2. Contents
Introduction to Boiler .......................................................................................................................... 3
Parts of Boiler ................................................................................................................................... 4
Types of Boilers................................................................................................................................. 5
Introduction to Welding ...................................................................................................................... 8
Gas Flow Meters ............................................................................................................................... 8
1. Shielded Metal Arc Welding (SMAW).................................................................................... 9
2. Gas Metal Arc Welding (GMAW)......................................................................................... 10
3. Gas Tungsten Arc Welding (GTAW) .................................................................................... 11
4. Submerged Arc Welding (SAW)............................................................................................ 13
Selection of the welding process .................................................................................................... 14
Welding Symbols ............................................................................................................................ 15
Gas Cutting ......................................................................................................................................... 17
Oxy-Fuel Cutting ............................................................................................................................ 17
Plasma Arc Cutting (PAC) ............................................................................................................ 17
Shearing machine ............................................................................................................................... 19
Sand Blasting ...................................................................................................................................... 19
Silica Sand or Silicon Dioxide........................................................................................................ 20
Soda.................................................................................................................................................. 21
Steel sandblasting............................................................................................................................ 21
Glass Bead ....................................................................................................................................... 21
Bristle blasting ................................................................................................................................ 21
Post Weld heat treatment (PWHT) .................................................................................................. 21
Introduction to Non Destructive Testing.......................................................................................... 21
Visual inspection:............................................................................................................................ 21
Radiography:................................................................................................................................... 22
Liquid (Dye) penetrant method:.................................................................................................... 22
Magnetic particles Testing:............................................................................................................ 23
Ultrasonic Inspection: .................................................................................................................... 24
3. Introduction to Boiler
Boilers are pressure vessels designed to heat water or produce steam, which can then be used to provide
space heating and/or service water heating to a building. In most commercial building heating applications,
the heating source in the boiler is a natural gas fired burner. Oil fired burners and electric resistance heaters
can be used as well. Steam is preferred over hot water in some applications, including absorption cooling,
kitchens, laundries, sterilizers, and steam driven equipment.
Boilers have several strengths that have made them a common feature of buildings. They have a long life,
can achieve efficiencies up to 95% or greater, provide an effective method of heating a building, and in the
case of steam systems, require little or no pumping energy. However, fuel costs can be considerable, regular
maintenance is required, and if maintenance is delayed, repair can be costly.
Guidance for the construction, operation, and maintenance of boilers is provided primarily by the ASME
(American Society of Mechanical Engineers), which produces the following resources:
Rules for construction of heating boilers, Boiler and Pressure Vessel Code, Section IV-2007
Recommended rules for the care and operation of heating boilers, Boiler and Pressure Vessel Code, Section
VII-2007
Working of Boiler
Both gas and oil fired boilers use controlled combustion of the fuel to heat water. The key boiler components
involved in this process are the burner, combustion chamber, heat exchanger, and controls.
The burner mixes the fuel and oxygen together and, with the assistance of an ignition device, provides a
platform for combustion. This combustion takes place in the combustion chamber, and the heat that it
generates is transferred to the water through the heat exchanger. Controls regulate the ignition, burner firing
rate, fuel supply, air supply, exhaust draft, water temperature, steam pressure, and boiler pressure.
Hot water produced by a boiler is pumped through pipes and delivered to equipment throughout the building,
which can include hot water coils in air handling units, service hot water heating equipment, and terminal
units. Steam boilers produce steam that flows through pipes from areas of high pressure to areas of low
pressure, unaided by an external energy source such as a pump. Steam utilized for heating can be directly
utilized by steam using equipment or can provide heat through a heat exchanger that supplies hot water to the
equipment
.
4. Parts of Boiler
1. Feed pump
A feed pump needed to deliver water to the boiler. The pressure of feed water is 20% more than that in
the boiler. The feed pump may be classified as simplex, duplex, triplex pumps according to the
number of pump of cylinder.
2. Combustion Air Blowers
In many packaged boiler installations, the combustion air fan is designed and provided by the boiler
manufacturer and is integral with the boiler housing. In installations where a stand-alone fan is
provided, low-pressure centrifugal blowers are commonly used and are fitted in cyclones.
3. Feed water Heaters
Feed water heaters are energy recovery devices generally found only in large steam generating plants
where all of the steam generated is not reduced to condensate by the steam user. This "waste steam" is
reduced to condensate for return to the boiler in the feed water heater. The boiler feed water is used as
a cooling medium to reduce the steam to condensate, which increases the temperature of the feed
water and, thereby, increases the thermal efficiency of the boiler.
4. Deaerators
The purpose of a deaerator is to reduce dissolved gases, particularly oxygen, to a low level and
improve plant thermal efficiency by raising the water temperature. In addition, they provide feed water
storage and proper suction conditions for boiler feed water pumps
5. Feed water Heaters
A feed water heater is a heat exchanger that has function to heat feed water before to be supplied to a
steam boiler. The feed water heater is used to bring feed water closer to temperature of the steam
boiler water. This increase efficiency can make saving in required fuel to heat steam boiler water.
6. Flue
Flue gas is the gas exiting to the atmosphere via a flue, which is a pipe or channel for conveying
exhaust gases from a fireplace, oven, furnace, boiler or steam generator.
7. Economizer
An economizer uses the waste heat from the boiler exhaust that would otherwise be lost to atmosphere
to (in most cases) preheat the feed water into the boiler. This improves the boiler efficiency and
reduces fuel costs.
8. Steam drum
The drum stores the steam generated in the water tubes and acts as a phase-separator for the
steam/water mixture. The difference in densities between hot and cold water helps in the accumulation
of the "hotter"-water/and saturated-steam into the steam-drum.
9. Headers
Headers form an important part of all types of boilers. Steam from the generating tubes is collected in
headers which are therefore always under pressure.
10. Super heater
It is integral part of boiler and is placed in the path of hot flue gases from the furnace. The heat
recovered from the flue gases is used in superheating the steam before entering into the turbine (i.e.,
prime mover).Its main purpose is to increase the temperature of saturated steam without raising its
pressure therefore removing moister from the steam making it dry steam which exerts more power
than wet steam.
5. Types of Boilers
Boilers are classified into different types based on their working pressure and temperature, fuel type, draft
method, size and capacity, and whether they condense the water vapor in the combustion gases. Boilers are
also sometimes described by their key components, such as heat exchanger materials or tube design. These
other characteristics are discussed in the following section on Key Components of Boilers.
Two primary types of boilers
Fire tube
Water tube boilers
A fire tube boiler is a type of boiler in which hot gases / flue gases (products of combustion) from a fire
(heat source) pass through one or more tubes running through a sealed container of water. The heat energy
from the gases passes through the sides of the tubes by thermal conduction, heating the water and ultimately
creating steam. A fire-tube boiler is sometimes called a "smoke-tube boiler" or "shell boiler" or sometimes
just "fire pipe".
Figure 1: Fire tube Boiler
Advantages of Fire Tube Boiler
1. It is quite compact in construction.
2. Fluctuation of steam demand can be met easily.
3. It is also quite cheap.
Disadvantages of Fire Tube Boiler
1. As the water required for operation of the boiler is quite large, it requires long time for rising steam at
desired pressure.
2. As the water and steam are in same vessel the very high pressure of steam is not possible.
3. The steam received from fire tube boiler is not very dry.
6. A Water tube design is the exact opposite of a fire tube. Here the water flows through the tubes and are
incased in a furnace in which the burner fires into. These tubes are connected to a steam drum and a mud
drum. The water is heated and steam is produced in the upper drum. Large steam users are better suited for
the Water tube design. The industrial water tube boiler typically produces steam or hot water primarily for
industrial process applications, and is used less frequently for heating applications.
Figure 2: Watertube Boiler
7. Advantages
Water tube Boilers are:
• Available in sizes that are far greater than the fire tube design. Up to several million pounds per hour of
steam.
• Able to handle higher pressures up to 5,000 psig.
• Recover faster than their fire tube boiler.
• Have the ability to reach very high temperatures.
Disadvantages of the Water tube design include:
• High initial capital cost
• Cleaning is more difficult due to the design
• No commonality between tubes
• Physical size may be an issue
8. Introduction to Welding
A weld is made when separate pieces of material to be joined combine and form one piece when
heated to a temperature high enough to cause melting. Filler material is typically added to strengthen
the joint.
Welding is a dependable, efficient and economic method for permanently joining similar metals. In
other words, you can weld steel to steel or aluminum to aluminum, but you cannot weld steel to
aluminum using traditional welding processes.
Welding is used extensively in all sectors or manufacturing, from earth moving equipment to the
aerospace industry.
The most popular processes are shielded metal arc welding (SMAW), gas metal arc welding
(GMAW) and gas tungsten arc welding (GTAW).
All of these methods employ an electric power supply to create an arc which melts the base metal(s) to
form a molten pool. The filler wire is then either added automatically (GMAW) or manually (SMAW
& GTAW) and the molten pool is allowed to cool.
Finally, all of these methods use some type of flux or gas to create an inert environment in which the
molten pool can solidify without oxidizing.
Gas Flow Meters
9. 1. Shielded Metal Arc Welding (SMAW)
Shielded Metal Arc Welding (SMAW)
SMAW is a welding process that uses a flux covered metal electrode to carry an electrical current.
The current forms an arc that jumps a gap from the end of the electrode to the work. The electric arc
creates enough heat to melt both the electrode and the base material(s). Molten metal from the
electrode travels across the arc to the molten pool of base metal where they mix together. As the arc
moves away, the mixture of molten metals solidifies and becomes one piece. The molten pool of
metal is surrounded and protected by a fume cloud and a covering of slag produced as the coating of
the electrode burns or vaporizes. Due to the appearance of the electrodes, SMAW is commonly
known as ‘stick’ welding.
SMAW is one of the oldest and most popular methods of joining metal. Moderate quality welds can
be made at low speed with good uniformity. SMAW is used primarily because of its low cost,
10. flexibility, portability and versatility. Both the equipment and electrodes are low in cost and very
simple. SMAW is very flexible in terms of the material thicknesses that can be welded (materials
from 1/16” thick to several inches thick can be welded with the same machine and different settings).
It is a very portable process because all that’s required is a portable power supply (i.e. generator).
Finally, it’s quite versatile because it can weld many different types of metals, including cast iron,
steel, nickel & aluminum.
Drawbacks to SMAW
(1) That it produces a lot of smoke & sparks,
(2) There is a lot of post-weld cleanup needed if the welded areas are to look presentable,
(3) It is a fairly slow welding process and
(4) It requires a lot of operator skill to produce consistent quality welds.
2. Gas Metal Arc Welding (GMAW)
Gas Metal Arc Welding (GMAW)
In the GMAW process, an arc is established between a continuous wire electrode (which is always
being consumed) and the base metal. Under the correct conditions, the wire is fed at a constant rate to
the arc, matching the rate at which the arc melts it. The filler metal is the thin wire that’s fed
automatically into the pool where it melts. Since molten metal is sensitive to oxygen in the air, good
shielding with oxygen-free gases is required. This shielding gas provides a stable, inert environment
to protect the weld pool as it solidifies. Consequently, GMAW is commonly known as MIG (metal
inert gas) welding. Since fluxes are not used (like SMAW), the welds produced are sound, free of
contaminants, and as corrosion-resistant as the parent metal. The filler material is usually the same
composition (or alloy) as the base metal.
11. GMAW is extremely fast and economical. This process is easily used for welding on thin-gauge
metal as well as on heavy plate. It is most commonly performed on steel (and its alloys), aluminum
and magnesium, but can be used with other metals as well. It also requires a lower level of operator
skill than the other two methods of electric arc welding discussed in these notes. The high welding
rate and reduced post-weld cleanup are making GMAW the fastest growing welding process.
3. Gas Tungsten Arc Welding (GTAW)
12. Gas Tungsten Arc Welding (GTAW)
In the GTAW process, an arc is established between a tungsten electrode and the base metal(s). Under
the correct conditions, the electrode does not melt, although the work does at the point where the arc
contacts and produces a weld pool. The filler metal is thin wire that’s fed manually into the pool
where it melts. Since tungsten is sensitive to oxygen in the air, good shielding with oxygen-free gas is
required. The same inert gas provides a stable, inert environment to protect the weld pool as it
solidifies. Consequently, GTAW is commonly known as TIG (tungsten inert gas) welding.
Because fluxes are not used (like SMAW), the welds produced are sound, free of contaminants and
slags, and as corrosion-resistant as the parent metal.
Tungsten’s extremely high melting temperature and good electrical conductivity make it the best
choice for a non-consumable electrode. The arc temperature is typically around 11,000° F. Typical
shielding gasses are Ar, He, N, or a mixture of the two. As with GMAW, the filler material usually is
the same composition as the base metal.
13. GTAW is easily performed on a variety of materials, from steel and its alloys to aluminum,
magnesium, copper, brass, nickel, titanium, etc. Virtually any metal that is conductive lends itself to
being welded using GTAW. Its clean, high-quality welds often require little or no post-weld
finishing. This method produces the finest, strongest welds out of all the welding processes.
However, it’s also one of the slower methods of arc welding.
4. Submerged Arc Welding (SAW)
Submerged Arc Welding (SAW)
Submerged arc welding is a process in which the joining of metals is produced by heating with an arc
or arcs between a bare metal electrode or electrodes and the work. The arc is shielded by a blanket of
granular fusible material on the work. Pressure is not used. Filler metal is obtained from the electrode
or from a supplementary welding rod.
In SAW welding the flux and wire are separate. Both impact the properties of the weld, requiring the
selection of the optimal combination by the engineer for each project.
Major Uses
The submerged arc process is widely used in heavy steel plate fabrication work. This includes the
welding of structural shapes, the longitudinal seam of larger diameter pipe, the manufacture of
machine components for all types of heavy industry, and the manufacture of vessels and tanks for
pressure and storage use. It is widely used in the shipbuilding industry for splicing and fabricating
sub-assemblies, and by many other industries where steels are used in medium to heavy thicknesses.
It is also used for surfacing and buildup work, maintenance, and repair.
Process Limitations
A major limitation of SAW (submerged arc welding) is its limitation of welding positions. The other
limitation is that it is primarily used only to weld mild and low-alloy high-strength steels.
Advantages
The major advantages of the SAW or submerged arc welding process are:
1. High quality metal weld.
2. extremely high speed and deposition rate
14. 3. Smooth, uniform finished weld with no spatter.
4. Little or no smoke.
5. No arc flash, thus minimal need for protective clothing.
6. High utilization of electrode wire.
7. Easy automation for high-operator factor.
8. Normally, no involvement of manipulative skills.
Selection of the welding process
The selection of the joining process for a particular job depends upon many factors. There is no one
specific rule governing the type of welding process to be selected for a certain job. A few of the
factors that must be considered when choosing a welding process are:
1. Availability of equipment
2. Repetitiveness of the operation
3. Quality requirements (base metal penetration, consistency, etc.)
4. Location of work
5. Materials to be joined
6. Appearance of the finished product
7. Size of the parts to be joined
8. Time available for work
9. Skill experience of workers
10. Cost of materials
11. Code or specification requirements
17. Gas Cutting
Oxy-Fuel Cutting
Oxy-fuel cutting is a cost-effective method of plate edge preparation for bevel and groove welding. It
can be used to easily cut rusty and scaled plates and only requires moderate skill to produce
successful results.
The oxy-fuel gas cutting process creates a chemical reaction of oxygen with the base metal at
elevated temperatures to sever the metal. The necessary temperature is maintained by a flame from
the combustion of a selected fuel gas mixed with pure oxygen.
Oxy-fuel cutting applications are limited to carbon and low alloy steel. These materials can be cut
economically, and the setup is quick and simple. For manual oxy-fuel gas cutting there is no electric
power requirement and equipment costs are low. Materials from 1/16in (1.6mm) to 4in (102mm)
thick are commonly cut using manual oxy-fuel gas cutting. Materials 12in (0.3m) and greater in
thickness are successfully severed using machine cutting.
Plasma Arc Cutting (PAC)
Plasma Arc cutting system utilizes heat generated by arc discharge between the cutting object
material and the electrode inside the torch. Arc discharge heat forms working gas into the plasma
state of high temperature; the plasma jet of high temperature and high-speed is blown out from the
nozzle; and the cutting object material is fused to be cut.
18. Typical materials cut by this process include steel, aluminum, brass and copper though other
conductive metals may be cut as well.
Application of Plasma cutting is often in fabrication and welding shops, automotive repair and
restoration, industrial construction. Due to the high speed, precision cuts, combined with low cost of
operation, plasma cutting sees a widespread usage from large scale industrial CNC applications down
to small hobbyist shops.
19. Shearing machine
The shearing process is performed on a shear machine, often called a squaring shear or power shear,
that can be operated manually (by hand or foot) or by hydraulic, pneumatic, or electric power. A
typical shear machine includes a table with support arms to hold the sheet, stops or guides to secure
the sheet, upper and lower straight-edge blades, and a gauging device to precisely position the sheet.
The sheet is placed between the upper and lower blade, which are then forced together against the
sheet, cutting the material. In most devices, the lower blade remains stationary while the upper blade is
forced downward. The upper blade is slightly offset from the lower blade, approximately 5-10% of the
sheet thickness. Also, the upper blade is usually angled so that the cut progresses from one end to the
other, thus reducing the required force. The blades used in these machines typically have a square edge
rather than a knife-edge and are available in different materials, such as low alloy steel and high-
carbon steel.
Figure : Shearing Technique
Sand Blasting
Abrasive blasting which is also commonly referred to as sandblasting is a process in which a
medium is used to smoothen out or polish a rough surface of machinery and metal parts having rust
and corrosion. Abrasive blasting is a quick and efficient solution to getting these metal parts
functioning and looking their optimum best. This process can also be used to prepare surfaces that
need repainting.
Figure : Sand Basting Equipment
20. Silica Sand or Silicon Dioxide
Silicon Dioxide refers to ordinary sand, which is also known as silica or quartz.
Silica Sandblasting was a commonly used method of removing impurities from surfaces; this is
because sand particles are almost the same size and the edges of the particles are sharp, hence making
this type of grit efficient in abrasive blasting. However, this kind of abrasive blasting is no longer a
21. popular choice as there are other blast mediums that work better than sand, and also, silica can cause
some types of respiratory diseases.
Soda
Soda sandblasting refers to the use of baking soda or bicarbonate of soda in the blasting process. Soda
is used as an abrasive to remove rust from metals without causing depression or damaging the metal
beneath the rough surface. Soda is also a great grit to use on delicate materials that may be destroyed
by tougher abrasives.
Steel sandblasting
In this process, steel grit is used as an abrasive in the removal of paint and rust from steel metals. The
use of steel leaves a smooth finish. Steel grit is often preferred due to its fast cutting nature.
Glass Bead
For a matte and satin finish glass bead sandblasting is best; this is because this grit has very fine
materials that polish the surface of the object being sandblasted. This type of abrasive blasting is
often used on cabinets.
Bristle blasting
In this type of abrasive blasting, no separate medium is used. Instead, steel wire bristles are rotated on
a surface. This rotating action aids in the removal of impurities, hence leaving the surface smooth.
This method is often used to clean metal surfaces with some form of corrosion.
Post Weld heat treatment (PWHT)
Welding is an essential part of operating and maintaining assets in the petroleum (upstream,
midstream, downstream) and chemical processing industries. While it has many useful applications,
the welding process can inadvertently weaken equipment by imparting residual stresses into a
material, leading to reduced material properties.
In order to ensure the material strength of a part is retained after welding, a process known as Post
Weld Heat Treatment (PWHT) is regularly performed. PWHT can be used to reduce residual
stresses, as a method of hardness control, or even to enhance material strength.
If PWHT is performed incorrectly, or neglected altogether, residual stresses can combine with load
stresses to exceed a material’s design limitations. This can lead to weld failures, higher cracking
potential, and increased susceptibility to brittle fracture.
Introduction to Non Destructive Testing
Nondestructive testing (NDT) is the process of inspecting, testing, or evaluating materials,
components or assemblies for discontinuities, or differences in characteristics without destroying the
serviceability of the part or system. In other words, when the inspection or test is completed the part
can still be used.
Visual inspection:
Visual testing is the most commonly used test method in industry. Because most test methods
require that the operator look at the surface of the part being inspected, visual inspection is inherent
in most of the other test methods. As the name implies, VT involves the visual observation of the
surface of a test object to evaluate the presence of surface discontinuities. VT inspections may be by
Direct Viewing, using line-of sight vision, or may be enhanced with the use of optical instruments
such as magnifying glasses, mirrors, boroscopes, charge-coupled devices (CCDs) and computer-
22. assisted viewing systems (Remote Viewing). Corrosion, misalignment of parts, physical damage
and cracks are just some of the discontinuities that may be detected by visual examinations.
Radiography:
Scientific Principles
X-rays are used to produce images of objects using film or other detector that is sensitive to
radiation. The test object is placed between the radiation source and detector. The thickness and the
density of the material that X-rays must penetrate affects the amount of radiation reaching the
detector. This variation in radiation produces an image on the detector that often shows internal
features of the test object.
Main Uses
It is used to inspect almost any material for surface and subsurface defects. X-rays can also be used
to locates and measures internal features, confirm the location of hidden parts in an assembly, and to
measure thickness of materials.
Disadvantage
1. Can be used to inspect virtually all materials.
2. Detects surface and subsurface defects.
3. Ability to inspect complex shapes and multi-layered structures without disassembly.
4. Minimum part preparation is required.
Liquid (Dye) penetrant method:
Scientific Principles
Penetrant solution is applied to the surface of a precleaned component. The liquid is pulled into
surface-breaking defects by capillary action. Excess penetrant material is carefully cleaned from the
surface. A developer is applied to pull the trapped penetrant back to the surface where it is spread
out and forms an indication. The indication is much easier to see than the actual defect.
23. Main Uses
It is used to locate cracks, porosity, and other defects that break the surface of a material and have
enough volume to trap and hold the penetrant material. Liquid penetrant testing is used to inspect
large areas very efficiently and will work on most nonporous materials.
Main Advantages
1. Large surface areas or large volumes of parts/materials can be inspected rapidly and at low cost.
2. Parts with complex geometry are routinely inspected.
3. Indications are produced directly on surface of the part providing a visual image of the discontinuity.
4. Equipment investment is minimal.
Disadvantage
1. Detects only surface breaking defects.
2. Surface preparation is critical as contaminants can mask defects.
3. Requires a relatively smooth and nonporous surface.
4. Post cleaning is necessary to remove chemicals.
5. Requires multiple operations under controlled conditions.
6. Chemical handling precautions are necessary (toxicity, fire, waste)
Magnetic particles Testing:
Scientific Principles
A magnetic field is established in a component made from ferromagnetic material. The magnetic
lines of force travel through the material and exit and reenter the material at the poles. Defects such
as crack or voids cannot support as much flux, and force some of the flux outside of the part.
Magnetic particles distributed over the component will be attracted to areas of flux leakage and
produce a visible indication.
24. Main Uses
It is used to inspect ferromagnetic materials (those that can be magnetized) for defects that result in a
transition in the magnetic permeability of a material. Magnetic particle inspection can detect surface
and near surface defects.
Main Advantages
1. Large surface areas of complex parts can be inspected rapidly.
2. Can detect surface and subsurface flaws.
3. Surface preparation is less critical than it is in penetrant inspection.
4. Magnetic particle indications are produced directly on the surface of the part and form an image of
the discontinuity.
5. Equipment costs are relatively low.
Disadvantage
1. Only ferromagnetic materials can be inspected.
2. Proper alignment of magnetic field and defect is critical.
3. Large currents are needed for very large parts.
4. Requires relatively smooth surface.
5. Paint or other nonmagnetic coverings adversely affect sensitivity.
6. Demagnetization and post cleaning is usually necessary.
Ultrasonic Inspection:
Scientific Principles
High frequency sound waves are sent into a material by use of a transducer. The sound waves travel
through the material and are received by the same transducer or a second transducer. The amount of
energy transmitted or received and the time the energy is received are analyzed to determine the
presence of flaws. Changes in material thickness, and changes in material properties can also be
measured.
Main Uses
It is used to locate surface and subsurface defects in many materials including metals, plastics, and
wood. Ultrasonic inspection is also used to measure the thickness of materials and otherwise
characterize properties of material based on sound velocity and attenuation measurements.
Main Advantages
1. Depth of penetration for flaw detection or measurement is superior to other methods.
2. Only single sided access is required.
3. Provides distance information.
4. Minimum part preparation is required.
5. Method can be used for much more than just flaw detection.
25. Disadvantage
1. Surface must be accessible to probe and couplant.
2. Skill and training required is more extensive than other technique.
3. Surface finish and roughness can interfere with inspection.
4. Thin parts may be difficult to inspect.
5. Linear defects oriented parallel to the sound beam can go undetected.
6. Reference standards are often needed.
