Non-Destructive Testing (NDT) Visual Inspection

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10 Questions

What is the purpose of a couplant in non-destructive testing?

To exclude air between the transducer and the specimen

What is the primary function of an immersion transducer?

To transmit sound waves through a liquid coupling medium

What is the typical medium used in immersion transducers?


What is the purpose of a focusing lens in an immersion transducer?

To focus the sound waves

What is the characteristic of a couplant material that prevents rapid flow off the material?


In pulse-echo testing, what is the function of the second transducer?

To listen for reflected energy

What is the term for the initial pulse sent out by the transducer in pulse-echo testing?

Initial pulse

What is the purpose of a planar acoustic lens in an immersion transducer?

To focus sound waves

What is the term for the reflected energy received by the transducer in pulse-echo testing?


What is the requirement of a couplant material that prevents it from absorbing water?


Study Notes

Non-Destructive Testing (NDT)

  • Inspectors should not work continuously for more than 2 hours to prevent fatigue and missing defects.

Visual Inspection

  • Visual inspection can reveal:
    • General condition of the component
    • Presence or absence of oxide film or corrosive product on the surface
    • Potential sources of mechanical weakness such as sharp notches or misalignment
    • Presence or absence of cracks, orientation of crack, and position of cracks relative to various zones in the case of welds
    • Surface porosity, unfilled crater, contour of the weld beads, and probable orientation of the interface between the fused weld bead and the adjoining metal

Defects Detectable by Visual Inspection

  • Underbead cracking
  • Lack of fusion
  • Weld metal crack
  • Toe crack
  • Heat affected zone crack
  • Weld interface crack
  • Root crack
  • Endbead crack
  • Root surface crack

Advantages of Visual Inspection

  • Simple and easy to apply
  • Quickly carried out
  • Usually low in cost
  • Requires minimum part preparation
  • Can lead to immediate rejection and save time and money

Applications of Visual Inspection

  • Inspection of plant system/component for leakage, abnormal operation, etc.
  • Misalignment of parts in the equipment
  • Corrosion, erosion, cracks, fractures, etc.
  • Defects in new/repaired elements such as gross surface cracks, lack of penetration, tear cracks, excess reinforcement, porosities, mismatch, etc.
  • Minute discontinuities in instruments, engines, etc. in pumps, compressors, turbo generator parts, etc.

Liquid Penetrant Testing

  • Suitable to check for cracks, porosity, or other types of faults on the surface of the component
  • Defects can be classified into surface defects, sub-surface defects, and internal defects

Methods of Liquid Penetrant Testing

  • Post-emulsifiable method (Method B and D)
  • Solvent removable method (Method C)

Sensitivity Levels of Liquid Penetrant Testing

  • Level 1: Ultra-low sensitivity
  • Level 2: Low sensitivity
  • Level 3: Medium sensitivity
  • Level 4: High sensitivity
  • Level 5: Ultra-high sensitivity

Forms of Developers in Liquid Penetrant Testing

  • Form a: Dry powder developer
  • Form b: Water-soluble developer
  • Form c: Water-suspendible developer
  • Form d: Non-aqueous wet developer
  • Form e: Specific application non-aqueous wet developer

Ultrasound Testing

  • Immersion transducers are designed to transmit sound whereby the transducer and test specimen are immersed in a liquid coupling medium (usually water)
  • Cylindrical focus and spherical focus immersion transducers are manufactured with planar, cylindrical, or spherical acoustic lenses (focusing lens)

Couplant in Ultrasound Testing

  • Couplant is placed at an interface between a liquid/gas and solid to exclude air between the transducer and the specimen
  • Requirements of a couplant material:
    • Wets transducer and surface
    • Non-corrosive, non-hygroscopic, and non-toxic
    • Applied and removed easily
    • Homogeneous and free of air bubbles
    • Viscous enough to prevent rapid flow off the material

Pulse Echo and Through Transmission Methods

  • Pulse-echo method: a transducer sends out a pulse of energy and the same or a second transducer listens for reflected energy (an echo)

Test your knowledge of non-destructive testing methods, specifically visual inspection techniques used to detect defects in components. Learn about the importance of regular breaks for inspectors and the types of defects that can be identified through unaided visual inspection.

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