Article
A blind flange is a solid disc with bolt holes. It closes the end of a pipe, valve or vessel nozzle and can be removed later for inspection, cleaning or extension of the line. It is simple, but it carries some of the highest loads of any flange.
Where blind flanges are used
- Ends of lines planned for future extension
- Vessel and tank manways and nozzles
- Pressure test closures during hydrotesting
- Isolation points during maintenance
Why blind flanges are thick
A blind flange has no bore, so the full line pressure acts on its whole face, and it must also resist bolt loading without bending. For that reason blind flanges are often heavier than weld neck flanges of the same size and class, and in larger sizes the weight difference is significant.
Classes and facings
Blind flanges follow ASME B16.5 up to 24" and ASME B16.47 above that, in the same classes as other flanges: 150, 300, 400, 600, 900, 1500 and 2500. Facing must match the mating flange:
- RF – raised face, most common
- FF – flat face, against cast iron or non-metallic flanges
- RTJ – ring type joint, for high-pressure service
Tapped and special blinds
A blind flange can be drilled and tapped in the centre for a vent, drain, pressure gauge or instrument. Some are supplied with a raised hub or lifting lugs for heavy sizes. These should be described clearly with a sketch if needed.
Blind flange vs cap vs spectacle blind
| Item | Removable | Typical role |
|---|---|---|
| Blind flange | Yes | End closure with future access |
| Buttweld cap | No | Permanent closure |
| Spectacle blind | Swung between open and closed | Positive isolation between two flanges |
A complete description
Blind Flange 8" Class 300 RF, ASTM A182 F316L, ASME B16.5 – 4 nos
Frequently asked questions
Why is a blind flange heavier than a weld neck flange?
It has no bore, so pressure acts over the whole face and the disc must be thick enough not to bend under pressure and bolt load.
Can a blind flange have a hole in it?
Yes. Tapped blind flanges have a threaded centre hole for a vent, drain or instrument.
Does a blind flange need a pipe schedule?
No. Blind flanges have no bore, so only size, class, facing and material are needed.
Key takeaways
- Blind flanges close lines and nozzles but allow future access.
- They are thick because pressure acts on the full face.
- Match class and facing to the mating flange.
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Sawariya Metal Industries supplies stainless steel pipes, flanges and buttweld pipe fittings from Mumbai to buyers in India and overseas. Send your size, grade, standard and quantity through our enquiry form and we will reply with a clear quotation and the test documents you need. You can also browse our stainless steel pipes, flanges and buttweld fittings.