Cylinders and spherical shells

For a cylindrical shell the minimum thickness required to resist internal pressure can be determined from equation 13.7 the cylindrical stress will be the greater of the two principal stresses. 

If Di is internal diameter and e the minimum thickness required, the mean diameter will be (Di + e) substituting this for D in equation 13.7 gives  

This is the form of the equation given in the British Standard PD 5500. 

An equation for the minimum thickness of a sphere can be obtained from equation 13.9  

The equation given in the British Standard PD 5500 differs slightly from equation 13.40, as it is derived from the formula for thick-walled vessels see Section 13.15. 

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