Should the forming thinning rate of the head be deducted when calculating pressure vessel heads?
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Should the forming thinning rate of the head be deducted when calculating pressure vessel heads?
Are you referring to a conical shape, an elliptical shape, or a flat lid?
To calculate the strength of an ellipse, it is necessary to subtract the thinning rate
A reduction in thickness is generally proposed where there is a transition, and this is also one of the factors that limit the range of openings in end caps. When calculating openings in the head, the minimum forming thickness should be taken into account; this value is then used along with the corrosion allowance (i.e., reduction amount minus negative deviation). People who design frequently have this awareness.
The last edit to this post was made by zjq1962 on 2018-11-10 at 16:01. In the diagrams I have reviewed, two common approaches can be seen: one is that the thickness value indicated on the diagram’s header represents the starting thickness (the minimum thickness required for forming); when performing calculations, the nominal thickness is taken as this starting thickness； Use the sum of the thinning amount and the corrosion margin as the input for the corrosion margin. Second, when performing the calculation, enter the minimum formability thickness for the nominal thickness, 0 for the corrosion allowance, and 0 for the negative thickness deviation. The second method requires attention to the issue of allowable stress jumps.
However, using the second method requires much more calculation. The instructor mentioned during the certificate renewal process that the value must be based on the nominal thickness (the thickness indicated on the drawings). The first option is more reasonable; we enter the corrosion allowance as corrosion + reduction amount – negative deviation
We enter the corrosion allowance as corrosion + reduction amount – negative deviation. Why do we need to subtract the negative deviation?
The negative deviation itself implies that there’s a box there that doesn’t need to be checked.