Indian Railways has more than 64,215 km of rail track and 7083 stations says the Wikipedia. It is the world’s fourth largest railway network and carries some 25 million people and 2.5, million tons of freight daily. Considering the vastness of the network and the number of lives it carries, it is imperative that the railways are kept absolutely safe and hazard free.
It is shocking to know that the corrosion of the rails is enhanced by the human excreta. Since millions travel each day, the rail tracks have become susceptible to worse kind of corrosion problem. Being a tropical country the microbes reproduce pretty fast. Hence the rails face the brunt of our own doing. The following description will make the train travelers in India think twice before using the train’s loo. The feculent rails are prone to disasters.
Railways have their own mechanism of implementing safety devices and all possible loop holes are constantly monitored and plugged to ensure mishaps. Of late a strange phenomenon has come to light. S. Maruthamuthu, T. Nagendran, M.S. Karthikeyan and N. Palniswamy of Corrosion Protection Division, Central Electrochemical Research Institute, Karaikudi and B. Anandkumar of Corrosion Science and Technology Division Indira Gandhi Centre for Atomic Research Kalapakkam and G. Narayanan of Southern Railway joined hands together to study the corrosion of rail tracks in south India. They found that rails in South India were getting corroded fast due to human excreta. The results though sound amusing indicate how damaging and corrosive the microbes can be! In this case persistent corrosion could lead to a rail disaster.
Railway tracks have a great attraction for people in rural India. Not that they want to run on them. For want of proper sanitary facilities they use the tracks as a platform to defecate. Of course the numbers of such people is now gradually reducing. However, there is no let up in the number of passengers traveling. The train toilets are still the old types with a hole at the bottom to flush down the deed. Lot of muck thus falls on the tracks everyday all over the country.
Md. Safiuddin of Department of Civil Engineering, University of Waterloo, Canada in one of his papers about corrosion says, ‘microbial corrosion is another form of corrosion that often occurs in metals contacted with soil or sludge.’ He says the causes of such corrosion could be due to direct contact of rails with damp soil; dominant de-aerated sheltered environment; aerobic and anaerobic soil microbes; dominant presence of sulfate reducing bacteria; highly resisting and water-logged condition of soil; long residence time of water on metal surface; higher clay content of soil; poor drainage facility; removal or leaching of iron and catalyzing effect of biological slime deposits.
However, Maruthamuthu et al say that the corrosion rate at the rail base is affected by humidity and deposited salts, but most importantly by stray DC currents that generate electrolytic reactions. Such reactions accelerate the rate of corrosion. Microbes in the environment dictate the severity of atmospheric corrosion. The rails laid near coastal regions are more prone to atmospheric corrosion warranting frequent replacement of rails. One of the reasons they cite is that the rails near major junctions, where trains halt in the early hours of mornings show pronounced corrosion at bottom flanges and fittings. This corrosion, quoting the Railway officials and corrosion engineers, Maruthamuthu et al say that it is due to the microbes present in the human excreta.
However, Maruthamuthu et al found something more interesting and glaring. The accelerated corrosion is due to accumulation of moisture from the atmosphere and also due to discharge from the open toilets of the trains. It is amazing to know that human urine contains 0.4 to 0.5 mg urea. Annually an adult human being releases 10 kg urea. The ureolytic enzymes present in the urine convert urea into carbonic acid and ammonia. These researchers were able to isolate ureolytic bacteria by using synthetic urine on rails and were able to study the behavior of rails under the impact of these bacteria.
For the purpose they collected corrosion product from a steel rail near a major junction. Since microbes are not seen by the naked eye and they are omnipresent, these researchers took extreme care to collect contamination free samples. For example they used sterile knife and sterile saline containers kept in ice. Thus the material was shifted to the lab in freezing conditions. It is understood that cold reduces the chances of microbes multiplying. They found that the ureolytic bacteria produce carbonic acid and a second molecule of ammonia, which probably creates differential pH on the metal surface and accelerates the corrosion process. The biofilm formed on the surface of the rails is heterogeneous and the surface faces dry and wet conditions. All these factors enhance corrosion in open atmosphere.
It is not that that the Indian Railways is not aware of the problem. Infact the researchers like R. Balasubramaniam, B. Panda, G. Dwivedi and S. Mahapatra of the IIT, Kanpur; A.K. Manuwal of the Research Designs and Standards Organisation, Indian Railways, Lucknow, A. Bhattacharyya and K. Srikanth of Research and Development Centre for Iron and Steel, SAIL, Ranchi and R.K. Rathi of Steel Mining Shop and Research Control Laboratory, Bhilai have developed a novel chromium, copper and nickel rail which has a superior corrosion resistance ability than the modern rails made of high carbon steels. Despite a better combination of strength, hardness and ductility, these rails are susceptible to crevice corrosion along the sea coasts or discharge from the toilets of passenger trains they claim.
The rail made of new alloy by the above researchers is still being tested before starting a large scale production. Meanwhile the railways are also working on installing ‘dry toilets’ in the trains, to avoid the tracks being littered with excreta.
Indian Railways carry millions of passengers daily; hence safety of rails is of paramount importance to all. It is time that the material developed by academia-industry-user collaboration is well tested on priority and safer rails installed. The studies show that most vulnerable places are either the train junctions or near the junctions, where passenger trains halt. Maximum pollution of rails takes place in the early hours of the morning. Such areas need to be watched and warnings displayed and announced to let the passengers know that their lives are at risk on feculent rails.
1. Vulnerable parts of the rail prone to fecund corrosion curtsey Editor Current Science.