Hydrogen is the smallest molecule there is, it burns over an unusually wide range of mixtures with air, and it ignites at very little energy. None of that damages a stainless hose. What it does is raise the standard for every joint in the assembly and for how leak tightness is proved, and it introduces one materials question — embrittlement — that has to be answered honestly rather than waved away.
What this service does to a hose
Leak tightness stops being a pressure test. A hydrostatic test proves an assembly holds water at 1.5 × its working pressure. It does not prove it holds hydrogen. On this duty leak tightness is a separate property, measured with a tracer gas at a stated leak rate, and it is the property that matters. If your specification calls for a helium leak test to a numbered rate, that is the test that decides whether we can supply, not the hydro.
Hydrogen embrittlement. Hydrogen dissolves into metal lattices and reduces ductility. Stable austenitic grades — 316L in particular, with sufficient nickel — are substantially more resistant than martensitic or high-strength steels, which is why austenitic stainless is the usual choice for hydrogen service. But cold-worked material is more susceptible than annealed material, and a corrugated hose and a wire braid are both heavily cold worked by definition. That is a real consideration and we will not pretend otherwise. It is also why the pressure, the temperature and the intended life have to be on the enquiry before we will quote.
The flammable range is very wide. Hydrogen burns in air from roughly 4 % to 75 %, against about 5 % to 15 % for natural gas. A leak that would disperse harmlessly on another gas is an ignitable cloud on this one, and the flame is nearly invisible.
Pressure varies enormously with the application. An electrolyser outlet may be at 30 bar, a fuel cell feed at a few bar, a storage line at 350 bar or more. Our published small-bore double-braid figures top out at 180 bar on DN6. Above that we are not the right supplier for the part and we will say so.
What we would fit
| Element | What we would supply | Why |
|---|---|---|
| Hose | 316L annular corrugated, in the annealed condition wherever the duty allows | Stable austenitic grades are the standard choice for hydrogen service |
| Braid | 316L wire, double braid, sized on the full system pressure | The stored energy in a hydrogen line justifies the second braid |
| Ends | Welded or metal-to-metal seal faces. No thread sealant, no tape | Every joint is a potential leak path and hydrogen finds them all |
| Testing | Hydrostatic as standard; helium leak test to a stated rate where specified | The hydro proves strength; only a tracer test proves tightness |
| Bonding | Continuous metallic path end to end, verified | Ignition energy is low and static is a credible source |
What we would not fit, and what happens
Threaded joints with sealant. They are not a hydrogen-tight joint and no tape makes them one.
High-strength or martensitic components anywhere in the wetted path. These are the grades most susceptible to embrittlement.
Interlock hose. Not pressure-tight, on the most leak-prone gas there is.
An assembly above our published pressure range. We will decline rather than extrapolate the table.
What we need to size it
| We need | Because |
|---|---|
| System pressure and temperature, and the relief setting | It decides immediately whether this is within our range |
| Purity requirement, if any | It changes the cleaning route and the internal finish |
| Required leak rate and the test standard | This is the acceptance criterion, not the hydro |
| Any material clauses in the client specification | Hydrogen specifications frequently name grades and conditions |
| Whether third-party witness or certification is required | It changes who does the work and how it is documented |
| Application — electrolyser, fuel cell, blending, storage | Each sits at a very different pressure |