Flanges for US power plants
Combined cycle, cogeneration and industrial power plants run steam at high temperature and pressure, and cooling water in large diameter mains. The flanges on both sides of the plant are different, and so is how they are specified.
US power plant piping is built to ASME B31.1. Steam, feedwater and boiler piping uses weld neck flanges in Class 600 to 2500 in carbon steel A105 or the alloy grade your specification calls for, and the cooling water side uses Class 150 weld neck, slip-on and flat face flanges, with ASME B16.47 or AWWA flanges on the large mains. We forge and machine flanges to ASME B16.5 and B16.47 in Class 150 to 2500, and in 2025 BHEL, India's largest power equipment maker, awarded us a contract for carbon and stainless steel flanges.
Where flanges are used in power generation
| System | Flange | Class and material |
|---|---|---|
| Main and reheat steam | Weld neck RF, butt welded; few flanged joints by design | Class 900 to 2500, alloy grade per spec |
| Feedwater and boiler feed pumps | Weld neck RF at pump nozzles and valves | Class 900 to 2500, A105 |
| HRSG and auxiliary steam | Weld neck RF | Class 300 to 900, A105 |
| Circulating and cooling water | Weld neck and slip-on RF; flat face at cast iron | Class 150, A105; B16.47 or AWWA above NPS 24 |
| Fuel gas | Weld neck RF or RTJ | Class 300 to 600, A105 |
ASME B31.1 and high temperature ratings
ASME B31.1 Power Piping governs boiler external piping and the plant piping around it, and accepts flanges to ASME B16.5 and B16.47. At steam temperatures the flange ratings fall steeply: ASME B16.5 rates an A105 Class 600 flange at 1,480 psig at 100 °F and at a fraction of that above 800 °F, where carbon steel starts to lose strength to creep. For hotter lines, specifications move to chromium-molybdenum grades such as ASTM A182 F11, F22 or F91. Tell us the grade on your specification and we confirm it in the quotation.
| Grade | Specification | Typical service |
|---|---|---|
| A105 | ASTM A105 | Feedwater, auxiliary steam, cooling water |
| A350 LF2 | ASTM A350 | Outdoor water and fuel lines in cold climates |
| Chrome-moly grades | ASTM A182 (F11, F22, F91 and others) | Main steam and reheat above the carbon steel range |
| F304L, F316L | ASTM A182 | Condensate polishing, chemical feed, sampling lines |
Cooling water and large mains
The cooling side of a plant is low pressure but large: circulating water mains often run NPS 36 and larger. Up to NPS 60 these take ASME B16.47 flanges, Series A or Series B to match the valves and pumps; larger waterworks-style mains use AWWA C207 steel flanges. Our AWWA vs ASME flanges guide explains why the two do not bolt together.
Documents for a power plant turnover package
Each heat ships with an EN 10204 3.1 mill test report giving chemistry, tensile and hardness results and the heat treatment. Flanges are stamped with grade, size, class and heat number before they leave the machine shop. Third-party inspection and EN 10204 3.2 certificates can be arranged with your inspector, and NTPC and BHEL are among the Indian power companies we have supplied.
Ordering for a US project
Send your line list with the standard, type, size, class, bore or schedule, facing, material and quantity for each line, and we quote every line as specified. Every order ships from our works in Gujarat, India; we have no US office or warehouse. Each line is supplied to your line list, and ordering from India explains the documents, marking, packing and customs.
Frequently asked questions
Do you supply chrome-moly flanges?
Tell us the ASTM A182 grade, size and class on your specification and we confirm what we can supply in the quotation. Carbon steel A105, low temperature A350 LF2 and the stainless grades are standard for us.
What is the highest pressure class you make?
Class 2500 to ASME B16.5, the highest class in the standard, in weld neck, blind and the other forged types.
Can you supply large diameter flanges for cooling water mains?
Yes. ASME B16.47 Series A and B weld neck and blind flanges, and AWWA C207 and C228 flanges. Give the size, series or class and the mating equipment.
Sources
- ASME B31.1, Power Piping
- ASME B16.5, Pipe Flanges and Flanged Fittings, NPS 1/2 through NPS 24
- ASME B16.47, Large Diameter Steel Flanges, NPS 26 through NPS 60
- ASTM A182/A182M, Forged or Rolled Alloy and Stainless Steel Pipe Flanges, Forged Fittings, and Valves and Parts for High-Temperature Service
- AWWA C207, Steel Pipe Flanges for Waterworks Service, Sizes 4 In. Through 144 In.