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.
