Process Equipment and Plant Design
For a cylindrical shell, (subject to the thickness of uppermost course being more than the minimum for diaofthe tank in question), the thickness of the courses of shell

Decreases upwards
Remains same throughout
May decrease or increase upwards depending upon whether vacuum or positive pressure would be maintained inside the shell
Increases upwards

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Process Equipment and Plant Design
Triangular pitch tube layout as compared to square pitch in a shell and tube heat exchanger

Facilitates comparatively easier external cleaning because of large clearance
Permits the use of less tubes in a given shell diameter
Both B and C
Permits the use of more tubes in a given shell diameter

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