as shown on the att. picture.
for Tee 20" sch.40 , 20 deg c, 1MPa, it seems the TEE needs to be rounded with enough radius. the model is built with solid elements and shell elements.
What are your element qualities in that area? (RMB on Mesh > Details)
You might have some problem with that which could be minimized with mesh refinement.
whatever may be the element size, you will get the stress more near the junction area (2 different geometry union area)
any way check the quality of the mesh
First check your mesh . You should mesh the thickness at least 2 element.
Second check is there any hot spot in your model
What's New in SOLIDWORKS Simulation 2017 Hot Spots Diagnostic - YouTube
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