This set of Casting, Forming and Welding Multiple Choice Questions & Answers (MCQs) focuses on “Inspection Procedures”.
1. Which of the following methods of inspection is mostly used for ferromagnetic materials?
a) Acoustic emission test
b) Ultrasonic inspection
c) Magnetic particle inspection
d) Visual inspection
View Answer
Explanation: Magnetic particle inspection (MPI) is a method of locating surface and subsurface discontinuities in ferromagnetic materials. In this method, the material or part is magnetized and then the magnetic discontinuities occur which indicates the size, shape and extent of discontinuities.
2. In MPI method, the magnetic discontinuities lie in a direction parallel to the direction of the magnetic field.
a) True
b) False
View Answer
Explanation: In MPI method, after the magnetization of the material or part which to be inspected, the magnetic discontinuities that lie in a direction generally transverse to the direction of the magnetic field. This causes a leakage field to form at and above the surface of the part, which indicates the presence of surface discontinuities.
3. Any type of particles can be used for the detection of surface discontinuities of material in MPI method.
a) True
b) False
View Answer
Explanation: In MPI method, the presence of discontinuities and the leakage field is mainly detected by the use of finely divided ferromagnetic particles applied over the surface, with some of the particles being gathered and held by the leakage field. This magnetically held collection of particles to form an outline of discontinuity, which defines the characteristics of the surface discontinuities.
4. Magnetic particle inspection is a very sensitive technique for the detection of defects in the castings.
a) True
b) False
View Answer
Explanation: Magnetic particle inspection is a highly effective and sensitive technique for revealing cracks or similar defects at or just beneath the surface of castings made of ferromagnetic metals. This method is widely used where high accuracy and complete defects free castings are required.
5. For the detection of discontinuities beneath the surface, liquid penetrant testing method can be used.
a) True
b) False
View Answer
Explanation: It is very important to detect discontinuities just beneath the surface because such cleaning methods as a shot or abrasive blasting tend to close a surface break that may go undetected in visual or liquid penetrant testing. So, magnetic particle inspection is preferred for the detection of discontinuities beneath the surface.
6. Which of the following methods is best for detecting interior flaws in the castings?
a) Liquid penetrant test
b) Visual inspection
c) Magnetic particle inspection
d) Ultrasonic inspection
View Answer
Explanation: In the ultrasonic inspection, a beam of high frequency sound waves is introduced into material for the detection of interior flaws in the material. Then the sound wave travels through the material with some loss of energy and are reflected at interfaces, which are further analyzed to define the presence and location of flaws in the casting.
7. Coarse grained structures of casting material lead to increase attenuation in ultrasonic inspection.
a) True
b) False
View Answer
Explanation: Coarse grained structures in thick plates, ingots and cast materials cause considerable increase in attenuation, that shows more loss of energy during an inspection of the castings. It mainly occurs due to scattering and diffraction at grain boundaries of the casting material. This is known as ultrasound attenuation.
8. Ultrasound attenuation has no affects on the detection of discontinuities or defects in the castings.
a) True
b) False
View Answer
Explanation: In ultrasonic inspection, ultrasonic beam intensity decreases exponentially with the metal travel distance. Ultrasound attenuation in metal influences discontinuity detection greatly and also the material characterization technique. So, it is very important to establish attenuation measurement practices to carefully perform the inspection.
9. Which of the following formulas is used for the calculation of ultrasonic attenuation coefficient (α)?
a) α = 10 log(A0/A)/X
b) α = 20 log(A0/A)*X
c) α = 10 log(A0/A)*X
d) α = 20 log(A0/A)/X
View Answer
Explanation: Ultrasonic attenuation coefficient (α) is calculated from the following equation-
α = 20 log(A0/A)/X
Where, A0 and A are the ultrasound amplitudes before and after travelling through the material, and X is the travel distance. The measurement of attenuation coefficient is mainly used to find qualitative and quantitative information on the internal structure of products or castings.
10. In ultrasonic inspection, some standards are taken as a reference to measure the size of discontinuity in the material.
a) True
b) False
View Answer
Explanation: In ultrasonic inspection, the instrument is adjusted using a series of reference standards in the form of cylindrical blocks containing some flat bottom holes of specified sizes at different depths. So the discontinuity size is easily determined by comparing the reflected signal amplitude with that reflected by a flat bottom hole at a similar depth.
11. Monitoring of porosity defects in casting by ultrasonic inspection is very difficult.
a) True
b) False
View Answer
Explanation: Individual pores do not produce any distinguishable indications under testing conditions. The ultrasonic indication of centre line porosity is typically presented or revealed in the form of noise. This makes it very difficult to distinguish between porosity and large grained structure that gives similar ultrasonic indications.
12. In ultrasonic inspection, there is no chance of rejection of good material.
a) True
b) False
View Answer
Explanation: In ultrasonic inspection, plates or ingots with large grain structure may produce a similar effect or indication as produce by the porosity defects in the castings, so this can result in rejection of good material. In such cases, ultrasonic data acquisition systems are used, which offer digital filtering to eliminate the problem.
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