CAN WE CONSIDERED VESSEL MAWP VALUE FROM FLANGE MAWP REDUCTED PRESSURE VALUE ?

[staticmh]

Hi Folks,

I'm designing an vessel (by manual calculation) which is limited by the standard flange. i'll draw an picture of case below with the major and minor component calculated MAWP values. As everybody knows the MAWP shall be always considered the lowest values among all the major and minor component pressure concluded value.

Let say Major component & Minor component MAWP is depicted below.

Major component
Component value MAWP(Corroded)(Mpa)
1- LEFT Head = 2.5855 Mpa
2- Shell-1 = 2.9933 Mpa
3- Shell-2 = 2.9933 Mpa
4- RIGHT Head = 2.5855 Mpa

Minor Component : Nozzle Flange MAWP Results: (N/mm² & °C)
Nozzle-3-300# = 4.39 Mpa
Nozzle-2-300# = 4.39 Mpa
Nozzle-4-300# = 4.39 Mpa
Nozzle-2-300# = 4.39 Mpa
Nozzle-3-300# = 4.39 Mpa
Nozzle-2-300# = 4.39 Mpa
Nozzle-2-300# = 4.39 Mpa
Nozzle-3-300# = 4.39 Mpa
Nozzle-2-300# = 4.39 Mpa

After Using Kellogs method, which is computes an equivalent pressure using the applied forces and moments. This pressure rating from the B16 table is then reduced by this amount.

Nozzle & Rating Pmax

Nozzle-3-300# = 1.936 Mpa
Nozzle-2-300# = 1.436 Mpa
Nozzle-4-300# = 1.936 Mpa
Nozzle-2-300# = 1.436 Mpa
Nozzle-3-300# = 2.634 Mpa
Nozzle-2-300# = 1.436 Mpa
Nozzle-2-300# = 1.436 Mpa
Nozzle-3-300# = 2.634 Mpa
Nozzle-2-300# = 1.436 Mpa


As highlighted, 1.436 is the lowest value which concluded after the flange rating pressure reduction.

From Major component lowest MAWP is = 2.5855 Mpa
From Minor component Lowest MAWP is = 4.39 Mpa
From Minor component Lowest MAWP (After Reduction) is = 1.436 Mpa

However, my question is that can we say vessel MAWP is now the flange MAWP reducted pressure value?
Please advice based on my case and also share reference of same approach.

 

[Some Curious Guy]

Good to know that someone is keen to do the calculation manually to learn things better.

The Rated pressure of the flanges before applying loads is 4.39 MPa. This was without applying any external loads. After application of external loads its capacity to handle pressure was reduced. These loads were converted into an equivalent pressure and this equivalent pressure was deducted from the rated pressure to arrive at the final MAWP of the flange. I have done the math below from the values of equivalent pressure you gave above.

Final MAWP of Nozzle = Flange rated Pressure ( before applying loads ) - External loads converted into an equivalent pressure.

Final MAWP of Nozzle-3-300# = 4.39 - 1.936 = 2.454 Mpa
Final MAWP of Nozzle-2-300# = 4.39 - 1.436 = 2.954 Mpa
Final MAWP of Nozzle-4-300# = 4.39 - 1.936 = 2.454 Mpa
Final MAWP of Nozzle-2-300# = 4.39 - 1.436 = 2.954 Mpa
Final MAWP of Nozzle-3-300# = 4.39 - 2.634 = 1.756 Mpa
Final MAWP of Nozzle-2-300# = 4.39 - 1.436 = 2.954 Mpa
Final MAWP of Nozzle-2-300# = 4.39 - 1.436 = 2.954 Mpa
Final MAWP of Nozzle-3-300# = 4.39 - 2.634 = 1.756 Mpa
Final MAWP of Nozzle-2-300# = 4.39 - 1.436 = 2.954 Mpa

As you can see the weakest component is the one having the MAWP of 1.756 MPa. This is the weakest component of the entire Vessel. Hence the Vessel MAWP is 1.756 Mpa.

I do not have a reference of the above approach. This is just how you do it. You can check any software report. The vessel is strong as its weakest component. Hence the weakest component MAWP would be limiting MAWP of the entire vessel.

Why don't you use Code Case 2901 / UG-44(b) to arrive at the final flange MAWP instead of Kellogs pressure method. It is a little modification of Kellogs method. In UG-44(b) method you can multiple the factor ( 1+Fm) to the rated pressure before deducting the equivalent pressure from it.

Final MAWP of the flange = Flange rated pressure per B16.5/B16.47 x( 1 + Fm) - Equivalent pressure due to loads.

Kellogs method is very conservative. If you use that method almost all small size, lower rating flanges would become endangered species in the industry. Kellogs equivalent pressure method adds loads on the flange twice. One is by increasing the hydrostatic end forces by increase in equivalent pressure ( increased Pressure x Same Area ). The other is by increasing the gasket seating stress via the gasket factor m ( m x Increased Pressure ).

 

[saplanti]

You are at the design stage, you are not evaluating a pressure vessel in operation.
I would read the specification of the vessel ones more, check where the nozzle loads are (I believe they are on the nozzle-shell intersection, not on the flange face. Even if they are on the flange face the following will not change dramatically, you will need to convert/transfer the external loads on to the shell-nozzle intersection, check flanges seperatelly. If the flange fails under both pressure and external loads increase the class of the flange as required). I would not design the pressure vessel for lesser pressure than the shell or head can handle. So ı suggest you to consider the minimum shell design pressure/MAWP to design the nozzles.

The normal process to design the nozzles is to design them for the design pressure/MAWP for shell, and check them for pressure and external loads using WRC 107, WRC 298 or WRC 537. Common stress analysıs software have these options, or you may write spreadsheets for this purpose.

Hope it helps.

 

[CuMo]

Some of our clients have the requirement that minor components such as nozzle flanges shall not govern the MAWP of the vessel.
But sometimes if you are designing a replacement vessel and the pipework doesn't change, also there are some other factors involved,
the nozzle flanges might become the component that limit the MAWP. So yes - you could state this.

But for a new design from scratch - it is recommended that nozzle flanges have higher MAWP than shells/heads/etc.

 

[soletto]

As far as i know the Kellog formula is very conservative so you will like have twice the required wallthickness and nobody want to use / buy this part.... Or am i wrong?

 

[Morcuse]

Use the new ASME Section VIII Div. 1 UG-44(b) method instead of the Kellog formula. It's based on the Koves method.

 

[TGS4]

UG-44(b) it's based on work from Brown, not Koves.

 

[Some Curious Guy]

The method used by Brown also consider the stiffness of bolts and gaskets to increase the margin of rated flange pressure. Brown has authored a couple of books about bolted connection design. The books are not easily available on the net. However the same concepts can be refreshed by the following lectures series on you tube.

https://www.youtube.com/watch?v=-ZS0PULp4bg&list=PLZOZfX_TaWAHfpBzrqHBNjd9G1_SxMvfr&index=12

https://www.youtube.com/watch?v=mQz79NFNTzY&list=PLZOZfX_TaWAHfpBzrqHBNjd9G1_SxMvfr&index=13

After these lecture you can read Paper ASME PVP2013-97814. This was the paper which eventually led to code case 2901 / UG-44(b)

https://asmedigitalcollection.asme.org/PVP/proceedings-abstract/PVP2013/55676/V003T03A026/284093.

Thanks to Mr @TGS4 who guided me previously on this site on a similar subject.

 

[soletto]

nice lecture videos ill stress my brain now thank you for the link

i see there are much moore lectures on the site will be helpful