For standard sizes, blind flange thickness is read from the table and no calculation is needed. Calculation comes in for non standard sizes, custom blanking plates and blinding elements.
What sets the thickness
- Design pressure: Thickness increases with the square root of pressure
- Diameter: Thickness rises quickly as the effective diameter grows
- Material: Allowable stress varies with grade and temperature
- Service temperature: Allowable stress falls as temperature rises
- Corrosion allowance: Added to the calculated thickness
- Gasket type and face form: They affect bolt load and effective diameter
The method is defined in rules such as ASME VIII Div.1 and ASME B31.3. Bending from bolt load is considered alongside pressure, and it is often the governing case.
When the standard table is enough
ASME B16.5 and B16.47 blind flanges are already calculated for the design conditions of their class. No extra calculation is needed for service within the pressure temperature table. Changing material group (F316 instead of A105) changes the allowable pressure, not the thickness.
When calculation is required
- Spectacle blind and figure 8 plates
- Non standard diameters or classes
- Long term service at high temperature
- Lines with a large corrosion allowance
- Temporary blinds for testing
As plate thickness grows, so does the required stud length; the two must be planned together.
A practical warning
"Make it the same thickness as the flange" is wrong. A blind flange is thicker than a drilled one, and a blanking plate may differ from both. An unverified thin plate bulges permanently under pressure and leaks.
Send sizes and pressures for your blinds: enquiry form. Related: what is a blind flange, spectacle blinds and line blinds.
FAQ
Is calculation needed for a standard blind flange?
No. Standard thickness is sufficient for service within the pressure temperature table of the class.
What governs the thickness?
Diameter and design pressure, with bending from bolt load often being the governing case.
Are blanking plate and blind flange thickness the same?
No. A blanking plate sits between two flanges and is calculated differently.
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