Dished covers with bolting flanges - minimum flange thickness

[mech8790]

Hello!

I am looking for some help in calculating the flange thickness. I have got a dished end (torispherical head) welded to rolled ring. The figure 1-6 Asme VIII sketch a) is my design situation here. 1.6 d)3) is pointing me to Appendix 2 for flange wall thickness calculations. I have performed it as a loose type flange and the minimum required thickness is 100mm (both sitting and operating checks done + flange rigidity check). Is there any way to reduce 100mm down to something like 30-40 mm?

If the flange is considerate as optional type figure 2-4 sketch (8) will I it be thinner?

I have seen on internet many applications of swing bolt brackets with two rolled rings welded to dished head and cylinder, but I am not sure will this type of closure fitting have any impact on flange/rolled ring thickness?

Regards!

 

[Vikko]

Loose flange according to Apx 2 does not have a hub normally (example fig 2-4 3a, 4a), so it is quite thicker. But you can consider it as an optional flange 2-4(c) (fig 2-4 8) and calculate it as an integral flange, (see Note (6) of fig 2-4, it tells you to consider than sketch 7, which takes into account the fillet weld legs, as the hub (so you have g1 and h) !!!).

Also according to appendix 2, if the bolts are "oversized", the flange dimensions will go with the bolts dimensions, (which makes sense), so sometimes to decrease the flange thickness you have to evaluate if it is possible to use less bolting area.


Finally, the flange thickness, depends also on many other things (other than pressure, temperature and flange material), bolts, gasket, bolt and gasket materials and dimensions of bolt circle (too high bolt circle increases the moment arm!) and dimension of the gasket). So you should evaluate all these parts together, to see what can be done.


Otherwise you Division 2, which has a different method which results usually with lower thickness.

 

[BJI]

If you are designing a dished cover you should be following mandatory appendix 1, 1-6 Dished Covers (Bolted Heads).

 

[mech8790]

Thanks Vikko! That is the proper answer I have been looking for, thanks mate!