It would appear that the pressure of the liquid being filtered will force the tube sheet against the internal ring that you propose to weld in place.
The first question that a mechanical engineer has is what is the maximum pressure that the vessel will experience if the filter clogs?
The second thought might be what strength reduction or internal stress might be the result of your welding inside?
The third thought might be, can you sandwich the tube sheet between the bolted flange at the end of the vessel and weld the connector onto the cap? It would seem that you need to remove the cap for filter servicing anyway.