the meaning of note G5

[FSKeng]

Dear all
Usually materials with "note G5" have allowable stresses higher than the same material without "note G5";
Why allowable stresses for these materials are higher?
when can I use materials with "note G5"?
is there any diferrence in fabrication of these materials?

any help is appreciated!!

 

[metengr]

FSKeng;
You need to review Note 5. The higher allowable stress lines are based on short term tensile properties, where these materials have low yield strength and will locally deform at stress risers or locations of increased stress. The bulk yield strength will not be exceeded at the service temperature.

What this means is that if you select the high stress value for service, you can expect some local deformation. If this is tolerable, you are permitted to use the higher stress line.

 

[Shmulik]

metengr,
Is it still necessary to use lower allowable stress value for design of loose type (ring) flange made of G5 noted material, since using of flange rigidity factor in calculations became mandatory (2005)?

 

[metengr]

Shmulik;
I believe flange designer expierence plays a role here, and I will defer this specific question to one of my esteemed colleagues.

 

[unclesyd]

I'm aware of several design groups and fabricators where the use of Hi values, mainly 304L, has been limited to shell segments only, where distortion isn't a big problem. I can't recall where Lo values was ever under consideration for flanges and nozzles.

That said, there was one time where the Hi values for 304L were used after the fact to allow some flanges to be compliant. This was done after the actuals were confirmed
which would then permit the Hi allowables for 304L to be used. The original problem with the flanges was the hub length. This was motivated by the fact that there were 32 48" 600 Class flanges laying on the shop floor.

 

[FSKeng]

THank you all
one question that still remains for me is that, the G5 materials are produced through a diffrenet fabrication procedure or they are exactly same as the material with no G5 note and only different test conditions lead to higher allowables for these materials??
what dose short term tensile property mean?
thank you?

 

[Shmulik]

FSKeng,
There is no difference in fabrication procedure or in test conditions.
Only difference is in service conditions that material is subjected to. In application that permanent strain exists and slight amount of distortion may cause leakage or malfunction - the use of low stress value is recommended by G5.

 

[metengr]

what dose short term tensile property mean?

It means that under tensile tension testing conditions to determine yield and ultimate tensile strength at the designated test temperature, the value to assure no general (bulk) yield is 90% of the tensile yield strength, and not 0.67 of the yield strength (as is typically selected).

 

[FSKeng]

THank you very much
it was realy helpfull,