What’s Inside a Flexible Metal Hose?

By: Abby Svitana | On: February 24, 2020
corrugated metal flex hoses

What Makes Up a Flexible Metal Hose?

In order to understand flexible metal hose assemblies and how they serve various applications it’s best to review their anatomy. In its simplest form, a metal hose is made of four basic components:

  • Corrugated tubing
  • Braid
  • Braid collars
  • End-fittings

Separately, these parts are really quite simple. However, they can be customized to form a variety of configurations, enabling flexible metal hoses to be an optimal solution in a number of industries.  Let’s examine each of these components individually and discuss how they all work together to create value.

Corrugated metal flex hose

Corrugated Tubing

The corrugated tubing is the core component of a flexible metal hose. Not only does it comprise the bulk of an assembly, but it also plays a part in key value-added attributes of the assembly, such as corrosion resistance, pressure rating, and flexibility.

Corrosion Resistance

Corrosion resistance is simply a matter of selecting the correct alloy for the media that is being conveyed. For most applications, 321 stainless steel provides sufficient corrosion resistance. If additional chemical resistance is needed, 316 stainless steel can be used, which contains more nickel and other alloying elements to increase chemical resistance. Chlorine transfer applications require the highest degree of corrosion resistance. For chlorine and other highly-critical applications, C276 may be the best choice.

Pressure Rating

Pressure rating (also referred to as “maximum allowable working pressure” or “MAWP”) is the term use to express the ability of a hose to handle internal pressure. At Hose Master, the pressure ratings of our hose is determined by conducting various pressure testing in our in-house Product Analysis Lab.

The pressure rating that “creates value” for an assembly depends on the application in which the assembly is going to be used. For many standard applications, a hose with a lower pressure rating can be used, whereas more critical applications may demand the use of a hose that can withstand higher pressures.

Flexibility
flexible metal hose

The corrugation geometry aids in a hose’s ability to flex.

Flexibility can mean different things to different people. To some, it may refer to a hose’s ability to be bent into a tight radius. To others, it may mean a hose has a high cycle life. Or, it may mean that a hose will bend easily without exerting high spring forces on the surrounding equipment.  Fortunately, there is some flexibility allowed in this definition thanks to Hose Master’s proprietary forming processes, which create metal hose that provides all three of these qualities.

For corrugated metal hose, flexibility is expressed by the “minimum dynamic bend radius” (MDBR), which is derived through testing in our in-house lab. Depending on the application, a larger MDBR may be acceptable or a tighter MDBR may be required.  If an application requires a tighter MDBR, then a close-pitched hose would provide a valuable solution. Close-pitched hoses feature more corrugations per foot than standard hose, which distributes the bending stresses over more corrugations and allows the hose to be bent more tightly.

Braid

braided metal hose

A high-coverage braid package can help add to a hose assembly’s cycle life.

The second component of metal hoses is the braid. Along with hose selection, the braid contributes to an assembly’s ability to withstand high pressures.

There are multiple factors that can contribute to the functionality of the braid, such as the wire diameter, the number of wires per carrier, the number of carriers on the braiding machine and the percentage of braid coverage. The pressure rating of a hose may also be increased by adding additional layers of braid or using braided braid. Proper braid design has a significant effect on the working pressure and cycle life of the hose. Utilizing a braid package with a high-percentage braid coverage that is braided directly onto the hose helps to ensure that the braid is well-secured on the hose, protecting the assembly from potential deformation and ensuring maximum cycle life.

Braid Collars

While only accounting for a small portion of a hose assembly, the braid collars have an important role. Braid collars serve to join the inner corrugated hose and the braid together during the cap welding process, in which a TIG weld joins the hose, braid and braid collar together into the cap weld bead. This cap weld needs to be perfect, as it will be the base for the subsequent attachment weld and is the connection point holding all of the components of the hose together.

Along with helping join the hose components together, the braid collars also serve to protect and isolate the corrugations near the cap weld from any movement. After the cap welding process, these corrugations are now a “heat-affected zone” and are thus unable to functionally cycle with the rest of the hose. The braid collars ensure that any bending stresses are properly distributed over the right corrugations, preserving the cycle life of the assembly.

End-Fittings

fittings for flexible metal hoses

A small sampling of the fittings able to be welded to metal hoses.

The final component added to an assembly is the fittings. There are a lot of options available when it comes to fittings selections, allowing flexible metal hose assemblies to be customized to fit into a variety of applications. Therefore, it is important that the fittings selected fit the needs of the application. Be sure to verify the size, alloy, and pressure requirements of an application before making a definitive fittings selection.

Designing a Flexible Metal Hose Assembly: Creating Value

Ultimately, what creates value for a flexible metal hose assembly comes down to the specific demands of each application.  No matter the complexity, Hose Master’s skilled engineering staff and dedicated customer support personnel are able to supply not only exceptional quality in each assembly, but stellar service, resulting in the greatest value for our customers. For more information on Hose Master’s solutions contact us at (216)-481-2020 or visit us online and we’d be happy to assist you.

 

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