Special attention ｜ Good intentions to do bad things!The crew cleans up the pressure -loading water system filter, and the operational improper operation causes the cabin to get water in

Recently, the UK MAIB (UK MAIB) shared a case of "good intentions to do bad things" in the 2022 "Safety Abstract" released by it: the crew on a small dry loose cargo boat Improper operation leads to water in the cabin, and the ship has to enter the dry dock for maintenance.

✍The incident pass

During a small dry bulk carrier stop at the port, the turbines on the boat were investigating why the operation was spent longer than normal. Their plan is to clean up the seawater filter of the pressure -loading water system and check the condition of the carrier pump.

In order to isolate the filter, the large tube wheel (2/e) went to the pressure control panel and closed the automatic butterfly valve between the hull entrance and the filter (Figure 1). The valve is displayed on the voltage control panel as a closed state. Then the large tube wheel enters the cabin and manually close the isolation valve between the filter and the pump (Figure 1).

Figure 1 Pressure water valve and filter arrangement schematic diagram source/ UK MAIB

Strainer Box lid: filter box cover

Lifting Eye: Hanging

Strainer Box Bolts: filter box bolt

Test plug: measuring stress plug

Manual Gate Valve: Manual Valve

Automatic Butterfly Valve: Automatic Butterfly Valve

In the case of the head of the turbine, the large tube was loosened by the fixed bolt of the filter cover, and tried to pry the filter cover with a screwdriver, but the lid was not loose. The turbines then installed a Chain Block on the filter to completely remove all bolts. When the inverted chain was affected, the filter flies out, and the seawater begins to pour into the cabin. The turbines tried to replace the lid but did not succeed, and then they decided to evacuate the cabin and issue an alarm.

The water level in the cabin rose above the bottom plate, until the pressure of the sea water was balanced, and the ship began to sink, and the cabin was flooded (Figure 2). A diver was installed on the hull valve to install an external supplement, and the ship stopped water. Subsequently, the polluted water was pulled out and handled, and the ship also entered the dry dock for maintenance.

Figure 2 The cabin source of the water inlet/ uk maib

After the accident, a technical survey was carried out on the ship and found that the automatic butterfly valve was defective. When the valve was turned off on the carrier control panel, the valve actually kept partially open. The survey also found that the filter is actually clean, but the pressure pump has a defect that causes the pressure to be slow. After that, the company revised the cleaning and safety operation system of the pressure -loading water system.

✍ Experience lessons

Observe the program: The filter cover is equipped with a measuring plug (Figure 1), which is to ensure that the system is not under pressure before removing the lid. However, the turbines involved in the accident did not clean the filter according to the approval procedure nor opened the test plug. Therefore, they did not realize that the valve was faulty and this meant that the system was still undergoing sea water pressure. In addition, when they tried to remove the lid with a screwdriver, no leaks appeared, which made them more convinced that the judgment of "isolate the system".

Careful inspection: In view of the display valve on the carrier control panel, the turbines have reason to think that the situation is indeed the case. However, if there is a doubt, or when the system and the seawater are only one valve, it is best to check the mechanical location indicator of the valve and check its remote indication. Further prevention measures are to release the nut and then open the lid with a wedge; if there is water overflow, you can tighten the fixed nut to keep the filter cover.

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