basis for low allowable stresses for flanged joints

[abhimech1991]

Hi all,

may I know whats the basis for providing low allowable stresses for flange applications???


Thanks in advance

Atish

 

[racookpe1978]

?

Low allowable stresses compared to what other stresses?
For what applications?
under what conditions of pressure, temperature, materials, and fluids?

 

[abhimech1991]

Dear Racookpe1978,

Section-II part D provided 2 types of allowables for same material e.g.SA-240 gr. 316L. When we use this material for flange design ( or we can say strain sensetive applications), code cautions to use lower allowable stress ( note G5 of section-II part D). But for other applications we can use higher allowable stress. May I know what is the basis to decide these high allowable stresses???

Thanks in adavance.

 

[SnTMan]

abhimech1991, lower allowables are used for components in which a small distortion may cause a leak or other problem such as gasketed joints. Flanges, tubesheets, etc. For most other uses the higher allowables are appropriate.

Note G5 explains pretty well.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[abhimech1991]

SntMan,


I would like to know how these ( higher and lower) values of allowables are derived. Whats is the theory / basis behind it?

 

[SnTMan]

abhimech1991, basis for allowables is contained in Sec II, Part D, Appendix 1. I suppose selection of 2/3 yield for lower allowables is somewhat arbitrary and based on failure theories used by the various Codes.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[abhimech1991]

SnTman,

I know the theories of failure. 2/3 of yield is taken as allowable for flnage design. But what is the basis of arriving at the higher values of allowable stresses for same material.?????

 

[TGS4]

It's all covered in ASME Section II, Part D, Appendix 1. What part(s) there don't you understand?

 

[abhimech1991]

I think I am not able to explain my problem in right way. What I want to know is, code has given higher and lower allowable stresses for same material e.g. SA-240 Gr. 316L. Lower allowable stresses shall be used for flange or strain sensetive applications. These lower allowable strsses are 2/3 of yield stress at that temperature. But there is no relation given for higher allowable stress and yield stress/? Do anyone know how these values of higher allowable stresses have been derived???

SnT man / TGS4 can u help me????

 

[SnTMan]

abhimech1991, higher allowables are based on the lowest value of several criteria. Again, this is explained in ASME Section II, Part D, Appendix 1. You have consulted this material, right?

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand