UG-16(b) value for nozzle neck thickness 1

[Alaitz]

Hello everybody!

I'm calculating a nozzle neck thickness per UG-45 and I'm not sure about which is the minimum thickness specified by UG-16(b).

My equipment works with steam / water and the material is in the Table UCS-23, then for shell and heads the minimum thickness is 2.4 mm per UG-16(b)(4).

Do I have to use this same value for nozzles? or Can I use 1.6 mm? In the UG-16(b) only speaks about shells and head.

Thank you very much!

 

[jamesl]

The only way you can use 1.6mm as your nozzle wall is that the nozzle pipe size is so small that the standard pipe thickness is 1.6mm and there is no C.A. There is only one pipe size that meets this requirement - 1/8" nozzle. Otherwise you have to have 2.4mm+C.A. for minimum nozzle thickness.

 

[Alaitz]

Thank you very much Jamesl!!

 

[Alaitz]

One more question...

I have take a corrosion allowance of 3 mm for shell / heads and 1.5 mm for the nozzles (as is said in the Heat Exchange Institute Standard for Deaerators).

In the calculation of the values of UG-16(b), UG-45(b)(1) and UG-45(b)(2), which value of CA shall be use, 3 or 1.5 mm?

Thanks in advance!!

 

[vpl]

Alaitz

Two questions:

1) What Code are you using to design this vessel? Or, more importantly, what Code did you tell your customer that you were going to use to design the vessel? Since you reference UG-16(b) and UG-45, I was under the impression that you were using the ASME Boiler and Pressure Vessel Code Section VIII.
2) If you are designing to ASME Section VIII, why are you going to other standards (such as the Heat Exchanger Institute Standard) to pick minimum values? Should you not be using the minimum value from the Code?

From both your first question and your second, it appears that you are trying to minimize the amount of steel being used while still claiming to meet the Code -- and are looking for this forum to help justify your actions.

Patricia Lougheed

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Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of the Eng-Tips Forums.

 

[SnTMan]

Alaitz, in my opinion your nozzle min thickness is governed by UG-16(b)(4), 2.5 mm. Note that UG-45 refers specifically to UG-16, and since your class of work falls under UG-16(b)(4) you are bound by it.

As for the corrosion allowances, apply 3 mm to the UG-45 tb1, tb2 thickness, apply 1.5 mm to the UG-45 ta and tb3 thicknesses.

I believe you are correct, in the absence of specified corrosion allowances to use HEI guidelines. Sec VIII, Div 1 so far as I know does not specify a corrosion allowance, only that it be considered.

Regards,

Mike

 

[Alaitz]

Thank you very much Mike! I will use the CA coeficients as you say, although I think is not so logical ;D

Ummm... How you know that you have to take the CA of the vessel instead of the CA of the nozzle? In the ASME only is talk about the thicness calculation without the CA.

I know you are right (I have see it in a very very old and not official documentation too) but, why?

Patricia, as Mike has said the ASME and the HEI codes are not mutually exclusive. ASME don't say which must be de CA value and the HEI don't say how to calculate the thickness. I know that is a bad idea to use two codes like ASME and AD-Merkblatter, I understand your concern and I thank you to coment because it would have taken place.

Of curse, i want to take the minimum thickness (like everybody I understand, otherwise why are so much formulas in the ASME? It will be more easy to use the more restrictive one) but, always by the side of safety.

On the other hand, I will like to thank you all for this forum, is the first time I ask something but, i have use it so many times to solve doubts.

Finally, sorry for my poor English.

See you!

 

[SnTMan]

Ummm... How you know that you have to take the CA of the vessel instead of the CA of the nozzle? In the ASME only is talk about the thicness calculation without the CA.

You just use relevant corrosion allowance for the relevant part. In my class of work it is not uncommon for an owner specification to require greater CA for nozzles than for the vessel. It just depends on the service and life desired.

Code nomenclature for sizes nearly always states "exclusive of corrosion allowance" or "in the corroded condition".

Regards,

Mike

 

[Alaitz]

I think that I have explain incorrectly. Im not asking how much should be de CA value, always I take 3mm for this type of equipment (maybe you have understand this?).

Say in another way:

The formulas in the ASME (commonly) are without CA and, after you calculate the value of t you add the CA.

In the UG-45 you are calculating the thickness of the nozzle, so I calculated ta, tb1, tb2, tb3, tb4 or t16 and after I added the CA of the nozzle (becase I'm calculating the thickness of the nozzle).

Now, I now this is wrong but, I don't understand why.

In your case, that CA of the nozzle is greater than the CA of the vessel, do you use the CA of the vessel to calculate UG-45 tb1, tb2? I shold use the CA of the nozzle.

Don't worry. I like to understand why I do something but, is suficient to know which is the correct procedure.

Thanks.

 

[SnTMan]

Alaitz, suppose you had, say, a CS vessel with CA with a SS nozzle with zero CA.

When calculating tb1, tb2 and UG-16 thickness the vessel CA would have to be added, rather than zero CA.

When calculating ta and tb3 nozzle CA is added, in this case zero, rather than the vessel CA.

The UG-45 thicknesses are the minimum required in the new condition, thus the relevant CA is added to the relevant component.

As a check I ran this problem in one commercial software that I use and it applied the CA's in this way.

Hope this helps.

Mike

 

[Alaitz]

Sorry, I have been out this week.

Mike, I'm very grateful to you for your detailed explanations, it have been very useful.

See you!!!