CWI NDE Methods and Symbols 4 — Questions and Answers
Question 1: In liquid penetrant testing, what is the minimum recommended dwell time for most standard penetrants on steel weldments per ASME standards?
- 10 minutes (Correct answer)
- 2 minutes
- 30 seconds
- 1 minute
Correct answer: 10 minutes
ASME Section V typically specifies a minimum penetrant dwell time of 10 minutes for standard penetrants on steel to allow adequate capillary action into discontinuities.
Question 2: What is the primary limitation of liquid penetrant testing compared to other NDE methods?
- It can only detect surface-open discontinuities (Correct answer)
- It cannot detect cracks smaller than 1/4 inch
- It only works on ferromagnetic materials
- It requires X-ray equipment
Correct answer: It can only detect surface-open discontinuities
PT relies on penetrant entering open discontinuities at the surface, so it cannot detect sub-surface or embedded defects.
Question 3: In RT, the wire-type IQI is placed on the source side of the part. If the required 2T wire is visible on the radiograph, what does this confirm?
- The technique has sensitivity sufficient to detect a flaw equivalent to 2% of the material thickness (Correct answer)
- The weld has no defects larger than 2mm
- The film density is within acceptable range
- The source energy is correct for the material
Correct answer: The technique has sensitivity sufficient to detect a flaw equivalent to 2% of the material thickness
The visible 2T wire confirms the radiographic technique sensitivity meets code requirements, typically 2% of material thickness for most codes.
Question 4: Which scanning pattern in ultrasonic testing involves moving the transducer perpendicular to the weld axis while indexing along the weld?
- Raster scan (Correct answer)
- Circular scan
- Linear scan along the weld axis
- Orbital scan
Correct answer: Raster scan
A raster scan moves the probe perpendicular to the weld in parallel passes, systematically indexing along the weld length to provide full volumetric coverage.
Question 5: What type of radiation source is commonly used in industrial radiography for field inspection of thick steel welds where X-ray machines are impractical?
- Iridium-192 (Ir-192) (Correct answer)
- Cobalt-57 (Co-57)
- Technetium-99m (Tc-99m)
- Uranium-235 (U-235)
Correct answer: Iridium-192 (Ir-192)
Ir-192 is the most widely used gamma-ray isotope for field radiography of steel welds due to its appropriate energy level, portability, and practical half-life of 73.8 days.
Question 6: In magnetic particle testing, what is the difference between circular and longitudinal magnetization?
- Circular magnetization detects longitudinal defects; longitudinal magnetization detects transverse defects (Correct answer)
- Circular magnetization detects transverse defects; longitudinal magnetization detects longitudinal defects
- Both methods detect the same types of defects
- Circular magnetization is used only for flat plates
Correct answer: Circular magnetization detects longitudinal defects; longitudinal magnetization detects transverse defects
Discontinuities are best detected when they are perpendicular to the magnetic field; circular fields reveal longitudinal flaws and longitudinal fields reveal transverse flaws.
Question 7: What does the term 'back reflection' indicate during an ultrasonic test of a sound weld?
- A strong signal from the back wall confirms adequate sound transmission through the part (Correct answer)
- A signal indicating a major defect at the back surface
- The echo from the weld root area
- An artifact caused by couplant contamination
Correct answer: A strong signal from the back wall confirms adequate sound transmission through the part
A strong back wall echo (back reflection) in UT indicates the sound is traveling through the material without significant attenuation or scattering from major internal defects.
CWI NDE Methods and Symbols 4
In liquid penetrant testing, what is the minimum recommended dwell time for most standard penetrants on steel weldments per ASME standards?