lenght of thickened shell for non-standard flange 2

[billeeee]

Hi All, I am designing a large diameter (>2400mm) slip-on plate flange connecting two parts of a vessel using the Taylor Forge method. The vessel is 10mm thick and in order to come out with a reasonable flange thickness I have thickened up the shell at the connection with the flange. Question is, how long does this thickened up section need to be before I can taper back down to the main vessel thickness? There doesn't seem to be any code limit.

 

[cbPVme]

What figure are you following? Typically a plate type flange is considered to be a loose type and the connected shell material is not considered to provide additional strength.

 

[billeeee]

cbPVme, Thanks for your reply. The detail in PD5500 is Suggested Working Form2, or in EN13445-3 it's figure 11.5-2, not sure about ASME but it's a narrow faced flange with a stepped bore. With the shell thickness being greater than 16mm I think this prevents it from being a Loose Flange design. But with the shell thickness being 'go', and 'g1' being 'go' plus the weld leg length, the shell thickness ('go') affects the value of the ratio g1/go and also two of the shape constants. So the shell thickness does have an influence on the flange stresses. If this is purely a local affect at the welded connection, presumably I don't need much of a length of thicker shell before I can taper down to a thinner shell?

 

[Cobra17]

VIII-1 Figure 2-4 (6a) has the neck as 1.5*g0 min.

 

[GD2]

OP,
You can also look up figures UW 9-2 and UW 13-4. Use whichever you feel appropriate.

GDD
Canada

 

[billeeee]

Thanks very much for your answers guys, much appreciated.

 

[r6155]

Never welding neck flange for large diameter.
More info from (OP): design pressure/temp., material, corrosion, corrosion, ...etc.

Regards

 

[GD2]

r6155,
What is large diameter? PV Code allows to use ASME 16.47 flanges in pressure vessels - 36/60 inches depending on pressure class.
Integral type (hub type WN) flanges are allowed in ASME Sec VIII-1 Appendix 2, Fig 2-4 (6a, 6b)but no where puts the limit on size.
Any specific reason for this?

GDD
Canada

 

[r6155]

GD2
Large diameter > 2400 mm, as mentioned (OP).

The welding neck flange must be forged. For >2400 mm the reason is the high cost.

Regards

 

[GD2]

r61555,
Thank you.

GDD
Canada