CWI NDE Methods and Symbols 3 — Questions and Answers
Question 1: Which NDE method is MOST sensitive to surface cracks in ferromagnetic materials?
- Magnetic particle testing (MT) (Correct answer)
- Liquid penetrant testing (PT)
- Radiographic testing (RT)
- Eddy current testing (ET)
Correct answer: Magnetic particle testing (MT)
MT is most sensitive to surface and near-surface flaws in ferromagnetic materials because the magnetic field leaks strongly at discontinuities.
Question 2: In radiographic testing, what does IQI stand for and what is its purpose?
- Image Quality Indicator; verifies the radiograph has sufficient sensitivity to detect defects (Correct answer)
- Inspection Quality Index; ranks the overall quality of a weld
- Internal Quality Inspector; certifies the RT technician
- Integrated Quality Instrument; measures radiation output
Correct answer: Image Quality Indicator; verifies the radiograph has sufficient sensitivity to detect defects
An IQI (also called a penetrameter) is placed on the part to verify that the radiographic technique has sufficient sensitivity to reveal defects of concern.
Question 3: What is 'geometric unsharpness' (Ug) in radiography, and how is it minimized?
- Blurring caused by source size and geometry; minimized by increasing source-to-film distance or using a smaller source (Correct answer)
- Shadow darkening from material thickness; minimized by increasing voltage
- Film grain noise; minimized by using faster film
- Scatter radiation; minimized by lead screens
Correct answer: Blurring caused by source size and geometry; minimized by increasing source-to-film distance or using a smaller source
Geometric unsharpness (Ug = Fd/D) increases with larger focal spot size (F) or shorter source-to-object distance; using a small source far from the object minimizes it.
Question 4: In ultrasonic testing, what type of wave travels along the surface of a material and is useful for detecting near-surface defects?
- Rayleigh (surface) wave (Correct answer)
- Longitudinal wave
- Shear wave
- Lamb wave
Correct answer: Rayleigh (surface) wave
Rayleigh waves travel along the surface with particle motion in an elliptical pattern, making them effective for detecting surface and very near-surface discontinuities.
Question 5: When the NDE symbol includes an 'R' in the tail of the weld symbol, what does it signify?
- Radiographic testing is required (Correct answer)
- The weld is to be radiographed and repaired
- Residual stress testing is required
- Rejection of the weld joint
Correct answer: Radiographic testing is required
Per AWS A2.4, placing 'RT' or 'R' references in the symbol tail indicates that radiographic testing is required for that weld.
Question 6: Which electromagnetic NDE method is commonly used to detect corrosion and cracks in non-ferromagnetic tubing without contact?
- Eddy current testing (ET) (Correct answer)
- Magnetic particle testing (MT)
- Flux leakage testing (MFL)
- Ultrasonic testing (UT)
Correct answer: Eddy current testing (ET)
Eddy current testing induces currents in the conductive material electromagnetically, making it ideal for non-contact inspection of non-ferromagnetic tubes and thin materials.
Question 7: A weld is inspected by visual testing (VT) and an NDE symbol with 'MT' appears on both sides of the reference line. What does this mean?
- MT is required on both the arrow side and the other side of the weld (Correct answer)
- MT is optional on both sides
- MT was performed previously on both sides
- MT is required only on the most accessible side
Correct answer: MT is required on both the arrow side and the other side of the weld
When an NDE designation appears both above and below the reference line, it specifies the examination is required on both sides of the weld joint.
CWI NDE Methods and Symbols 3
Which NDE method is MOST sensitive to surface cracks in ferromagnetic materials?