Non-Destructive Testing (NDT) Visual Inspection

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)