Metal hose: a guide to corrugated, braided, exotic-alloy and specialty hose

Rubber hose has limits that no compound fixes: it softens with heat, becomes brittle in cryogenic cold, burns, lets some gases permeate, and is attacked by some media whatever it is made of. Metal hose has none of those limits. It has its own — it must not be twisted, it fatigues if moved in the wrong way, and it costs more — but within them it is the only flexible connection for a great deal of process, energy and industrial gas duty.

/01How metal hose is built.

The core is a thin-walled tube formed into corrugations — usually annular, each a separate ring, for pressure and vibration; sometimes helical, a continuous spiral, for extra flexibility and full drainage. Under pressure a corrugated core extends like a bellows, so it is covered by a braid of woven wire welded to the end fittings, which restrains it and carries most of the load. Add a second or third braid and the rating rises; compress the corrugations tightly and it rises again. The details are in corrugated stainless steel hose.

/02Choosing the material.

Most metal hose is stainless: 316L for general corrosion resistance and 321 for sustained high temperature, with 304 or 316L braid, all listed from −200 to +650 °C. When the medium attacks stainless or the temperature passes its limit, the core changes alloy — Monel 400 for chlorine and hydrofluoric service, Hastelloy C276 for strong acids and hot chlorides, Inconel 625 to +815 °C, bronze for marine and non-ferrous systems. The braid needs the same thought, because it is exposed to the atmosphere; see exotic alloy metal hose.

/03Pressure.

Metal hose ratings are quoted at the smallest size and fall as the bore rises, so always ask for the figure at your size. A standard braided stainless hose covers most process duty; for hydraulic pressures, compressed and closed-pitch cores with double or triple braid reach 350 to 414 bar on our listings — see high-pressure metal hose. At room temperature a spiral rubber hose is lighter and cheaper at the same pressure; metal earns its place where heat, fire, permeation or an all-metal requirement rule rubber out.

/04PTFE: the non-metallic alternative.

Where the problem is chemistry rather than heat, a PTFE hose under a stainless braid is often the better answer: PTFE is inert to almost every medium, runs from −73 to +260 °C, and our smoothbore PTFE hose is rated to 350 bar at the smallest size. Convoluted PTFE gives a tighter bend at lower pressure. The constructions are compared in PTFE hose explained.

/05Specialty assemblies.

Several duties have assemblies built around them. Cryogenic transfer hose for LIN, LOX, argon, LNG and CO₂ is covered in cryogenic transfer hose. Chlorine transfer hose for tankers and rail loading is Monel, double braided, listed to Chlorine Institute Pamphlet 6. Steam-jacketed hose keeps asphalt, pitch and molten products flowing, with an outer jacket around the product core. Electrically heated hose does the same with a heater, including an ATEX and IECEx Zone 1 rated version for hazardous areas. And pipe loops absorb thermal expansion in pipework in a U or V shape.

/06Fire protection and guarding.

Metal hose survives fire far better than rubber, and some duties require proof of it: our Senior Flexonics Bartlett fire-safe assembly is API 6FA fire-test certified, rated 200 bar to +815 °C. Other hoses can be protected: silicone fire jackets and fire tape rated to +1,093 °C, smooth-flex stainless and galvanised hose, interlocked lock-section hose and ball-joint armour guards that stop a hose being crushed or abraded.

/07Couplings and end fittings.

Metal hose is welded to its end fittings — flanges, threaded ends, unions, sanitary and cam lock ends — in carbon steel, stainless or a matched exotic alloy. On the coupling shelf: O-seal pipe unions (1/2" to 6"), swivel joints at 35 or 200 bar, Met-O-Seal tanker couplings, the T92H dry-break quick coupling and non-valved cryogenic couplings. A union or swivel at one end is the simplest way to install a hose without twisting it.

/08Installation: how metal hose dies.

Metal hose fails at installation far more often than in service. Never twist it — torsion concentrates stress in the corrugations and can halve the hose's life. Keep movement in one plane; a hose that moves in several planes fatigues quickly. Use the dynamic bend radius, not the static one, where the hose moves; leave a straight length at each end fitting; allow the live length the maker gives for vibration — 102 mm on our S9x series. Make up the second end with a union or a floating flange so the hose hangs straight before anything is tightened.

/09Standards and certificates.

Our metal hose listings cite ISO 10380, the corrugated metal hose standard, and many list NACE MR0175 / ISO 15156 compliance for sour service and CSA B51. Industrial gas assemblies carry CGA references, the oxygen and some heated hoses UL536, and the S99Z nuclear-grade hose a CRN monogram with CSA N299.1 and N285.0. Ask for the certificate the duty requires at quotation — it can rarely be produced after the hose has shipped.