In high-velocity applications, the media impacts the corrugation valleys inside of corrugated metal hoses and expansion joints, resulting in resonant vibration. This makes them susceptible to fatigue and premature assembly failure. One way to prevent this is to add a flow liner to the assembly. Today, we will review the conditions when a flow liner should be considered.

The minimum flow velocity (measured in feet per second) at which a liner should be used depends on several variables, including: a) the media conveyed, b) any bends in the assembly, and c) whether the assembly is braided or unbraided. According to the NAHAD Hose Safety Institute Handbook, a liner should be added to a braided corrugated assembly (if it is installed in a straight installation conveying a dry gas) for any flow velocity exceeding 150 feet per second. However, the flow velocity at which a liner is recommended drops significantly with any changes in the above variables. For example, if an unbraided hose is conveying liquids while bent at a 180-degree angle, the velocity requiring a flow liner drops to 12 feet per second.

Metal expansion joints also use flow liners, typically made from a rigid tube that is inserted into one or both ends of the assembly. These liners can be permanently attached by welding them into the assembly, or they can be removable for easy cleaning or replacement. These liners must be carefully designed and installed so they do not hinder the expansion joints designed movements. According to the Expansion Joint Manufacturer’s Association (EJMA), the following guidelines should be followed in order to determine of a flow liner is required in an expansion joint:

For air, steam, and other gases:

• Up through 6” Diameter: 4 feet per second per inch of ID of the expansion joint
• Over 6” ID: Any velocity exceeding 25 feet per second

For water and other liquids:

• Up through 6” Diameter: 2 feet per second per inch of ID of the expansion joint
• Over 6” ID: Any velocity exceeding 10 feet per second

Your customer may provide a flow volume - gallons per minute (GPM), pounds of steam per hour (lb/h), standard cubic feet per minute (SCFM), etc. - rather than a flow velocity in feet per second. These volumetric flow rates should be converted to linear velocity so the above charts can be consulted. The manufacturer can assist with these conversions.

Flow liners may also be used to protect the corrugations from excessive wear when transferring abrasive media. By preventing erosion of the hose material, the liner acts to extend hose life without restricting the bend radius of the corrugated hose it is protecting. Because stripwound hose liners are not pressure-tight by themselves, special considerations must be taken into account if special cleaning or testing is required for a lined metal hose assembly. Again, the manufacturer can offer valuable insight in these circumstances.

Image: Hose Master metal hose assembly with liner

A properly designed and installed flow liner can greatly increase the life of a hose or expansion joint, providing a better value to the customer. Contact Hose Master today if you have a high-velocity application and need assistance requesting a quote. 

Still have questions? Reach out to Hose Master today and let our team of experts help you design the safest and most reliable assembly for your application.