Magnetic Flux Leakage Testing (MFL) Review Questions

Question 1

1. In magnetic flux leakage inspection for discontinuities using an active field, the part being inspected should be magnetized:
   A. Beyond saturatation
   B. To saturation or near saturation
   C. Well below saturation
   D. Near the point of maximum permeability

Answer 1

D. Near the point of maximum permeability

Question 2

2. An advantage that magnetic flux leakage testing has in comparison with eddy current testing is that magnetic flux leakage testing is:
   A. Less sensitive to interferences caused by surface roughness
   B. Useful on products at temperatures above the Currie point
   C. Useful on austenitic steels
   D. Easier to use on ferromagnetic materials

Answer 2

D. Easier to use on ferromagnetic materials

Question 3

3. What particular type of discontinuity would not typically be indicated by magnetic flux leakage techniques?
A. Laps
B. Pitting with cracking
C. Surface contamination 
D. Longitudinal seams

Answer 3

C. Surface contamination

Question 4

4. The strength of the magnetic field in the interior of a coil is determined by the:
   A. Number of turns in the coil only
   B. Strength of the applied current obly
   C. Number of turns in the coil and the strength of the applied current
   D. Direction of applied current in the coil

Answer 4

C. Number of turns in the coil and the strength of the applied current

Question 5

5. The current used for magnetization when performing magnetic flux leakage inspection must be a:
   A. Steady non fluctuating current
   B. Current that reverses direction at a consistent rate
   C. Current that fluctuates on and off at a consistent rate
   D. Current that varies based on the thickness of the material

Answer 5

A. Stead non fluctuating current

Question 6

6. As a general rule, hard (high strength) ferromagnetic materials have:
   A. High coercive force and are easily demagnitized
   B. High coercive force and are not easily demagnitized
   C. Low coercive force and are easily demagnetized
   D. Low coercive force and are not easily demagnitized

Answer 6

B. High coercive force and are not easily demagnetized

Question 7

7. In magnetic flux leakage testing, the greatest tube wall thickness for which maximum sensitivity can be maintained is:
A. 0.003”
B. 0.03”
C. 0.318 “
D. 3”

Answer 7

C. 0.318”

Question 8

8. In the examination of above-ground storage tanks where the flux sensor is on the top surface:
   A. Only top surface discontinuities are detected
   B. Only bottom surface discontinuities are detected
   C. Both top and bottom surface discontinuities can be detected but generally cannot be distinguished from each other
   D. Both top and bottom surface discontinuities can be detected and can generally be distinguished from each other

Answer 8

C. Both top and bottom surface discontinuities can be detected debut generally cannot be distinguished from each other

Question 9

9. Materials that are weakly repelled magnetically are called:
A. Diamagnetic
B. Nonmagnetic 
C. Paramagnetic 
D. Ferromagnetic

Answer 9

A. Diamagnetic

Question 10

10. In a break in the magnetic uniformity of a part that is called a magnetic discontinuity is related to a sudden change in:
A. Resistivity
B. Inductance
C. Permeability
D. Capacitance

Answer 10

C. Permeability

Question 11

11. A hysteresis curve describes the relation between:
    A. Magnetizing force and flux density
    B. Magnetizing force and applied current
    C. Strength of magnetism and alignment of domains within the material
    D. Magnetic flux density and the current generated

Answer 11

A. Magnetizing force and flux density

Question 12

12. When inspecting wire rope, a magnetic flux loop is used to monitor:
A. Broken external wires
B. Broken internal wires
C. Changes in inspection speed
D. Reductions in cross sectional area

Answer 12

D. Reductions in cross sectional area