Continue to Site

Eng-Tips is the largest engineering community on the Internet

Intelligent Work Forums for Engineering Professionals

  • Congratulations SDETERS on being selected by the Eng-Tips community for having the most helpful posts in the forums last week. Way to Go!

ASME Local Membrane Stress Distance

MSL68

Nuclear
Jun 23, 2023
2
ASME BPVC (Section III Appendix XIII-3100, or in older Code versions, this is described in the Definitions section) says "A stressed region may be considered local if the distance over which the membrane stress intensity exceeds 1.1S does not extend in the meridional direction more than 1.0*sqrt(Rt), where R is the minimum midsurface radius of curvature and t is the minimum thickness of the region considered.

The only example the Code gives is based on an axisymmetric shell (Figure XIII-1300-1), and this requirement makes sense for this type of geometry. However, what is supposed to be considered R and t in the case of a nozzle in a shell? Is the "region considered" the entire shell/nozzle junction (circled in red in the figure), where the R and t values come from MIN(r.shell, r.nozzle), and similar for the thickness? If that is the case, should that distance be considered for the entire 'region considered', as in sqrt(Rt) is the length from 'a' to 'b'?

Or, would the shell and nozzle be considered separately, where a sqrt(Rt) is calculated individually with their respective geometries, and that length for the shell is arrow 'a', and 'b' for the nozzle?

My thinking is the first interpretation is more reasonable, because when you think about a infinitely large plate with a small hole, you would expect the attenuation length of the local membrane stress to be quite small and the size/thickness of the shell has little bearing on how it attenuates.
 

Attachments

  • Shell_Nozzle_PL.PNG
    Shell_Nozzle_PL.PNG
    9.9 KB · Views: 2
Replies continue below

Recommended for you

That distance is measured away from the SCL, using the value of R and t for the respective components. You cannot draw a valid SCL in the junction ring (transition region) - see WRC 429 for the definitions, so the only possible option is to measure away from the SCL that is located at the intersection of the structural region and the transition region.

So, your second option.
 

Part and Inventory Search

Sponsor