Double-Wall Protection

Double-Wall Protection

Turning a Silent Failure Into a Visible One

A single-wall tube separates two fluids with one barrier. If it develops a pinhole, the higher-pressure fluid crosses into the lower-pressure one, and nothing about the exchanger announces it. The failure is discovered by a water quality test, a taste complaint, or a chemical analysis, all of which happen well after the event.

Double-wall construction interposes a vented gap. Two tubes are drawn together so their walls are in intimate mechanical contact for heat transfer. Between them runs a deliberate path to the tube end, outside the pressure boundary of either fluid. A leak through either wall discharges there, visibly, and does not cross between streams.

Decide on consequence, not probability. Tube failures are uncommon. The question is what happens if one occurs and goes unnoticed for a week. Where the answer involves drinking water in an occupied building, a food product or a regulated process, the arithmetic favours double-wall regardless of how reliable a single tube is.

Where it is not warranted. A closed glycol loop interchanging against tower water in a plant room does not need it. Both fluids are already non-potable and a cross-leak is a maintenance matter, not a safety one. Specifying double-wall there adds surface and cost for a consequence nobody would notice.

Four ranges provide it. DSU for steam-to-liquid, DWU for liquid-to-liquid, and DTCS and DTCW for steam and water heated tank bundles respectively. All four use naval brass tubesheets on the shell and tube ranges and carry separate catalogue number series.