The industrial boiler’s external inspection usually is once a year and internal inspection is once every two years. 

In addition, a boiler should accept hydraulic test every six years. 

Those boilers that cannot be inspected internally should accept hydraulic test every three years. 

Utility boiler’s internal inspection and hydraulic test cycle can be adjusted according to the overhaul cycle of power plant.

 The boiler can be put into operation only when its internal inspection, external inspection and hydraulic test are qualified within the validity period.