Considerations for Duplex or Steam Jacketed Hoses

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End users sometimes have requirements to maintain media at an elevated or cryogenic temperature while also needing the flexibility and corrosion resistance of a flexible metal hose. To achieve both aims, a Duplex or Jacketed Assembly is an option to consider.

What is a jacketed hose?

A jacketed assembly is a hose within a hose. Hot or cold media flowing through the outer hose affects the temperature of flow media within the inner hose. In the case of a Steam Jacketed Hose, steam flows through the outer hose to keep flow media within the inner hose hot. This is necessary when working with media that solidifies at room temperature.

The concept applies when keeping flow media cold as well, but in this scenario we would design a vacuum jacketed hose.

Jacket hoses are also a used when containment of the media within the inner hose is critical.

Pressure difference between inner and outer hoses

With two hoses and two kinds of flow media, there’s potential for a pressure differential.

The consequence of building an assembly with such a difference in pressures could result in buckling of the inner hose. This could then lead to failure. Additional testing and analysis is needed when designing duplex or steam jacketed hoses. We recommend designers avoid a scenario where the pressure of the outer hose exceeds that of the inner hose.

Beyond concerns around buckling, if the inner hose has a higher internal pressure how can we be sure it will elongate and bring the braid into tension? This is critical as the braid’s primary function is that of pressure carrier.

If the pressure of the inner hose should exceed that of the outer hose, couldn’t the outer hose be stronger structurally so that the force needed to elongate it will be higher than the force exerted on it by the internal pressure of the inner hose?

A critical assumption for any catalog pressure rating for braided metal hose is that the hose must be able to elongate enough to put the external braid wires into tension. This will not happen if there is net external pressure.

Please see drawing below that demonstrates the standard design concepts of a steam jacketed hose assembly.

Please contact us if you have further interest in this topic.

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