Jacket Hydrotest Pressure

[Rahulvaland]

Dear all,

I am working on one shell & tube heat exchanger (TEMA Type : BKM )

channel side is steam jacketed as per ASME Sec.VIII.Div.1 Appendix-9 Type-2 jacket.

Channel Shell MAEP is governing Jacket MAP.Client Specification requires hydrotest pressure as per UG-99(C).

If we multiply 1.3 * Inner shell MAEP than that component will fail.

Incase of internal hydrotest we can go for 0.9*Yield stress.

What about value of Compressice stress B from external pressure chart.Does code/specification permits this.

What to be done in this situation....Please share your views.

 

[fegenbush]

Compressive failure is generally controlled by geometry rather than material strength. The value of the compressive stress from the chart should not be modified for hydrotest or you will risk collapsing tubes. The answer is either shorter or thicker tubes.

If my assessment of your question is incorrect, please restate and I will take another attempt.

 

[Rahulvaland]

Put it in simple way,

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 than 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.

I found one software programe does it based on reference of code guidebook,Jaward & farr.It takes yield stress = 2*B factor

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

 

[prex]

I do not understand why you state "...then that inner shell will fail".
B factors include, of course, a factor of safety with respect to theoretical buckling pressure, that I believe is nearly 3 (easy to determine by comparison with theoretical formulae from Roark or other texts). So at 1.3*MAEP your shell should not fail.

prex
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[vesselfab]

We design our inner shells with external pressure induced by the jacket.

we test jacket at 1.3 X MAWP jacket.

we have never had the problem you are encountering with failure.

 

[Rahulvaland]

Dear Vesselfab,

We have design inner vessel considering external design pressure of jacket + FV in inner shell.

But that is design case.My concern is with hydrotest case that is also UG-99(c) not UG-99(b).

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.

 

[vpl]

rahulvand,

What Code are you building this to? Generally that's something that is decided before you start the design not afterwards.

Patricia Lougheed

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[Rahulvaland]

@vpl,

ASME Sec.VIII Div.1 Edition 2010 Add.2011

I think it is understood from the clauses refered in my query.