A new boiler or pressure vessel may not be installed and operated in the State unless: the boiler or pressure vessel conforms to the regulations adopted under this subtitle that govern new construction and installation; or the Board issues a special installation and operating permit for the boiler or pressure vessel. The Board may issue a special installation and operating permit for a boiler or pressure vessel if it: is of special design or construction; and is not inconsistent with the spirit and safety objectives of the regulations adopted under this subtitle. For existing boiler and pressure vessel installations: the maximum allowable pressure of a boiler or pressure vessel that carries the ASME Code symbol shall be determined by the applicable provisions of the ASME Code under which it was constructed and stamped; and the maximum allowable pressure of a boiler or pressure vessel that does not carry the ASME Code symbol shall be computed in accordance with the Inspection Code of the National Board of Boiler and Pressure Vessel Inspectors. This subtitle does not prevent the use, sale, or reinstallation of an existing boiler or pressure vessel if the boiler or pressure vessel: has been made to conform to the regulations adopted under this subtitle that govern existing installations; and has been inspected and found not to be in an unsafe condition.