G5 Material Allowable Stresses for Flange Hub Design as per UG-27

[ashaykadam]

As per ASME Sec. VIII Div. 1 - App. 2 -> 2-1,
"The hub thickness of weld neck flanges designed to this Appendix shall also comply with the minimum thickness requirements in Subsection A of this Division", i.e. small hub thickness (g0) shall be checked as per UG-27.

For flange design we consider lower allowable stresses (of non G5 material).

Now I have following two questions:-

1. Can we consider higher allowable stresses (of G5 material) while checking adequacy of small hub thickness (g0) as per UG-27?
I feel that though being part of flange, hub part is not coming under application defined in note G5 "where slight amounts of distortion can cause leakage or malfunction."

2. Is there any ASME Interpretation / Code Case accepting this?

Thanks.

Ashay Kadam
Mechanical Engineer
India.

 

[SnTMan]

ashaykadam, I tend to agree that the higher allowables may be used to satisfy the 2-1 sentence quoted, commonly UG-27. The hub then, using the lower allowbles, is designed per and meets all requirements of Appendiix 2. Unfortunately the software I am familiar with is not capable of this distinction.

I don't know of any Interp / CC to support thiv view however.

Regards,

Mike

 

[sharmass]

Sf in App 2 is defined as allowable design stress for material of flange at design temperature (operating condition) or atmospheric temperature (gasket seating), as may apply. This indicates that for operating and seating condition, we can take different Sf
You can consider a higher allowable stress for hub portion (operating condition only).
You are right, hub portion is not subjected to distortion causing leakage or malfunction