NDT - Non-Destructive Testing Magnetic Particle Testing Methods Questions and Answers — Questions and Answers
Question 1: An inspector is using the wet continuous method to perform a magnetic particle test on a steel weld. At which point should the application of the magnetic particles be stopped?
- After the magnetizing current is turned off
- Just before the magnetizing current is turned on
- Just before the magnetizing current is turned off (Correct answer)
- Simultaneously with turning the magnetizing current off
Correct answer: Just before the magnetizing current is turned off
In the wet continuous magnetization technique, the magnetic particle bath is applied to the part, and the flow is stopped just before the magnetizing current is turned off. This ensures that the particles are on the surface and mobile while the magnetic field is at its peak strength, providing maximum sensitivity for detecting discontinuities.
Question 2: Which of the following magnetization methods is most effective for detecting transverse discontinuities in a long, solid cylindrical bar?
- Circular magnetization using prods
- Longitudinal magnetization using a coil (Correct answer)
- Circular magnetization using a central conductor
- Longitudinal magnetization using a yoke on the end
Correct answer: Longitudinal magnetization using a coil
Longitudinal magnetization creates magnetic field lines that run parallel to the long axis of the bar. This orientation is perpendicular to transverse discontinuities, creating the strongest flux leakage and therefore the most detectable indications. A coil is the standard method for inducing a longitudinal field in this type of component.
Question 3: When inspecting a large casting with a rough surface for potential surface-breaking cracks, which magnetic particle testing method and particle type combination would be most suitable?
- Wet fluorescent method
- Dry powder method (Correct answer)
- Wet visible method on a light-colored part
- Residual method with wet particles
Correct answer: Dry powder method
The dry powder method is highly effective for inspecting rough surfaces, such as those on castings, because the larger particles are less likely to get trapped in minor surface irregularities, leading to fewer non-relevant indications. Wet methods can be less effective on very rough surfaces as the liquid carrier can pool and obscure indications.
Question 4: A technician is tasked with performing a magnetic particle inspection on a critical aerospace component made of a high-strength steel alloy. The procedure specifies using the residual method. This implies that the material must have:
- High permeability and high retentivity (Correct answer)
- Low permeability and low retentivity
- High permeability and low retentivity
- Low permeability and high retentivity
Correct answer: High permeability and high retentivity
The residual method relies on the magnetism that remains in the part after the magnetizing force is removed. For this to be effective, the material must be easily magnetized (high permeability) and must retain a strong magnetic field (high retentivity) to create sufficient flux leakage at any discontinuities.
Question 5: Which of the following is a significant disadvantage of using the prod technique for inducing a circular magnetic field?
- It is only suitable for detecting transverse defects.
- It cannot be used on large or irregularly shaped parts.
- It has a high risk of causing arc strikes or localized overheating. (Correct answer)
- It is the least portable of all magnetic particle methods.
Correct answer: It has a high risk of causing arc strikes or localized overheating.
The prod technique involves passing a high amperage current directly through a localized area of the test piece via two handheld electrodes (prods). This creates a risk of arcing between the prods and the part surface, which can cause localized heating and metallurgical changes, potentially damaging the component.
Question 6: Demagnetization of a component after magnetic particle testing is crucial in which of the following scenarios?
- When the part is to be immediately painted.
- When the part is made of low-carbon steel with low retentivity.
- When the part is a moving component in an assembly, like a bearing. (Correct answer)
- When the part will be subsequently heat-treated above the Curie point.
Correct answer: When the part is a moving component in an assembly, like a bearing.
Residual magnetism in moving parts, such as bearings or gears, can attract and hold metallic debris during operation. This can lead to increased wear, friction, and premature failure of the component. Therefore, demagnetization is essential for such applications.
NDT - Non-Destructive Testing Magnetic Particle Testing Methods Questions and Answers
An inspector is using the wet continuous method to perform a magnetic particle test on a steel weld.
At which point should the application of the magnetic particles be stopped?