTM A182 F91
Composition:
9% Cr, 1% Mo, 0.2% V, 0.07% Nb, 0.04% N (modified 9Cr-1Mo per ASTM A182 F91)
Temperature Range:
Room to 1200°F
Yield Strength:
60 ksi min yield, 85 ksi min tensile (per ASTM A182 F91)
Applications:
Advanced power plants, extreme temperature service
F11 vs F22 vs F91
Strength Progression:
F11 → F22 → F91 (increasing strength)
Cost Progression:
F11 (lowest) → F22 → F91 (premium)
Selection:
Choose based on temperature and pressure requirements
Key Advantages for High Temperature Service
Strength Retention
- ✓ Maintains yield strength to 1000°F+
- ✓ Creep resistance at temperature
- ✓ Time-dependent property control
- ✓ Superior to carbon steel above 600°F
Power Generation Focus
- ✓ Industry standard for steam systems
- ✓ Proven reliability in power plants
- ✓ Code-approved for boiler service
- ✓ Long-term performance track record
Pressure-Temperature Capability
- ✓ High pressure at elevated temperature
- ✓ Creep-rupture design codes
- ✓ ASME Section I, VIII compliance
- ✓ Long service life assurance
Industrial Applications
Alloy steel flanges are essential for power generation and heat-intensive applications.
Power Generation
- • Boiler main steam lines
- • Superheater connections
- • Reheater outlet piping
- • Turbine inlet connections
- • Main steam isolation valves
Petrochemical
- • Cracking furnace piping
- • Reactor connections
- • High-temperature process lines
- • Heat exchanger connections
- • Recovery system piping
Other Industries
- • Refinery reformer units
- • Heat recovery systems
- • Pulp and paper mill systems
- • District heating networks
- • Industrial furnaces
Heat Treatment & Welding
Alloy steel requires controlled heat treatment for optimal properties and weldability.
Heat Treatment (PWHT)
Post-weld heat treatment is critical for alloy steel to restore mechanical properties and relieve stresses.
- • PWHT temperatures vary by alloy: F11 ~1150°F minimum, F22 ~1250°F minimum, F91 ~1375-1425°F (critical control required to stay below Ac1). See ASME B31.3 Table 331.1.1.
- • Cooling rate controlled per ASME
- • Mandatory for most applications
- • Improves creep resistance
Welding Procedures
Specialized welding techniques essential to maintain alloy steel performance post-weld.
- • Low hydrogen welding rods
- • Controlled preheat required
- • Interpass temperature limits
- • Matching filler materials
Temperature Service Windows
F11, F22, and F91 each have distinct temperature service windows. F11 is suitable to ~900°F continuous service; F22 to ~1050°F; F91 to ~1200°F. Allowable stresses at temperature follow ASME B31.3 Table A-1.
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