Stress Ratio in hydrotest

Dear Mandeep, I have the following query:

As per code, hydro test shall be 1.3*MAWP(or)MAP(or)DP*stress ratio.OK

Now, This stress ratio is ratio of {allowable stress @ amb temp / allowable stress @ design temp)of pressure components such as shell, dish ends, nozzles, their flanges & to be precise also of nozzle bolting.

But as all of us know that at elevated temperature allowable stress would decrease.

in PVelite, I have observed that it doesn't calculates the stress ratio of nozzle bolting.

& as per my knowledge, it should calculate the bolting stress ratio.

2) My suggestion to PVelite is that pvelite to show the additional report wherein allowable stress @ amb temp, allowable stress @ design temp, thier ratio shall be shown in expanded form. Please consider the same.

There is an interpretation VIII -1-83-260, which states that bolt stress ratio of the calculated flanges should be considered.

This is not required for the std. flanges, which most of the time the nozzle flanges are.

Dear Mandeep,

can you please send me this interpretation (VIII-1-83-260) on my mail ID

MANISHSHUKLA@LTCIS.LTINDIA.COM

i will be obliged for the response.


Regards,
Manish Shukla
L&T-Chiyoda Limited

Dear Manish,

Here is the Interpretation: VIII-1-83-260

Question: A forged vessel has a seamless shell and two bolted flat heads. Under the provisions of UG-99(b) in Section VIII, Division 1, may the ratio (S test temperatures/S design temperature) for the bolting material be used if it results in the lowest ratio for the material of which the vessel is constructed?

Reply: Yes.

Thank you very much for your support

I am interested with HT over-stress check, but with subject on nozzles.

We knew PVElite published check result on HT over-stress for major elements like head and shell under internal pressure calculation report.

Due to calculation steps and max/min judgement in concluding nozzle neck thickness (UG-45) and adequate reinforcement (UG-37), should be rather difficult to reverse check the nozzle be over-stressed at HT pressure & temperature. Is this the reason PVElite did not publish HT-overstress check on nozzle calculation reports?

Due to the mentioned reason, I feel design engineers have to provide sufficient thickness and reinforcement for nozzles with capabality (MAWP) > shell/head. Only when nozzles are stronger than head/shell, then no worry on over-stressing nozzles during HT. This might be be the reason where some project specifications restricted nozzles from being the governing elements of overall MAWP.

Coade's opinion on above personal view are welcome.

Dear Mandeep,

Can PVElite do stress check on nozzles during Hydrotest, just like head/shell?

Thank you!

Dear SK,

Your first post illustrates the difficulties associated with trying to check nozzles for hydrotest case. Another important aspect is what allowables should be used for the various checks for the nozzle.

If you computed hydrotest pressure as 1.3 * design pressure or 1.3 * MAWP then the equipment should be ok during hydrotest test. This is just a function of the factor of safety built in to code allowables.

Also note that, ASME Sec. VIII Div. 1 code does not explicitly state that you have perform the calculation under hydrotest condition. Neither does it prescribe the allowables for HT case.

But, I think a reasonable approach is to check shells and heads under hydrotest condition and making sure the nozzle does not control the MAWP of whole vessel (specially if you choose 1.3* MAWP as HT pressure).