Right......so when you check out components from OPMS and then check in the dgn file into the PW repository, the components remain locked in the dgn file. You can Free the components from OP Administrator which you do want to use so here is what you can do.
1. Check In the dgn file/document into PW Explorer.
2. Open another dgn file from PW Explorer and connect to the OPMS repository.
3. From the items browser or Model Server task pane, launch OpenPlant ModelServer Operations History Tool.
4. This will bring up the grid showing CheckOut History and CheckIn History.
5. Select the correct/relevant entry (look for the dgn file name) and then hit Free from the tool strip at the top.
6. This will free the components from your other dgn file.
But remember, this will mark the components as available for use but the components in the other dgn file will be still in the dgn file and treated as orphan.
So next time you open the other dgn file, first thing you will need to do is select all and delete all components and also pipelines from pipeline manager.
It is recommended to first check out the other dgn file and then free them if you still want to work with that dgn file.
Hope this helps.