Thickness of spades, spectacle blinds or line blanks for various pressure-temperature ratings are defined in ASME B16.48 - "Line Blanks". However this standard covers blank thicknesses only up to 24" pipe size.

This online calculator can be used to calculate spade/blank thicknesses for Class 150, Class 300, Class 600 and Class 900 RF/FF flanges from sizes DN15 to DN600 and for Class 150, Class 300 and Class 600 RF/F Flanges for sizes DN650 to DN1500 using flat ring gaskets and for a range of materials. Note that the flat ring gasket ID for the above mentioned class and size ranges are same. Select the appropriate material from the drop-down and enter the design pressure, design temperature and corrosion allowance values to calculate the spade thickness.

Note that for sizes above 24", the blank thicknesses are in accordance with inside diameter of flat ring gaskets for series A and series B Flanges. The thickness calculator is based on equation provided in para 304.5.3 of ASME B31.3. As per this section, The minimum required thickness of a permanent blank shall be calculated in accordance with the following equation.

tm = dg$$\sqrt[]{\frac{3P}{16SEW}}$$ + c

where

c = sum of allowances.

dg = inside diameter of gasket for raised or flat face flanges, or the gasket pitch diameter for ring joint and fully retained gasketed flanges.

P = Internal design pressure (gauge)

S = Allowable stress of material from Table A-1 of ASME B31.3

tm = Pressure design thickness of spade calculated as per above formula

W = Weld joint strength reduction factor in accordance with para 302.3.5(e)

E = Quality factor from Table A-1A or Table A-1B of ASME B31.3

This calculation applies to -
ASME B16.5 flanges: Class 150-900 up to 24" (DN600) and ASME B16.47 Series A and Series B flanges: Class 150-600 for sizes 26"(DN 650) to 60" (DN1500).

Note that the ID of Gaskets for series A and series B flanges is same for Class 150-600. Hence spade thickness calculation will be same for Series A and B flanges.

Sr.No Nom
Pipe
Size
Nom
Pipe
Dia
ID (mm)
Minimum
(mm)
Corrosion
Allowance
(mm)
Design
Thickness (mm)
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