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How to prevent water hammer and surging during routine ballast operations at sea ?
During ballast water or liquid cargo handling operations, always handle the valves and pumps with care so that there is no sudden change in the pressure or the flow rate of the liquid. On recently introduced larger sized vessels operation hitherto deemed routine, there is a higher possibility of water hammering and/or surging..
AA. For offsetting Negative pressures in relevant pipelines to prevent the Water Hammer Effect
Confirm the pressure in the ballast line is Positive by the suction gauge on Water Ballast Pump (hereinafter WBP) or Water Ballast Eductor (hereinafter WBED).
If the line pressure is Negative, the following is required to avoid a Water Hammer which may be caused by the negative pressure at the initial stage of ballasting : make the line pressure positive prior to ballasting by slightly opening (10% / crack open) the suction valve of the empty ballast tank or the overboard discharge valve which is above the water line.
Note on the in-line-pressure judgment. When the ships trim is more than usual and the water remains in the line as well, there is a possibility that the suction gauge does not indicate the negative pressure. The remaining water in the ballast line near the pump may cause the gauge to indicate positive pressure, though the other end of line is under extreme negative pressure.
BB. Procedure for leading water in the lines / Filling up water in WB suction pipes
: Prior to start of ballasting, the relevant lines should be filled up with sea water to prevent the acceleration of the water flow in the ballast suction line. Confirming above (1), open the Water Ballast Pump sea-chest valve 10 % (Slight open) to lead seawater into the line. Moreover, stop operation of the valve until: i) The Water Ballast Pump suction gauge indication corresponds to the water head of the Ships draft and indicates a stable reading. ii) Confirm sea water comes out from the Air purge cock on the suction strainer of WBP.
Letting in the water to WBP through sea chest valve:
- Priming the suction line of WBP through the sea-chest valve is for preventing the occurrence of Water Hammer because of the short water flow distance between the BWP and the valve.
- If the intermediate valve opening is not available, adjust the working speed of the valve as per diameter value such as less than one inch (25mm) per 3 seconds (For example: 96 sec. for the valve with diameter of 800 mm)
CC. Prevention of Surging / the existence of Air lump in the line
When the process AA. and BB. are complet the ballast suction line is filled up with sea water and it is confirmed is at a positive pressure, the Water Hammer possibility is quite low, it is the time to proceed Line-up for ballasting on a full scale.
In the meantime, countermeasures for preventing Surging possibly triggered by Air lump in the line shall be carried out. The line-up should be done observing following basic practices.
- Priming the ballast suction line with sea water, ensure successful air purging.
- To avoid accelerating water flow in the ballast suction line, start the ballasting operation from the closest tank to the WB sea chest valve, and the de-ballasting from the closest tank to WBP (or WB overboard discharging valve).
- To ease the impact of Surging by extraction of Air lump in the ballast suction line, gentle gravity shall be used for checking water-heads.
- Principle procedure to Stop the ballast operation by gravity When sustaining Ballasting, De-ballasting or Shifting ballast water internally by gravity, close from the furthermost valve to upstream water source one by one (i.e. from the lowest water-head to higher water-head) so as not to detain enormous volume of air in the ballast suction line,.
Preventing Liquid block in suction lines
On a ballast voyage of bulk carriers, when suction lines are filled with water, the suction-filling valve of one of the Water Ballast Tanks shall always be open as a precaution against Liquid block; so that the pressure inside ballast line does become negative.
*Liquid block is the boosting of internal pressure by liquid volume expansion in closed pipe space due to temperature rise. Sometime, excessive Liquid block results in damages to the valve seat ring or other, thus care should be taken to avoid a liquid block in any pipe.
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Safety precautions during ballast operation
Loading of high density cargo and water ballast distribution for bulk carriers
Regulation of pumping system of bulk carriers
Risk of partially filled ballast tanks
Handling water ingress problems in bulk carrier, investigation and countermeasures
Our detail pages illustrated many safety aspects of Bulk carrier
- MARPOL 73/78
- IMO Resolution A.774 (18) Guidelines for Preventing the Introduction of Unwanted Aquatic Organisms and Pathogens from Ships Ballast Water and Sediment Discharged
- Ships Procedure and Arrangements manual (Approved by Class)
- Guide to Port Entry
- US NPDES Vessel General Permit Compliance Manual
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