To properly design a flexible metal hose assembly for a particular application, certain parameters must be determined first. Sometimes you may have a drawing with all of this information already on it but if you don’t we have a nifty way to remember what information we need to quote and fabricate your metal hose assembly. To help remember them, we have arranged them to form the acronym “S.T.A.M.P.E.D.”
The temperatures both inside and outside of the hose can have a major impact on the working pressure of the hose. As the temperature gets hotter the material gets weaker so a hose rated at 500 psi @ ambient will not reach 500 psi at 1000°F. Each alloy has its own derating factor based on temperature.
Flexible metal hose and braid is manufactured in sizes from 1/4″ up to 12″ in diameter. Typically it comes with a single layer of braid or if you need a higher pressure rating you can add a second layer of braid. Typically the smaller the hose diameter the higher the pressure it can withstand. The exact opposite happens as you get larger in diameter. The larger the diameter the lower the maximum pressure rating is.
The reason flexible metal hose assemblies are widely used in a variety of industries is because of the extreme temperature range they can perform well in. For example a cryogenic application like liquid hydrogen or oxygen transfer hoses where temperatures can get down to -320°F.
In contrast by using a flexible metal hose assembly you can reach much higher temperatures than a PTFE or rubber hose. This is because of the materials the hose is made from. Stainless steel can tolerate temperatures much higher and lower than a PTFE or rubber hose assembly.
Flexible metal core and braid comes in a variety of different alloys. Each alloy of core and braid is tailored to a specific application. Typically the core and braid comes in 321ss, 316ss, Alloy 400 (Monel) and Nickel 625. The standard braid alloy is 304 stainless steel, however this can also be substituted with 316ss, Alloy 400 and Nickel 625.
In general, 321 stainless steel is used for higher temperature applications while 316L stainless steel is used in corrosive environments. The low carbon content and the addition of molybdenum provides the protection from salt and other chemicals used in manufacturing.
The diameter of the hose and number of layers of wire braid determines the maximum allowable working pressure of a flexible metal hose. The temperature of what’s going through the hose or the environment its in can also affect the MAWP of a flexible metal hose.
For example a 1/4″ ID flexible metal hose with 2 layers of braid can handle 6000 psi working pressure while a 12″ flexible metal hose with 2 layers of braid handles 325 psi working pressure. Furthermore, if the temperature goes up past 300°F we would need to downgrade the pressure rating based on the higher temperature.