LARSEN & TOUBRO Ltd.

TRAINING REPORT

Contents

1. An Overview of an Organization 2. Thermodynamics

a. Laws of Thermodynamics i. Zeroth law of thermodynamics

ii. First law of thermodynamics iii. Second law of thermodynamics iv. Third law of thermodynamics

b. Vapour power cycle i. Carnot cycle

ii. Rankine cycle iii. Reheat cycle iv. Regenerative cycle

3. Thermal power plant a. Different Components and their Working

4. Steam Generators or Steam Boilers a. Boiler Definition b. Boiler application c. Boiler classification

5. Supercritical Technology a. Supercritical cycle b. History of SC Technology c. Comparison of subcritical boilers vs. supercritical boilers d. Advantages of supercritical Technology

6. Material properties a. Iron-carbon Equilibrium diagram b. TTT-Time Temperature Transformation diagram

7. Steel a. Properties of different type of steel

i. Plane carbon steel ii. Low and medium alloy steel

iii. High alloy steel 1. Austenitic stainless steel 2. Martensitic stainless steel 3. Ferritic stainless steel

8. Stress and Strain a. Mechanical properties of matter b. Stress and strain curve c. Stress and strain Relationship

9. Task on Materials used in boilers a. Tubes b. Pipes c. Plates d. Fittings e. Forging f. Casting

10. Solid edge a. Part enhancement b. Assembly enhancement c. Draft enhancement

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An Overview of Organization

L&T L&T was founded in Bombay (Mumbai) in 1938 by two Danish engineers, Henning Holck-Larsen and Soren Kristian Toubro. Both of them were strongly committed to developing India's engineering capabilities to meet the demands of industry. Beginning with the import of machinery from Europe, L&T rapidly took on engineering and construction assignments of increasing sophistication. Today, the company sets global engineering benchmarks in terms of scale and complexity. Larsen & Toubro (L&T) is a technology-driven USD 12.8 billion company that infuses engineering with imagination. Larsen & Toubro Limited (L&T) is a technology, engineering, construction and manufacturing company. It is one of the largest and most respected companies in India's private sector. In response to changing market dynamics, L&T has gone through a phased process of redefining its organization model that facilitates growth through greater levels of empowerment. The new structure is built around multiple businesses designated ‘Independent Companies’ or ‘ICs’. L&T-MHI Boilers Private Limited is a 51:49 Joint Venture Company formed on 16th April, 2007 in India between Larsen & Toubro Limited (L&T), India and Mitsubishi Heavy Industries Limited (MHI), Japan for engaging in the business of design, engineering, manufacturing, selling, maintenance and servicing of Supercritical Boilers and Pulverisers in India. The Company has established manufacturing facility that can manufacture pressure parts and pulverisers at Hazira, near Surat in the state of Gujarat with the technological support from Mitsubishi Heavy Industries Limited.

MHI

Mitsubishi Heavy Industries Limited (MHI), Japan is one of the world’s leading heavy machinery manufacturers, with consolidated sales of over USD 34 billion. Its diverse line-up of products and services encompasses energy, material handling and transportation equipment, aerospace, machinery & steel structures and shipbuilding & ocean development. MHI has over five decades of experience in manufacturing supercritical boilers and turbine-generators. It possesses state-of-the-art technology, and has the world's most extensive references of large capacity supercritical boilers and turbines.

Thermodynamics

Thermodynamics is a branch of physics which deals with the energy and work of a system. It was born in the 19th century as scientists were first discovering how to build and operate steam engines. Thermodynamics deals only with the large scale response of a system which we can observe and measure in experiments.

Laws of Thermodynamics

Zeroth Law of Thermodynamics:- "When two systems are each in thermal equilibrium with a third system then the two systems are also in thermal equilibrium with one another.

First Law of Thermodynamics:- a. The First Law of Thermodynamics states that for a cyclic process the algebraic sum of all the

heat energy is equal to the algebraic sum of all the work energy.

∑∆Q= ∑∆W b. The energy can neither be created nor be destroyed though it can be transformed from one

form to another. ∆Q= ∆W+∆U

Where, ∆Q-Change in heat energy

∆W-Change in work energy

∆U-Change in Internal energy Second Law of Thermodynamics:-

1. Kelvin-Planck statement, "It is impossible to construct an engine working on a cyclic process whose sole purpose is to convert heat energy from a single thermal reservoir into an equivalent amount of work.”

2. Clausius statement, "It is impossible for a self acting machine working in cyclic process, to transfer heat from a body at lower temperature to a body at a higher temperature without the aid of an external agency."

Third Law of Thermodynamics The entropy of a system approaches a constant value as the temperature approaches zero.

The constant value (not necessarily zero) is called the residual entropy of the system. Physically, the law implies that it is impossible for any procedure to bring a system to the absolute zero of temperature in a finite number of steps.

Vapour power Cycle

Carnot Cycle

It is a reversible cycle. It consists of two constant pressure operations (1-2) and (3-4) and two frictionless adiabatic (2-3) and (4-1). These operations are discussed below:- Process (1-2):- The saturated water at point 1 is isothermally converted into dry saturated steam, in a boiler, and heat is absorbed at a constant temperature T1 and pressure P1. The dry saturated of steam is represented by point 2. Heat absorbed during isothermal expansion Q1-2= (s1 –s2) T2 = (s1 –s2) T1

Process (2-3):- The dry steam at point 2 now expands isentropically in a steam engine or turbine. The temperature and pressure falls from P2 to P3 and T2 to T3 respectively. Process (3-4):- The wet steam at point 3 is now isothermally condensed in a condenser and the heat is rejected at a constant temperature T3 and pressure P3. Heat rejected during isothermal compression Q3-4= (s3- s4) T3 = (s3- s4) T4

Process (4-1):- The wet steam at point 4 is finally compressed isentropically in a compressor, till it returns back to its original state (point1). The pressure and temperature rises from P4 to P1 and T4 to T1. Work done during the cycle= heat absorbed – heat rejected. = (s1 –s2) T2 - (s3- s4) T3 Efficiency of Carnot cycle:-

η = work done/ heat absorbed

= (s1 –s2) T2 - (s3- s4) T3/ (s1 –s2) T2

= T2-T3 / T2

From T-s diagram; T1=T1=T2, T2=T3=T4

η = (T1- T2)/ T1

Rankine cycle

The Rankine cycle is an ideal cycle for comparing the performance of steam plant. It is modified form of Carnot cycle, in which the condensation process (4-1) is continued until the steam is condensed into water. The schematic diagram of a steam engine plant is shown in fig. given below:-

T-s diagram of Rankine cycle

There are four processes in the Rankine cycle. These states are identified by numbers in the above Ts diagram.

Process 1-2: The working fluid is pumped from low to high pressure. As the fluid is a liquid at this stage the pump requires little input energy.

Process 2-3: The high pressure liquid enters a boiler where it is heated at constant pressure by an external heat source to become a dry saturated vapor. The input energy required can be easily calculated using mollier diagram or h-s chart or enthalpy-entropy chart also known as steam tables.

Process 3-4: The dry saturated vapor expands through a turbine, generating power. This decreases the temperature and pressure of the vapor, and some condensation may occur. The output in this process can be easily calculated using the Enthalpy-entropy chart or the steam tables.

Process 4-1: The wet vapor then enters a condenser where it is condensed at a constant temperature to become a saturated liquid.

Reheat Cycle

In this variation, two turbines work in series. The first accepts vapor from the boiler at high pressure. After the vapor has passed through the first turbine, it re-enters the boiler and is reheated before passing through a second, lower pressure turbine. Among other advantages, this prevents the vapor from condensing during its expansion which can seriously damage the turbine blades, and improves the efficiency of the cycle, as more of the heat flow into the cycle occurs at higher temperature. The diagram below shows a basic circuit with one stage of reheating.

In the h-s diagram of reheat cycle, the steam enters the turbine in a superheated state at point 2. The steam then expands isentropically while flowing through the turbine, as shown by the vertical line 2-3, in the fig. given below. After expansion the steam becomes wet, which is reheated at a constant pressure up to at point 4, where it is again in superheated state. The steam again expands isentropically while following through the next stage of the turbine as shown by the vertical line 4-5 in figure.

T-s and h-s diagram of reheat cycle

Regenerative cycle

The regenerative Rankine cycle is so named because after emerging from the condenser (possibly as a subcooled liquid) the working fluid is heated by steam tapped from the hot portion of the cycle. On the diagram shown, the fluid at 2 is mixed with the fluid at 4 (both at the same pressure) to end up with the saturated liquid at 7. This is called "direct contact heating". The Regenerative Rankine cycle (with minor variants) is commonly used in real power stations.

Another variation is where bleed steam from between turbine stages is sent to feedwater heaters to preheat the water on its way from the condenser to the boiler. These heaters do not mix the input steam and condensate, function as an ordinary tubular heat exchanger, and are named "closed feedwater heaters".

The regenerative features here effectively raise the nominal cycle heat input temperature, by reducing the addition of heat from the boiler/fuel source at the relatively low feedwater temperatures that would exist without regenerative feedwater heating. This improves the efficiency of the cycle, as more of the heat flow into the cycle occurs at higher temperature.

Thermal Power Plant

Electricity is generated in Thermal Power Plants. In coal fired power stations, Thermal energy is derived from Boilers by burning Coal and the steam produced in Boilers is led to rotate Steam Turbines, which in turn act as the prime movers of Alternators for generating Electrical Power.

1. Cooling tower 10. Steam Control valve 19. Superheater

2. Cooling water pump 11. High pressure steam turbine 20. Forced draught (draft) fan

3. transmission line (3-phase) 12. Deaerator 21. Reheater

4. Step-up transformer (3-phase) 13. Feedwater heater 22. Combustion air intake

5. Electrical generator (3-phase) 14. Coal conveyor 23. Economiser

6. Low pressure steam turbine 15. Coal hopper 24. Air preheater

7. Condensate pump 16. Coal pulverizer 25. Precipitator

8. Surface condenser 17. Boiler steam drum 26. Induced draught (draft) fan

9. Intermediate pressure steam turbine 18. Bottom ash hopper 27. Flue gas stack

Diagram of a typical coal fired Thermal Power Plant

Components of Thermal Power Plant

Boiler:-The boiler is constructed of special high temperature steel tubing supported by a steel frame. The steel tubes are filled with water. Heat inside the boiler boils the water, and the steam flows to the turbine. Ash is collected at the bottom of the boiler and precipitator, where it is conveyed to an ash collection system.

High Pressure Turbine:-The high pressure turbine primarily consists of fan-type blades attached to a shaft. Steam flows against the blades, causing the shaft to turn.

Intermediate and Low Pressure Turbine:-The intermediate and low pressure turbine, while constructed like the high pressure turbines, are designed to add efficiency to the cycle.

The Generator: -The shaft of the generator is connected to the turbine shaft. When the turbine rotates the generator, electricity is produced.

Condenser: -A steam condenser is a closed vessel into which the steam is exhausted, and condensed after doing work in an engine cylinder or turbine.

Heaters:-The heaters are used to heat the water on its return back to the boiler. Small amounts of steam are removed from the turbine at different pressures to heat the water.

Deaerator:-One of the heaters is called the Deaerator because, in addition to heating the water, it removes air and other dissolved gases from the water.

Cooling Tower:-The cooling tower is used to cool the circulating water. This is done by lowing air across water that is falling through the cooling tower.

Circulating Water Pumps:- These pumps are used to transfer water from the cooling tower to the condenser and back to the cooling tower.

Coal Bunker:-Coal is delivered to the Platte Generating Station by rail. Belt conveyors are used to transfer the coal to the storage bunkers.

Coal Pulverizer:-The coal flows by gravity into the pulverizers from the coal feeders. When the coal is in the pulverizer, it is ground into the approximately fineness of talcum powder. It is then blown into the furnace, where it mixes with air, and burns at high temperature.

Fans:-The boiler has two large fans. The forced draft fan blows air into the boiler so that coal will burn and produce heat to produce steam and the induced fan pulls gases from the boiler and precipitator.

Electro Static Precipitator:-The electro static precipitator eliminates about 99.6% of the fly ash from the boiler flue gases by means of many fine wires and static electricity, so that smoke from the chimney will be eliminated.

Steam Generators or Steam Boilers

BOILER DEFINITION

In General……

Boiler is, usually, a closed vessel made of steel. Its function is to transfer the heat produced by the combustion of fuel (solid, liquid or gaseous) to water, and ultimately to generate steam.

As per IBR……

"Boiler" means any closed vessel exceeding 22.75 litres in capacity which is used expressly for generating steam under pressure and includes any mounting or other fitting attached to such vessel, which is wholly or partly under pressure when steam is shut off.

BOILER - APPLICATIONS

• In Industries – where process steam / captive power is reqd.

• Paper and Pulp Industry

• Sugar mills

• Oil & Gas industries i.e., refineries, petrochemical complex etc.,

• Textile industries

• Cement industry

• Aluminium industry

• Steel industries

• Chemical industry and many more..

• In power generation plants – where power is exported to grid

• All coal based power generating stations

CLASSIFICATION OF BOILERS

1. According to the Application Industrial Boiler:-Used for generation of process steam for industrial purpose, small capacity boilers. Utility Boiler:-Used for power generation purpose in major power plants.

2. Acc. to the contents in the tube Fire Tube Boilers:-Fire tube boilers consist of long steel tubes through which hot flue gases from the furnace pass and water around the flue gets heated to form steam and gets collected in the vessel from where it is tapped. These boilers are limited to small capacity and pressure range only.

Fire tube boiler

Water Tube Boilers:-In Water tube boilers, water flows in tubes and hot flue gases pass around the tubes (also known as heating surfaces). These boilers are generally used for power generation purpose.

Water tube boiler

3. Acc. to the axis of the shell Vertical Boiler:-In the vertical boilers, the axis of the shell is vertical e.g.-simple vertical boiler and Cochran boilers.

Cochran boiler

Horizontal Boiler:-In the horizontal boilers, the axis of the shell is horizontal e.g.-Lancashire boiler, Locomotive boiler and Babcock and Wilcox boiler.

Babcock and Wilcox boiler

4. Acc. to the Firing Technology

Stoker Fired:-Coal is fed onto one end of a moving chain grate. As the grate moves along, the coal burns before dropping off at the end as ash. Coal must be uniform as large lumps will not burn completely before reaching the end of the grate.

Fluidized Bed Combustion (FBC):- Fluidized bed combustion (FBC) has emerged as a viable alternative and has significant advantages over conventional firing system and offers multiple benefits – compact boiler design, fuel flexibility, higher combustion efficiency and reduced emission of noxious pollutants such as SOx and NOx. The fuels burnt in these boilers include coal, washery rejects, rice husk, bagasse & other agricultural wastes. The fluidized bed boilers have a wide capacity range- 0.5 T/hr to over 100 T/hr.

Fluidized Bed Combustion (FBC)

Pulverized Coal Fired:- Most coal-fired power station boilers use pulverized coal, and many of the larger industrial water-tube boilers also use this pulverized fuel. This technology is well

developed, and there are thousands of units around the world, accounting for well over 90% of coal-fired capacity.

Pulverized coal fired boiler

The coal is ground (pulverized) to a fine powder, so that less than 2% is +300 micro meter (μm) and 70-75% is below 75 microns, for a bituminous coal. It should be noted that too fine a powder is wasteful of grinding mill power. On the other hand, too coarse a powder does not

burn completely in the combustion chamber and results in higher unburnt losses. The pulverized coal is blown with part of the combustion air into the boiler plant through a series of burner nozzles. Secondary and tertiary air may also be added. Combustion takes place at temperatures from 1300-1700°C, depending largely on coal grade. Particle residence time in the boiler is typically 2 to 5 seconds, and the particles must be small enough for complete combustion to have taken place during this time.

This system has many advantages such as ability to fire varying quality of coal, quick responses to changes in load, use of high pre-heat air temperatures etc.

One of the most popular systems for firing pulverized coal is the tangential firing using four burners corner to corner to create a fireball at the center of the furnace.

5. Acc. to the method of circulation of water and steam

Natural circulation boilers:-In natural circulation boilers, the circulation of water is by natural convection currents, which are set up during heating of water.

Forced circulation boilers: - In forced boilers, there is forced circulation of water by a centrifugal pump driven by some external power. Use of forced circulation is made in high pressure boilers such as Loeffler boiler and Benson boiler. 6. Acc. to the Pressure Application

Subcritical Boilers:-Heat addition is done at a pressure below critical pressure, that is 221 bar.

Supercritical Boilers:-Heat addition is done at a pressure above critical pressure, that is 221 bar. It increases the efficiency considerably.

7. Some other types of industrial boilers Coal based:-Sub bituminous and Lignite coal are generally used.

Oil & Gas based:-For oil based boilers Light Diesel Oil (LDO), Furnace Oil and Low Sulphur Heavy Stock (LSHS) Oil are generally used. And for gas based boilers Natural gas, Blast furnace gas, Coke oven gas etc are used.

Oil & Gas based boiler

Biomass Fuel:-Saw dust, Rice husk, Wood and other agro fuels are generally used in this category.

Biomass fuel boiler

Heat Recovery:-Heat is recovered from industrial processes and combustion by using heat exchangers. No firing is done here. It is an important way of increasing thermal efficiency.

Heat recovery boiler

Super Critical Technology The term "supercritical" refers to main steam operating conditions, being above the critical pressure of water (221.5 bar). The significance of the critical point is the difference in density between steam and water. Above the critical pressure there is no distinction between steam and water, i.e. above 221.5 bar, water is a fluid.

In supercritical cycle, equipment is designed to operate above the critical pressure of water. Supercritical boilers are once-through where in the feedwater enters the economiser and flows through one path and main steam exits the circuit. Typically current supercritical units operate at 242 bar main steam pressure, 565ºC main steam temperature and 593ºC reheat steam temperature.

History of SC Technology:- Supercritical technology has evolved over the past 30 years. Advancements in metallurgy and design concepts have made supercritical technology units extremely reliable and highly efficient. Modern supercritical technology is largely available in Japan and Europe for Boilers & Turbines ranging upto 1000 MW.

Comparison of Subcritical Vs Supercritical Boilers

S.no. Parameters Subcritical boilers Supercritical boilers

1. Pressure (bar)

< 220 ~220 to 300

2. Temperature(⁰C)

<565 ~565 to 600

4. Efficiency ~30 to 37% ~40 to 42%

5. Emission levels Higher CO2, NOx, Sox emissions

CO2 emission 5% lower. NOx/Sox lower.

6. Size Upto 700 MW Upto 1300 MW

7. Material of construction Carbon steels/Low alloy steels

Advanced steels/Inconels/Chromium-based/austenitic

8. Steam drum Required for steam separation

None

9. Start-up time required Higher Lower

10. Water circulation Natural or Forced Once-through

11. Furnace Vertical Spiral wound, Vertical

12. Engineering Comparatively simple

Complex

13. Response Time 3%(MCR)/min. 5%(MCR)/min

14. Capital cost Lower 3 to 5 % higher

15. Availability & Operating cost Comparable availability but higher operating costs

Comparable availability but lower operating costs due to higher efficiency

Advantages of SC Technology

1. Higher Efficiency:- Supercritical steam conditions improve the turbine cycle heat rate significantly over subcritical steam conditions. The extents of improvement depend on the main steam and reheat. steam temperature for the given supercritical pressure. A typical supercritical cycle having turbine throttle pressure of 242 bar with temperatures for main steam and reheat steam as 565ºC and 593ºC respectively, will improve station heat rate by more than 5%. This results in fuel savings to the extent of 5%. Overall supercritical power plant efficiency of 42% is achievable with current supercritical parameters.

2. Emissions:- Improved heat rate results in 5% reduction in fuel consumption and hence 5% reduction in CO2 emissions per MWh energy output. Typically for 800 MW supercritical unit the annual reduction in CO2 emission will be about 725,000 tonnes of CO2 with respect to baseline emission established by CEA for 2008 – 2009.

3. Operational Flexibility:- Supercritical technology units also offer flexibility of plant operation such as: Shorter start-up times Faster load change flexibility and better temperature control Better efficiency even at part load due to variable pressure operation High reliability and availability of power plant

Material Properties

Iron–Carbon Equilibrium Diagram

This diagram is essentially a map of the phases that exist in iron at various carbon contents and temperatures under equilibrium conditions. From room temperature to 912oC, pure iron exists as ferrite (also called alpha iron), from 912 to 1394oC, it exists as austenite (gamma iron), from 1394 to 1538oC it exists as ferrite again (delta iron), and above 1538oC it is liquid. In other words, upon heating, iron undergoes allotropic phase transformations from ferrite to austenite at 912oC, austenite to ferrite at 1394oC, and ferrite to liquid at 1538oC. When added to iron, carbon has very limited solubility in ferrite but is about 100 times more soluble in austenite. The maximum solubility of carbon in ferrite is about 0.022% C at 727oC while the maximum solubility of carbon in austenite is 100 times more, 2.11% C at 1148oC. At room temperature the solubility of carbon in iron is only about 0.005%. Any amount of carbon in excess of the solubility limit is rejected from solid solution and is usually combined with iron to form an iron carbide compound called cementite. This hard and brittle compound has the chemical formula Fe3C and a carbon content of 6.7%. As the carbon content in steel is increased, another form of cementite appears as a constituent called pearlite, which can be found in most carbon steels. Pearlite has a lamellar (parallel-plate) microstructure and consists of layers of ferrite and cementite. Thus, in these examples, in increasing the carbon level from 0.002 to 0.02 to 0.08 to 0.20%, the excess carbon is manifested as a carbide phase in two different forms, cementite particles and cementite in pearlite. Both forms increase the hardness and strength of iron. However, there is a trade-off; cementite also decreases ductility and toughness. Pearlite forms on cooling austenite through a eutectoid reaction as seen below:

Austenite ↔ Fe3C + ferrite

A eutectoid reaction occurs when a solid phase or constituent reacts to form two different solid constituents on cooling (a eutectic reaction occurs when a liquid phase reacts to form two solid phases). The eutectoid reaction is reversible on heating. In steel, the eutectoid reaction (under equilibrium conditions) takes place at 727°C and can be seen on the iron– carbon diagram as the ‘‘V’’ at the bottom left side of the diagram. A fully pearlitic microstructure forms at0.83%C at the eutectoid temperature of 727oC (the horizontal line on the left side of the iron–carbon diagram). Steels with less than0.83%C are called hypoeutectoid steels and consist of mixtures of ferrite and pearlite with the amount of pearlite increasing as the carbon content increases. The ferrite phase is called a proeutectoid phase because it forms prior to the eutectoid transformation that occurs at 727oC. Steels between0.83%C and about 2% C are called hypereutectoid steels and consist of pearlite with proeutectoid cementite. Cementite forms a continuous carbide network at the boundaries of the prior austenite grains. Because there is a carbide network, hypereutectoid steels are characterized as steels with little or no ductility and very poor toughness. This means that in the commercial world the vast majority of carbon steels are hypoeutectoid steels. Thus, according to

the iron–carbon diagram, steels that are processed under equilibrium or near-equilibrium conditions can form (a) Pure ferrite at very low carbon levels generally under 0.005% C, (b) Ferrite plus cementite particles at slightly higher carbon levels between 0.005% C and 0.022% C, (c) Ferrite plus pearlite mixtures between 0.022% C and0.83%C, (d) 100% pearlite at0.83%C, and (e) Mixtures of pearlite plus cementite networks between0.83%C and 2% C. The higher the percentage of cementite, the higher the hardness and strength and lower the ductility and toughness of the steel.

EUTECTOID REACTION:-

At 0.83%C and 727:C the transformation is eutectoid, called pearlite.

Gamma (austenite) --> alpha + Fe3C (cementite)

EUTECTIC REACTION:-

At 4.3% C and 1130:C, the transformation is eutectic, called ledeburite.

L (liquid) --> gamma (austenite) + Fe3C (cementite)

PERITECTIC REACTION:-

At 0.1 to 0.5% C and 1494:C the transformation is peritectic.

δ (delta iron) + L (liquid) -->Gamma (austenite)

Different phases present in Iron Carbon diagram and their properties

Name Phase Properties

Ferrite(α) BCC (Carbon in solid solution) Soft, Ductile, Magnetic

Austenite(γ) FCC (Carbon in solid solution) Soft, moderate strength, non-magnetic, ductile

Cementite Fe3C Hard & brittle

Delta(δ) BCC Exists at high temperature upto 0.1%

TTT-Time Temperature Transformation Diagram

Isothermal transformation diagrams (also known as time-temperature-transformation

diagrams) are plots of temperature versus time (usually on a logarithmic scale). They are generated from percentage transformation-vs. Logarithm of time measurements, and are useful for understanding the transformations of an alloy steel that is cooled isothermally. An isothermal transformation diagram is only valid for one specific composition of material, and only if the temperature is held constant during the transformation, and strictly with rapid cooling to that temperature. Though usually used to represent transformation kinetics for steels, they also can be used to describe the kinetics of crystallization in ceramic or other materials. Time-temperature-precipitation diagrams and time-temperature-embrittlement diagrams have also been used to represent kinetic changes in steels. Figure given below shows the TIME TEMPERATURE TRANSFORMATION Diagram.

Picture of Different type of microstructures

S.no. Microconstituents Phase present Arrangement of phase

Mechanical properties

1. Spheroidite α-ferrite+ cementite Relatively small cementite sphere like particle in an α-ferrite matrix

Soft and ductile

2. Coarse pearlite α-ferrite+ cementite Alternating layers of α-ferrite that are relatively thick

Harder and stronger than spheroidite but not ductile as spheroidite

3. Fine pearlite

α-ferrite+ cementite Alternating layers of α-ferrite that are relatively thin

Harder and stronger than coarse pearlite but not as ductile as coarse pearlite

4. bainite

α-ferrite+ cementite Very fine and elongated particles of cementite in an α-ferrite matrix

Hardness and strength greater than fine pearlite.hardness less than martensite ,ductility greater than martensite

5. Tempered martensite

α-ferrite+ cementite Very small cementite sphere like particles in an α-ferrite matrix

Strong, not as hard as martensite, but much more ductile than martensite

6. Martensite Body centered tetragonal single phase

Needle shaped grains Very hard and very brittle

Different type of microstructures and their properties

Steel Steel is defined as an alloy of Iron and Carbon, when the Carbon content varies from 0.025-0.55%. It is the most common and widely used metallic material in today’s society. It can be cast or wrought into numerous forms and can be produced with tensile strengths exceeding 5 GPa. Steel is strong and is used in the body frame, motor brackets, driveshaft, and door impact beams of the vehicle. Steel is corrosion resistant when coated with the various zinc-based coatings available today. Steel is dent resistant when compared with other materials and provides exceptional energy absorption in a vehicle collision. Steel is recycled and easily separated from other materials by a magnet. Steel is inexpensive compared with other competing materials such as aluminum and various polymeric materials. By definition, steel must be at least 50% iron and must contain one or more alloying elements. These elements generally include carbon, manganese, silicon, nickel, chromium, molybdenum, vanadium, titanium, niobium, and aluminum. Each chemical element has a specific role to play in the steelmaking process or in achieving particular properties or characteristics, e.g., strength, hardness, corrosion resistance, magnetic permeability, and machinability.

Properties of different types of steels

Steels can be considered as 3 types- Plain Carbon Steels, Low Alloy Steels and High Alloy Steels.

1. Plain Carbon Steels:-

Plain Carbon Steels are divided into 4 classes

1. Low Carbon Steels C < 0.15% 2. Medium Carbon Steels 0.15 < C < 0.23% 3. Medium High Carbon Steels 0.23 < C < 0.44% 4. High Carbon Steels C > 0.44%

Plain carbon steels are used for Pressure parts operating at low to moderate temperatures. Their limitation is that they don’t have good corrosion resistance and elevated temperature properties. So they can’t be used for high temperature applications. Hence, for some pressure parts in boilers, low and high alloy steels are used.

2. Low and Medium Alloy Steels:-

Low and Medium alloy steels contain Chromium (Cr) up to 11.5%. Chromium gives good corrosion resistance properties as it forms a stable protective oxide film of Cr2O3 which prevents further corrosion. The most common steels from this group seen in boiler applications are- C- ½ Mo, 1 Cr- ½ Mo, 2¼ Cr-1Mo, 9Cr-1Mo-V etc. These steels can be used for pressure part applications even at high temperatures. However, they are prone to graphitization above 468oC. Their Oxidation resistance increases with Cr content. ½ Cr- ½ Mo has same strength as C-Mo, hence it has displaced the latter in many applications. For high temperature strength, 2¼ Cr-1Mo and 9 Cr-1 Mo-V are commonly used.

3 High Alloy Steels:-

High alloy steels are those containing more than approximately 11.5% Cr. They are also referred to as Stainless Steels. The Cr forms a protective self-healing oxide film which is the reason why these steels have their characteristic stainlessness or corrosion resistance. The ability of the oxide layer to heal itself means that the steel is corrosion resistant, no matter how much of the surface is removed.

Although all stainless steels depend on the presence of Cr, other alloying elements are often added to enhance their properties. The subcategories of Stainless Steels are- Austenitic, Ferritic, Martensitic stainless steel

1. Austenitic Stainless Steels: These are non-magnetic grades of Stainless Steel. This group contains at least 16% Cr and 6% Ni. The most common of this group are the Fe-Cr-Ni steels. They cannot be hardened by heat treatment but can be hardened by solid cold-working. They are suitable for cryogenic applications because the effect of the nickel content in making the steel austenitic avoids

the problems of brittleness at low temperatures. They are also very suitable for high temperature applications.

2. Martensitic Stainless Steels: The Nickel content is less in Martensitic Grade Stainless Steels; rather they are straight Cr steels. They can be hardened by heat treatment. So they are used where hardness, wear resistance and strength are required. They are magnetic grade Stainless Steels.

3. Ferritic Stainless Steels: These are also magnetic grade Stainless Steels. They cannot be hardened by Heat Treatment. However, they can be cold worked of softened by annealing. They have more corrosion resistance than Martensitic Grades but less than Austenitic Grade. There is very less Ni used (0.5% max). These steels are easy to fabricate and less susceptible to SCC (Stress Corrosion Cracking). They are used for decorative trims, sinks and automobile applications (exhaust).

A compositional difference between Ferritic and Martensitic Stainless Steel is that Martensitic grades have higher Carbon and lower Chromium content than ferritic types.

The ferritic stainless steels are somewhat stronger than austenitic stainless steels, the yield stresses being in the range 300-400 MPa, but they work harden less so the tensile strengths are similar, being between 500 and 600 MPa. However, ferritic stainless steels, in general, are not as readily deep drawn as austenitic alloys because of the overall lower ductility. However, they are suitable for other deformation processes such as spinning and cold forging. Welding causes problems due to excessive grain growth in the heat affected zone but, recently, new low-interstitial alloys containing titanium or niobium have been shown to be readily weldable. The higher chromium ferritic alloys have excellent corrosion resistance, particularly if 1-2% molybdenum is present.

Finally, there are two phenomena which may adversely affect the behavior of ferritic stainless steels. Firstly, chromium-rich ferrites when heated between 400 and 500°C develop a type of embrittlement.

The most likely cause is the precipitation of a very fine coherent chromium-rich phase arising from the miscibility gap in the Fe-Cr system, probably by a spinodal type of decomposition. This phenomenon becomes more pronounced with increasing chromium content, as does a second phenomenon, the formation of sigma phase. The latter phase occurs more readily in chromium-rich ferrite than in austenite, and can be detected below 600°C. As in austenite, the presence of sigma phase can lead to marked embrittlement.

Anodizing, or anodising in British English, is an electrolytic passivation process used to increase the thickness of the natural oxide layer on the surface of metal parts. The process is called "anodizing" because the part to be treated forms the anode electrode of an electrical circuit. Anodizing increases corrosion resistance and wear resistance, and provides better adhesion for paint primers and glues than does bare metal. Anodic films can also be used for a number of cosmetic effects, either with thick porous coatings that can absorb dyes

MECHANICAL PROPERTIES

DUCTILITY- It is the ability of a material to sustain large permanent deformations in tension, such as drawing into a wire.

MALLEABILITY- It is the ability of a material to sustain large permanent deformations in compression, such as beating or rolling into thin sheets.

BRITTLENESS- It is that property of a material that permits it to be only slightly deformed without rupture. Brittleness is relative, no material being perfectly brittle, that is, capable of no deformation before rupture. Many materials are brittle to a greater or less degree, glass being one of the most brittle of materials. Brittle materials have relatively short stress–strain curves. Of the common structural materials, cast iron, brick, and stone are brittle in comparison with steel.

TOUGHNESS- It is the ability of the material to withstand high unit stress together with great unit strain without complete fracture. The distinction between ductility and toughness is that ductility deals only with the ability to deform, whereas toughness considers both the ability to deform and the stress developed during deformation.

STIFFNESS- It is the ability to resist deformation under stress. The modulus of elasticity is the criterion of the stiffness of a material.

HARDNESS- It is the ability to resist very small indentations, abrasion, and plastic deformation. There is no single measure of hardness, as it is not a single property but a combination of several properties.

CREEP, or flow of metals, is a phase of plastic or inelastic action. Some solids, as asphalt or paraffin, flow appreciably at room temperatures under extremely small stresses; zinc, plastics, fiber-reinforced plastics, lead, and tin show signs of creep at room temperature under moderate stresses. At sufficiently high temperatures, practically all metals creep under stresses that vary with temperature; the higher the temperature, the lower the stress at which creep takes place. The deformation due to creep continues to increase indefinitely and becomes of extreme importance in members subjected to high temperatures, as parts in turbines, boilers, super heaters, etc.

STRESS STRAIN CURVE

Stress-Strain curve for ductile materials

Stress-Strain curve for different materials

Strain – It is the amount by which a dimension of a body changes when the body is subjected to a load, divided by the original value of the dimension.

Proportional limit -It is the point on a stress-strain curve at which it begins to deviate from the straight-line relationship between stress and strain.

Elastic limit - It is the maximum stress to which a test specimen may be subjected and still return to its original length upon release of the load. A material is said to be stressed within the elastic region when the working stress does not exceed the elastic limit, and to be stressed in the plastic region when the working stress does exceed the elastic limit. The elastic limit for steel is for all practical purposes the same as its proportional limit.

Yield point - It is a point on the stress-strain curve at which there is a sudden increase in strain without a corresponding increase in stress. Not all materials have a yield point.

Yield strength:- is the maximum stress that can be applied without permanent deformation of the test specimen. This is the value of the stress at the elastic limit for materials for which there is an elastic limit. Because of the difficulty in determining the elastic limit, and because many materials do not have an elastic region, yield strength is often determined by the offset method. Yield strength in such a case is the stress value on the stress-strain curve corresponding to a definite amount of permanent set or strain, usually 0.1 or 0.2 per cent of the original dimension.

Ultimate strength, Su, (also called tensile strength) is the maximum stress value obtained on a stress-strain curve.

Modulus of elasticity, E, (also called Young's modulus) is the ratio of unit stress to unit strain within the proportional limit of a material in tension or compression.

Modulus of elasticity in shear, G, is the ratio of unit stress to unit strain within the proportional limit of a material in shear.

Poisson's ratio, μ, is the ratio of lateral strain to longitudinal strain for a given material subjected to uniform longitudinal stresses within the proportional limit.

STRESS AND STRAIN RELATIONSHIPS

As with stresses, two types of strains are defined – normal and shear strains which are represented by ε and γ respectively. Normal strain is the rate of change of the length of the stressed element in that particular direction, whereas, shear strain is the measure of the distortion of the element parallel to the plane in study. The relations between shear/ normal stresses and shear/normal strains are given below,

[

]

[

]

[

]

Shear strains corresponding to the given shear stresses are given by,

Where G is the shear modulus given by,

TASK ON MATERIALS USED IN BOILERS

This Task is related with those materials which are used in boilers. In different parts of the boilers (e.g.- tubes, pipes and plates etc. ), different types of materials are used as per their requirements. The following charts are plotted between the Maximum allowable stresses and the Temperatures. In all the charts, Horizontal axis represents the temperature in 0C and the vertical axis represents the maximum allowable stress in MPa.

1. Tubes

0

20

40

60

80

100

120

140

160

180

SA 178 A

SA 192

SA 210 C

SA 213 T2

SA213T11

SA213T12

SA213T22

SA213T91(t ≤ 75)

SA213T91(t > 75)

SA213TP304H

SA213TP310H

SA213TP316H

SA213TP321H

SA213TP347H

CC2328

2. Pipes

0

20

40

60

80

100

120

140

160

180

SA 106GrB

SA 106Grc

SA 335P2

SA 335P12

SA 335P11

SA 335P22

SA 335P91(t > 75)

SA 335P91(t ≤ 75)

SA 312TP304

SA 312TP309H

SA 312TP310H

3. Plates

0

20

40

60

80

100

120

140

160

180

SA 36

SA 515Gr60

SA 515Gr70

SA 387Gr11(C1)

SA 387Gr11(C2)

SA 387Gr12(C1)

SA 387Gr12(C2)

SA 387Gr22(C1)

SA 387Gr22(C3)

SA 387Gr91(t ≤ 75)

SA 387Gr91(t > 75)

SA 240 304

SA 240 347H

SA 240 309H

SA 240 310H

4. Fittings

0

20

40

60

80

100

120

140

160

180

SA 234WPB

SA 234WPC

SA 234WP1

SA 234WP12

SA 234WP11

SA 234WP22

SA 234WP91(t ≤ 75)

SA 234WP91(t > 75)

SA 403 304

SA 403 3047H

SA 403 309

SA 403 310S

5. Forgings

0

20

40

60

80

100

120

140

160

180

SA 105

SA 182F2

SA 182F12(C1)

SA 182F12(C2)

SA 182F11(C1)

SA 182F11(C2)

SA 182F22(C1)

SA 182F22(C3)

SA 182F91(t ≤ 75)

SA 182F91(t > 75)

SA 182F304(t>125)

SA 182F304(t≤125)

SA 182F347H(t>125)

SA 182F347H(t≤125)

SA 182F310(t>125)

SA 182F310((t≤125)

6. Castings

0

20

40

60

80

100

120

140

160

180

200

SA 216WCB

SA 216WCC

SA 217WC6

SA 217WC9

SA 217C12

SA 335P11

SOLID EDGE

Solid Edge is an industry-leading mechanical design system with exceptional tools for creating and managing 3D digital prototypes. With superior core modeling and process workflows, a unique focus on the needs of specific industries, and fully integrated design management, Solid Edge guides projects toward an error free, accurate design solution. Solid Edge modeling and assembly tools enable your engineering team to easily develop a full range of products, from single parts to assemblies containing thousands of components. Tailored commands and structured workflows accelerate the design of features common in specific industries and you ensure accurate fit and function of parts by designing, analyzing and modifying them within the assembly model.

Solid Edge is made up of several components called environments. These environments are tailored for creating individual parts, weldments, assemblies, and detail drawings.

The three main enhancements in solid edge are as follows:-

Part enhancements Assembly enhancements Draft enhancements

Part Enhancements

Solid Edge: Part has two environments (ordered and synchronous) which allows you to construct a base feature and then modify that base feature with additional features such as protrusions, cutouts, holes, and ribs—to construct a finished solid model.

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Picture of part drawing

Assembly Enhancements

An assembly drawing is a type of drawing that shows the intended assembly of mechanical or other parts. It shows all parts of the assembly and how they fit together. In mechanical systems usually the component closest to the center are assembled first, or is the main part in which the other parts get assembled. This drawing can also help to represent the disassembly of parts, where the parts on the outside normally get removed first.

Picture of assembly drawing

Draft Enhancements

A detail or draft drawing is the most important drawing in your fabrication work. A detail drawing gives all the dimensions, fabrication methods and types of materials required to manufacture the article.

During the draft Enhancement we learnt to do the following:-

Retrieve dimensions from the model.

Add new dimensions to the drawing views, such as: o Distance between o Chamfer dimension

Picture of draft drawing

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