Allowable stress for austenitic stainless steel

[Cristiana]

Hi!
I’m designing a vessel in 316L.
Usually in these cases I adopt the higher allowable stress values for shells and heads, whereas the lower values for girth flanges (according to note G5).
If I have selfreinforcing nozzles, integral with flanges, what do you think is the right values to adopt for this non-standard piece calculation? The higher values or the lower ones?
And what about the same situation with the nozzle selfreinforcing part welded to a standard flange (in this case I should calculate only the forged nozzle part, not the std flange)?

 

[vesselfab]

The Flange face and hub are the only thing that requires the lower stress value.
the necks on self reinforcing nozzles can be higher stress value

 

[JoeTank]

In ASME VIII, Div 1, the flange cannot be used in the reinforcement calcs (unless it is a stud pad). Use the higher vessel allowables.

Joe Tank

 

[gr2vessels]

I agree with vesselfab, use typically the lower allowable stress for the flange (obviously, including the hub) and the higher allowables for the rest of the vessels, like shell, nozzle neck, heads, etc...
However, bear in mind that the G5 is a recommendation, ie is not mandatory. An experienced designer can decide to use the higher values for a non-essential flange design, for pressure / temperature conditions where the gasket seating are the prevailing design conditions or similar application.
cheers,
gr2vessels

 

[unclesyd]

gr2vessels,
Am I reading your post correctly?
Wouldn't you want to use the lower stress value on a flange where gasket seating controls?

 

[gr2vessels]

For a relatively small flange, yes I would use rather the higher values, but for a large girth flange where the distorsion is likely to lead to leak during the hydrotest, I would use the lower values and even increase the calculated thickness by 10% or so. It depends. Usually the m, y figures are so high in the code, that the only way to make a small flange economical is to use the higher allowables. As I said, when and how to apply the rules comes with experience...Using always the higher allowable stress values is safer, but more expensive than it could be otherwise.
cheers,
gr2vessels

 

[unclesyd]

I'm OK with that and agree that the m and y values in the code are high which is due to the original materials used for their derivation. We do tweak the calculations based on the gasket material and experience. The factors are way off for materials we use like Gore Tex and Grafoil. The lower allowables gave us a crutch in our very corrosive areas as they gave us more meat to chew on without raising any alarms.