(a) The maximum allowable pressure consistent with the maximum and minimum operating temperatures of a boiler carrying the ASME Code symbol or of a pressure vessel carrying the ASME Code symbol shall be determined by the applicable section of the Code under which it was constructed and stamped or a later edition of the ASME Code, provided the rating conforms with the rules of the later edition.
     (b) The maximum allowable pressure consistent with the maximum and minimum operating temperatures of a boiler or pressure vessel that does not carry the ASME Code symbol shall be computed in accordance with the rules and regulations of the Board, unless the boiler or pressure vessel is of special design or construction, in which case the Board may grant, at its discretion, a special operating permit consistent with the safety objectives of the rules and regulations of the Board.
     (c) This Act does not prohibit the use, sale, or reinstallation of a boiler or pressure vessel referred to in this Section, provided it has been made to conform to the rules and regulations of the Board governing existing installations, and provided, further, it has not been found upon inspection to be in an unsafe condition.