فحوصات لااتلافية

• NDT


  Non Destructive Testing
• Course Objectives


  • Introduce basic principles, techniques, equipment, applications, and limitations of NDT methods
  • Enable selection of appropriate NDT methods
  • Identify advantages and limitations of NDT methods
  • Make aware of developments and future trends in NDT
• Syllabus


  • Introduction to NDT
  • Visual Inspection
  • Liquid Penetrant Inspection
  • Magnetic Particle Inspection
  • Ultrasonic Testing
  • Radiography Testing
  • Eddy Current Testing
• Expected outcome: Students will be able to differentiate various defect types and select the appropriate NDT methods for the specimen
• Destructive Testing


  Test methods where the specimen is destroyed/damaged/broken to determine physical and mechanical properties
• Non-Destructive Testing (NDT)


  Techniques for determining materials' characteristics and locating defects without damaging the specimen
• Advantages of NDT


  • Does not damage the specimen
  • 100% testing on actual components is possible
  • In service testing is possible so that breakdown can be prevented
  • Repeated checks over a period can reduce accidents and safety issues
  • Test results are rapid
• Disadvantages of NDT


  • High initial investment required
  • A skilled and experienced worker is required to conduct the test and interpret the result
• Scope of NDT


  • Provide quality control during manufacturing/fabrication
  • Ensure item conforms to required specification
  • Examine plant, equipment, or components during service to ensure requirements are met and prevent breakdown/failure
  • As a diagnostic tool in research and development
• Types of Defects


  • Inherent defects - Caused during initial production of base/raw materials
  • Processing defects - Caused during processing of material or part
  • Service defects - Caused during operating cycle of material or part
• Defect detection techniques


  • Surface Techniques - Dye Penetrant Inspection, Eddy Currents, Magnetic Particle Inspection
  • Volumetric Techniques - Radiography, Ultrasonics

  
• Visual Inspection


  Simple method using inspector's eyes to look for defects, using tools like magnifying glasses and mirrors
• Visual Inspection


  • Most basic and commonly employed NDT method
  • Applicable to wide variety of material types and product forms
  • Can be performed by direct or indirect methods during manufacturing or in-service
• Basic Principles of Visual Inspection

  Examine surface condition of a component, can be simple or use optical equipment
• Types of Visual Inspection

  • Direct visual testing - using naked eye, magnifying lenses, mirrors
  • Remote/Indirect visual testing - using fiberscope, borescope, robotic crawlers

  
• Microscope


  Combination of lenses used to magnify image of small object
• Borescope


  Instrument to inspect inside surface of narrow tubes, bores, chambers
• Endoscope


  Similar to borescope but with superior optical system and high intensity light source
• Fiberscope


  Flexible fiber optic borescope to access corners and passages with directional changes
• Telescope/CCTV


  Used to obtain magnified images of distant objects, or inspect inaccessible areas
• Robotic crawlers


  Used for inspecting crude oil pipelines
• Applications of Visual Inspection

  • Inspection of plant/systems/components for leakage, abnormal operation
  • Misalignment of parts in equipment
  • Corrosion, erosion, cracks, fractures
  • Defects in weldments like surface cracks, lack of penetration, porosities

  
• Fundamentals of Visual Test

  • Vision - human eye is most valuable NDT tool, sensitivity varies with light
  • Lighting - proper lighting is vital, 800-1000 lux required
  • Material Attributes - cleanliness, color, physical conditions
  • Environmental Factors - atmosphere, humidity, temperature, safety
• Computer-enhanced visual inspection system


  Includes process control, sensing, image processing, flaw analysis, and microprocessor/software
• Advantages of computer-enhanced visual inspection


  • Can be re-programmed for wide range of products
  • Can operate continuously without intervals
  • Increased speed compared to human
  • Consistent inspection
  • 100% inspection possible
• Disadvantages of computer-enhanced visual inspection


  • Skilled labor required
  • High initial investment
  • Complex programming required
  • Complex lighting system required
  • Real time decision making impossible
• Advantages of visual inspection

  • Simple and effective, cheapest NDT method
  • Experienced operators can be very sensitive
  • Allows seeing discontinuities, not just blips
  • Many different surface-breaking discontinuities can be found
  • Short training and experience times
  • Can examine virtually any component surface
  • Gives instantaneous results
  • Applicable at all stages
• Disadvantages of visual inspection

  • Many variables can lead to discontinuities being missed
  • Relies totally on human factor
  • Little attention paid to proper operator training
  • Sub-surface discontinuities not seen
  • Requires good eyesight and lighting
• Liquid Penetrant Inspection (LPI)


  Also known as Dye Penetrant Inspection (DPI) or Penetrant Testing (PT), a low-cost inspection method for locating surface-breaking defects in non-porous materials

  
• Eight steps in penetrant flaw detection

  • Surface preparation
  • Penetrant application
  • Penetrant dwell
  • Removal of excess penetrant
  • Application of developer
  • Indication Development
  • Inspection
  • Clean surface

  
• Capillary action


  Ability of a liquid to flow in narrow spaces without assistance of external forces
• Surface tension


  Cohesive/attractive force between liquid molecules
• Desirable Properties of Penetrants


  • Wetting ability - good wetting improves penetrability and bleed-back
  • Less Volatile - highly volatile would evaporate too quickly
  • Chemically inert - non-corrosive
  • Viscosity - related to thickness/body of fluid
• Eight steps in penetrant flaw detection

  1. Surface preparation

  2. Penetrant application

  3. Penetrant dwell

  4. Removal of excess penetrant

  5. Application of developer

  6. Indication Development

  7. Inspection

  8. Clean surface

  
• Capillary action


  The ability of a liquid to flow in narrow spaces without the assistance of (or even in opposition to) external forces like gravity
• Surface tension


  The cohesive/ attractive force between liquid molecules
• Desirable Properties of Penetrants

  • Wetting ability
  • Less Volatile
  • Chemically inert
  • Viscosity
  • Solubility
  • Health hazard
  • Availability
• Viscosity


  Relates to the thickness or body of a fluid and is a result of molecular or internal friction
• Excessive viscosity results in long dwell times, low viscosity leads to reduced dwell times but makes the penetrant prone to overwashing
• Liquid Penetrant Testing


  One of the oldest and simplest NDT methods, used to reveal surface discontinuities by bleeding out a colored or fluorescent dye from the flaw