Reducing flange ASME B16.5 used with ASME B31.3 design

[abbver98]

Hi,

I see that the reducing flange are allowed according to ASME B16.5. for example you can have a face of 10'' Class 150 and a hub of 2''. But i'm wondering if it's allowed to be used with design according to ASME B31.3. I think stress analysis should be made. What are your thoughts ?

 

[aburafdi]

According to Table 326.1 of ASME B31.3, the Flanged fittings of ASME B16.5 is allowed to be used in B31.3 (listed as "component standard"). In para 303, it's said that components listed in table 326.1 is considered suitable for use at pressure-temperature rating in accordance with para 302.2.1.

 

[abbver98]

aburafdi,
Table 326.1 allows to use those component as standard flange covered by ASME B16.5.But in reallity we knows that flange with face of 10'' and socket weld hub of 2'' can't be used as such. a huge stress on the hub !! How this could be accepted by B31.3 ?

 

[moltenmetal]

Sorry, but I don't understand your particular concern. What difference does the size of the flange make to the socket weld connection? The socket weld connection itself, irrespective of the large flange size, already has a considerable stress intensification factor that has to be considered in the design of the piping.

 

[abbver98]

the flange ring (10'') will induce an abnormal stress on the hub (2''). in the normal situation with standard flange the stress level is limited and in any case there is a successuful experience with.

 

[austsa]

abbver98,
I agree with moltenmetal's comments (unless your case requires some special consideration). Can you explain how abnormal stress is induced on the hub?

 

[moltenmetal]

At a 10x2 size reduction, you'd be permitted to do this with a blind flange (i.e. without a hub)...

 

[abbver98]

It's permitted but it's in own risk of the designer. Water theory shows that this kind of construction is not recommended.

 

[moltenmetal]

Again, pardon my ignorance but I have no idea what you're talking about. What are you referring to with your reference to "water theory"?

You asked if this practice (a 10x2 reduction using a hubbed reducing or even a blind flange) was permitted per B16.5 and B31.3 without special additional analysis, and the answer is yes. You are of course free to go beyond code in this and in all other respects if you don't think code-permitted fabrication is up to your particular task.