Shell-and-tube heat exchanger layout rules: which combined statement best reflects common preliminary design practices (cleaning lane on square pitch, tubesheet minimum thickness versus tube OD, and standard tube ODs/lengths used)?

Introduction / Context:
Early-stage shell-and-tube heat exchanger design uses rules-of-thumb before detailed thermal and mechanical rating. Common choices include tube pitch patterns, cleaning access lanes, tubesheet thicknesses, and preferred tube sizes/lengths—each affecting manufacturability, maintenance, and cost.

Given Data / Assumptions:

• Conventional exchanger (not special high-pressure or exotic alloy design).
• Square pitch layouts permit through-rod cleaning lanes; triangular pitch favors higher area density but poorer mechanical cleaning.
• “Minimum tubesheet thickness” refers to preliminary guidance, not a code calculation replacement.

Concept / Approach:
Design practices often specify a narrow cleaning lane between tubes on square pitch (about 6.5 mm) to allow brushes/rods. Tubesheet thickness is initially tied to tube outside diameter (OD), recognizing code checks will refine it later. Tube OD and standard stock lengths are chosen to balance heat transfer area, pressure drop, and availability.

Step-by-Step Solution:

Verification / Alternative check:
Vendor catalogues and plant standards list these practice ranges; final selection is validated by TEMA/API and pressure design codes after thermal rating.

Why Other Options Are Wrong:

• Picking only one of (a), (b), or (c) ignores the broader set of accepted practices.

Common Pitfalls:
Assuming triangular pitch can be rod-cleaned; ignoring fouling when choosing very small tube ODs; treating preliminary thickness guidance as a substitute for full code calculation.

Final Answer:
All (a), (b) & (c)