Alloy Steel Flanges
Giriraj Impex is a manufacturer, stockist, supplier and exporter of alloy steel flanges to ASTM A182 in chrome-moly grades F5, F9, F11, F22 and F91. We manufacture alloy steel flanges to ASME B16.5 from ½" to 24" NB in Class 150 to 2500 and to ASME B16.47 Series A and B for larger sizes, in weld neck, slip-on, blind, socket weld, threaded, lap joint and orifice types, with raised face and ring type joint facings.
Alloy steel flanges join chrome-moly pipe, fittings and valves in high-temperature service – power plant steam lines, boiler connections, refinery heater and hydroprocessing piping – where the flange must keep its strength and resist oxidation at temperatures beyond the range of carbon steel.
Specifications
| Item | Details |
|---|---|
| Material standard | ASTM A182 / ASME SA182 |
| Grades | F5, F9, F11 (Class 1, 2, 3), F22 (Class 1, 3), F91 |
| Dimensional standards | ASME B16.5, B16.47 Series A and B, B16.36, B16.48, EN 1092-1 |
| Sizes | ½" to 24" NB (B16.5); 26" to 60" NB (B16.47) |
| Classes | 150, 300, 600, 900, 1500, 2500 |
| Facings | Raised face, ring type joint, flat face |
| Heat treatment | Annealed, normalised and tempered, or quenched and tempered, as the grade and class require |
| Documents | Mill test certificate (MTC) showing heat treatment; third-party inspection on request |
Grades and matching pipe
| Flange grade | Nominal composition | Matching pipe | Matching fittings | Typical service |
|---|---|---|---|---|
| F11 | 1¼Cr-½Mo | A335 P11 | A234 WP11 | Steam lines, refinery piping |
| F22 | 2¼Cr-1Mo | A335 P22 | A234 WP22 | Main steam, hot reheat, hydroprocessing |
| F5 | 5Cr-½Mo | A335 P5 | A234 WP5 | Refinery heaters, sulphur-bearing hydrocarbons |
| F9 | 9Cr-1Mo | A335 P9 | A234 WP9 | Higher-temperature refinery service |
| F91 | 9Cr-1Mo-V | A335 P91 | A234 WP91 | High-temperature, high-pressure steam |
The pipe chemistry and strength for these grades are shown on our alloy steel pipes and tubes page; A182 forgings have their own composition and property limits by grade and class, as given in the standard, and are reported on the mill test certificate.
F11 and F22 classes
ASTM A182 offers F11 in Class 1, 2 and 3 and F22 in Class 1 and 3. The class sets the strength level and, with it, the heat treatment: Class 1 has the lowest strength, and the higher classes have higher tensile and yield requirements. Because the class affects the flange's allowable stress in design, it must be stated on the order – "F11 Class 2" rather than just "F11". Where the class is not specified in the piping specification, ask your designer which one the calculations assume.
Flange types for high-temperature service
- Weld neck flanges – the usual choice in alloy steel, as the tapered hub handles thermal cycling and high loads.
- Blind flanges – to close nozzles and line ends.
- Socket weld flanges – for small-bore drains, vents and instrument connections.
- Slip-on flanges – where the piping specification allows them.
- Ring type joint (RTJ) facings for high-pressure steam and hydrogen service.
Manufacturing, heat treatment and inspection
Alloy steel flanges are forged from A182 material of the specified grade and then heat treated – normalised and tempered or quenched and tempered depending on grade and class – before machining. Heat treatment is critical for chrome-moly steels, and especially for F91, whose creep strength depends on correct normalising and tempering; the heat-treatment cycle is recorded on the mill test certificate. Each flange is dimensionally inspected, hardness checked where specified, and marked with the manufacturer's identification, grade and class, size, pressure class, bore schedule and heat number. Ultrasonic testing, positive material identification and third-party inspection can be arranged on request.
Welding alloy steel flanges
Weld neck flanges in F11, F22, F5, F9 and F91 are welded to matching pipe with preheat, controlled interpass temperature and post-weld heat treatment as required by the design code. The flange and pipe should be of the same nominal composition so that one welding procedure and one PWHT cycle suit the joint. Bolting is normally ASTM A193 B7 or B16 with A194 2H nuts, chosen for the design temperature; see alloy steel fasteners.
Ordering
Please state the flange type, standard, size, pressure class, facing, bore schedule, grade and class (for example F22 Class 3), quantity, and any hardness, testing or inspection requirement.
Applications and related products
Alloy steel flanges are used in thermal and combined-cycle power stations, boilers and heat-recovery steam generators, refinery heaters, hydrocrackers and hydrotreaters, petrochemical crackers and fertiliser plants. They are installed with alloy steel pipes and tubes, alloy steel pipe fittings and fasteners. Nozzle forgings and blind flanges can also be made from alloy steel plates and round bars where the specification permits. See all flange materials on the flanges page and grade guidance on the alloy steel page.
Frequently Asked Questions
ASTM A182 (ASME SA182) covers forged alloy and stainless steel pipe flanges, fittings and valve parts for high-temperature service. Chrome-moly grades include F5, F9, F11, F22 and F91.
F11 is 1¼Cr-½Mo and F22 is 2¼Cr-1Mo steel. F22 has higher allowable stresses at elevated temperatures and is used for hotter or higher-pressure lines. Each is matched to P11 or P22 pipe.
ASTM A182 gives F11 three strength classes. The class sets the minimum tensile and yield strength and the heat treatment, so it must be stated on the order along with the grade.
F91 is a modified 9Cr-1Mo steel whose high creep strength depends on precise normalising and tempering. Errors in heat treatment, welding or post-weld heat treatment can reduce its strength, so it is produced and inspected under tighter controls.
ASTM A193 B7 studs with A194 2H nuts are common up to their temperature limit; B16 studs are used for higher temperatures. The design code sets the bolting for each service.
Yes. A182 alloy flanges are supplied in the heat-treated condition the grade and class require – normalised and tempered, or quenched and tempered – and the heat treatment is recorded on the mill test certificate.
Request a Quote for Alloy Steel Flanges
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