Introduction to forensic engineering
6 Containment problem: storage tanks
The second containment case study deals with storage tanks. They are products that must be correctly designed to perform their function of containment of a hazardous fluid safely over a reasonable lifetime. The consequences of failure can be catastrophic if the stored contents are released into the environment, and so it was in the example described in Papers 4 and 5. It was a tank made by the thermal welding of sheet polypropylene, and was designed to store 30 tonnes of concentrated caustic soda. Papers 4 and 5 are attached as pdf documents which should be printed out (if possible) to gain the maximum benefit from the discussion of this case study (they should at least be kept open on the desktop throughout Section 6).
Click on the 'View document' link below to read Paper 4.
Click on the 'View document' link below to read Paper 5.
A brief description of the hazards of caustic soda is useful at this point (Figure 74). It is one of the most corrosive agents in common commercial application, being a by product of the electrolytic manufacture of chlorine. Figure 74 shows the hazard notice of the fluid caustic soda, and warns of the dangers. It is a syrupy liquid with a concentration of about 40 per cent caustic soda (NaOH). It is extremely aggressive in contact with a wide range of materials, especially living tissue. Human skin, for example, is rapidly dissolved with no pain to the victim because the nerves are consumed at the same rate as surrounding tissue – unlike attack by strong acids. Escape into streams and rivers would kill a range of plant and animal life.
Plastic tanks have been in use in industry for a long period of time, at least from the early 1970s, and continue to expand in usage owing to the ease of fabrication, the excellent resistance to corrosive chemicals, and the low cost of the material. The tanks are made individually to order by hand construction with fairly simple equipment, so manufacturing costs are low.
The increased usage encouraged smaller companies to enter the field with competitive prices. But the only standard covering their design, use and testing is German, and not easily available in English in the UK – although partial translations can be obtained from the larger manufacturers.