Minimum blank thickness
The thickness of a flat blank (a spade or a blind) from the gasket diameter, the design pressure and the allowable stress you type.
Inputs
The working
- Design pressure in MPa (typed in bar)
P in bar / 102.5 MPa (gauge) - Root term
sqrt(3 x P / (16 x S x E x W))0.0583 - Blank thickness before allowance
d_g x root11.656 mm - Minimum blank thickness
t_m = d_g x root + c13.156 mm
For guidance only. Verify against the code edition in force and your own design basis.
This blank thickness calculator gives the minimum thickness of a flat blank (a spade or a blind) from gasket diameter, design pressure and allowable stress, by the ASME B31.3 form. Free, no sign-up.
The formula
- t_m = d_g x sqrt(3 x P / (16 x S x E x W)) + c, with P and S in the same unit (MPa) and c the allowance.
Worked example
Limits
Common questions
How do you calculate the thickness of a blank, spade or blind?
Use t_m = d_g x sqrt(3 x P / (16 x S x E x W)) + c, the ASME B31.3 form for a flat blank, with pressure and stress in the same unit. A 200 mm gasket diameter at 2.5 MPa with S = 138 MPa, E = 1, W = 1 and a 1.5 mm allowance gives 13.156 mm.
Which diameter do I enter for a blank?
Enter the gasket diameter d_g as the code defines it for your type of joint. It depends on the joint, so check the code text and its figure rather than using the pipe size.
Is this a blind flange calculation?
No. It is for a flat blank, such as a spade or a blind fitted between flanges. The rating of a blind flange comes from its flange standard and pressure class.
Does the blank thickness include a corrosion allowance?
Yes. Whatever you enter as the allowance is added to the thickness the pressure needs. Enter the corrosion allowance, plus any mechanical allowance, from your design basis.
Unit conversions
Reference values for the units this tool works in. Rounded for reading; the calculator itself works to full precision.
Pressure and stress
| MPa | bar | psi | ksi |
|---|---|---|---|
| 0.1 | 1 | 14.5 | 0.0145 |
| 0.5 | 5 | 72.52 | 0.0725 |
| 1 | 10 | 145 | 0.145 |
| 2 | 20 | 290.1 | 0.2901 |
| 5 | 50 | 725.2 | 0.7252 |
| 10 | 100 | 1,450 | 1.45 |
| 20 | 200 | 2,901 | 2.901 |
| 50 | 500 | 7,252 | 7.252 |
| 100 | 1,000 | 14,504 | 14.5 |
| 138 | 1,380 | 20,015 | 20.02 |
| 200 | 2,000 | 29,008 | 29.01 |
| 250 | 2,500 | 36,259 | 36.26 |
1 MPa = 10 bar = 145.04 psi. 1 ksi = 6.895 MPa.
Length
| mm | in |
|---|---|
| 1.5 | 0.0591 |
| 3 | 0.1181 |
| 5 | 0.1969 |
| 6 | 0.2362 |
| 6.35 | 0.25 |
| 8 | 0.315 |
| 10 | 0.3937 |
| 12.7 | 0.5 |
| 16 | 0.6299 |
| 20 | 0.7874 |
| 25.4 | 1 |
| 50 | 1.969 |
| 100 | 3.937 |
1 in = 25.4 mm.
Temperature
| °C | °F |
|---|---|
| 20 | 68 |
| 100 | 212 |
| 150 | 302 |
| 200 | 392 |
| 250 | 482 |
| 300 | 572 |
| 400 | 752 |
| 500 | 932 |
| 600 | 1,112 |
°F = °C x 9/5 + 32.