Pages

August 27, 2018

Rupture of sulphuric acid tank


On 4th February 2005 a storage tank containing 16,300 t of 96 % sulphuric acid ruptured. The entire contents of the tank were spilled out into the bund and then overflowed out into the nearby dock. The environmental consequences of the accident were quite significant,the sulphuric acid emission had a serious effect on local flora in the inner and deepest parts of the harbor and harbor entrance area. When the sulphuric acid came into contact with the salt water an exothermic reaction occurred, producing a vapour cloud consisting of hydrogen chloride that drifted northwards along the coastline in the direction of the wind. Fortunately, the wind was blowing towards the sea and away from populated land areas and the cloud diluted very quickly. After the spill approximately 2,000 t of contaminated sulphuric acid remained in the bund. The acid also soaked into about 100,000 square metres of the ground surrounding the spill.
Causes
The cause of this incident was a leak in an underground coolant supply pipe of reinforced concrete installed over forty years before that resulted in a weakening of the ground under the tank farm. Apparently, water forced its way out of the pipe, eroding the ground near and around the sulphuric acid tank. This erosion damaged the ground under the tank which ultimately failed due to the lack of support of the tank floor. A study of the appearance of the involved part of the coolant supply pipe suggests that the corrosion was a result of an acidic attack on the concrete.
Important findings
• The damage indicates that the acid exposure occurred over a long period of time. However, it was not possible to determine the exact duration of the exposure.
• The pipe had been in use over many years and the operator had mno suspicion that the pipe was suffering severe degradation. The inspection of the failed pipe after the incident detected little or no internal corrosion, but heavy external corrosion to the concrete. In certain places the concrete had corroded so severely that the reinforcing steel was exposed.
• According to the German standard, DIN 4030 (equivalent to the European standard, EN 260) a strong attack on concrete occurs if the pH level in surrounding water is < 5.5 and a very strong attack can occur if the pH level is < 4.5. Fifteen years before the accident a ground pollution study was carried out in the area, during which one of the sample taking points was close to the failed coolant supply pipe. At this point the pH level was measured at 4 in the shallow groundwater. With this knowledge the company drew the conclusion that this pH level entailed risks for strong acidic attackson the concrete.
Lessons learned
• The uneven corrosion on the outside of the pipe can possibly be explained by the fact that it lay partly in groundwater flow. In this environment, the acid can pass through the barrier more easily, and the reaction products (gypsum) formed can be more easily dissolved. As such, the concrete barrier was not as effective as on the part of the pipe that remained in drier surroundings. Therefore, concrete piping exposed to ground water should be should be subject to protective measures, monitoring and inspection to take into consideration the increased risk from groundwater exposure.
• Similarly, underground piping that entail risks to foundations should be inspected and measured..
• There are a number of strategies that can be applied to piping where there is accelerated potential for degradation or where there are high consequences should significant degradation occur.
Pipes may, for example, be tested for stability (remains in place) and hydraulically checked on a regular basis. Alternatively, consideration should be given to positioning the pipe above ground. The pipe could also be placed in casings, especially where a leak may cause damage to the surroundings or where pressure and ground deformation may cause damage to the pipe.
Source: European commission

No comments:

Post a Comment