Cooling water is the most common duty in any plant and the one specified with least thought. It is also where more stainless assemblies fail than on any exotic chemical, for one reason: nobody sends the water chemistry. Chloride content, not pressure, is what decides whether a cooling hose lasts fifteen years or eighteen months.
What this service does to a hose
Chloride pitting. Austenitic stainless relies on a passive chromium oxide film. Chloride ions break that film down locally, and once a pit initiates the chemistry inside it becomes self-sustaining — acidic, chloride-concentrated and shielded from the bulk water that would repassivate it. 316L, with molybdenum, tolerates considerably more chloride than 304L does, but neither is immune, and the threshold falls as temperature rises. A cooling tower loop that concentrates dissolved solids through evaporation is the classic case: make-up water at 50 ppm chloride becomes circulating water at several hundred after a few cycles of concentration.
Stagnation multiplies it. A pit needs a shielded, low-flow region to establish itself, and a corrugation valley on a line that stands still over a weekend shutdown is exactly that. Assemblies on standby duty — a spare chiller, a backup pump — fail more often than assemblies in continuous service on the same water.
The temperature is mild and the pressure is mild. Chilled water at 6–12 °C and 6–10 bar is nothing at all for a DN50 assembly rated 30 bar. That is precisely why the specification gets no attention.
Condensation and external attack. A chilled water line runs below dewpoint, so it sweats. On an unlagged assembly the outside of the braid stays permanently wet, and in a coastal or process atmosphere that is an external chloride duty on the part that is carrying the load.
What we would fit
| Element | What we would supply | Why |
|---|---|---|
| Hose | 316L annular corrugated as the default. 304L only where the water chemistry is known and controlled | Molybdenum buys real chloride tolerance and it is the cheapest insurance here |
| Braid | 316L wire to match, particularly where the line sweats or runs outdoors | The braid is the load path and it is the part exposed to the atmosphere |
| Ends | Flanged or grooved to match the existing pipework | It has to fit what is there |
| Length | Sized so the assembly is above its bend radius in the installed position | Chiller and AHU connections are almost always tight for space |
| Lagging | Specified by you where the line sweats; we build to accept it | It changes the outside diameter and the support arrangement |
What we would not fit, and what happens
304L on an uncontrolled or concentrating loop. It will be fine for a while and then it will weep, usually at the worst accessible point.
An assembly on standby duty with no provision to drain. Standing water in a valley over a shutdown is the pitting case.
A hose cut to the shortest length that reaches. It will be below its bend radius with the flanges on, which is not how it was measured.
Mixed stainless and aluminium in a loop with no isolation. Galvanic attack, and the aluminium goes first.
What we need to size it
| We need | Because |
|---|---|
| Chloride content of the circulating water, in ppm | This is the single answer that decides the grade |
| Inhibitor package and glycol percentage if any | It changes the chemistry and sometimes the compatibility |
| Operating temperature and pressure, and the relief setting | The relief setting is the design pressure |
| Whether the line is continuous duty or standby | Standby means stagnation, which is the pitting multiplier |
| Whether the line sweats and whether it is lagged | It decides the external duty on the braid |
| Installed geometry, or a sketch of the space available | Bend radius in a plant room is the real constraint |