Piping Materials : Blinds, Spacers and Spectacle Blinds


Dimensional Standards

ASME B16.48 : Line blanks specifies dimensions of spectacle blinds. In this standard  Spectacle blinds are available only upto 24″. For 2500# spectacle blinds are upto 12″. No 400# spectacle blinds in this standadrd. Facings available are Raised Face, Female Ring Joint and Male ring joint.

Piping Material Specification

In PMS Specify NPD, Pressure Class, MOC, Dim Std and facing type.

Ring spacer replaces single blind, with same thickness as blind. Thick single blinds or rigid piping systems normally require ring spacers.
Single line blind or blank is installed adjacent to a valve to ensure positive shut-off. Their purpose is to prevent accidental flow through a pipeline to a vessel.

With the exception of cast iron, plastic, or fiberglass services, they are not drilled with bolt holes, but fit inside the bolt circle of mating flanges. Spectacle blinds are not manufactured in large size due to weight issues.

Jack Screw Flange is required for larger size blinds. Jack screw help in spreading the flanges and replacing the spacer/blind or turning of spectacle blind.

Normally upto 16″, spactacle blinds are used. For 18″ and above, spacer and blanks are used. Thickness of spectacle blind is specified based on the pressure and pipe size.

Materials of Construction

Carbon steel material : ASTM A516 Gr. 60
Stainless steel material : ASTM A240 Gr. 304L, 316L.

Layout Considerations

  1. Flanges shall be staggered with grouped.
  2. Spectacle blinds shall be accessible from grade, platform or if below 4500 mm by a portable ladder, or temporary scafolding.
  3. Blinds in pipeway, regardless of pipeway height, are considered accessible.

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