Process Equipment and Plant Design
Generally, elliptical dished heads

Resist half the pressure rating compared to hemi spherical head provided on the cylindrical shell of the same thickness and diameter
Are manufactured on 2:1 ratio of major to minor axis and is recommended to be used for pressure vessels operating above a pressure of 1.5 MN/m²
All of these
Are approximately as strong as seamless cylindrical shell having the corresponding I.D and O.D

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Process Equipment and Plant Design
In a shell and tube heat exchanger, the clearance of the tube is generally

Not less than one-fourth of the tube diameter or 3/16"
Equal to the tube diameter
More in case of triangular pitch as compared to the square pitch tube layout
More than the tube diameter

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