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Associate

Join Date: Sep 2008
Location: Vadodara,India
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Jacketed Hydrotest Pressure

08/22/2012 5:16 AM

Dear All,

During internal pressure hydrotest we take advantage of allowable stress = 0.9 * yield stress.

I have one case wehrein jacket chamber MAP is limited by MAEP of inner shell.

now if we do Hydrotest pressure as per UG-99(c) = 1.3*MAEP that inner shell will fail.

Does any body having any reference to increase stress value B from external pressure chart(CS-2) to 0.9*Yield stress for the hydrotest.

Note : Code is silent about external pressure hydrotest.Refer code interpretation : VIII-82-57

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Guru
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#1

Re: Jacketed Hydrotest Pressure

08/22/2012 11:52 AM

Logically, the pressure test has to based upon the pressure rating of the inner shell, then, the lower of the two ratings. After all, why would anyone want to press the vessel to failure <rhetorical question NNTR>?

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Associate

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Location: Vadodara,India
Posts: 40
#2
In reply to #1

Re: Jacketed Hydrotest Pressure

08/23/2012 2:54 AM

Concern part is inner shell MAEP.

Now when evaluating jacket side MAP/MAWP to determine hydrotest pressure we need to consider inner vessel's components MAEP/MAEWP because that are also part of pressure chamber.Correct me If I am wrong.we need to consider lowest value.

Now In my case this is limited by inner shell's MAEP - maximum allowable external pressure calculated with new & cold condition.

Now what I understand is MAEP is maximum external pressure which we find by using Factor B external pressure chart is the maximum pressure that component can withstand.But while doing hydro test we are going 1.3 times higher than this MAEP.If we consider same factor B than obviously component will fail.

As we know this external pressure chart is stress strain diagram.where factor B - stress,factor A - strain.

Does this factor B can be taken as 90% yield.& than recalculated MAEP which will be higher compare to the jacket hydrotest pressure means it will not fail in hydrotest.

One of software programe is taking basis of UG-28(2)Step-3 & taking Yield stress as = 2 * B factor for hydrotest check.But UG-28(2)step-3 is applicable for Do/t < 10 means thick cylinders.

As ASME Sec.VII Div.1 doesnot gives guideline to evaluate hydro test induced stress only div.2 says 0.95*yield but this is generally followed when we are doing internal hydrotest but in above mentioned jacketed vessel case hydrotest pressure will be applied externally.

Any body having any basis of any reference book/code/specification please share.

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Guru
Engineering Fields - Mechanical Engineering - New Member India - Member - New Member

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#3
In reply to #2

Re: Jacketed Hydrotest Pressure

08/23/2012 11:49 AM

Contact Abdel Halim Galala or search here for pressure vessel, design, testing.

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Associate

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Location: Vadodara,India
Posts: 40
#4
In reply to #3

Re: Jacketed Hydrotest Pressure

08/23/2012 11:11 PM

Already send him mail on CR4.....I know he is expert in ASME code issues....

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