Steel and Transmission of Electric Power...

Steel and Transmission of Electric Power  Transmission of electric power is a process by which the electric power produced at power plants is transported in bulk quantities over long distances for eventual use by consumers. The ultimate objective of electric power transmission is to provide power to customers economically, safely, reliably, efficiently, and with minimal environmental impact. Each of these aspects has one or more quantitative measure, such as price per kilowatt-hour, number and lethality of accidents, frequency and duration of service interruptions, generating plant heat rate, transmission and distribution losses, and emissions factors. Transmission systems are designed, and their individual components selected, with all of these objectives in mind, though they may be optimized differently in different systems. Power transmission process has got three main components (Fig 1). They are (i) substations, (ii) transmission poles and towers, and (iii) electricity conductors. Steel plays a major role in all these three components of transmitting power from the point of generation to the consumers. Fig 1 Components of power transmission process Steel use in substations Substations transform voltage from high to low, or the reverse, or perform any of several other important functions. Substation varies in size and configuration. Between the generating station and consuming point, electric power may flow through several substations at different voltage levels. A substation consists of (i) outdoor switch yard, (ii) a building which houses the control equipment, and (iii) the fencing. The outdoor switch yard has (i) structures at dead-end, (ii) static poles, and bus supports and equipment stands. It has also got the grounding arrangement. Structures at dead-end are those structures where the transmission line ends or angles off. They are typically constructed with heavier structural steels in case they are needed to carry heavier tension. The two most common dead-end...

Colour Coating of Steels Sep14

Colour Coating of Steels...

Colour Coating of Steels  Colour coating is a term used to describe the application of a decorative and/or protective organic coating to steel substrate supplied in coil form. Colour coated steel is also called as pre-painted steel. Colour coatings are paint coatings and are specialty products, which are used to give the steel a long term protection under a broad range of corrosive conditions, extending from atmospheric exposure to full immersion in strongly corrosive solutions. A colour coating provides little strength to the substrate steel, yet it protects the steel so that its strength and integrity can be maintained. Colour coating of steel is a continuous and highly automated industrial process for efficiently coating of coils of steel. In this process of application of colour coating, the substrate steel gets protective and decorative coating. This process of colour coating is also called a duplex coating. The process of colour coating of steel according to EN 10169:2010 is a ‘process in which an organic coating material is applied on rolled metal strip in a continuous process which includes cleaning, if necessary, and chemical pre-treatment of the metal surface and either one side or two side, single or multiple application of (liquid) paints or coating powders which are subsequently cured or / and laminating with permanent plastic films’. The first colour coating line was started in Europe during 1940s. It became immediately very popular due to its basic inherent advantages which are given below. Higher productivity A highly sophisticated and computerized controlled coating application Environmental benefits and energy saving More consistent properties of the coated sheets Lesser wastage of coating material Colour coating usually refers to the application of liquid paint coat over the substrate in an automatic, continuous process after pre-treatment. The pre-painted colour coated steel is a...

Galvanized Steel Reinforcement Bars...

Galvanized Steel Reinforcement Bars  Galvanized steel reinforcement bars (also called galvanized steel rebars) are the normal reinforcement steel bars which are coated with a protective layer of zinc (Zn) metal. Zn coating is usually carried out by hot dip galvanizing process. The Zn coating serves as a barrier to the corrosive environment which the rebars are exposed to when embedded in concrete. In addition to the barrier protection, Zn also provides cathodic protection where Zn corrodes preferentially when in contact with unprotected steel. This means that in case of any gap in Zn coating the surface of bare steel is protected by the surrounding Zn. The reaction between steel and molten Zn produces a coating on the steel made up of a series of iron -zinc alloy layers (gamma, delta and zeta) which grow from the steel-zinc interface with a layer of essentially pure Zn (eta) at the outer surface. What distinguishes galvanizing from other types of coatings is that the coating is metallurgically bonded to the steel. It actually becomes an integral part of the steel, as compared to the paints and epoxy coatings which are simply attached to the steel surface by physical bonding. The alloy layers in the coating are harder than the base steel resulting in a coating that is not only firmly adhered to the steel but is tough and hard and can resist abrasion and fairly heavy handling. It also allows the galvanized rebar to be handled, transported and fabricated in the same manner as ordinary steel. A typical galvanized coating structure is shown in Fig 1.  Fig 1 Galvanized coating structure  The first regular use of galvanized coating was done in USA during 1930s. Since then, and especially during the last 25 -30 years, it is being...

Metallurgical aspects of steel galvanization Jul14

Metallurgical aspects of steel galvanization...

Metallurgical aspects of steel galvanization Steel articles which are not protected on the surface can get serious damages because of various environmental conditions such as rain, snow, wind and extreme temperatures. These adverse environmental conditions convert iron into iron oxide and corrode steel with consequent increase in volume and decrease in strength. To avoid environment conditions acting on the steel surface various protective surface coatings are used. Out of the different types of surface coatings, galvanizing is most popular and reliable. Process of galvanization Galvanization is the process of applying a protective zinc (Zn) coating to steel. It can be done by hot dip, electro chemical and electro deposition processes. Hot dip galvanization process is most popular method presently being used for galvanizing. The process flow of galvanization process is in Fig 1. Fig 1 Process flow of galvanization process The galvanizing process consists of following three basic steps. Surface preparation – The surface preparation consists of three steps namely (i) caustic cleaning (ii) pickling and (iii) fluxing. Fluxing is done with zinc ammonium chloride. Surface preparation is an important step in galvanizing since zinc simply will not metallurgically react with steel surface if it is not perfectly clean. Any failure or inadequacies in surface preparation will immediately show after the steel is withdrawn from the molten zinc bath since the unclean areas will remain uncoated. Galvanizing – After surface preparation steel is immersed in the molten zinc bath where the steel surface is wetted by the molten zinc. The steel temperature in the bath should be in the range of 445 deg C to 465 deg C to have proper coating. The metallurgical reactions that result in the formation and structure of the zinc/iron alloy layers continue after the steel is withdrawn from...