Spectacle blinds, spacers and blanks
When a line has to be isolated for maintenance or a confined space entry, a closed valve is not enough. A spectacle blind between two flanges gives positive isolation and shows at a glance whether the line is open or shut.
A spectacle blind, also called a figure-8 blank, is a plate with a solid disc at one end and a ring at the other, joined by a web, that sits between two flanges: with the ring in the line the pipe is open, and with the disc in the line it is positively isolated. ASME B16.48 covers spectacle blinds and the separate paddle blanks and paddle spacers used where a figure 8 would be too large to handle. We make spectacle blinds, spacers and blanks in Class 150, 300, 600 and 900, in carbon steel and in 304L and 316L stainless, matched to the flange class on each line.
Spectacle blind, paddle blank or spacer
| Type | What it is | Where it is used |
|---|---|---|
| Spectacle blind (figure 8) | Disc and ring joined by a web; it stays in the joint | Lines that are isolated regularly; the web shows which end is in the line |
| Paddle blank | Solid disc with a handle | Larger sizes, or temporary isolation; swapped for a spacer |
| Paddle spacer | Ring with a handle, the thickness of the blank | Fills the gap when the blank is removed, so the piping stays the same length |
Because a spectacle blind stays in the joint, the flanges never have to be spread further than its thickness, and the open or closed end is visible from the walkway. Paddle blanks and spacers come into their own in large sizes, where one figure-8 casting would be too heavy to rotate.
Positive isolation
A closed valve can leak through its seat. A blind breaks the line completely. OSHA counts blanking or blinding among the isolation methods for permit-required confined spaces (29 CFR 1910.146), and refinery and chemical plant procedures call for blinds before vessel entry and hot work. Plant blind lists are often prepared months ahead of a turnaround, with every blind identified by line number.
Thickness and marking
ASME B16.48 sets the thickness of each blank by size and pressure class, so that the disc can carry the full line pressure on one side. Order the blank for the class of the flanges it sits between, not for the operating pressure. Paddle blanks and spacers carry their size, class and material on the handle so they can be identified while installed. Tell us the flange facing, raised face or ring type joint, and the pipe inside diameter for the ring bore.
Grades
| Grade | Specification | Typical service |
|---|---|---|
| A516 Grade 70 or A105 | ASTM A516 (plate), ASTM A105 (forging) | Carbon steel lines: hydrocarbons, steam, water |
| 304L, 316L | Stainless plate or forging | Stainless lines and corrosive service |
How to order
A typical line reads: "Spectacle blind, NPS 6, Class 300, raised face, to ASME B16.48, ASTM A516 Grade 70, 4 pcs". Send the type, size, class, facing, bore or schedule, material and quantity for each line, and we quote every line as specified. Every order ships from our works in Gujarat, India, with an EN 10204 3.1 mill test report for every heat; ordering from India explains the documents, marking, packing and customs.
Frequently asked questions
Which is better, a spectacle blind or a paddle blank?
A spectacle blind stays in the joint and shows at a glance whether the line is open or closed; a paddle blank and spacer pair is lighter to handle in large sizes. Many specifications use spectacle blinds up to a set size and paddles above it.
What class should the blind be?
The same class as the flanges it sits between. ASME B16.48 sizes the thickness for the full rating of that class.
Can you supply blinds with the flanges for a turnaround?
Yes. List the blinds with the flanges on one line list and we quote them together.
Sources
- ASME B16.48, Line Blanks
- ASME B16.5, Pipe Flanges and Flanged Fittings, NPS 1/2 through NPS 24 Metric/Inch Standard
- OSHA 29 CFR 1910.146, Permit-required confined spaces (definition of isolation)