(a) Time of inspection.

The exterior of every boiler or steam reservoir shall be thoroughly inspected before being put into service and whenever the jacket and the lagging are removed.

(b) Lagging to be removed.

The jacket and lagging shall be removed at least once every five years and a thorough inspection made of the entire exterior of the boiler while under hydrostatic pressure. The jacket and lagging shall be removed whenever, on account of indications of leaks, the commission's inspector or the operator's inspector considers it desirable or necessary.