Process Equipment and Plant Design
Generally, elliptical dished heads

Are approximately as strong as seamless cylindrical shell having the corresponding I.D and O.D
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

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Process Equipment and Plant Design
The function of manholes provided in the shell of a distillation column is to

All of these
Give access to the individual trays for cleaning, maintenance and installation
Guard against foaming & entrainment by dumping antifoaming agent through it
Keep a check on the liquid gradient over the plate by direct visual observation

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