Process Equipment and Plant Design
A cylindrical storage tank can have a self supported conical roof,

If its diameter is more than 50 meters
If its diameter is less than 15-20metres
Irrespective of its diameter
If the thickness of the roof is more than that of the cylindrical shell

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Process Equipment and Plant Design
A stuffing box is used for

Facilitating smooth opening and closing of a valve
Prevention of fluid leakage around moving parts
Reducing the resistance of fluid flow
Absorbing the contraction/expansion of pipeline due to temperature changes

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