Shear stress at the wall of a rubber hose caused by gas flow? 1

[enrjdean]

Hi all
I have been given the task of sizing a rubber gas flare hose. I've managed to do the sizing, and had a look at the pressure drop across the hose with which I'm quite happy. However, one of the other guys in the office said I should have a look at the shear stress at the wall to see if the lining can cope. With the media being gas its kinda stumped me, in my head, gas isn't highly viscous so it wouldn't really produce much of a shear stress at the wall?

Am I wrong? Most of the calculations I've looked at seem to be for liquids, I dont seem to be able to find one relating to gas? Is the shear stress caused by gas flow in a pipe deemed negligable?

Any thoughts or help much appreciated!

James

 

[zdas04]

Short answer is "yes it is negligible". I've had to do erosion calcs on many gas flows over the years and below around 10,000 psig (and near sonic velocity at that pressure) I can't get enough shear force to erode the passivisation layer off of steel. Delaminating rubber hose is about the same magnitude of shear as removing the passivisation layer from steel.

I would be concerned about the reaction of the hose to the temperature of the flare stack, but I'm sure from the tone of your question that you have evaluated that as well.

David

 

[enrjdean]

Your a star David! Thanks!