When 3D model is exported to DWG file, graphics of TEE disappear from DWG file. This article will cover what settings user should look for to fix this issue. As shown below graphics of TEE have disappeared from exported DWG file.
http://communities.bentley.com/products/plant/design___engineering/w/plant_design_and_engineering__wiki/24147.importexport-openplant-modeler