What are Class 900 Flanges?
Kalp Alloys is a leading manufacturer and supplier of Class 900 Flanges (also known as 900 lb flanges or 900# flanges) conforming to ASME B16.5 standard. We supply Class 900 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 24″. 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 900 flange is a pressure-class designation under the ASME B16.5 standard (Steel Pipe Flanges and Flanged Fittings). The "900" refers to the pressure class — engineered for severe-duty, high-pressure, and high-temperature piping systems. Class 900 flanges are rated at approximately 2220 psi (153 bar) at ambient temperature (38°C) for carbon steel.
They are widely used in oil & gas exploration, high-pressure steam lines, power generation, refinery process piping, and offshore platforms where extreme pressures and temperatures are encountered. Because of their heavy-duty construction and exceptional pressure capacity, ASME B16.5 Class 900 flanges are the preferred choice for critical service applications requiring performance well beyond Class 600.
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.
THREADED (THDF)
Screwed onto threaded pipe with no welding — suited to small sizes and flammable areas.
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.
Class 900 Flanges (ASME B16.5)
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 |
SOF (Min) |
LJF (Min) |
THDF Counter bore (Min) |
WNF T1 |
SOF THDF |
LJF T3 |
BCD C |
Number of Bolt Holes N |
Diam. of Bolt Holes (*) H |
|||||
| B2 | B3 | B | T2 | |||||||||||
| 1/2 | 120 | 38 | 34.9 | 22.3 | See Note (1) To be specified by Purchaser | 22.2 | 22.9 | 23.6 | 60 | 32 | 32 | 82.6 | 4 | 22.2 |
| 3/4 | 130 | 44 | 42.9 | 25.4 | 27.7 | 28.2 | 29.0 | 70 | 35 | 35 | 88.9 | 4 | 22.2 | |
| 1 | 150 | 52 | 50.8 | 28.6 | 34.5 | 34.9 | 35.8 | 73 | 41 | 41 | 101.6 | 4 | 25.4 | |
| 1 1/4 | 160 | 64 | 63.5 | 28.6 | 43.2 | 43.7 | 44.4 | 73 | 41 | 41 | 111.1 | 4 | 25.4 | |
| 1 1/2 | 180 | 70 | 73.0 | 31.8 | 49.5 | 50.0 | 50.6 | 83 | 44 | 44 | 123.8 | 4 | 28.6 | |
| 2 | 215 | 105 | 92.1 | 38.1 | 61.9 | 62.5 | 63.5 | 102 | 57 | 57 | 165.1 | 8 | 25.4 | |
| 2 1/2 | 245 | 124 | 104.8 | 41.3 | 74.6 | 75.4 | 76.2 | 105 | 64 | 64 | 190.5 | 8 | 28.6 | |
| 3 | 240 | 127 | 127.0 | 38.1 | 90.7 | 91.4 | 92.2 | 102 | 54 | 54 | 190.5 | 8 | 25.4 | |
| 4 | 290 | 159 | 157.2 | 44.5 | 116.1 | 116.8 | 117.6 | 114 | 70 | 70 | 235.0 | 8 | 31.8 | |
| 5 | 350 | 190 | 185.7 | 50.8 | 143.8 | 144.4 | 144.4 | 127 | 79 | 79 | 279.4 | 8 | 34.9 | |
| 6 | 380 | 235 | 215.9 | 55.6 | 170.7 | 171.4 | 171.4 | 140 | 86 | 86 | 317.5 | 12 | 31.8 | |
| 8 | 470 | 298 | 269.9 | 63.5 | 221.5 | 222.2 | 222.2 | 162 | 102 | 114 | 393.7 | 12 | 38.1 | |
| 10 | 545 | 368 | 323.8 | 69.9 | 276.4 | 277.4 | 276.2 | 184 | 108 | 127 | 469.9 | 16 | 38.1 | |
| 12 | 610 | 419 | 381.0 | 79.4 | 327.0 | 328.2 | 328.6 | 200 | 117 | 143 | 533.4 | 20 | 38.1 | |
| 14 | 640 | 451 | 412.8 | 85.8 | 359.2 | 360.2 | 360.4 | 213 | 130 | 156 | 558.8 | 20 | 41.3 | |
| 16 | 705 | 508 | 469.9 | 88.9 | 410.5 | 411.2 | 411.2 | 216 | 133 | 165 | 616.0 | 20 | 44.5 | |
| 18 | 785 | 565 | 533.4 | 101.6 | 461.8 | 462.3 | 462.0 | 229 | 152 | 190 | 685.8 | 20 | 50.8 | |
| 20 | 855 | 622 | 584.2 | 108.0 | 513.1 | 514.4 | 512.8 | 248 | 159 | 210 | 749.3 | 20 | 54.0 | |
| 24 | 1040 | 749 | 692.2 | 139.7 | 616.0 | 616.0 | 614.4 | 292 | 203 | 267 | 901.7 | 20 | 66.7 | |
Frequently Asked Questions
A Class 900 (also written 900# or 900 lb) flange is a pressure-class designation under ASME B16.5, rated at approximately 2220 psi (153 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.