We are analysing piping as per B31.3 for one of our projects and have been requested to add SIFs at all branch connections, irrespective of branch diameter. As a result we are ending up defining SIFs at all drain ,vent ,temperature,pressure connections.
Caesar calculates and applies same value of SIF on branch and header irrespective of branch size as most of SIF calculations are based on Header diameter and not on branch diameter.

As a case ,we have an 18” X 1.5” weldolet connection . Caesar uses an SIF of 3.31 for both header as well as branch. Due to this SIF value ,Caesar is reporting failure in the 18” header in some load cases.

Practically we are aware that a 1.5 “ connection will not matter at all for an 18” Header.
Is there any clause in B31.3 that speaks of any limitation of SIF values for very low d/D ratios.?
Any ideas or suggestions?