ACID ATTACK ON CONCRETE CAUSES AN INCIDENT

On 4 February, 2005, a storage tank containing 16,300 tons of 96 % sulphuric acid ruptured. The content of the reservoir spilled out into the bund and then the dock. The remaining 2,000 tons of acid in the bund came into contact with salt water that created an exothermic reaction, which produced an acid cloud consisting of hydrogen chloride. The vapour cloud drifted along the coastline and mostly over the sea. No one was affected by the event.
Key learning points
The incident was caused by a leak in the cooling water supply pipe passing under the tank farm. The leak undermined the ground under the foundations of a tank which then ruptured because of the uneven weight distribution resulting in the sudden release of the acid. The bund was filled with salt water when the rupture occurred and that caused the formation of hydrochloric acid. The pipe was made of concrete and came into use in the early 1960s. The only damage noted to the pipe was a leak at the pumping station in 1999. The inspection of the failed pipe following the incident detected little or no internal corrosion, but heavy external corrosion to the concrete. In certain parts of the pipe the concrete has corroded so severely that the reinforcing steel had also been exposed. It suggests that the corrosion was as a result of an acid attack on the concrete. According to the standards, a strong acid attack on concrete occurs if the pH level in surrounding water is < 5.5 and a very strong attack if the pH level is < 4.5. The company drew the conclusion that the pH level measured as 4 in the shallow groundwater in 1989 entailed risks for strong acid attack on the concrete. However, there was no risk assessment conducted.

Source:IChemE