Nozzle Reinforcement Configurations (ASME VIII) 2

[LPZ74]

Fellow Engineers,

Firstly, I apologize if this becomes a long question...

I currently have the task of reviewing a Vendors Code calculations for an ASME Div VIII pressure vessel operating at 515 kPa (75psi) and 160 degrees Celcius. The Vendor previously had selected a shell thickness of 15mm and has ordered the plate. Unfortunatley, they did not perform all the required nozzle calculations (i.e. WRC 107), and since performing these calculations, they have realized that the nozzle is not adequatly reinforced.

Their solution is to add an additional re-pad to the existing one. So, what they currently have is a 34" nozzle inserted into a shell of 15 mm thickness with a repad of 15mm thickness (sketch b-1, Fig UG-40) PLUS a 6mm repad on top of the existing repad. Is this allowed? I have looked UG-37 and through Figures UG-40, but do not see a similar nozzle configuration to what they are proposing. Can anyone out there tell me if this is an acceptable solution?

Also, is there a limit to the maximum thickness that a repad can be (dimension te) in relationship to the thickness of the vessel. Previously I had always thought that the thickness of a repad should be less than or equal to the thickness of the vessel. Is this just good practice or is it a code limit?

Thanks and Regards,

lpz74

 

[prex]

In my opinion it is allowed, as fig.UG-40 says 'some representative...' (hence non limitative). Also I'm not aware of any limitation to the thickness t_e.
Of course the rules of UG-41 (weld strength paths, to be adapted to the particular situation) and of UW-16 need be satisfied, where relevant.

prex

http://www.xcalcs.com

Online tools for structural design

 

[PVRV]

a) I would impose limits for nozzle re-inforcement for
both thickness and diameter of the RF-Pad.

b) If surplus material is used to reduce nozzle re-inforcement
I would downgrade MAWP to the adquacy of the first RF-Pad or
the limits of the RF-Pad in case the limits are exceeded.

RF limits (single pad), I dont believe they are a concern in your case.

What is the material of the shell and diameter. In addition the thickness of the nozzle, material and the diameter of 15mm RF-pad you have in place for the 34" nozzle. Furthermore, the leg lenghts of the fillet welds of the RF-Pad (34&quot in place.

Despite the absence of critical information I hope this helps and do not consider this more than a general recommendation in need of verification.

Assumptions:
34" Nozzle; required thickness 5mm provided 7.92mm
Shell : the required thickness 14mm provided 15mm

Required Area = 11,868 mm squared
Access Area (Shell+Nozzle) = 983 mm squared
Access Area in Fillet Welds (Legs 15mm) = 225 mm squared
Ar - Aa = 10,660 mm squared

RF-Pad provided thickness = 15mm
Required Diameter = 710mm (28&quot

Limits of RF for thickness (19.8mm; if 34" Sch. Std. is used
23.75mm)

Limits of RF for diameter (1726mm)

________________________________________________________________

Things that to consider for furture purposes:

1. Increased RF-Pad thickness to 19mm to lower the
diameter to 20" or so.

2. Regarding adding an additional RF-Pad I wouldnt allow that; but
that does not matter. AI should review this issue.



Cheers

 

[LPZ74]

Thanks for your quick responses PVRV and prex.

In regards to your questions PVRV, the shell material is super duplex SAF 2507 (UNS:32750)and the shell has a diameter of 4340mm (ID). The nozzle is actually mounted at a 45 degree angle wrt the axis of the shell. Therefore the length of the opening is 1222mm in the long direction. The repad width is 150mm, and the selected nozzle thickness is 14mm. The welds are 14mm as well. (Note an internal corrosion allowance of 3mm).

I do not have a problem with the required area being met, i.e. - I have sufficient area using the replacement method of UG-37...it is only a problem when I add the external loading to the nozzle. We have some significant nozzle/piping loads here and we are at a stage where it is difficult to change the routing. Unfortunately, we are not willing to de-rate the MAWP of the vessel, nor make changes to nozzle sizes at this stage.

I was only looking an answer to whether anyone was familiar with that configuration in their experience, as I have not seen that done before. I will run some other reinforcing scenarios to see if I can come to a possible solution to give to the vendor that does not require a double repad. If not, I guess it may have to do.

Again, I appreciate your responses.

Regards,

Lyle

 

[prex]

Aha! you didn't specify that in your first post.
If you meet the criteria of UG-37 with a single repad, then I suggest, to limit the discussions with the AI, that satisfaction of UG-37 is met, in the stress report, with the first repad. Then you consider nozzle loads and you need an additional repad only for that: in my opinion that's different, as pressure design is already satisfied with the first one.
However I'm surprised of what you state: with your proportions I would expect that the maximum stress under nozzle loads is at the periphery of the repad, where the added one is of no help...

prex

http://www.xcalcs.com

Online tools for structural design

 

[LPZ74]

Thanks to all for your replys.

I have been playing around with our Compress model and I believe that I have found a solution that satisfies both UG-37 and WRC107 without requiring the extra repad (using the original repad thickness of 15mm). And, it still falls within the limits of reinforcement set out in UG-37. Now I just have to convince the Vendor!

Thanks,

Lyle

 

[LPZ74]

Just wanted to let you guys know that I think I found the limit for the maximum reinforcemnt thickness...If I would have looked closely, I wouldn't have needed to ask the question. If you look at Fig UG-37.1, and the limits of reinforcement, the max limit of reinforcement perpendicular to the vessel is the smaller value of 2.5t OR 2.5tn+te. Therefore in this case, the max pad thickness would be 2.5*15=37.5mm.

Just thought I'd let you know.

Cheers!

 

[prex]

Just for the sake of precision: t is 12 mm in your case, as you mentioned a CA of 3 mm. So an added reinforcement thicker than 30 mm would be of no use, though this doesn't mean it wouldn't be allowed.

prex

http://www.xcalcs.com

Online tools for structural design

 

[LPZ74]

Yes Prex...you are correct...
t = 12mm.

Thanks,

Lyle

 

[LSThill]

Hi LPZ74 (Mechanical)

If your playing around with our Compress model, If you have FE-NOZZLE will do the WRC 107 AND WRC 297 and all load Cases from the pipe stress engineer.

You may want to look at Photo Gallery

http://www.thill.biz

FE-PIPE NOZZLE Pro ANALYSIS POLT: WRC 107-WRC 297


Leonard@thill.biz

http://www.thill.biz

 

[aybee]

is there any benefit in thickening the nozzle neck, this gives you more strength for external loading bigger weld and reduces your pad need as well