On a high-purity line the bore is the product. The hose is only the wrapper that holds it in the right shape. Everything that would normally decide a specification — pressure, movement, temperature — is usually undemanding, and everything that is normally a detail — surface finish, leak rate, particle count, moisture — becomes the specification.
What this service does to a hose
A corrugated bore has enormous surface area and a great many small re-entrant features. On a process line that is irrelevant. On a line carrying a semiconductor process gas it is a reservoir: moisture and contaminants adsorb onto that surface and then bleed off slowly for days, which is what a long pump-down is actually measuring. The rougher the surface, the longer that takes and the worse the plateau.
Leak rate is the second axis, and it is a different question from pressure tightness. An assembly that holds 40 bar hydrostatically without a drop can still leak at a rate that ruins a high-purity line, because the relevant number is helium at the 10⁻⁹ mbar·l/s level, not water at working pressure. It has to be measured with a mass spectrometer, not with a gauge and a bucket.
Particulate is the third. Every forming and handling operation generates particles, and on this duty they have to be removed and then kept out, which is a packaging and handling problem as much as a manufacturing one.
What we would fit
| Element | What we would supply | Why |
|---|---|---|
| Hose | 316L annular corrugated, electropolished bore on request — electropolishing is subcontracted | Electropolishing lowers the roughness and closes the surface, which is what shortens pump-down |
| Braid | 316L, conventional | Outside the bore; it has no purity role |
| Ends | Face-seal fittings, orbital-welded where the client spec calls for it — orbital welding is subcontracted | A face seal is the interface this industry actually uses; a threaded joint is not |
| Testing | Helium mass-spectrometer leak test in addition to hydrostatic | Two different questions, two different tests |
| Documentation | Material certificates to EN 10204 3.1, with 3.2 where a third party is involved | On this duty the paperwork is part of the deliverable |
| Packaging | Cleaned, capped and double-bagged; opened only in the target environment | A clean assembly stored badly is not a clean assembly |
What we would not fit, and what happens
An as-drawn bore where the spec calls for a finish. The assembly will pass every pressure test and fail the line.
Interlock hose. Mechanical seam, impossible to clean, not pressure-tight.
Threaded ends with sealant. The sealant is a contaminant and the thread is a particle trap.
A hose specified only by bore and pressure. On this duty those two numbers tell us almost nothing about what you actually need.
What we need to size it
| We need | Because |
|---|---|
| Surface finish required, as an Ra figure | “Polished” is not a specification; 0.4 µm Ra is |
| Leak rate required, and the test method | Helium mass spectrometry is a different test from hydrostatic |
| Media, including any corrosive process gases | Some process chemistries rule 316L out entirely |
| Cleanliness class and whether certification is required | It decides how the assembly is made, not just how it is finished |
| End interface — face seal type and size | This is the part that has to mate with the tool |
| Whether the assembly moves, and how far | Usually little, but it changes the length and the radius |