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Major Success in Fighting Rust

CECRTs anti-corrosion treatment on steel rebars consists of four steps subsequent to bending and shaping. Scientists first derust steel rods by dipping them in a derusting solution to obtain a bright surface, and then apply a phosphating jelly as a coating.

by T.V. Padma
INDIAN scientists are launching an all-out offensive to lay all rust to rest.
Undeterred by the site of the rust — be it in oil pipelines deep in the ocean or skyscrapers in cities, a small jetty bobbing in the sea or a massive petroleum refining complex — scientists have armed themselves with an array of inhibitors. alloys. jellies, primers, paints and oils to assault rusty and corroded structures.
The battle against corrosion is being chalked out in the laboratories of the Central Electrochemical Research Institute (CECRI), Karaikudi. whose new anti-corrosion technologies to protect vital installations such as bridges and offshore pipelines and platforms for oil drilling are expected to save over a -hundred million rupees every year.
Annual losses due to corrosion mount to 3 to 5 percent of a country’s gross national product (GNP) and 10 percent of the annual metal output invariably goes into replacing corroded materials.
Some of the CECRI processes, already made mandatory by the Ministry of Surface Transport, are being used in several places, including the Mandovt bridge in Goa, the , l’amban bridge near Rameshwaram, port trusts, thermal power stations, and the Oil and Natural Gas Commission's offshore pipelines, CECRI Director Prof S K Rangarajan says.
Corrosion manifests itself in different forms: there can be uniform corrosion of the metal surface leading to an average reduction in thickness, or a localised form of failure like pitting or cracking which Is sudden and unpredictable.
The danger comes mainly from pre-stressed concrete bridges which face considerable damage due to sudden snapping of corroded prestressed wires.
High strength prestressing steel, which is held tn permanent tension, is increasingly used in bridge constructions. The steel is highly sensitive to environmental cracking and snapping due to corrosion and hydrogen embrittlement.
It is also vulnerable lo severe co erosion due lo time lag between insertion in the cable duct, stressing and final cement grouting.
CECRI s proteclion package consists of surface modification of prestressed steel, temporary protection during transit and storage, temporary pro-lection while laying in cable duel and adding an inhibitor admixture to cement grout.
CECRI is laekling the problems on four fronts it has developed suitable coatings for rebars, for concrete surfaces, corrosion control measures for pre-stressed slcel wires during transport, laying down and actual service, and ways to
modify existing concrete composition.
CECRl's anti-corrosion treatment on steel rebars consists of four steps subsequent to bending and shaping. Scientists first derust steel rods by dipping them in a derusting solution to obtain a bright surface, and then apply a phosphating jelly as a coat-Ing-
Two more coats of inhibited cement slurry, followed by a sealing coating and the treatment is over In about three days to give a chloride-free protective environment around the steel bars.
The treatment which can be done on site and costs less than one percent of the total cost of construction, enhances • the durability of RCC structures by nearly five times tn marine climates. It does not affect the bonding, between steel and concrete, extensive tests have shown.
The institute has developed a package of technologies to protect pre-stressed steels at all stages, right from manufacture to grading coatings for steel-rebars and the concrete surfaces, as well as corrosion-resistant concrete mixers.
The new treatmenu to protect both the concrete structures and steel reinforcing bars (rebars) Inside.arc vital
for India where at least 700 bridges need either replacement or improvement at an es timated cost of Rs 10.000 crores.
Another CECJRI technique is cathodic protection, which involves application of an external negative voltage lo protect steel rebars in marine structures such as offshore platforms, jetties and ships as well as burled structures such as underground pipelines. The structure to be protected is converted into a cathode relative to an external anode.
The method uses galvanic or sacrificial anodes based on
metals which have more negative electrode potentials than the structure. A second method Is the impressed current anode technique in which the current is impressed from and external source.
Earlier India imported thousand-million rupees worth , galvanic anodes lo offer this protection, but now CECRI has the know-how for aluminum alloy anodes incorporating mercury or indium, zinc alloy and magnesium anodes.
Aluminium altoy anodes can be used in shiphulls, barges, dock structures, jetties, submarine pipelines and ballast tanks. Magnesium alloy anodes find use in pipelines, storage tank bottoms and towerfooling of overhead power lines, while zinc altoy anodes have potential application in water boxes, condensers and fresh water tanks.
CECRl's titanium substrate insoluble anode (TSIA) is currently being used for cathodic protection of Jetties, marine structures and Interiors of pipelines.
Cathodic protection slops corrosion even tn salt-contaminated concrete and strikes at the root of corrosion, unlike currently used patches, sealers and membranes which treat the Symptoms only.
To ensure that their protec-
tive measures arc working, CECRI scientists, have devcl oped a hi-tech SCADA -acronym for supervisory control and data acquisition —as a next generation monitoring system for the marine strut-tunes.
SCADA. which monitors from a control room, ensures adequate and continuous protection of the structure.
Another major development is water repellent polymer coatings to protect the marine structures.
Research on water-borne paints Is receiving attention, more so because of severe restrictions imposed in developed nations on the use of
harmful organic sohrents-based paints.
Organic coatings to protect structures and equipments account for 30-40 percent of the total cost of corrosion.
CECRI has made rapid advances In the field of high-bulld paints, water-soluble paints that minimise pollution and the less toxic anti-fouling paints.
The Institute's epoxy polyamide coating which can be applied over moist surfaces and prevents fires Is expected to find extensive use in bridges. ONGC and chemical Industries.
It has also synthesised a few water-soluble restns based on alkyd and epoxy restns that give highly corrosion-resistant clcctrocoaUngs for automobiles and appliances.
Its polycrystalline phosphate coatings can be also used as a pretreatment for automobiles, household electrical gadgets and appliances and steel furniture.
A water-based rust coh verier has been developed, which converts surface rust into a protective film in a three-in-one process that combines surface preparation, pretreatment and primer application.
The universal rust converter for marine and Indus-
trial structures can be used on any rusted surface without the usual treatment procedures. -
Other measures lo tackle rust in bridges, towers and tanks Include inhibitors and Jellies that remove rust from steel structures, primers based on zinc silicate, and rust preventive oils.
Similarly, the institute's calcium chromate pigment may be a boon to the paint industry as a substitute for costly zinc chromate pigments.
CECRI has established an off-shore laboratory at Tuticorin lo develop techniques to control marine corrosion and biofouling.'a phenomenon in which marine organisms attach themselves to ships and pipelines and damage them.
CECRl's Offshore Platform and Marine Electrochemistry Centre (Ol’MEC) at Tuticorin is studying the mechanics of barnacle corrosion and coltect-ing data on biofouling by ma-nm- species, and atmospheric corrosion of steel and copper in coastal regions.
Biofouling 1s a major prob lem In power-generating plants which use sea waler for cooling. In the worst case fouling can reduce the diameter of intake pipes by almost half.
So enormous is the problem that a 15 ems thick growth of marine micro-organisms on structures needs an additional 50-mm thick steel for offshore platforms.
Water used in heat exchangers, boilers and secondary oil wells causes problems of deposit formation, fouling due lo bacteria and corrosion of materials.
CECRI has developed less toxic inhibitors to control corrosion. a package of oxygen scavengers, antiscalanls and corrosion inhibitors for secondary oil wells, and special inhibitors for acid and alkaline media.
The. Institute's experts and experience arc being Increasingly used by both private and public sector undertakings in India In the form of sponsored projects and consultancies. It
problems faced by defence and space organisations.
—(PTf Science Service)