Current Values + Rules (2)

Question 1

Burning parts due to too high of a current can cause/do:

Answer 1

• damage the part
• change the metallurgical properties of the part
• cause excessive magnetic fields or magnetization

Question 2

High current issues using the Wet-Fluorescent application

Answer 2

Particles will:

• reduced mobility
• adhere to surface rather than leakage field migration (excessive “background”)
• highly attracted to non-relevant leakage fields

Question 3

High current issues using the Wet-Visible application

Answer 3

Particles will:

• reduced mobility
• adhere to surface rather than leakage field migration (excessive “background”)
• highly attracted to non-relevant leakage fields

Question 4

High current issue using the Dry Powder application

Answer 4

Particles will:

• reduced mobility
• adhere to surface rather than leakage field migration (excessive “background”)
• highly attracted to non-relevant leakage fields
• excessive longitudinal field attraction to magnetic poles of part under test (“furring”)

Question 5

How to tell if a part under test is being supplied a sufficient amperage?

Answer 5

• indications are evident after applying the pre-calculated amperage
• Indications are evident on a field strength indicator (gauss/hall meter)
• use of artificial defect shims (QQI’s)

Question 6

What are “rule of thumb” formulas?

Answer 6

From ASTM Standards as a way to provide a “starting amperage” necessary to test the part.
- always best to start with a low amp and work to higher ones

Question 7

Rule of thumb formula (Direct Contact - Headshot)

Answer 7

12-32amps per mm of specimen diameter/thickness/cross-section

(300-800amps/mm)
- should always be expressed using metric (mm)

Example: 30mm X 20amp/mm = 600amp

Question 8

Rule of thumb values are chosen with considerations to:

Answer 8

• Specimen geometry (range of thickness or diameters of the overall specimen)
• Specimen effective contact area (How much of the specimen in contact with conductive heads in comparison to specimen geometry)

Question 9

Rule of thumb formula (Direct Contact - Prod Method)

Answer 9

minimum prod spacing of 2-3” (50-75mm) and maximum spacing of 8” (203mm)

material <3/4” (19mm) thick = 90-115 amp/in of spacing (3.5-4.5amp/mm)

material >3/4” (19mm) thick = 100-125amp/in (4.0-5.0amp/mm)

Example: 100amp x 6” (prod space) = 560amp

Question 10

Rule of thumb formula (Coil Method)

Answer 10

Low fill: cross-sectional area of the part is less that 10% coil diameter
(45000/L/D) x (1/n)

High fill: diameter of coil is <2X cross-sectional area of part.
(35000/L/D+2)x(1/n)
n = coil turns

Question 11

Length/Diameter Ratio

Answer 11

specimen has a L/D greater than 15 it can still be inspected but must be done in sectioned magnetizing shots.

Coil limitation: section of specimen being inspected =/<9in out of either side of the coil.

Question 12

Rule of thumb formula (Indirect Contact - Central Conductor Method)

Answer 12

high fill conductor: 12-32amp/mm outside diameter

Example: 150mm x 20amp = 3000amp

low fill conductor: Central conductor diameter + 2x wall thickness of test specimen x 12-32amp/mm

Question 13

Effective inspection area on the specimen when using a central conductor

Answer 13

4X the diameter of the conductor