Circular on ballast tank pressure testing without overflowing
Where water pollution regulations prohibit the discharge of water from a vessel, the following procedures may be followed to pressure test ballast tanks. Care will be needed not to discharge the fire hose into the sea when topping up.
In all cases a proper ballasting plan and schedule for testing should be prepared and agreed beforehand, considering trim and vessel stresses.
Tanks should be topped up by opening the air vents and topping up by fire hose until the water level rises towards the top of the air vents. Preferably if air vent height allows, a head of one metre should be sought. This is the best that can be done without overflowing. Further, when overflowing, the pump should not increase pressure over and above that of the height of the air vent as this can pop deck plates and tank tops.
DB tanks. Fill tanks by gravity to sea level. A ballast pump can be used if the vessel wishes, but is not recommended. If there are scuppers, then block scuppers as would be required for bunkering operations. Close sounding pipes tightly if these are at deck level. Open, or take off, air vent tops. Top up tank through air vents by fire hose until (assuming stern trim) water level is close to top of aft air vents. Ensure that fire hose can be stopped quickly as water level nears top of air vent. Check by sounding or ullage through the air vent, that water level in forward air vents has also risen towards top of air vents. Hold level for 30 minutes minimum and check if level in vent is falling or steady. Look for leaks.
Top side tanks. Ask Master/owners to fill ballast db tanks to achieve as even trim as possible. If not possible to fully reduce trim using db tanks only, then consider filling forward side tanks and forepeak tank first to reduce trim. This is important for top side tanks, as an excessive trim can mean that when the aft vent is full, the water level at the forward end has not reached the main deck level. Prepare air vents and sounding pipes as above. Fill tank to near the main deck level by ballast pump. Complete top up into air vents by fire hose. Hold level for 30 minutes.
Fore peak tank. As for top side tanks, but trim is less of a problem.