46 CFR §61.05-5

1. (a)For internal inspection, manhole and handhold plates, and washout plugs must be removed as required by the marine inspector and the furnace and combustion chambers must be thoroughly cooled and cleaned.
2. (b)In preparing the boilers for the hydrostatic test, they must be filled with water at not less than 70 °F and not more than 160 °F for watertube boilers, and not more than 100 °F for firetube boilers. The safety valves must be secured by means of gags or clamps.