ASME VIII-1 VS PED Test Pressure Calculation: Material allowable stresses 1

[FPPE]

thread794-136321

Hi,
I would like to come back to the discussion in the thread mentioned above.
I believe, like JohnGP, that since the PED is not a design code, it is necessary to use the allowables given in the ASME, even though allowables are defined in the PED.

Section 7.4 of PED says:

For pressure vessels, the hydrostatic test pressure referred to in point 3.2.2 shall be no less than either of the following:

— that corresponding to the maximum loading to which the pressure equipment may be subject in service taking into account its maximum allowable pressure and its maximum allowable temperature, multiplied by the coefficient 1,25,
— the maximum allowable pressure multiplied by the coefficient 1,43, whichever is the greater.

In this section, reference is not made to the allowables to be used, but only to the pressures that the vessel can withstand (which can be evaluated by calculation, in this case ASME).
The first equation given in section 7.4 is in my opinion the same as in UG-99(b):

1.3*(MAWP or design pressure)*LSR

unless for the PED the MAWP is always Design Pressure and of course the coefficient 1.25 instead of 1.3.

In any case (it has never occurred to me otherwise) for the PED the governing equation is always the second one, so this question of allowable stresses is only a question of the correctness of the calculation in the mechanical calculation report, but I think it is necessary to clarify definitively.

Thanks in advance

 

[XL83NL]

What exactly is your question?

What is do is the following. Unless the code or PED prohibits it (which it doesnt), you’re allowed to go beyond a test pressure that’s higher than calculated. Provided one doesn’t overstress the vessel past yield.

Now, take all equations you need to satisfy, and find the answer that meets all requirements. PVElite does this for example for vessels that need to meet PED as well.

Now, if you need to know what the actual interpretation is of PED 7.4 ‘maximum loading to which the pressure equipment may be subject in service taking into account its maximum allowable pressure and its maximum allowable temperature’, take EN13445 and look up how that standards fulfills this PED requirement. Look up Annex ZA of EN13445-5, table ZA.1, which then refers to 3.2.2 of the PED and 10.2.3 of EN13445-5.

The above will give you all the answers and provide sufficient info to assist you in your engineering judgement to come up with a solution.

Huub
- You never get what you expect, you only get what you inspect.

 

[FPPE]

Thank you XL83NL, following this route, it seems that the EN allowables must be taken into account for the calculation of the test pressure in accordance with the PED.

The thing that continues to be unclear to me, or rather that does not convince me 100%, is that these guides are written on the EN, which consider itself a 'direct link to the PED'. This may well be true, but I cannot find any confirmation of this in the PED for the specific case of pressure test calculation.

Let me explain, after what you made me read, I believe more and more that the paragraph of the PED concerning test pressure can be interpreted in different ways.
The only thing I would like to be clear about is whether using ASME II allowables is prohibited or not, because the Notified Bodies have never refuted our calculations for PED test pressure with ASME allowables.

Is this a lack of preparation on that argument of several NoBo inspectors?

 

[XL83NL]

Well, they’re Annex I para 7.1.1 or 7.1.2 about allowable stresses. That may throw in some requirements/restrictions for certain cases and certain materials, maybe, but I can’t see how that will affect test pressure. Write out where (and have the nobo spell it out) where exactly you don’t meet the PED and it’s ESR’s.
On the website of the EU, you can download the official journal that links all harmonised standards to the PED.

Huub
- You never get what you expect, you only get what you inspect.

 

[r6155]

Be careful. In some circumstances, UG-99(c), I suggest Acoustic Emission Examination during hydrostatic testing. See ASME V.

Regards

 

[FPPE]

r6155, sorry but I didn't understand your answer.

XXL83NL, so are you saying that by using the allowable stresses of ASME II you are still implicitly complying with PED's Essential Safety Requirements? So when calculating a vessel according to ASME, by calculating the PED test pressure (referring to the first equation of PED test pressure of course, where the allowable ratio is present) you are not committing any illegality, right?

 

[r6155]

@ FPPE
Please read ASME VIII Div 1 2021 UG-99(c)
Hydrostatic pressure test also is dangerous. See “Case 102: Use caution when specifying a safe hydrotesting distance”, Hydrocarbon Processing magazine August 2018.

Acoustic Emission test may be used as a complementary measure for hydrostatic test.

You can pressure test as high as you like, if the inspector agrees. Both should be accountable to the user.
Try to do a pressure test that doesn't change from NDE to DE (destructive examination)

No manufacturer is interested in pressure testing beyond the UG-99(c) calculation: this is an unnecessary risk. If the user insists, UG-101 should be used.

Regards

 

[XL83NL]

XXL83NL, so are you saying that by using the allowable stresses of ASME II you are still implicitly complying with PED's Essential Safety Requirements? So when calculating a vessel according to ASME, by calculating the PED test pressure (referring to the first equation of PED test pressure of course, where the allowable ratio is present) you are not committing any illegality, right?

Thats difficult to say just like that, as there are a lot of cases/situations possible that cant be addressed by one denominator. All Im saying is that one doesnt rule out the other. You can do the calcs per ASME II allowables, and back check if those meet PED. IF they do, OK: go ahead with calculating the ASME hydrotest pressures.
If they dont, you can still calc the ASME hydrotest pressure, but may need to increase the PED required thickness. It also depends on the specific material; e.g. A312 TP 316 will suffice (35% or greater elong.), but A182-F316 does not (30%). Now, you may look up the results per MTR, and then even get away for F316. You may also do this by first setting the PMA requirements for A182-F316 to > 35% elongation.

Point is, calculating the thickness doesnt relate per se to the hydrotest pressure from a PED point of view (it gets, of course, different when the hydrotest pressure is based on the LSR and MAWP).

Huub
- You never get what you expect, you only get what you inspect.

 

[FPPE]

Thank you very much XL83NL and r6155!