Flux Cored Arc Welding (FCAW)

In document 108056140 DESCON Internship Report (Page 30-49)

Flux cored arc welding (FCAW) is an electric arc welding process which fuses together the parts to be welding by heating them with an arc between a continuously fed flux filled electrode wire and the work. Shielding is obtained through decomposition of the flux within the tubular wire (self shielded method). Additionally shielding may be obtained from an externally supplied gas or gas mixture (gas shielded method). Equipment is similar to that used for Gas Metal Arc welding (GMAW).

Welding is normally limited to the flat and horizontal positions with large diameter wires.

Smaller diameter wires are used in all positions. A layer of slag is left on the weld bead that must be removed after welding.

Advantages of FCAW

 Deposition rate is high with larger diameter wires, and for positional welding.

 Deeper penetration is possible than with GMAW.

 FCAW has high operator appeal: process is easy to use and welds are of good appearance.

 Good quality welds and appearance.

 Wide range of steel types over a range of thickness.

Disadvantages of FCAW

 High capital cost of machinery, maintenance required on wire feed system.

 Accessibility to the welding joint is restrictive because of the size of the gun.

 The available length of the welding lead can be restrictive.

 Electrode is more expensive ($/kg) than GMAW.

 Produces more smoke and fumes than GMAW.

 Slag covering needs to be removed.

 Storage of wires must be stored and handled to prevent damage and corrosion.

 Welding positions:

There are four basic welding positions, or orientations, that have been defined by the American Welding Society. They are

1. Flat 1G / 1F

2. Horizontal 2G / 2F

3. Vertical 3G / 3F

4. Overhead 4G / 4F

5. 5G & 6G is used for pipe welding 5G& 6G

These positions are designated by the number that relates to the position followed by a letter that designates the type of weld; (F) for fillet weld, and (G) for groove weld.

 Welding Joints:

The weld joint is where two or more metal parts are joined by welding. The five basic types of weld joints are the butt, corner, tee, lap, and edge, as shown in figure.

 A butt joint is used to join two members aligned in the same plane. This joint is frequently used in plate, sheet metal, and pipe work. A joint of this type may be either square or grooved.

 Corner and tee joints are used to join two members located at right angles to each other. In cross section, the corner joint forms an L-shape, and the tee joint has the shape of the letter T.

 A lap joint, as the name implies, is made by lapping one piece of metal over another. This is one of the strongest types of joints.

 An edge joint is used to join the edges of two or more members lying in the same plane.

 Weld symbols:

Welding symbols, like sign posts are informational directors. They are placed on drawings by Welding engineers and their purpose is to relay information to the weld operator. In many instances the information relayed is very simple.

Occasionally it is necessary for the engineer to relay complicated information. Therefore it is important that weld operators understand the symbols and are capable of interpreting the needs of the engineer.

For the most part weld symbols are standard throughout the world, although there are symbols that are devised and used only by the company that devised them.

When we put the above elements together we see the result in fig. 007. The finished symbol instructs the weld operator to deposit a 1/4” fillet weld both sides of the joint and that the preferred welding rod will be a E7018.

The symbol shown in following fig. indicates that the vertical component requires beveling prior to assembly. The remainder of the symbol indicates that a 1/4” fillet is required to complete the weld. This symbol would usually be accompanied with

additional notes and instruction. The additional notes would probably reference a specific weld procedure, which would indicate the number and sequence of multiple passes required to complete the finished weld.

The following illustrations show simple weld symbols and the resulting application.

Butt Welds:

Groove Joints:

Lap Joints:

Tee Joints:

Sandblasting:

Sandblasting is used to clean surfaces, remove rust, oxidation, or finishes, preparing surfaces for new coating applications. It is highly effective for large equipment, surface prepping and paint/rust removal. The pressure of is 120 psi or 7.5 bar used. Sandblasting is mostly used for Stainless steel and Mild Steel members.

Sand Blasting Equipments:

 Air Compressor

 Hopper (Sand blasting machine)

 Blasting pipe ( )

 Adopter for nozzle

 Nozzle (4mm to 9mm dia)

 Dead man switch for safety

Sand Blasting Materials:

Following materials are used,

 Steel shorts

 Aluminum oxide

 Glass beads

 Steel grit

 Garnet

 Silica sand

 Larnuspur sand

Galvanizing Galvanizing is the process of applying a zinc coating to fabricated iron or steel material by immersing the material in a bath consisting primarily of molten zinc. The simplicity of the galvanizing process is a distinct advantage over other methods of providing corrosion protection. The automotive industry depends heavily on this process for the production of many components used in car manufacturing. Galvanizing forms a metallurgical bond between the zinc and the underlying steel or iron, creating a barrier that is part of the metal itself.

Galvanizing process:

1. First of all dip the steel or iron material in caustic soda which is the cause of oil removing.

2. Then dip in fresh water which is called rinsing.

3. Then dip in HCL bath for 20 to 30 minutes which is the cause of rust removing.

4. Then dip in fresh water which is called rinsing.

5. Then dip in the flux bath (Ammonium chloride + Zinc chloride) for 2 to 3 minutes which is the cause of coating of flux.

6. Then put on heater for some time for drying the material.

7. Then dip in Zinc bath which has 4500C temperature for 4 to 5 minutes for the coating of zinc.

8. Then dip in fresh water for quenching the material.

9. The last step is the cooling, finishing and the inspection of the material.

Stress Relieving Furnace

Stress Relieving Furnace also called post welding heat treatment (PWHT) is used for relieving the stress from parts after machining and welding. This is used for C.S (Carbon steel) and Alloy parts. Machining and Welding induces stresses in parts. These stresses can cause distortions in the part long term. If the parts are clamped in service, then cracking could occur. Also hole locations can change causing them to go out of tolerance. For these reasons, stress relieving is often necessary.

Stress relieving is done by subjecting the parts to a temperature of about 75 ºC (165 ºF) below the transformation temperature, line A1 on the diagram, which is about 727 ºC (1340 ºF) of steel thus stress relieving is done at about 650 ºC (1202 ºF) for about one hour or till the whole part reaches the temperature. This removes more than 90% of the internal stresses.

Alloy steels are stress relieved at higher temperatures. After removing from the furnace, the parts are air cooled in still air.

Main parts of Stress Relieving Furnace:

 Bed of furnace

 Furnace

 Burners

 Thermocouples

 Main stack

 Control panel

Capacity of the furnace:

Length of the furnace = 20 meter Width of the furnace = 4.5 meter Height of the furnace = 4.5 meter

Maximum bed load = 300 Ton

Max temperature of the furnace = 750o C

Average time of Heating = 12 to 13 hours

Non Destructive Test (NDT)

Nondestructive testing (NDT) is a wide group of analysis techniques used in science and industry to evaluate the properties of a material, component or system without causing damage. The terms Nondestructive examination (NDE), Nondestructive inspection (NDI), and Nondestructive evaluation (NDE) are also commonly used to describe this technology.

Because NDT does not permanently alter the article being inspected, it is a highly-valuable technique that can save both money and time in product evaluation.

Methods:

Following methods are used in NDT DESCON.

a) Radiographic test (RT) b) Ultrasonic test (UT)

c) Penetrant test (PT) or Die penetrant test (DPT) d) Magnetic test (MT) or Magnetic particle test (MPT) a) Radiographic test (RT)

Radiographic Testing (RT), or industrial radiography, is a nondestructive testing (NDT) method of inspecting materials for hidden flaws by using the ability of short wavelength electromagnetic radiation (high energy photons) to penetrate various materials.

Either an X-ray machine or a radioactive source (Ir-192, Co-60, or in rare cases Cs-137) can be used as a source of photons. Neutron radiographic testing (NR) is a variant of radiographic testing which uses neutrons instead of photons to penetrate materials. This can see very different things from X-rays, because neutrons can pass with ease through lead and steel but are stopped by plastics, water and oils.

Principal

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 affect 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.

Application

Used for the inspection of 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.

Advantages

 Can be used to inspect virtually all materials.

 Detects surface and subsurface defects.

 Ability to inspect complex shapes and multi-layered structures without disassembly.

 Minimum part preparation is required.

Disadvantages

 Extensive operator training and skill required.

 Access to both sides of the structure is usually required.

 Orientation of the radiation beam to non-volumetric defects is critical.

 Field inspection of thick section can be time consuming.

 Relatively expensive equipment investment is required.

 Possible radiation hazard for personnel.

b) Ultrasonic Test (UT)

In ultrasonic testing (UT), very short ultrasonic pulse-waves with center frequencies ranging from 0.1-15 MHz and occasionally up to 50 MHz are launched into materials to detect internal flaws or to characterize materials. The technique is also commonly used to determine the thickness of the test object, for example, to monitor pipe work corrosion.

Ultrasonic testing is often performed on steel and other metals and alloys, though it can also be used on concrete, wood and composites, albeit with less resolution. It is a form of non-destructive testing used in many industries including aerospace, automotive and other transportation sectors.

Principal:

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. The machine displays these results in the form of a signal with amplitude representing the intensity of the reflection and the distance, representing the arrival time of the reflection.

Applications

Used for the location of 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.

Advantages

 High penetrating power, which allows the detection of flaws deep in the part.

 High sensitivity, permitting the detection of extremely small flaws.

 Only one surface need be accessible.

 Greater accuracy than other nondestructive methods in determining the depth of internal flaws and the thickness of parts with parallel surfaces.

 Some capability of estimating the size, orientation, shape and nature of defects.

 Nonhazardous to operations or to nearby personnel and has no effect on equipment and materials in the vicinity.

 Capable of portable or highly automated operation.

Disadvantages

 Manual operation requires careful attention by experienced technicians

 Extensive technical knowledge is required for the development of inspection procedures.

 Parts that is rough, irregular in shape, very small or thin, or not homogeneous are difficult to inspect.

 Surface must be prepared by cleaning and removing loose scale, paint, etc., although paint that is properly bonded to a surface need not be removed.

 Couplants are needed to provide effective transfer of ultrasonic wave energy between transducers and parts being inspected unless a non-contact technique is used. Non-contact techniques include Laser and Electro Magnetic Acoustic Transducers (EMAT).

 Inspected items must be water resistant, when using water based couplants that do not contain rust inhibitors.

c) Penetrant test (PT) or Die penetrant test (DPT)

Dye penetrant inspection (DPI), also called liquid penetrant inspection (LPI) or penetrant testing (PT), is a widely applied and low-cost inspection method used to locate surface breaking defects in all non porous materials (metals, plastics, or ceramics). The penetrant may be applied to all non ferrous materials and ferrous materials; although for ferrous components magnetic-particle inspection is often used instead for its subsurface detection capability. LPI is used to detect casting, forging and welding surface defects such as hairline cracks, surface porosity, leaks in new products, and fatigue cracks on in-service components.

Principle

DPI is based upon capillary action, where surface tension fluid low penetrates into clean and dry surface-breaking discontinuities. Penetrant may be applied to the test component by dipping, spraying, or brushing. After adequate penetration time has been allowed, the excess penetrant is removed, a developer is applied. The developer helps to draw penetrant out of the flaw where a visible indication becomes visible to the inspector.

Inspection is performed under ultraviolet or white light, depending upon the type of dye used - fluorescent or no fluorescent (visible).

Inspection steps

a) Cleaning the surface (1)

b) Adding the first chemical liquid (penetrant) (3) where it goes through to the crack (2) c) Cleaning the surface once more. Though, some of the first chemical remains inside of

the crack

d) Adding the second chemical liquid (developer) (4), where the first liquid (5) penetrate to the second, so that the area of the crack will be shown to our eyes in a bigger scale Applications

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.

Advantages

 Large surface areas or large volumes of parts/materials can be inspected rapidly and at low cost.

 Parts with complex geometry are routinely inspected.

 Indications are produced directly on surface of the part providing a visual image of the discontinuity.

 Equipment investment is minimal.

Disadvantages

 Detects only surface breaking defects.

 Surface preparation is critical as contaminants can mask defects.

 Requires a relatively smooth and nonporous surface.

 Post cleaning is necessary to remove chemicals.

 Requires multiple operations under controlled conditions.

 Chemical handling precautions are necessary (toxicity, fire, waste).

d) Magnetic test (MT) or Magnetic particle test (MPT)

Magnetic particle inspection (MPI) is a non-destructive testing (NDT) process for detecting surface and subsurface discontinuities in ferroelectric materials such as iron, nickel, cobalt, and some of their alloys. The process puts a magnetic field into the part. The piece can be magnetized by direct or indirect magnetization. Direct magnetization occurs when the electric current is passed through the test object and a magnetic field is formed in the material.

Indirect magnetization occurs when no electric current is passed through the test object, but a magnetic field is applied from an outside source. The magnetic lines of force are perpendicular to the direction of the electric current which may be either alternating current (AC) or some form of direct current (DC) (rectified AC).

Principal

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.

Application

Used for the inspection of 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.

Advantages

 Large surface areas of complex parts can be inspected rapidly.

 Can detect surface and subsurface flaws.

 Surface preparation is less critical than it is in penetrant inspection.

 Magnetic particle indications are produced directly on the surface of the part and form an image of the discontinuity.

 Equipment costs are relatively low.

Disadvantages

 Only ferromagnetic materials can be inspected.

 Proper alignment of magnetic field and defect is critical.

 Large currents are needed for very large parts.

 Requires relatively smooth surface.

 Paint or other nonmagnetic coverings adversely affect sensitivity.

 Demagnetization and post cleaning is usually necessary.

Applications of Non Destructive Testing

NDT is used in a variety of settings that covers a wide range of industrial activity.

Automotive

Maintenance, repair and operations

o Bridges

Manufacturing

o Machine parts

o Castings and Forgings

Industrial plants such as Nuclear, Petrochemical, Power, Refineries, Pulp and Paper, Fabrication shops, Mine processing and their Risk Based Inspection programmes.

o Pressure vessels

In-line Inspection using "pigs"

Pipeline integrity management

Leak Detection

o Railways

Rail Inspection

Wheel Inspection

o Tubular NDT, for Tubing material

o Corrosion Under Insulation (CUI)

o Amusement park rides

o Submarines and other Naval warships

o Medical imaging applications (see also Medical physics)

Quality Assurance & Quality control (QA & QC):

Quality control is the more traditional way that businesses have used to manage qualit y.

Quality control is concerned with checking and reviewing work that has been done.

Under traditional quality control, inspection of products and services (checking to make sure that what's being produced is meeting the required standard) takes place during and at the end of the operations process.

There are three main points during the production process when inspection is performed:

1. When raw materials are received prior to entering production, 2. Whilst products are going through the production process,

3. When products are finished - inspection or testing takes place before products are dispatched to customers.

The problem with this sort of inspection is that it doesn't work very well!

There are several problems with inspection under traditional quality control:

 The inspection process does not add any "value". If there were any guarantees that no defective output would be produced, then there would be no need for an inspection process in the first place!

 Inspection is costly, in terms of both tangible and intangible costs. For example, materials, labour, time, employee morale, customer goodwill, lost sales.

 It is sometimes done too late in the production process. This often results in defective or non-acceptable goods actually being received by the customer

 It is usually done by the wrong people - e.g. by a separate "quality control inspection team" rather than by the workers themselves

 Inspection is often not compatible with more modern production techniques (e.g. "Just in Time Manufacturing") which do not allow time for much (if any) inspection.

 Working capital is tied up in stocks which cannot be sold.

 There is often disagreement as to what constitutes a "quality product". For example, to meet quotas, inspectors may approve goods that don't meet 100% conformance, giving the message to workers that it doesn't matter if their work is a bit sloppy. Or one quality control inspector may follow different procedures from another, or use different measurements.

As a result of the above problems, many businesses have focused their efforts on improving

As a result of the above problems, many businesses have focused their efforts on improving

In document 108056140 DESCON Internship Report (Page 30-49)

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