You can try the following steps to bring in graphical equipment models from other applications:
1. Launch an OpenPlant Modeler session and open a new dgn file.
2. From the File > References > Tools > Attach option, select the file which contains the graphical equipment models.
3. Select everything in the model (by Select All or using Ctrl + A option) and then paste everything in the graphics.
4. After the graphics have been pasted, detach the reference file from File > References > Tools > Detach option.
5. Create a cell for the graphics in the dgn file and then create a custom equipment for the cell.
This should work for you. If not, kindly share the graphical equipment model that you are trying to work with.
Also kindly confirm if you are using the OpenPlant Modeler version 08.11.09.278