Internship Report

2016

Submitted by : Abdullah Mansoor

University of Central Punjab

Intern #1287

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

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

.

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.

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.

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

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

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

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,

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.

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)

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.

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

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

Welding Symbols

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.

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.

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

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

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-

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.

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.

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.

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.