Stress Intensification Factors for Fabricated Lateral Piping Connections

Stress intensification factors (SIFs) are published in the piping codes for tees; branch connections where the branch intersects the header pipe at 90 deg. These factors when multiplied by the nominal stress provide a measure of the increased local stresses at the junction of the two pipes. However, in cases where the branch pipe meets the header at an angle of other than 90 deg, the main piping codes do not provide a method of calculating the SIFs. This presents a difficulty for the pipe stress engineer who must determine appropriate SIFs, usually in a conservative way and then manually enter these into the pipe stress program. This paper summarizes some of the published methods of calculating SIFs for a limited range of lateral branch connections and makes recommendations based on comparisons with finite element analysis (FEA) studies. It also includes recommendations on how such FEA studies should be applied in order to provide suitable SIF values.