Corrugated stainless steel hose: core, braid and the pressure each layer adds

Where a rubber hose meets its limits — heat, cryogenic cold, aggressive media, fire risk, permeation — the answer is usually metal. A corrugated stainless hose is two parts doing two jobs: a thin corrugated core that bends and keeps the medium in, and a braid that stops the core stretching like a spring under pressure. Almost everything about choosing one follows from that split.

/01Core and braid.

Pressurise an unbraided corrugated core and it tries to extend, the way a bellows does. The braid — woven stainless wire over the core, welded to the end fittings — stops that, and in doing so carries most of the pressure load. That is why the same core is rated so differently with and without braid. On our Thorburn S9x series, the 316L core is rated up to 13 bar unbraided (S91), 146 bar with a single 304 braid (S92) and 215 bar with a double braid (S92Z).

/02316L or 321, 304 or 316L braid.

Our stainless corrugated hoses are built on 316L or 321 cores. 316L is the general corrosion-resistant choice; 321 is titanium-stabilised stainless, chosen for sustained high-temperature service. The S95 and S96 series mirror S91 and S92 with a 321 core. Braid is 304 as standard and 316L on the premium S93 series, for corrosive atmospheres where the braid is exposed. All are listed from −200 to +650 °C. Where stainless itself is not enough — chlorine, hot chlorides, strong acids — the next step is an exotic alloy core.

/03Annular or helical.

Most metal hose is annular: each corrugation is a separate ring. It flexes well, resists pressure and vibration, and is the norm for process and pressure service. Helical corrugations spiral along the hose like a thread; the hose is extra-flexible and drains fully, which suits low-pressure, frequently moved or drainable runs — our Thorburn S65 Extra Flex is helical 321 with a 304 braid, up to 35 bar, DN25 to DN250. Commercial grades such as our Adflex (up to 100 bar, DN6 to DN300) and the close-pitch Hyparflex (triple braid, up to 175 bar) sit alongside.

/04Installing metal hose.

Metal hose fails at the installation more often than in service. It must never be twisted: torsion on a corrugated core concentrates stress at the corrugations and fatigues them quickly, so make up the second end with the hose relaxed, using a union or a floating flange. Keep movement in one plane, respect the dynamic bend radius rather than the static one when the hose moves, and do not let it bend sharply at the end fitting. A hose that absorbs vibration needs a live length — the S91, S95 and S96 listings give 102 mm.