Pancake thickness calculator
To calculate the required thickness of a pancake (also known as a blind, blank, or spade) used to isolate a pipe between two flanges for pressure testing and maintenance, you can use a similar approach to the one used for calculating the minimum required wall thickness for pipes. The main difference is that the pancake is flat and subject to direct pressure loading.
Here is a general procedure to calculate the required thickness of a pancake:
Determine the internal design pressure (P) for the pressure test, which is typically higher than the normal operating pressure to ensure the integrity of the system.
Measure or obtain the inside diameter (d) of the pipe or the inner diameter of the flange's bolt circle (whichever is smaller) to estimate the area exposed to pressure loading on the pancake.
Identify the material of the pancake and obtain its allowable stress (S) at the design temperature, which can be found in relevant material specifications or codes.
Determine an appropriate safety factor (SF) to account for uncertainties in material properties, manufacturing tolerances, and potential pressure fluctuations during the test.
Use the following formula to estimate the required thickness (t) of the pancake:
t = (P * d) / (2 * S * SF)
- t is the required thickness of the pancake (mm or in)
- P is the internal design pressure (MPa or psi)
- d is the inside diameter of the pipe or the inner diameter of the flange's bolt circle (mm or in)
- S is the allowable stress for the pancake material at the design temperature (MPa or psi)
- SF is the safety factor (dimensionless)
Round up the calculated thickness (t) to the nearest standard thickness available for the pancake material.
Keep in mind that this approach provides a simplified estimate of the required pancake thickness. For a more accurate and detailed analysis, consider using relevant industry standards, such as ASME Boiler and Pressure Vessel Code, Section VIII, Division 1, or consulting with an experienced engineer or manufacturer.
Full download access to any calculation is available to users with a paid or awarded subscription (XLC Pro).
Subscriptions are free to contributors to the site, alternatively they can be purchased.
Click here for information on subscriptions.