Anhydrous ammonia and austenitic stainless steel get along well. The pressures are modest — a refrigeration plant runs 2 bar on the low side and perhaps 18 bar on the discharge — and the temperatures are unremarkable. What makes ammonia demanding is that copper and its alloys are excluded outright, that any water in the system changes the chemistry, and that a leak is an immediate life-safety event rather than a housekeeping one.
What this service does to a hose
No copper, anywhere. Ammonia attacks copper, brass and bronze rapidly, and the failure is not gradual. That rules out brass fittings, bronze bushes, copper gaskets and any silver or copper-bearing brazing alloy in the assembly. It is the reason an ammonia assembly has to be specified as a whole and not assembled from a general stores — it is nearly always a fitting, not the hose, that brings copper into the line.
Water changes it. Anhydrous ammonia is benign to carbon and stainless steel. Aqueous ammonia is alkaline and, at concentration and temperature, brings the same stress corrosion concerns that caustic does. Systems are meant to be dry; systems in service acquire water. Tell us which you actually have.
Temperature swings both ways. A refrigeration circuit runs down to −33 °C on the suction side and up to 100 °C or more at compressor discharge. Austenitic stainless is comfortable at both ends, which is a genuine advantage here, but the assembly sees the swing and the run either side of it changes length.
Pulsation at the compressor. Where the hose is fitted at a reciprocating compressor — which is where most ammonia hoses are — the duty is pulsation and vibration rather than static pressure, and that is what decides the length and the installation.
What we would fit
| Element | What we would supply | Why |
|---|---|---|
| Hose | 316L annular corrugated. 304L is adequate on dry anhydrous duty | Neither grade is troubled by dry ammonia |
| Braid | 304 or 316 wire, sized on the discharge pressure and the relief setting | The discharge side is the sizing case, not the suction |
| Ends | Flanged or welded, with every wetted component copper-free and stated as such | The fitting is where copper gets into an ammonia line |
| Seals | Ammonia-compatible gasket material, specified by you or agreed with us in writing | Elastomer choice on ammonia is a short list and getting it wrong is a leak |
| Length | Sized for the compressor movement, installed across it | Ammonia hoses are usually compressor hoses |
What we would not fit, and what happens
Any brass, bronze or copper-bearing component. It fails, and it fails quickly.
Interlock hose. Not pressure-tight, on a toxic gas.
A hose sized on suction pressure and fitted on the discharge. Obvious in writing, and it still happens.
An assembly with unspecified seal materials. On ammonia the seal is a design decision, not a stores decision.
What we need to size it
| We need | Because |
|---|---|
| Anhydrous or aqueous, and if aqueous, the concentration | It changes the corrosion question entirely |
| Where in the circuit — suction, discharge, liquid line, oil drain | It sets pressure, temperature and pulsation |
| Design pressure and the relief setting | The relief setting is the design case |
| Temperature range, both ends of it | Both the cold and the hot end change the length of the run |
| Permitted seal and gasket materials | It is a short list and it must be stated |
| The code or specification the plant is built to | It decides what we can certify against |