Dear Ms. Marina
This kind of equipments, OWS / STP etc, these are not required the annual maintenance service from IMO or Class. But, they only require the calibration
or replacement of sensor unit for 15ppm bilge alarm per 5 years.
( But, life saving equipments such as life boat / rescue boat and davit shall carry out the annual maintenance service from IMO or Class )
So, they, OWS or STP makers, have never carried out the annual maintenance service to visit the shipyard.
Again, we don't visit the shipyard to carry out the this kind of service.
Anyhow, this kind of equipments is not required the annual maintenance service from IMO and Class.