(a) Horizontal return tubular boilers over thirty-six-inch (36″) diameter with longitudinal lap-riveted seams shall not be operated at a pressure in excess of fifty pounds (50 lbs.) per square inch unless all of the following are done every five (5) years of operation:

1. (1) Sufficient tubes are removed to permit the internal surfaces of the shell to be completely cleaned of scale.
2. (2) Sufficient brickwork is removed to permit the external surfaces of the longitudinal seam to be cleaned.

3. (3) Before the tubes and brickwork are replaced the boiler shall be thoroughly inspected internally and externally by a qualified inspector. The tubes shall then be replaced and the boiler shall be subject to a hydrostatic test of one and one-half (1 ½ ) times the working pressure. This pressure shall be maintained for at least thirty (30) minutes after which a qualified inspector shall examine all riveted joints for leakage and/or cracks.

   The term five (5) years used in this section shall mean five (5) years under steam, but in no case shall the time of service be taken as less than six (6) months per calendar year; a hydrostatic test of one and one-half (1 ½ ) times the allowed pressure on the boiler shall be made in the presence of a qualified inspector at least every five (5) calendar years. Each boiler shall be subject to any additional requirements found necessary by the qualified inspector.