qa qc sepl nov 2017

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Siddhitech Engineering Pvt. Ltd.

QA/QC PRESENTATION

QUALITY CONTROL (QC)The concept of quality control is to look at work after the work is completed. it is the process of testing and inspecting work to determine if it complies with the adopted quality standard.In a quality management system, quality control should never be the primary process. However, it can be used to confirm that quality assurance processes are working properly. If a failure is detected during a quality control inspection or test, then it is evident that quality assurance is missing or, if not missing, the quality assurance process did not function properly and should be evaluated.

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QUALITY ASSURANCE (QA) all the planned and systematic activities implemented within the quality system that can be demonstrated to provide confidence that a product or service will fulfill requirements for quality.Quality assurance, as its name implies, assures that the outcome of a process will be a quality one. This involves taking measures that will reduce errors and omissions before and while performing the work. Some quality assurance processes may be verified using a quality control method.

TYPE OF JOINT ?

butt joint.:- a joint between two members aligned approximately in the same plane

Fillet weld:-A weld of approximately triangular cross section joining two surfaces approximately at right angles to each other

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OVERVIEW OF JOINING METHODS

Mechanical methods

➢ Screwed fasteners, rivets,

Brazing and Soldering

➢ Base metal does not fuse.

➢ Molten filler drawn into close-fit joints by capillary action (surface tension forces).

➢ Brazing filler melts >450 C, solder <450 C

Welding

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WELDING POSITIONS

1 F 1G

2 F 2G

3 F 3G

4 F4G

6-G

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WELDING PROCESSES

1) GTAW - gas tungsten arc welding (TIG)

2) SMAW -shielded metal arc welding

3) MIG-metal inert gas welding

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Tungsten inert gas welding or gas tungsten arc welding (GTAW) is a group of welding process in which the work pieces are joined by the heat obtained from an electric arc struck between a non-consumable tungsten electrode and the work piece in the presence of an inert gas atmosphere.A filler metal may be added if required, during the welding process.

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GAS TUNGSTEN ARC WELDING

Description•TIG equipment consists of a welding torch in which a non-consumable tungsten alloy electrode is held rigidly in the collet.•The diameter of the electrode varies from 0.5 -6.4 mm.•TIG welding makes use of a shielding gas like argon or helium to protect the welding area from atmospheric gases such as oxygen and nitrogen, otherwise which may cause fusion defects and porosity in the weld metal.•The shielding gas flow from the cylinder, through the passage in the electrode holder and then impinges on the work piece.•Pressure regulator and flow meters are used to regulate the pressure and flow of gas from the cylinder.•Either AC or DC can be used to supply the required current.

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Advantages•Suitable for thin metals.•Clear visibility of the arc provides the operator to have a greater control over the weld.•Strong and high quality joints are obtained.•No flux is used. Hence, no slag formation. This results in clean weld joints.

Disadvantages•TIG is the most difficult process compared to all the other welding processes. The welder must maintain short arc length, avoid contact between electrode and the work piece and manually feed the filler metal with one hand while manipulating the torch with the other hand.•Tungsten material when gets transferred into the molten metal contaminates the same leading to a hard and brittle joint.•Skilled operator is required.•Process is slower.•Not suitable for thick metals

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METAL INERT GAS (MIG) WELDING•Metal inert gas welding or gas metal arc welding (GMAW) is a group of arc welding process in which the work pieces are joined by the heat obtained from an electric arc struck between a bare (uncoated) consumable electrode and the work piece in the presence of an inert gas atmosphere.•The consumable electrode acts as a filler metal to fill the gap between the two work pieces.•Figure shows the MIG welding process.

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Description•The equipment consists of a welding torch in which a bare consumable electrode in the form of a wire is held and guided by a guide tube.•The electrode material used in MIG welding is of the same material or nearly the same chemical composition as that of the base metal.•Its diameter varies from 0.7 -2.4 mm.•The electrode is fed continuously at a constant rate through feed rollers driven by an electric motor.•MIG makes use of shielding gas to prevent atmospheric contamination of the molten weld pool.•Mixture of argon and carbon dioxide in a order of 75% to 25% or 80% to 20% is commonly used.•The shielding gas flow from the cylinder, through the passage in the electrode holder and then impinges on the work piece.•AC is rarely used with MIG welding; instead DC is employed and the electrode is positively charged. This results in faster melting of the electrode which increases weld penetration and welding speed.

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Advantages• MIG welding is fast and economical.•The electrode and inert gas are automatically fed, and this makes the operator easy and to concentrate on the arc. •Weld deposition rate is high due to the continuous wire feed•No flux is used. Hence, no slag formation. This results in clean welds.•Thin and thick metals can be welded.•Process can be automated.

Disadvantages•Equipment is costlier•Porosity (gas entrapment in weld pool) is the most common quality problem in this process. However, extensive edge preparation can eliminate this defect.

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FLUX SHIELDED METAL ARC WELDING (MMAW OR SMAW)

•It is an arc welding process wherein coalescence is produced by heating the work piece with an electric arc set up between a flux coated electrode and the work piece.•The flux covering decomposes due to arc heat and performs many functions, like arc stability, weld metal protection, etc., •The electrode itself melts and supplies the necessary filler metal.

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Principle of the process:•Heat required for welding is obtained from the arc struck between a coated electrode and the work piece.

•The arc temperature and thus the arc heat can be increased or decreased by employing higher or lower arc currents.

•A high current arc with a smaller arc length produces very intense heat.•The arc melts the electrode end and the job.

•Material droplets are transferred from the electrode to the job, through the arc, and are deposited along the joint to be welded.

•The flux coating melts, produces a gaseous shield and slag to prevent atmospheric contamination of the molten weld metal.

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Advantages of Shielded Metal Arc Welding (SMAW)•SMAW is the simplest of all the arc welding processes.•The equipment can be portable and the cost is fairly low.•This process finds innumerable applications, because of the availability of a wide variety of electrodes.•A big range of metals and their alloys can be welded.•Welding can be carried out in any position with highest weld quality.

Limitations

•Because of the limited length of each electrode and brittle flux coating on it, mechanization is difficult. •In welding long joints (e.g., in pressure vessels), as one electrode finishes, the weld is to be progressed with the next electrode. Unless properly cared, a defect (like slag inclusion or insufficient penetration) may occur at the place where welding is restarted with new electrode.•The process uses stick electrodes and thus it is slower as compared to MIG welding.•Because of flux coated electrodes, the chances of slag entrapment and other related-defects are more as compared to MIG or TIG welding. .

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Introduction to Nondestructive Testing

The use of noninvasive techniques to determine the integrity of a material, component or structure

orquantitatively measure some characteristic of an object.

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Methods of NDT

➢Visual

➢ Liquid Penetrant

➢ Magnetic Partical

➢ Ultrasonic

➢X-ray

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• A liquid with high surface wetting characteristics is applied to the surface of the part and allowed time to seep into surface breaking defects.

• The excess liquid is removed from the surface of the part. • A developer (powder) is applied to pull the trapped penetrant out the defect

and spread it on the surface where it can be seen. • Visual inspection is the final step in the process. The penetrant used is often

loaded with a fluorescent dye and the inspection is done under UV light to increase test sensitivity.

Liquid Penetrant Inspection

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Step 1. Pre-Cleaning Ensure surface is very Clean normally with the use of a solvent

Step 2. Apply penetrant After the application, the penetrant is normally left on the components surface for approximately 15-20 minutes (dwell time).The penetrantenters any defects that may be present by capillary action.

Step 3. Clean off penetrant the penetrant is removed after sufficient penetration time (dwell time).Care must be taken not to wash any penetrant out off any defects present

Step 4. Inspection / development time Inspection should take place immediately after the developer has been applied. any defects present will show as a bleed out during development time. After full inspection has been carried out post cleaning is generally required.


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Penetrant Fluorescent Penetrant

Bleed out viewed under a UV-A light source Bleed

Bleed out viewed under white light

Colour contrast PenetrantFluorescent

Disadvantages•Surface breaking defect only•little indication of depths•Penetrant may contaminate component•Surface preparation critical•Post cleaning required•Potentially hazardous chemicals•Can not test unlimited times•Temperature dependant


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Advantages•Simple to use•Inexpensive•Quick results•Can be used on any non-porous material•Portability•Low operator skill required

The part is magnetized. Finely milled iron particles coated with a dye pigment are then applied to the specimen. These particles are attracted to magnetic flux leakage fields and will cluster to form an indication directly over the discontinuity. This indication can be visually detected under proper lighting conditions

Magnetic Particle Inspection

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Advantages•Simple to use•Inexpensive•Rapid results•Little surface preparation required•Possible to inspect through thin coatings

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Disadvantages•Surface or slight sub-surface detection only•Magnetic materials only•No indication of defects depths•Only suitable for linear defects•Detection is required in two directions

Radiography (RT)

Radiography involves the use of penetrating gamma or X-radiation to examine parts and products for imperfections. An X-ray generator or radioactive isotope is used as a source of radiation. Radiation is directed through a part and onto film or other imaging media. The resulting radiograph shows the dimensional features of the part. Possible imperfections are indicated as density changes on the film in the same manner as a medical X-ray shows broken bones.

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Advantages

•Permanent record

•Little surface preparation

•Defect identification

•No material type limitation

•Not so reliant upon operator skill

•Thin materials

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Disadvantages•Expensive consumables•Bulky equipment•Harmful radiation•Defect require significant depth in relation to the radiation beam (not good for planar defects)•Slow results•Very little indication of depths•Access to both sides required

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High frequency sound waves are introduced into a material and they are reflected back from surfaces or flaws.

Reflected sound energy is displayed versus time, and inspector can visualize a cross section of the specimen showing the depth of features that reflect sound.

f

plate

crack

0 2 4 6 8 10

initial pulse

crackecho

back surfaceecho

Oscilloscope, or flaw detector screen

Ultrasonic Inspection (Pulse-Echo)

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f

plate

crack

Ultrasonic Inspection (Pulse-Echo)

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Advantages• Rapid results• Both surface and • sub-surface detection • Safe• Capable of measuring the depth of defects• May be battery powered• Portable

Disadvantages• Trained and skilled operator required• Requires high operator skill• Good surface finish required• Defect identification• Couplant may contaminate • No permanent record• Calibration Required• Ferity Material (Mostly)

Welding Defects

A welding defect is any type of flaw in a welding job that compromises the use and function of the object that received the welding.

Lack of Fusion

Undercutting

Pinholes

Cracking

Misalignment

Gas Inclusions

Porosity

Craters

Overlap

Lamellar Tearing

Reheat cracking

Root and Toe Cracks

TYPES OF WELDING DEFECTS

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Lack of Fusion

Lack of fusion is the poor adhesion of the weld bead to the base metal. If the weld heat was not high enough, the metals being welded together may not have become molten during the welding process and the two pieces did not join.

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Under Cutting

Welding along a line or using an arc voltage that is too low can produce a groove or a slight ditch in the metal right along the weld line. This is known as undercutting.

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Pinholes

Welding defect caused by the high welding temperatures is known as Pinholes. If the temperature of arc making of the weld is very high, then tiny holes resembling pin holes may appear on the surface of the weld.

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Cracking

This defect typically occurs because the welder was using the wrong type of wire electrode to make the weld. A combination of poor design and inappropriate procedure may result in high residual stresses and cracking.

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Misalignment

This type defect is generally caused by a setup/fit up problem, or trying to join plates of different thickness.

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Gas Inclusions

Gas inclusions is also a defect that includes porosity, blow holes, and pipes. The cause for gas inclusions is the entrapment of gas within the solidified weld.

It can be from any of the following causes: high sulphur content in the electrode, excessive moisture from the electrode or wrong welding.

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Porosity

Gas inclusions is also a defect that includes porosity, blow holes, and pipes. The cause for gas inclusions is the entrapment of gas within the solidified weld.

It can be from any of the following causes: high sulphur content in the electrode, excessive moisture from the electrode or wrong welding.

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Craters

Crater cracks occur when a crater is not filled before the arc is broken. This causes the outer edges of the crater to cool more quickly than the crater, which creates sufficient stresses to form a crack.

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Reheat Cracking

Reheat cracking is a type of cracking that occurs in HSLA steels, particularly chromium, molybdenum and vanadium steels, during post heating.

It is caused by the poor creep ductility of the heat affected zone.

It can be eliminated by heat treating first with a low temperature soak and then with a rapid heating to high temperatures, grinding or peening the weld toes

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Thank you.

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