Why is it effective to control the critical thickness for elliptical heads rather than calculating the thickness?

Since the elliptical head thins during the pressing process, and this thinning is not uniform, there is a parameter name for the minimum thickness of the head.

The calculated thickness is obtained using a formula: Effective thickness = Nominal thickness – C1 – C2. Clearly, the effective thickness can only be controlled through the nominal thickness; the calculated thickness cannot be used for such control

Agree with the answer from the 4th floor. Upon reflection, it makes sense too. By examining the formula in GB150.3-2011 (5-1), it is easy to see that the calculated thickness is determined by the design temperature, design load, inner/outer diameter of the shell, welding joint coefficient, and the shape coefficient K. Once these parameters are determined, the calculated thickness resulting from the calculations is also a fixed value that cannot be adjusted or controlled at will. By referring to page 172 of Volume 1 of the Practical Handbook on Chemical Vessels and Equipment, a better understanding of the following terms can be achieved. 1. Calculated thickness: The theoretical wall thickness required to safely withstand the calculated pressure. 2. Effective thickness: The thickness that can actually be used to withstand the pressure of the medium. Thank you very much to all my colleagues for taking part in answering the questions!

It is definitely the thickness after shaping and thinning that is required. If the design margin is already small, then it’s essential to ensure the actual thickness obtained after thinning. Sometimes, due to high curvature, more thinning is necessary; in such cases, thicker sheets must be used to maintain the desired thickness after shaping.