The gasket which was removed from the LÉ Aoife has been sent for further testing after it was not possible to ascertain whether it contains asbestos.
The compartment which it was in was the subject of an air surveillance test, which was found to be normal.
The vessel has now weighed anchor and returned to its operational patrol.
The Defence Forces investigation into whether the gasket contained asbestos came after another item from the vessel tested positive for the substance.
The issue came to light when the engine on the vessel was being repaired.
The Defence Forces said concern was raised in the last 48 hours, during a routine maintenance procedure on LÉ Aoife.
The vessel returned closer to the coast last night in order to meet a contractor and have the gasket examined.
It said after a full risk assessment was completed, a gasket that was being removed gave cause for further examination.
It said the gasket was sealed in a protective bag and removed from the area.
The gasket was also covered in lubricant, in good condition and had not been handled or ground in such a manner that could potentially lead to the release of any harmful fibres if they existed.
Concern was raised over several gaskets, lagging and other material by staff after maintenance on the vessel last week.
One of these items subsequently tested positive for asbestos.
The Naval Service said it has communicated with its personnel on every concern raised.
In addition, it said it has introduced further precautionary protocols on all vessels and the level of awareness of the potential threat has also been raised to mitigate any potential risk.
There had been concern recently about asbestos on LÉ Ciara and LÉ Orla.
It is expected that the vessels will return to service when the remedial works are complete.
The Defence Forces said this is estimated to take a number of weeks.