Pressure vessel nozzle sch/thk 1

[darrenyee88]

If the shell and head thickness increases, do we have to also increase the nozzle schedule/ thickess eventhough the desing pressure and design temperature is the same throughout?

The vendor agrue that the nozzle sch/ thk has to be increase because the hydrotest pressure increase from 8.9barg to 21.9 barg. of course initially the vendor take the MAWP as the design pressure but in the second rev , the vendor calculated the MAWP and the MAWP increases from 6.9barg design pressure to 16.8 barg .

1. So what I wanted to know is why is there a need to increase the nozzle sch /thk ? Is it really neccessary?
Can someone please explain to me?

Thanks alot . Cheers.

 

[XL83NL]

If 'desing pressure and design temperature is the same throughout' then why ' the hydrotest pressure increase from 8.9barg to 21.9 barg'?

 

[darrenyee88]

Because the thickness of the pressure increase due to 3mm corrosion allowance required.

 

[XL83NL]

The nozzle schedule/thickness has to satisfy the code requirements in the same way as for heads, shells and other parts under (internal) pressure.
The answer is probably yes, but you'd need to provide more details to check. I suggest you review UG-45 of VIII-1 (assuming ASME is the CoC).

 

[SnTMan]

There is much unknown here, but I suppose it is possible that after whatever change occurred, nozzle reinforcing was inadequate, or that UG-45 (if Sec VIII, Div 1, don't even know that) was no longer met. Who knows?

Regards,

Mike

 

[chicopee]

Something does not make sense here and that is an increase in MAWP because of corrosion allowance. The thickness of the part without corrosion allowance is first figured out based on the MAWP then you add the corrosion allowance.

 

[gr2vessels]

It is a good practice to not limit the MAWP by any standard flange. That will provide for higher rating of the vessel, with a minimal change of flange rating. Obviously, you cannot simply increase the rating of nozzle flanges unless agreed by process and piping requirements. Raising the MAWP increases the test pressure accordingly, which for vessel means increased rating, more bang for your buck! That is your vendor suggestion and recommendation, but you don't need/have to accept it.
Cheers,
gr2vessels

 

[jte]

Another unknown here is purchase spec's. It is possible that the vessel was origninally designed to meet the construction code and then after that a owner/user spec was checked and it was found that changes had to be made to meet the spec. For example, it is possible that the nozzles were originally governing the MAWP or that the MAWP was not calculated (DP was used for MAWP). Then somebody read the spec and discovered that changes had to be made to meet the spec.

Another possible cause (given the OP's reference to CA) would be a confusion between MAWP and MAP. For a relatively thin wall vessel, a 3mm CA could cause a substantial difference between MAWP and MAP. And if this vessel is designed to my company's spec's (or several others') then the hydrotest shall be MAP based (for VIII Div. 1 that would be UG-99(c)).

Lots of unknowns here. Darrenyee - can you provide some more detail, if only to close the loop with the forum?

 

[pksingla11]

darrenyee88: Which software are you using for equipment design?

What I understand is that initially MAWP was limited equal to design pressure and nozzle was designed for MAWP.

Now, you have calculated the MAWP and by default, software is calculating nozzle parameters for MAWP considering it as a design pressure. If you are using COMPRESS, this may be the case.

If I have not understood your query, please elaborate it.

 

[GenB]

A complete different design and different vessel, different materials. Just start from scratch.