Hello,

I'm working on a project analyzing an existing system where braided metal hoses are used at tank nozzles. There's an anchor approximately 15ft from the nozzle and a braided metal hose installed axially in the pipe without offsets.

I've searched previous metal hose threads and most of those were discussing the more typical hose applications (with offsets or bends) and essentially concluded the hose is significantly less stiff than the pipe.

I feel like this is based on the assumption the hose is installed per the manufacturer recommendations. Every braided hose catalog I've seen explicitly says do not use them in situations with axial compression.

In the above scenario, is the metal hose still infinitely less stiff than pipe?

I believe it is still less stiff than the pipe however it could be damaged if displacement is not negligible.
size and temperature also need to be taken into account,
and sometimes seismic.
if the displacement on the both sides of the hose is less than the installation/fit up tolerances, it should be ok.

Flex hoses are many orders of magnitude less stiff than the pipe axially. Here's a video of me demonstrating that on a couple of 4in braided metallic flex hoses, one less of them is less stiff than the other. Metallic flex hoses are basically long expansion joints.


Yeah I'd agree that it's okay to compress it axially IF the displacement is very small. Otherwise the hose may deflect too much out of plane. And doing so will cause the pressure thrust to be taken by the anchor since the braid becomes ineffective in absorbing the force when it's compressed axially. In your case I'm guessing that the pressure is quite low since it's a tank?

Thanks for the replies.

Yeah it's a small amount of displacement but combined with a pretty stiff anchor and tank nozzle deflection, the stiff hose assumption was resulting in high forces.

I'll re-run it with an expansion joint and try to iterate the axial stiffness so it will compress slightly and hopefully reduce the loads

I don't think any flex hose manufacturer will bat an eye if we're talking about a few MM associated with installing an anchor at an almost immediate location from the flex hose, and would likely wholeheartedly prefer it as it eliminates as much piping load as possible onto their unit.

If we're talking about a typical steel nozzles on an API tank, you should have adequate load capacity with the addition of the flex hose. It's common for nozzles to not be analyzed with a properly installed flex hose (see manufacturer's recommendations).

I speculate the manufacturer's concern is that fully axially loading the hose (i.e. when the braids bend and lock against one another) will have deleterious effects on the pressure and lateral/angular displacement capacity of the hose.

Allowable loads for a given nozzle is an 8 dimensional problem (Fx, Fy, Fz, Mx, My, Mz, P, T), which sometimes can be brought down to a 6 dimensional problem (Fr, Fa, Mr, Ma, P, T) depending on symmetry, a flex hose is also the same kind of 6 dimensional problem, except where axial loading has a much faster deleterious effect on the others. (In this case, I treat forces and displacements as analogous, but also understand that they are not necessarily linear with each other.)