Convoluted stainless steel flexible hose

• Aug 27, 2002

• #2

mcguire

Materials

Nov 2, 2001

1,086

US

There are reasons besides corrosion for limited life in stainless components. Braids abrade themselves, creep under stress, even fatigue. The OEM should have some knowledge of potential failure modes. If this is an ISO 9001 supplier, the potential failure modes should be spelled out by him and available for you to audit.

 

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• Aug 27, 2002

• #3

Kenneth

Aerospace

Jun 12, 2001

334

US

"If this is an ISO 9001 supplier, the potential failure modes should be spelled out by him and available for you to audit."

?

 

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• Sep 3, 2002

• #4

mcguire

Materials

Nov 2, 2001

1,086

US

Kenneth
Many manufacturers have Their quality control systems certified to the ISO standard number 9001. It is a stringent system that among other things requires a designer to document how his product could conceivably fail in service and what testing he has done to make sure it won't. The standard further stipulates that customers must be given access to these records. No more caveat emptor.

 

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• Sep 11, 2002

• #5

rhc

Materials

Jul 29, 2002

25

AU

Stainless steel if continually worked hard becomes stiff & brittle. We have tried ss springs but they did'nt last as long & were unpredictable. We went back to conventional spring steel.

 

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• May 27, 2003

• #6

JOM

Chemical

Oct 16, 2001

232

AU

engsup,

I know of a failure of flexible fuel lines on a ship that resulted in a disatrous fire in 1998. The cause was fatigue from pressure pulses from the fuel pump.

Do you want more info?

John.

Cheers,
John.

 

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• May 27, 2003

• #7

boo1

Mechanical

Oct 31, 2001

2,129

US

Yes this is common for SST braded flex lines. Studies we did showed additional supports, and reducing the bend radius increased service life.

 

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• May 28, 2003

• #8

JOM

Chemical

Oct 16, 2001

232

AU

Here's a report on a flexible fuel hose failure. The hose needed periodic replacement. The full report is available.


28 June 1999
D07/99

RUPTURED FLEXIBLE FUEL HOSE DISABLES RESEARCH SHIP

A worn flexible fuel hose caused a fire aboard the Australian supply ship Aurora Australis en route to the Antarctic, according to a report released today.

more...

http://www.atsb.gov.au/marine/incident/incident_detail.cfm?ID=143

The other important incident was the Westralia fire in 1998. This is an Australian Navy supply ship. The engines had 56 short s/s flexible fuel lines installed. After less than 50 hours engine time, one of these failed due to fatigue and two others showed signs of failure. There was a fire and four sailors died.

There is a picture of the failed hose - I'll try to grab it.

In both incidents, the vibration from positive displacement fuel pumps was thought to be the cause of cyclic stresses.

Cheers,
John.

 

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• May 28, 2003

• #9

TEV

Materials

Oct 31, 2002

100

US

Although it looks like fatigue is the issue in this post, let me add another story from the annals of experience.

I was involved in analyzing an incident in which hose reinforced with stainless steel braid failed at the connector. It was learned that the connectors were mounted onto the hose by peeling the outer cover back to reveal the braiding, lubricating the end with common hand soap (!), and sliding the connection on, which was secured by swaging. Well, the soap was found to contain 2000 ppm chlorides, and the braiding was highly strain hardened, so guess what? Chloride stress corrosion failure! No surprise.

Moral of story - avoid mechanical engineers making decisions that affect material performance. No offense intended to mechanical engineers, as I would consult them for assistance in their area, but I would request that they reciprocate.

 

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• May 29, 2003

• #10

JOM

Chemical

Oct 16, 2001

232

AU

TEV,

Apart from the soap, is that the normal procedure for fitting the connectors?

Cheers,
John.

 

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• May 29, 2003

• #11

TEV

Materials

Oct 31, 2002

100

US

JOM:

It depends on the design of both the fitting and the hose, but for some of the high strength hose-fitting applications, you want the connector to be tied to the strengthening braiding of the hose. But here I go, straying into the mechanical engineer's realm! I forgot to mention that the joint was recovered with a polymeric shield after swaging the fitting on, but the chloride in the soap was captured in the area of the braiding.

 

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• May 29, 2003

• #12

monkeydog

Aerospace

Jul 15, 2002

825

US

TEV Said: "I forgot to mention that the joint was recovered with a polymeric shield after swaging the fitting on, but the chloride in the soap was captured in the area of the braiding."

And all the experts collectively Said: "AHHHHH"

 

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