Shell-and-tube exchanger tubing: Considering fouling services, what is the commonly recommended minimum outside diameter (OD) of tubes to facilitate cleaning and reduce blockage risk?

Introduction / Context:
Tube outside diameter (OD) selection affects heat transfer area, pressure drop, mechanical strength, and cleanability. In fouling services (e.g., dirty cooling water, slurries), larger tube bores help slow fouling deposition and facilitate mechanical cleaning with brushes or scrapers.

Given Data / Assumptions:

• Shell-and-tube exchanger handling fluids prone to fouling.
• Standard tube gauges (B.W.G. 14–16 are common).
• Mechanical cleaning options (rodding, brushing) are anticipated.

Concept / Approach:
Small tubes provide more area per shell diameter but clog more easily and are harder to clean. Industry practice often discourages very small OD tubes for fouling duties. A 3/4 inch OD (about 19 mm) tube is a widely recommended minimum for such services, balancing area density with maintenance practicality.

Step-by-Step Solution:

Verification / Alternative check:
Maintenance guidelines from exchanger suppliers and plant standards frequently call for 19 mm or larger OD in dirty services, with 25 mm (1″) common where space permits.

Why Other Options Are Wrong:

• 16 mm: more prone to plugging and difficult to clean.
• 28 mm or 38 mm: feasible but not a “minimum”; larger ODs increase bundle size and cost.

Common Pitfalls:
Optimizing only for area density and ignoring maintainability; underestimating fouling factors and cleaning intervals; selecting thin gauges that deform under rodding.

Final Answer:
19 mm