Shell-and-tube heat exchanger detailing: which statements about corrosion allowance (CA) are appropriate?

Introduction / Context:
Corrosion allowance (CA) is added metal thickness to compensate for expected corrosion during service. In shell-and-tube exchangers, CA is applied to pressure-retaining parts exposed to corrosive fluids, while non-pressure hardware typically does not receive CA. Proper allocation of CA helps maintain code compliance and service life without overdesigning every component.

Given Data / Assumptions:

• Carbon steel or cast iron in general chemical service.
• Industry-typical CA values (order of millimetres) unless client specifies otherwise.
• Tube material and thickness often governed by separate rules and corrosion data.

Concept / Approach:
Pressure parts exposed to corrosion (shells, channels, heads, covers, tube sheets) require CA. Non-pressure parts like tie rods, spacers, and baffles are not pressure boundaries and normally do not receive CA. Typical baseline CA values around 1.5 mm are common for carbon steel in moderate service; severe conditions justify higher CA (~3 mm or as specified). Tube sheets and internal covers may see corrosive attack from both sides and therefore can need CA on both faces.

Step-by-Step Solution:

Verification / Alternative check:
Project standards and TEMA practices generally align with these guidelines; client specifications may refine exact values.

Why Other Options Are Wrong:

• Each of (a), (b), and (c) is individually correct; the best choice is the combined statement.

Common Pitfalls:
Applying CA uniformly to all components, which can add weight and cost without improving safety; or neglecting CA on the second face of a tube sheet that is exposed on both sides.

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