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Fatigue life of pipe

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lidbasky

lidbasky

Materials
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Hi Dear friends
We have pipe with outer diameter 62 mm and thikness of 2 mm. we made it by machinnig a thiker pipe with thikness of 5 mm. we machined both inner and outter face of thiker pipe. How we can test the new pipe fatigue life while it work in 120 C with 6 bar inner pressure?
Is there any standard test for estimating fatigue life of a pipe?
 
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You've got a very highly modified piece of metal.

"Standard" vibration analysis and standard tables for standard pipe will NOT be accurate - and even be misleading! -

So the only accurate way is to take your metal to a vibration analysis lab - like SouthWest Research Institute in San Antonio TX and tell them to test it for your needed number of tens of thousands of cycles at your needed load at your needed deflection and time interval. Anything less is only guessing.
 
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lidbasky (Materials)

Google: Search for ASME B31.3 APPENDIXW3-25-09.doc

also:
DOC] APPENDIX WFile Format: Microsoft Word - Quick View
This appendix addresses the fatigue evaluation of B31.3 piping subjected to cyclic ... The methodology in ASME BPV Section VIII Division 2 may be applied to ...
files.engineering.com/download.aspx?...APPENDIXW3-25-09.doc
 
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Thank to all.
Machinning of inner surface and outer surface may reduce life time of tube?
it use as air duct and inner pressure in tube is 6 bar, Is vibration analysis help us determining life time of tube under inner pressure?
 
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Geometrically we actually don't even know if its more like a pipe, a circular bar, or a cylindrical block. Even a pipe might not "act like a pipe", if its length is relatively short in relation to its diameter.

Let your acquaintances be many, but your advisors one in a thousand’ ... Book of Ecclesiasticus
 
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The length of tube is 0.3 m and outer diameter is 69 mm. It passed Hydrostatic test of vessels in pressure of 6 bar.
but we want estimate life time of tube.
 
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So like 3 times long as wide isn't a very long pipe and natural frequency probably quite high and I imagine keeping you well out of natural resonant range, resulting in a relatively long lifetime. To be sure I suppose you would want to check frequency generation by internal flow velocity and/or from any cyclic nature of attached pumping, compressors or other equipment.

Let your acquaintances be many, but your advisors one in a thousand’ ... Book of Ecclesiasticus
 
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Being that short, it seems like the end conditions (how the tube is attached at both ends,
and to what it is attached,
and how stiff both ends are,
plus the actual (expected) vibration environment that the assembly will be subjected to ...

The combination of everything is going to determine the lifetime of everything. If you decide to accept the recommended solution and test the tube, then you need to test the whole assembly, not just the tube all by itself.
 
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What sort of loading does your manufactured tube experience? From the sound of it, you should be able to calculate the static stress states fairly easily.

If your forcing frequency is well below the natural frequencies of the tube, you can use the high and low stress states to determine the fatigue life. Usually, you'll use something like a signed von Mises stress to calculate the mean stress and the stress ratio. You'll then have to find a fatigue curve for the material that you're using (at the proper temperature). The ASM Atlas of Fatigue Curves might be a good place to start.
 
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Thank you my friends for your great guidances.
Our concern about this pipe is that we machinned inner and outter surface of it and now we dont know how to test it and according to wich standard. I study APPENDIXW3-25-09 and DNV-RP-C203 but I did not find method for testing fatigue life of tube or pipe. If it is possible tell me the standard that explain procedure for fatigue testing of tube.
 
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As we attempted to explain above, it is not only the shape that you must consider.

Let your acquaintances be many, but your advisors one in a thousand’ ... Book of Ecclesiasticus
 
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