Each company operating boilers and/or pressure vessels covered by owner or user inspection service meeting the requirements of Section 45-23-21(b) shall maintain in its files an inspection record which shall list, by number and such abbreviated description as may be necessary for identification, each pressure vessel covered by this chapter, the date of the last inspection of each such unit, and for each pressure vessel the approximate date for the next inspection thereof arrived at by applying the appropriate rules therefor to all data available at the time such inspection record is compiled. Such inspection record shall be readily available for examination by the chief inspector or his authorized representative during business hours.