What is a spectacle blind flange?

A spectacle blind – also known as a figure-8 blind – is generally a piece of metal that is cut to fit between two pipe and usually sandwiched between two gaskets. A spectacle blind is often made from two metal discs that are attached to each other by a small section of steel.

Spectacle blind flange spacers
Spectacle blind flange spacers
The shape is similar to a pair of glasses or “spectacles” – hence the name spectacle blind. One end of the blind will have an opening to allow flow through the pipe during operation and the other end is solid to block flow during maintenance. They are generally installed as a permanent device to separate process systems.

The whole idea of a spectacle blind is so that one can be absolutely sure that an item of equipment is properly and securely blanked off with no possibility of any flow or leakage through a valve during maintenance. The flow can be diverted to other items of equipment but not just bypassed around the blank as this would compromise the safety function of the spectacle blind. The flow has to valved off and pressure relieved prior to loosening flange bolts and swinging the blind.

All Dims Per ASME B16.48

  1. For use with Flat or Raised Face Flanges
  2. Specify Surface in Microinch ASA 500, 250, 125, 63 or 32. If Not Specified Mill Finish Supplied.
  3. Available with Phonographic Serrated Surface or Ground Finish. Available with Ring Type Joint
  4. Normally Supplied in A285 Gr. C, A515 Gr 70, A516 Gr. 70, 304SS, 316SS. Other Materials Available
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