Problem:
How are the stress concentration factors Kn and Kb are determined in AutoPIPE Vessel local load calculations and how these factors vary with the fillet radius (r) at the nozzle-to-shell junction.
Solution:
AutoPIPE Vessel estimates stress concentration factors Kn and Kb using the correlations provided in Annex B of WRC Bulletin 107, where the primary controlling parameter is the ratio of fillet radius to shell thickness (r/T)
Where:
-
- Kn = Membrane Stress Concentration Factor
- Kb = Bending Stress Concentration Factor
- r = fillet radius
- T = shell thickness
As the fillet radius increases, the geometric transition becomes smoother and both Kn and Kb decrease. This reduces the stress concentration at the nozzle-shell junction.
Kn and Kb Values Used in the Estimation:
Following values are used by AutoPIPE Vessel to estimate the local stress concentration effects associated with the attachment fillet radius.