Braided stainless steel hose failure
 

I'm sure most of you have heard the stories about braided stainless steel brake hoses failing.
The original design was a hose with the braided stainless wrapped around it. problem was, chaffing. the braided stainless tended to chafe and wear through the hose.
One fix was to wrap the hose with a teflon sheath and then put the braid over that. it worked.

Fast forward to today:
We have a couple of pratt and Whitney jet engines at work we use for co-generation. they're old aero-derivative style, similar to what they put in the F-104 starfighters. Yes, they are that old. Been rebuilt a zillion times.

We recently experienced a failure on the main lube oil pump discharge hose. then another a couple months later. Weird. Then a third failure.
That's when I was called in.
I asked some basic questions and was told the center hose is made of 304 stainless and has "pinhole leaks".

I called BS. Pinholes would be indicitive of either a product quality issue (not on three consecutive hoses after 2 months) or chemical attack. There are no chemicals anywhere near those hoses that would atack 304.
I said it sounds like the hoses are chaffing and wearing holes in the tube.
They looked at me like i was a nutjob. "Stainless steel hoses are supposed to last forever" is what they said.
Well, here's a close-up of the center tube with the braided stainless stripped away.
Failure was due to crappy design/application of the hose and too high of pressure pulsation from the pump (positive displacement screw pump). which caused abnormal chaffing. The severe wear was on the outside radius of a bend in the hose.
This is what happens when a maintenance supervisor decides how to fix something without a PITA engineer studying it first.


http://forums.pelicanparts.com/uploa...1280246815.jpg
http://forums.pelicanparts.com/uploa...1280246929.jpg

A hose with ridges covered in steel braid? Even I could understand that friction would be a problem!

What type of oil are you running in it? Mobil Jet 2 or 2380? Hope its not running skydrol through it...

Mobil jet 2. Stinks.

The problem stemmed from the fact that no one involved realized how the hose was internally constructed or what kinds of problems that might lead to.
A maintenance supervisor went to the local hose shop and had some hoses made up, evidently with whatever they had available. No study of contruction or compatibility or proper application. No consulitng with engineers, no consulting with experts. As long as it was rated for the pressure and fit.
"A hose is a hose".

We have rules against that.

That's not an aircraft hose, might be a steel braided hose but not FAA/PMA approved. Looks like a vacuum type or low pressure high flex hose. What is the ID of that?

1 1/2"

I had one fail on my old 280Z so they do fail. Probably more then rubber hoses.

Try Aeroquip hose. Im sure it is available like up to 21/2" Good to 3000 psi and looks cool. Any hose shop, like Parker, can hook you up.