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Nozzle neck minimum required thickness

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cespi82

cespi82

Materials
Dec 23, 2009
36
Hello everybody!

I am new in this forum, and also kind of new in this Pressure Vessel field.

I have a question regarding the Nozzle Neck minimum required thickness for an in-service vessel. What is UG-45 table based on? are those values considering structural loads for the nozzle itself? What about nozzle length and weight?

The question comes from the fact that running calculations for Nozzles as per UG-27, the outcome will be a very low thickness required as the Desing Pressure of the vessel is low (75 psi). For a 2" nozzle at this DP the minimum required thickness would be 0.007" which is like the thickness of a paper sheet. Long before we have reached that thickness, the nozzle would have collapsed already. Besides that, if I use this minimum required thickness values for performing Remaining Life calculations, the result will be over hundred years. It does not make any sense for me.

I checked in both API-510 and NB-23 and I did not find any other calculation path than use ASME Code. Can I use the design code ASME Sec VIII Div 1 for calculating these minimum required thickness values despite of the equipment has been in service for over 20 years?

Thank you very much in advance...

Kind regards,
 
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Obviously, a process nozzle is assumed loaded with external piping loads, therefore the nozzle thickness has included allowance for those loads. Also, corrosion allowance, piping wall thickness reduction allowance (-12.5%). You need to evaluate all of those in order to make a correct assessment of the remaining nozzle capacity. Converselly, you don't include external loads for instrument nozzles.
Cheers,
gr2vessels
 
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cespi82, first, welcome to the forum.

Second, UG-45 exists so that we dont wind up with 0.007" thick nozzles :) It is my opinion (only) that it is present to assume some degree of mechanical strength in the nozzle. Additionally, UG-27, UG-28, UG-37 and UG-45, each may govern nozzle thickness.

It is for NEW construction. I don't believe a vessel would have to be repaired or retired because a nozzle eventually fell below UG-45 thickness.

UG-45 was revised in recent years, 2010 maybe, incorporting the table now present. Previously, the requirement was something like "schedule standard + corrosion."

The current version is much easier to navigate thru, in my opinion.

Regards,

Mike



 
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I'm going to ask a question within the same subject - hope its ok!

Its about using UG-28 for finding the minimum nozzle thickness due to external pressure.

UG-28 seems rather complicated compared to UG-27. It there any shortcut when the nozzle is not subject to any external pressure (other than atmospheric pressure of 101kPa) ?

My best guess so far is using U-1(c)(2)(h) and then use UG-16 to set min. thickness. Any suggestions on this? :)

Best regards
Jonas
 
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Sjqlund, U-1(c) states whether or not pressure vessels are in the scope of Sec VIII, Div. 1. Only.

Your nozzle neck does not have to be designed for conditions to which it is not exposed. It does have to be designed for all conditions to which it is exposed.

So, briefly, a neck thickness is the thickest required by UG-16, UG-27, UG-28, UG-45. UG-27 and/or UG-28 may not apply as per the design condtions. UG-16 and UG-45 always apply.

Regards,

Mike
 
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Ok, i think i see your point. Thank you :)

So if i design against vacuum in the nozzle, there's no shortcut and i'll have to go through UG-28, and find the thickness (by iteration) that gives me a pressure of ~1 bar (pressure difference of vaccum). Correct?
 
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Yes, correct. If you are doing these "by hand" use the external pressure charts. It is faster than doing all the artihmetic.and close enough.

Unless you need the minimum required for external pressure, such as in UG-37, you may just show that a previously selected thickness is good for the external pressure. If the former, I recommend you get some software.

Regards,

Mike
 
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Hi everyone,

I am sorry for not answering before. I actually thought these answers will take some time to arrive.

gr2vessels and SnTMan thank you very much for answering.

gr2vessels said:
You need to evaluate all of those in order to make a correct assessment of the remaining nozzle capacity"
Click to expand...

This is basically one of my questions, How do I conduct this evaluation? Through ASME Sec VIII Div 1 despite of the vessels has been in service for over 20 years?

SnTMan said:
It is for NEW construction. I don't believe a vessel would have to be repaired or retired because a nozzle eventually fell below UG-45 thickness.
Click to expand...

Ok, what about In-service equipment? What are the criteria or code/standard to determine when a nozzle requires to be repaired or retired?


Sjqlund no big deal! the more the people ask, the more we all learn!!


Regards and thanks again!!
 
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In service for twenty years... Use the in service Codes...
 
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Hi GenB,

Thanks for your reply.

In my original question I wrote this:

cespi82 said:
I checked in both API-510 and NB-23 and I did not find any other calculation path than use ASME Code. Can I use the design code ASME Sec VIII Div 1 for calculating these minimum required thickness values despite of the equipment has been in service for over 20 years?
Click to expand...

I wouldn't make this question If I were clear about this. In Service codes do not clearly specify how to run these calculations for retirement thickness and the need for repairing... That's is why I quoted and asked SnTMan about this...
 
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I guess we all been mislead by the question itself, regarding exclusively the nozzle neck thickness. One only nozzle cannot be segregated from the entire assembly, including the shell thickness and material condition around the nozzle, if you need to evaluate the fitness for service of the corroded vessel with that corroded nozzle. The remaining life of the vessel and implicitly its nozzles have to be evaluated as per API 579. Just remember, you cannot evaluate the nozzle to last 5 more years when the whole vessel will be rendered unsafe in 3 years. This is because the nozzle strength lies in the shell strength in addition to the nozzle wall strength and they only exist (and be evaluated) in assembly. Obviously, when a close scrutiny/inspection has detected excessive decay of one only nozzle, the focus will be on that nozzle, but still will be evaluated in assembly with the strength of the shell around the nozzle, to the extent specified in ASME VIII. Hope this helps.
 
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cespi82,

There is no code that will tell you exactly how to run calcs for an in-service vessel, per se. First and foremost, keep in mind that the codes are not meant to be design "cookbooks." They require your engineering judgment and experience as well.

I agree with SnTMan - UG-45 is for NEW construction only. It's there for the reason he stated - so that vessel manufacturers don't try to save material/weight in the nozzles. At least this is my understanding after having spoken with several individuals on the ASME PV code committee about this very topic.

In general, once the nozzle has corroded below t=Nominal Thickness - Corrosion Allowance, you enter the realm of Fitness-for-Service. API 579 will give you guidance on performing calculations for this purpose; however, I recommend that you have an engineer experienced in API 579 work with you and check your calculations. It requires good, very specific inspection data on your component, and the recommended practice itself can be daunting to those who have not used it before. Also, you did not mention if the vessel was originally designed per code - that is a basic requirement in order to use API 579. Good luck.

-KLee
 
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Thank you very much all for your replies... clearer now.

Regards,
 
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