What are Class 2500 Flanges?
Kalp Alloys is a leading manufacturer and supplier of Class 2500 Flanges (also known as 2500 lb flanges or 2500# flanges) conforming to ASME B16.5 standard. We supply Class 2500 pipe flanges in all standard types — Slip-On (SOF), Welding Neck (WNF), Socket Welding (SWF), Threaded (THDF), Lap Joint (LJF), and Blind (BLF) — in sizes ranging from NPS 1/2″ to NPS 12″. Our flanges are manufactured in a wide range of materials including Stainless Steel (SS 304, 316L, 321), Carbon Steel, Alloy Steel, Duplex, and Nickel Alloys to meet the most demanding industrial requirements.
A Class 2500 flange is a pressure-class designation under the ASME B16.5 standard (Steel Pipe Flanges and Flanged Fittings). The "2500" refers to the pressure class — the highest pressure class defined in ASME B16.5, engineered for the most extreme high-pressure and high-temperature piping applications. Class 2500 flanges are rated at approximately 6170 psi (425 bar) at ambient temperature (38°C) for carbon steel.
They are used in the most critical and demanding service conditions — including ultra-high-pressure hydraulic systems, deep-sea oil & gas exploration, high-pressure chemical reactors, and supercritical steam pipelines — where no lower pressure class can meet the design requirements. As the heaviest and most robust flange class in ASME B16.5, Class 2500 flanges represent the pinnacle of pressure-containing capability in industrial piping.
Class 2500 Flanges (ASME B16.5)
SLIP-ON (SOF)
Slips over the pipe and is fillet-welded top and bottom — easy to align and economical at this pressure class.
WELDING NECK (WNF)
Butt-welded to the pipe through a tapered hub for the strongest, most fatigue-resistant joint.
LAP JOINT (LJF)
Used with a stub end so the flange rotates freely for fast bolt-hole alignment.
BLIND (BLF)
Solid disc that blanks off the end of a line, valve or vessel.
ASME B16.5 Pipe Flanges
Unit : mm
| NPS | Outside Diam. D |
Diam. of Hub X |
OD of RF G |
Thickness (Min) t |
Bore | Length Thru Hub | Drilling | ||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| WNF B1 |
LJF (Min) |
THDF Counter bore (Min) |
WNF T1 |
THDF T2 |
LJF T3 |
BCD C |
Number of Bolt Holes N |
Diam. of Bolt Holes (*) H |
|||||
| B3 | B | ||||||||||||
| 1/2 | 135 | 43 | 34.9 | 30.2 | See Note (1) To be specified by Purchaser | 22.9 | 23.6 | 73 | 40 | 40 | 88.9 | 4 | 22.2 |
| 3/4 | 140 | 51 | 42.9 | 31.8 | 28.2 | 29.0 | 79 | 43 | 43 | 95.2 | 4 | 22.2 | |
| 1 | 160 | 57 | 50.8 | 35.0 | 34.9 | 35.8 | 89 | 48 | 48 | 108.0 | 4 | 25.4 | |
| 1 1/4 | 185 | 73 | 63.5 | 38.1 | 43.7 | 44.4 | 95 | 52 | 52 | 130.2 | 4 | 28.6 | |
| 1 1/2 | 205 | 79 | 73.0 | 44.5 | 50.0 | 50.6 | 111 | 60 | 60 | 146.0 | 4 | 31.8 | |
| 2 | 235 | 95 | 92.1 | 50.9 | 62.5 | 63.5 | 127 | 70 | 70 | 171.4 | 8 | 28.6 | |
| 2 1/2 | 265 | 114 | 104.8 | 57.2 | 75.4 | 76.2 | 143 | 79 | 79 | 196.8 | 8 | 31.8 | |
| 3 | 305 | 133 | 127.0 | 66.7 | 91.4 | – | 168 | – | 92 | 228.6 | 8 | 34.9 | |
| 4 | 355 | 165 | 157.2 | 76.2 | 116.8 | – | 190 | – | 108 | 273.0 | 8 | 41.3 | |
| 5 | 420 | 203 | 185.7 | 92.1 | 144.4 | – | 229 | – | 130 | 323.8 | 8 | 47.6 | |
| 6 | 485 | 235 | 215.9 | 108.0 | 171.4 | – | 273 | – | 152 | 368.3 | 8 | 54.0 | |
| 8 | 550 | 305 | 269.9 | 127.0 | 222.2 | – | 318 | – | 178 | 438.2 | 12 | 54.0 | |
| 10 | 675 | 375 | 323.8 | 165.1 | 277.4 | – | 419 | – | 229 | 539.8 | 12 | 66.7 | |
| 12 | 760 | 441 | 381.0 | 184.2 | 328.2 | – | 464 | – | 254 | 619.1 | 12 | 73.0 | |
Frequently Asked Questions
A Class 2500 (also written 2500# or 2500 lb) flange is a pressure-class designation under ASME B16.5, rated at approximately 6170 psi (425 bar) at ambient temperature for carbon steel.
Slip-On (SOF), Welding Neck (WNF), Socket Weld (SWF), Threaded (THDF), Lap Joint (LJF) and Blind (BLF), in raised face, flat face and RTJ facing as applicable.
NPS 1/2 inch to 24 inch to ASME B16.5, with larger diameters supplied to ASME B16.47 on request.
Stainless Steel (304, 316L, 321), Carbon Steel (A105, A350 LF2), Alloy Steel (F11, F22, F91), Duplex, Super Duplex and Nickel Alloys.
Material Test Certificates per EN 10204 3.1 and 3.2, plus radiography, ultrasonic, magnetic particle and hydrostatic testing, with third-party inspection on request.
Yes. We regularly export to the UAE, Dubai, Abu Dhabi and the wider GCC along with 100+ countries, with correct export documentation and on-time delivery.