In shell-and-tube exchangers, tubes are attached to the tube sheet (a thick, circular plate) either permanently (rolling and brazing) or removably (ferrules). As a practical rule, the tube sheet thickness is normally about what fraction of the tube outside diameter, with a minimum of approximately 22 mm (7/8 inch)?

Introduction / Context:
The tube sheet anchors tubes and seals the shell-side from the tube-side. Its thickness must resist ligament stresses around tube holes, differential pressure loads, and bending from channel/shell connections. Practical sizing rules offer a starting point before detailed mechanical analysis (e.g., TEMA/ASME).

Given Data / Assumptions:

• Conventional shell-and-tube exchanger with straight tubes.
• Moderate differential pressures and standard tube pitch patterns.
• Fabrication practice requiring a minimum machinable thickness.

Concept / Approach:
A common rule-of-thumb sets tube sheet thickness on the order of the tube outside diameter, subject to a practical minimum (≈ 22 mm) for structural integrity and machining. Final thickness is refined by code calculations considering pressure, temperature, gasket seating, and tube-to-tubesheet joint configuration (fixed, floating, U-tube).

Step-by-Step Solution:
Start with baseline: t_ts ≈ OD_tube.Check against minimum shop limit: t_ts ≥ ~22 mm.Perform code checks (ligament efficiency, bending) and adjust as required.Confirm compatibility with tube expansion/brazing or ferrule details.

Verification / Alternative check:
Comparisons to TEMA guidelines and past proven designs typically place tube sheet thickness around the tube OD for many standard services, increasing for high pressure or large spans.

Why Other Options Are Wrong:
Half or three-fourths: often too thin for structural and machining needs.1.5 times OD: overly conservative for routine services, raising cost and weight.Fixed 10 mm: ignores OD and load effects.

Common Pitfalls:
Using the rule-of-thumb without code verification for high-pressure exchangers.Ignoring gasket seating stresses that govern required thickness.

Final Answer:
About equal to the tube OD (but not less than ~22 mm)