Welding-quality-on-QA.ppt , non destructive testing, inspection activities.
- 1. Quality Control Quality: Degree of goodness. Quality Control: It is the Engineering and management activities by which we can measure the quality characteristics of the product, compare them with standards/specifications and take appropriate remedial actions wherever there is deviation of actual products w.r.t standard/specification. Quality Assurance: Confidence given on the product of quality achieved is as per standard/specification.
- 2. Project site- Quality procedure Vs Documentation a) QAP (Quality Assurance Plan) : It is a document which reveals the stage wise inspection process, by which a particular product is inspected. For Ex; Starting from Incoming raw material inspection , fabrication, erection, alignment,WQT, welding, until final painting. QAP also suggests the Quantum & Class of checks, measuring instrument required, reference document, format of record, a) WPS(Welding Procedure Specification): This document defines the process of welding procedure of a particular material, which includes all welding parameters such as Joint design,Material specification,filler/Electrode , Position of weld,pre heat,post heat, Shielding and backing gas used,Electrical chracteristics,Weld cleaning methods etc. c) EWS(Erection Welding Schedule): It gives detail of Welding, Quantum of NDT and PWHT requirements.
- 3. WELDING Welding is the process of bridging the gap between two similar or dissimilar, metals or nonmetals with or without applying pressure, adding filler or without adding filler.
- 4. Types of Welding Basically there are two different types of Welding. 1) Pressure Welding 2) Fusion Welding
- 5. 1)Pressure Welding The Welding takes places under pressure and either with or without additional heating. The material is brought into plastic state and fillers are not used. Here are some methods. 1) Spot welding 2) Flash welding 3) Resistance welding
- 6. Fusion welding The joint of the two components are formed in the fluid state by external heating (gas, electric) with adding filler metals. This method is widely used in construction industries. Some methods are 1) SMAW (MMAW) 2) MIG 3) TIG (GTAW) 4) SAW
- 7. SAW In Submerged Arc welding (SAW), the arc is buried under a granular flux bed. The noise, light and fumes generated are submerged in the flux. SAW uses a consumable electrode. The tip of the electrode and weld zone are surrounded and shielded by the molten flux which is used in the granular state. It is an Automatic Welding process which is widely used in production shops.
- 8. SMAW Shield Metal Arc Welding: In this method, the electric arc is drawn between the tip of an electrode and the metal being welded. The electrode has a metal core covered by a coat of flux. The electrode is used up as the work piece is welded. The flux shields the metal ions in the arc (Molten weld pool) from the atmosphere and ensures arc stability. As the flux decomposes, it produces airborne gases and a slag blanket is formed to protect the hot weld metal from the atmosphere as it cools.
- 9. GMAW The Gas Metal Arc Welding (GMAW) is also known as Metal Inert Gas Welding (MIG). In this type of welding, a continuous solid wire is supplied through the welding gun from the wire feeder. Shielding is provided by argon, helium or a mix of these with Carbon dioxide. No slag is produced, since no flux is used. It is a Semi automatic process. Its main advantage is its speed. More productivity can be achieved.
- 10. GTAW • Gas Tungsten Arc Welding (GTAW) is also known as Tungsten Gas Inert Gas Welding (TIG). Here the electric arc is established between the work piece and the tungsten electrode. In contrast to SMAW, it is a non consumable electrode process. The arc is protected by a shielding gas commonly argon or helium, which displaces atmospheric gases from the weld zone. The arc can fuse two metals without adding of filler. A hand held filler can be used to melt and fill any gaps. The welding produces no slag, but produces small amount of fumes which when inhaled are hazardous.
- 12. Joint weld detail Root Opening Groove Face Bevel Angle Groove Angle Root edge Root face
- 13. NDT Non Destructive Testing : It is a testing technology based on applied physics. It is a method of identifying material for any flaws or discontinuities without damaging their physical structure. The complex products and new materials that are developed and available in market need freedom from defects and assurance for trouble free performance. On the contrary, NDT plays a vital part in judging the product service life. There are basically five methods of NDT. These are the follows. 1.Visual Test (VT) 2. Radiography Test (RT) 3. Ultrasonic Testing (UT) 4. Liquid Penetrant Test(LPI) 5. Magnetic Particle Inspection(MPI)
- 14. Visual Inspection This is the most preliminary stage of NDT. Visual test is an important inspection, easy to perform as well as very effective. For ex. In welding, visual examination is very much necessary before proceeding with the next NDT stages. We can check the surface defects such as un-uniform weld appearance, surface undercuts, surface porosity, uncleaned surfaces including foreign particles such as slag and spatters on the welds. Similarly in equipments or pressure vessels such as boiler pressure parts, the visual examination helps in finding any surface dents, corrosive areas, painting defects etc.
- 15. Radiography Test Radiography is a non-destructive testing tool widely used in industry. Its capability to penetrate into opaque materials especially, steel is remarkable. As the need for engineering materials of high quality increased with the dawn of Nuclear age, radiography attained very great importance. Radiography employs the penetrating capacity of ionizing radiation like X-rays or Gamma rays to produce a shadow of the internal condition of jobs on a recording medium. The record in a film is known as Radiography. Its unique advantage over other NDT method is that it presents a permanent record, simple to read out. Its greatest handy cap is its hazardous nature of harmful radiation and the recurring cost involved. Basic requirements for radiography are a) An enclosure or a cordoned area to operate the equipment. b) X-Ray source (X-Ray Machine) or Gama Ray source (Radio Isotopes) c) Recording medium like X-ray film and accessories to handle and process them. d) Evaluating equipments like illuminator and the knowledge of RT standards.
- 16. Radiography X-Ray Object Cassette or film holder Film d t
- 17. Radiography Isotopes Some frequently used radio isotopes are 1) Radium 226. 2) Cobalt 60. 1) Cesium 137. 2) Iridium 192. 3) Thulium 170. Though Iridium192 is the isotope used widely in India.
- 18. Radiography Techniques There are four techniques of radiography. 1) Single Wall, Single Image. 2) Double Wall, Double Image. 3) Double Wall, Single Image. 4) Panoramic Radiography.
- 19. Single wall technique A B A B C C D D FILMS : A-B, B-C, C-D, D-A
- 20. Double Wall Technique Source Weld joint
- 22. Radiography Isotopes Iridium192 is the isotope used widely in industry. Source Half Life Iridium 192 74.4 days Cobalt 60 5.27 years Thulium 170 127 days Cesium 137 33 years
- 23. Latent Image & Film processing • Latent Image The silver bromide grains in the emulsion layer when exposed to radiation (X rays or Gama rays) are ionized by these radiations and a latent image is formed on the film. The latent image in film is noticeable only after developing the film. . Film processing: The purpose of film processing is to transform the invisible latent image to permanent visible image. There are four main stages involved. 1) Developing: The creation of the visible image. 2) Fixation: The removal of unexposed silver halide. 3) Washing: The removal of fixation products. 4) Drying: The removal of unwanted water.
- 24. RADIATION DETECTION AND MEASUREMENT DOSIMETER : To measure the dose or dose rate (Roentgen) SURVEY METER : To measure the Intensity Of Radiation DENSITOMETER : To judge the density of Film.
- 25. Ultrasonic Test • Mechanical vibrations which have frequency higher than the audible range of human ear viz.20 to 20KHz are called Ultrasonic waves. When the waves are passed on to any object, it reflects back from its another end, if there is discontinuity in between the waves reflect back without moving further, thereby indicating the defect. Most common modes of propagation of ultrasonic waves are; • 1. Longitudinal waves: The waves generated are parallel to the direction of propagation. These waves are readily used in liquids and gases as well as in elastic solids. • 2.Transverse waves: The waves generated are perpendicular to the direction of propagation. • 3. Surface/Rayleigh waves: The waves travel along with the flat or curved surfaces . It is used for checking the soundness of surfaces.
- 26. Major variables in UT • Probes: It works on the theory of Piezo electric effect. The piezo electric crystal in the probe develops electric charges when pressure is applied. This vibration in turn develops sound waves of high frequency which penetrates into the material. • Reference blocks: Ultrasonic inspection is basically comparison process and requires the use of ref blocks for calibration of the equipment and probe set up before put to use on actual job. The calibration is done with standard reference blocks. The calibration of set up is done to check the following: a) Time base b) Linearity c) Resolution d) Sensitivity e) Beam path f) Probe Index
- 28. Distance Amplitude curve DISTANCE Initial echo Defect Indication Backwall echo A M P L I T U D E 20% 50% 80%
- 29. Inspection methods UT can be performed by a)Pulse echo method b)Through transmission method c)Resonance method Pulse echo is widely used in industries. Pulse echo method can be accomplished by longitudinal, shear, surface waves. In this method short bursts of ultrasonic energy(pulse or wave brackets) are introduced into the test piece at a regular interval of time.If the pulses encounter the reflecting surfaces/ Discontinuities, some or all of the energy is reflected.
- 30. No Defect
- 32. SMALL DEFECT
- 34. Liquid penetrate testing This is a method to detect surface as well as sub surface defects. In industrial components surface defects can be visually checked upto an extent with assistance of magnifying glasses. But in case of surface cracks it is difficult to detect by VT, so here DPT comes in picture. Principle: The surface defects like crack , porosity are bleeded with penetrant, which has the property to penetrate any voids. Developer exposes the discontinuities by its reverse capillary action. Following steps are involved: a) Surface preparation b) Application of the penetrant c) Controlling time for penetration d) Removal of excess penetrant e) Application of developer f) Observation of developing process g) Interpretation and evaluation h) Post cleaning.
- 35. Magnetic Particle Inspection It is used to detect the surface/sub surface defects. MPI is a technique used for inspecting ferromagnetic material. The technique is simple and can be applied for raw material, billets, plates,castings, finished components, hot rolled bars etc. The technique enables detection of cracks, seams,inclusions,lack of fusion, lamination and similar flaws. The detection is possible to max depth of 6mm. Principle: The job is magnetized and magnetic lines of forces(Flux) is made available. Discontinuities in the path of magnetic flux create disturbance in the uniform magnetic field, causing flux leakage, which attracts iron powder when it is sprayed on the testing zone and forms a pattern of discontinuity.
- 36. Steps in testing • Magnetize the job suitably • Apply the examination medium(i.e. Iron powder) over the test surface. • Interpret and evaluate the indications. Kinds of Magnetizations: • Longitudinal magnetization:Magnetisation is parallel to the long axis of component, Eg:Yoke method,Coil method. • Circular magnetization:magnetic field is transverse to the length of the component and flux path is contained within the article. Eg:Prod method, Head shot method.
- 37. Welding Discontinuities • If welding is done, defects are bound to occur. The intensity of defects may be more or less which may vary in different welds. The tolerance limit of particular defect varies from that of the other. Following are some Welding defects which are likely to occur : a) Lack of Fusion b) Lack of Penetration c) Cracks d) Slag Inclusion e) Porosities/Blow hole f) Tungsten Inclusion g) Overlap/Mismatch h) Excess Penetration i) Undercuts j) Surface Depression/Excess capping k) Burn through
- 38. Comparison of Defects in different welding Weldin g Proces s Welding Defects SMAW LOP/LF - Slag Inclusion Crack Porosity Burn through TIG LOP/LF Tungsten Inclusion Crack Porosity _ MIG LOP/LF - Crack Blow holes _
- 39. Preheating & Post Heating Preheating: It is the process of Heating the parent metal around the welding area to a specified temperature before welding and maintaining the same during welding. The purpose of preheating are as follows: 1) To minimise the risk of cracking in the weld and heat affected zone of steels this is achieved by a) Reducing the rate of cooling experienced by the weld and HAZ which retards the formation of hard martensite. b) allowing the Hydrogen/moisture to diffuse away from the weld at a faster rate. c) Reducing the Residual stresses induced in the weld region. 2) Uniform preheating reduces the distortion due to welding. Post Heating: It is the heat applied to the joint immediately after completion of welding before the joint cools down to ambient temperature.
- 40. PWHT • Post Weld heat Treatment: It is a type of heating Process applied in High thickness materials ranging from carbon steel to high alloy steels. It is done after welding completion. It consist of heating the weldment at a controlled rate to temp range below the transformation temperature and Holding(Soaking) it for certain time and cooling it down at a controlled rate. • Purpose of PWHT: • a) To Relieve the Residual stresses produced during welding. & this stress are heavily restrained & susceptible for cracking. • b)To obtain machinability & also to increase the material resistance against stress corrosion cracking. • c) To obtain Hard surfaces • d) To obtain the required Hardness and improve the toughness & ductility.
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