New alloy to save Indian rails from toilet corrosionMay 8th, 2009 - 2:39 pm ICT by IANS
By K.S. Jayaraman
Bangalore, May 8 (IANS) A new alloy steel developed at the Indian Institute of Technology in Kanpur (IIT-K) has provided the answer to one of the major problems faced by the Indian railway system - corrosion of rails by toilet discharge.
Indian Railways is the second largest railroad in the world under a single management, running more than 11,000 trains every day, 7,000 of which are for passengers. The network comprises 108,706 km and ferries 14 million passengers daily from 6,853 stations across the length and breadth of the country.
The stuff leaving the toilets of speeding trains in the form of fine spray corrodes the rails, says R. Balasubramaniam, professor of materials science at IIT-K. “It is a unique problem faced in India where long distance trains are quite common. Longer travel times invariably result in greater use of toilets and, in turn, more corrosion.”
“Rail corrosion is a major problem especially along the salt-laden sea coasts,” admits H.S. Pannu, director-general of the railways’ Lucknow-based Research Designs and Standards Organisation (RDSO). Environmental corrosion combined with “toilet corrosion” shortens the life of rails and according to the railways, nearly Rs.4.4 billion ($89 million) is spent annually on replacement of rails withdrawn prematurely due to corrosion.
The solution to the problem is now at hand thanks to the new corrosion resistant rail steel developed by a team led by Balasubramaniam of IIT-K in collaboration with RDSO and the Steel Authority of India (SAIL).
While atmospheric corrosion of rails may not endanger safety, “crevice corrosion”, taking place under the liners of the rail fastening system - and hence not visible from outside - is particularly worrisome, Balasubramaniam told IANS. “Crevice corrosion is accelerated in the presence of chloride ions near sea coasts as well as in discharge from the toilets of passenger trains.”
The rails currently in use are high carbon steels containing about 0.7 to 0.8 percent carbon and 1.0 percent manganese. “The presence of high amount of iron carbide also called ‘cementite’ renders these rails susceptible to corrosion,” he explained.
The railways’ own efforts to combat crevice corrosion by trying out different types of coatings in field trials failed to work. Extensive trials at a corrosion-prone location near Visakhapatnam showed that even four coats of epoxy could not stop crevice corrosion. Zinc coating was found effective but expensive. “So we decided to tackle this problem through alloy chemistry,” Balasubramaniam said.
A clue for developing the new rail steel came from Balasubramaniam’s earlier research with the 1,600-year-old Iron Pillar of Delhi. The research showed that the pillar’s excellent resistance to atmospheric corrosion was due to presence of traces of phosphorus in the iron that catalysed the formation of a “protective” layer on the steel surface.
Extrapolating the idea, the researchers reasoned that the corrosion rate in the rails could be markedly lowered by micro-alloying the steel with small amounts (0.1 to 1.0 percent) of copper, silicon, nickel and chromium in certain combinations. And they turned out to be right.
The IIT-K group was however not the first to think of alloy chemistry to attack rail corrosion. There were efforts earlier by SAIL to develop a corrosion-resistant rail that used copper and molybdenum as alloying additions. Again, the high cost of molybdenum was an issue.
The aim of IIT-K scientists was to reduce the cost of the rail. So, in their new rail chemistry, they deliberately kept higher levels of chromium and copper alloying elements that are relatively cheap. “We found the alloy containing copper and chromium along with a small amount of nickel gave the best results and this was recommended to the railways,” Balasubramaniam said.
The new rail’s superior corrosion resistance as compared to the standard copper-molybdenum rails has been confirmed in laboratory trials. The evaluation was made using several different types of tests - long term and short term, from simple immersion to complex electrochemical tests, and testing in a simulated environment corrosion chamber. The chromium-copper-nickel rail composition has since been incorporated in the Indian Rail Standard specification.
“We are happy with the laboratory results of the new corrosion resistant rail,” Pannu told IANS. He said the railways have ordered a substantial number of the new rails from SAIL’s Bhilai Steel Plant for large-scale field trials along the coast. If these trials showed promise, he said, the railways may switch over to the new rails. “Our calculations show use of the new rails will be economical in the long run.”
(K. S. Jayaraman can be contacted at firstname.lastname@example.org)
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Tags: alloy steel, atmospheric corrosion, balasubramaniam, chloride ions, crevice corrosion, fastening system, fine spray, indian institute of technology, indian railway system, indian railways, jayaraman, kanpur, materials science, pannu, passenger trains, rail steel, rdso, sea coasts, steel authority, travel times