MSF: Tank corrosion

The Marine Safety Forum has published Safety Alert 21-07 relating to the discovery of a leak in a tank caused by corrosion. 

What happened

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.

Actions taken

• 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.

Members may wish to refer to:

• IMCA pocket safety card Hazardous substances safety guide.  
• Failure of pipework in fuel tanks
• Aluminium fresh water tanks: Near collapse due to serious corrosion
• Chemical spill leads to costly deck replacement