The Marine Safety Forum has published Safety Alert 21-07 relating to the discovery of a leak in a tank caused by corrosion.
During daily tank sounding routines in the engine room on a vessel, there was an unexpected rise in liquid level in the tank. A close check was made which confirmed this finding, and it was decided to open the tank for investigation.
A pinhole leak was discovered in the structure beneath the sounding pipe. This allowed salt water to enter the space from outside the tank. The vessel was sent for repairs.
What was the cause?
Initial investigation by the ship’s engineers concluded that the striking plate at the bottom of the sounding pipe was missing. This allowed the brass weight to repeatedly strike the steelwork, damaging the paint coating and exposing the steelwork to corrosion.
Further investigation revealed the following:
- The tank had been inspected and maintained in accordance with company procedure;
- The brass weight of the sounding tape had damaged the paint coating on the striking plate and steelwork below;
- A corrosive chemical had been incorrectly disposed of and introduced to the tank, accelerating the corrosion process;
- The acid may have become trapped under bubbles of damaged paint, allowing concentrated corrosion over the short time;
- The combination of exposed steelwork and caustic solution destroyed the striking plate and steelwork below.
- Effective repairs were carried out onboard in collaboration with third party welders and divers;
- All crew were reminded of the importance of correct chemical handling – including safe disposal. On board a vessel, there are many different chemicals used; some of these chemicals pose a serious health risk with some being extremely caustic. These chemicals should be used in the appropriate and prescribed way and not misused;
- MSDS (Material Safety Data Sheet) sheets are provided for safety and information and contain all relevant information about the chemical, such as the physical and chemical properties, hazard identification, handling and storage and disposal considerations;
- Caustic or otherwise dangerous chemicals, and their containers, should be disposed of to an authorized hazardous or special waste collection point in accordance with any local regulation.
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