Corrugated stainless steel hose fails differently from rubber hose: it performs flawlessly until a fatigue or corrosion threshold is crossed, then fails fast. That behaviour makes the specification stage decisive — torsion, chlorides, wrong alloy grade and undocumented pressure ratings cannot be inspected away later. This article covers the pitfalls engineers must close before ordering: alloy selection against chlorides and temperature, why the pressure rating must be read per DN and braid count, which certificates to demand, and the installation constraints that belong on the drawing. For construction fundamentals, see the complete stainless steel hose technical guide; for the metal-vs-PTFE decision, stainless steel hose vs PTFE hose.
What is the difference between corrugated hose and interlocked hose — and why does it matter on a P&ID?
Corrugated stainless steel hose is a pressure-tight, cold-formed tube with annular or helical convolutions, normally covered by one or two layers of stainless wire braid that carry the pressure thrust. It is the pressure-rated product, governed by EN ISO 10380, and every assembly carries a defined proof- and burst-pressure regime.
Interlocked (strip-wound) hose is profiled strip wound and hooked together. It is not leak-tight and carries no pressure rating — its jobs are cable protection, exhaust ducting where minor leakage is acceptable, and external armour over other hoses. Writing "flexible metal hose" on a P&ID without distinguishing the two has put non-pressure-rated interlocked product into pressure-boundary positions; the error surfaces at hydrotest, or worse, in service. Always specify "corrugated hose assembly to EN ISO 10380" for pressure duty.
Which alloy grade — and what does chloride exposure change?
| Grade | Key property | Typical service | The pitfall |
|---|---|---|---|
| 304 / 1.4301 | Economical austenitic | Water, steam, mild media | Pitting and stress corrosion in chlorides |
| 316L / 1.4404 | ~2 % Mo, low carbon | Seawater spray, chlorinated media, chemicals, food | Still SCC-susceptible in hot concentrated chlorides |
| 321 / 1.4541 | Ti-stabilised | Sustained high temperature (exhaust, steam) | Choose it above ~400 °C continuous, not 316L |
| Duplex / super-austenitic | High strength + Cl⁻ resistance | Offshore, hot saline | Cost — reserve for real SCC risk |
The molybdenum in 316/316L is what buys resistance to chlorides, seawater and many acids over standard 304 — which is why 316L is the industry default for chemical, marine and food duty. The specification pitfall is chloride-induced stress corrosion cracking (SCC): austenitic grades (304 and, less readily, 316L) can crack under the combination of tensile stress, elevated temperature and chlorides. If the hose sees hot, chloride-bearing media or washdown, flag it in the RFQ so the manufacturer can propose duplex or a higher alloy — SCC is a materials-selection problem, not a maintenance problem.
Why is "what's the pressure rating of stainless hose?" the wrong question?
Because the rating depends on DN, braid count, corrugation geometry and temperature — there is no single number. As an orientation, a single-braid DN 25 assembly typically works in the tens of bar; a double braid raises that substantially; and small bores rate far higher than large ones. Working pressure falls as DN rises across every construction family, so read the manufacturer's pressure table for the exact DN and braid count — never extrapolate from a neighbouring size.
Three more numbers to fix in the specification:
- Temperature derating. EN ISO 10380 ratings are stated at ambient. Austenitic steel loses yield strength with temperature — at several hundred °C an assembly may retain only 60–70 % of its ambient rating. Request the derating curve for the alloy and construction.
- Proof and burst. Proof test is typically 1.5 × working pressure; the burst margin is defined by the standard — verify it on the assembly certificate rather than accepting catalogue prose.
- Bend radius, static vs dynamic. Metal hose has two minimum bend radii: a static one for fixed installation and a much larger dynamic one for flexing duty. Specifying against the static figure for a vibrating pump connection guarantees convolution fatigue.
Unbraided corrugated hose deserves its own warning: without braid, pressure makes the hose elongate and squirm, and the rating collapses to a fraction of the braided figure. Braid is not decoration — it is the pressure-carrying member.
Which documents should the purchase order demand?
- EN 10204 3.1 material certificates for the pressure-wetted parts (core, braid, fittings) as the baseline; 3.2 (independently witnessed) where the site or class rules require it.
- PED 2014/68/EU conformity assessment appropriate to the fluid group and pressure–size category; most small-bore moderate-pressure assemblies fall into the lower categories, but the classification must be stated, not assumed.
- Assembly marking and test certificate — manufacturer, DN, pressure rating, date, and the proof-test record. Unmarked assemblies fail site audits.
- For food or pharmaceutical contact: a Declaration of Compliance under EC 1935/2004 for the assembly, with hygienic fittings (Tri-Clamp to DIN 32676, or DIN 11851 dairy unions — two different systems, chosen to match the plant, not mixed). Elastomeric seals at the ends are certified separately (for rubber, FDA 21 CFR 177.2600 — note EU Regulation 10/2011 covers plastics only, so it cannot certify a rubber gasket).
- For fire or cryogenic duty: fire-test or thermal-shock evidence for the specific assembly type — ask for the test report rather than a standard number quoted from memory; for LOX service, certified oxygen cleaning.
Browse stainless steel hose assemblies and the wider industrial hoses range; dimensional and pressure tables are in the technical catalogues. Where the real problem is pipework thermal expansion rather than flexible connection, consider metal expansion joints and compensators instead of hose — a hose absorbs misalignment and vibration, a compensator absorbs axial movement, and swapping their roles shortens the life of both.
Where is stainless hose the right tool — and where is it over-specified?
Corrugated stainless hose earns its premium where elastomers cannot go: steam and thermal-oil connections, exhaust and flue-gas flexibility, cryogenic transfer (liquid nitrogen, LNG — with thermal-shock-qualified assemblies and, for oxygen service, certified cleaning), high-temperature chemical duty, and fire-rated positions where a rubber hose would be the weak point. Its combination of temperature span (cryogenic to several hundred °C by grade) and permeation-tightness (welded metal is diffusion-tight in a way no polymer is) is unmatched.
It is over-specified — and underperforms — in three common cases. High-frequency vibration with tight amplitude: metal hose absorbs vibration well only when sized and oriented for it; a too-short assembly on a vibrating pump fails at the fitting weld faster than a correctly chosen elastomer connector. Abrasive external environments: an unprotected braid dragged over concrete loses wires and, with them, the pressure rating. Dynamic flexing duty: every flex cycle consumes fatigue life; where a hose moves constantly, PTFE or elastomer constructions with far larger allowable cycle counts are often the better economics. The specification question is never "is metal stronger?" but "which failure mode governs here?"
Inspection intervals follow duty: vibration service warrants inspection roughly every 6 months, high-temperature static service every 12, and undisturbed static connections at each planned shutdown — with braid-wire breakage, corrosion staining at terminations and any convolution deformation as immediate withdrawal criteria.
What are the installation constraints that belong in the specification?
Field investigations of failed metal hose assemblies point overwhelmingly at installation, and the fixes cost nothing at the design stage:
- Zero torsion. Corrugated hose has effectively no torsional flexibility. The pipework must be aligned before connection, and a second spanner must hold the hose-side fitting during tightening. If the connection rotates in service, design in a swivel or a dog-leg of two hoses.
- No pressure-boundary bending at the fitting. Specify a straight tangent at each end; the transition from fitting to first convolution is the highest-stress point in the assembly.
- Support the weight. Long horizontal runs sag, concentrating bending at the ends — specify supports.
- Movement in one plane. A single hose accommodates lateral movement perpendicular to its axis; it does not accommodate axial compression/extension well. Orient the hose so the movement is lateral.
- Inspection criteria in the maintenance plan: broken braid wires, corrosion staining at fitting terminations (crevice corrosion), visible convolution deformation, and any weeping — each is a withdrawal criterion, not an observation.
The pre-order checklist
- Medium, concentration, temperature — including chlorides and cleaning agents (SCC screening).
- Corrugated (pressure) vs interlocked (protection) — stated explicitly.
- Alloy grade for core, braid and fittings — braid and fittings at least matching the core.
- Working pressure at operating temperature, for the exact DN and braid count, with derating curve.
- Static or dynamic duty — and the corresponding minimum bend radius against the routed geometry.
- End connections: flanges (EN 1092-1 / ASME B16.5), threads (G/BSPP parallel vs R/NPT tapered — not interchangeable), or hygienic (DIN 32676 Tri-Clamp / DIN 11851).
- Certificates: EN 10204 3.1/3.2, PED category, proof-test record, food-contact DoC where relevant.
- Length including movement allowance and installation tolerance.
Specification support and tested assemblies
Tubes International Capital Group fabricates corrugated stainless steel hose assemblies with welded fittings, pressure-tests every assembly and delivers the certificate package with it. Send the checklist data through the RFQ form — our engineering team confirms alloy, construction and end fittings against your medium and movement case, and flags SCC or temperature issues before they reach the plant.