SELECTION, DESIGN & INSTALLATION NOTES

Selection of the proper metal hose assembly for any given application should take into account the following seven considerations. They are known by the acronym STAMPED  

S    Size of hose considering existing piping and flow requirements.  

T    Temperature of media, hose and alloy ratings, temperature/pressure correction factors.  

A    Type of alloy (stainless, monel, etc.) for proper corrosion resistance, temperature,        motion and pressure.

M   Motion and its frequency.  

P   Pressure- constant, pulsing, shock.  

E   End fittings- compatibility with medium and pressure.  

D   Developed assembly length, live length and overall length.

There are many design concerns with respect to metal hose. The following examples are merely representative of some of these.

  1. In pulsating or shock applications, the assembly can have no loose or slack braid after installation, or failure can result.

  2. Unbraided assemblies should be used for vacuum or exhaust applications only.

  3. Applications that involve axial compression or expansion require the use of expansion joints, not corrugated metal hose assemblies.

  4. Flow velocity can cause metal hose failure. If flow velocity exceeds 150 ft/sec. for a gas or 75 ft/sec. for a liquid a metal interlocked liner should be welded into the corrugated assembly (100 ft/sec. gas and 50 ft/sec. liquid in unbraided assemblies). If the assembly is to be installed in a bent position, reduce the preceding values as follows: 50% for a 90 degree bend, 25% for a 45 degree bend, etc.. If velocity exceeds these figures match the liner size to the conveying pipe size and use a larger metal hose assembly.

  5. Motion definitions have been given in the glossary. Some general rules for extending hose life in applications involving motion are as follows: Vibration- for normal vibration make sure the live length of the assembly matches what is called for in the specification charts for vibration applications. For strong vibration applications it is recommended that Double Wall Hose be used. To calculate live length for various classes of motion, use the formula shown at the end of this section. Caution, corrugated metal hose assemblies give no indication when their minimum bend radii are being exceeded. In applications of mechanical motion proper design can assure that minimum bend requirements are not being exceeded. This is not the case in applications involving manual handling.

  6. End fittings should be ordered with fluid compatibility and pressure capacity in mind. Just because the hose, braid, and weld of a 1/2" assembly can withstand 1425 psi operating pressure, if the end fittings are only 150# female unions, the unions' maximum pressure becomes the limiting factor for the entire assembly.

  7. Torque, or twisting, of metal hose assemblies causes failure. Care should be taken to avoid torquing the hose during installation. The motions that an assembly is subjected to must always be in the same plane.

  8. Never apply a wrench to weld collar or the braided hose section of an assembly, as failure will occur, or at a minimum, life expectancy will be reduced significantly.

  9. Use the proper length hose to avoid sharp bends or stresses. Where these occur, use 90 degrees or 45 degrees fittings to protect the assembly. Never compress an assembly to fit, as this will loosen the braid and cause pressure failure. Never stretch an assembly to fit as this will cause the cougations to wear against the braid and cause failure.

  10. Avoid abrasion as failure can result from braid ends tearing. Contact our office for various covers such as Spring Guards, Armor Guards, Integral Rubber Covers, PVC covers, Fire Jackets, Fire Sleeves, etc..

  11. Never use hose assemblies to support piping weight.

  12. Never exceed the recommended pressure rating of the assembly as catastrophic failure can result.

  13. Clean hoses after use. Corrosive agents may solidify in corrugations and cause failure.

  14. Store hose assemblies properly so that they are protected and supported.

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