GUIDE 3295552 - Caterpillar

Illustration 24 g06084042
Typical example of cracks found during Liquid Penetrant Testing (PT).
Allow the developer to dry completely for 10–15 minutes before inspecting for cracks. Defects will show as red lines in white developer background, refer to Illustration 24. Clean the area of application of the developer with solvent cleaner.Dry Magnetic Particle Testing (MPT)
Materials and Equipment Required
Refer to Tooling and Equipment Table 3 for part numbers.
Illustration 25 g06085930
(A) Indications shown by Dry Magnetic Particle Testing (MPT).
(B) Electromagnetic Yoke
(C) Dry Powder Bulb
Dry magnetic powder shall be of high permeability and low retentively and of suitable sizes and shapes to produce magnetic particle indications. The powder shall be of a color that will provide adequate contrast with the background of the surface being inspected.
Dry magnetic particles shall be stored in suitable containers to resist contamination such as moisture, grease, oil, non-magnetic particles such as sand, and excessive heat. Contaminants will manifest in the form of particle color change and particle agglomeration. The degree of contamination will determine further use of the powder.
Dry magnetic powder shall be tested in accordance with ASTM E709 Section 18 (Evaluation of System Performance/Sensitivity) when not performing.
Equipment should include a "U" shaped electromagnetic yoke made from highly permeable magnetic material, which has a coil wound around the yoke. This coil carries a magnetizing current to impose a localized longitudinal magnetic field into the part. The magnetizing force of the yoke is related to the electromagnetic strength and can be tested by determining the lifting power of a steel plate. The yoke shall have a lifting force of at least 4.5 kg (10 lbs).
Check dry powder blower routinely to ensure that the spray is a light, uniform, dust-like coating of the dry magnetic particles. Blower should also have sufficient force to remove excess particles without disturbing those particles that are evidence of indications.
All equipment shall be inspected at a minimum of once a year or when accuracy is questionable.Procedure
Ensure surface to be inspected is dry and free from oil, grease, sand, loose rust, mil scale, paint, and other contaminants.
Apply the magnetic field using the yoke against the faces and inside diameter of each bore.
Simultaneously apply the dry powder using the dry powder blower.
Remove excess powder by lightly blowing away the dry particles.
Continue around the entire circumference of each bore. Position the yoke twice in each area at 1.57 rad (90°) to ensure that multiple directions of the magnetic field are created.
Observe particles and note if any clusters of particles appear revealing an indication.
Record the size and shape of any discontinuities or indications found.Wet Magnetic Particle Testing (MPT)
Materials and Equipment
Refer to Tooling and Equipment Table 3 for part numbers.
Illustration 26 g06085937
(A) Indications shown by Wet Magnetic Particle Testing (MPT).
(B) Electromagnetic Yoke
(D) Ultraviolet Lamp
Illustration 27 g06003178
Pear Shaped Centrifuge Tube
Wet magnetic particles are fluorescent and are suspended in a vehicle in a given concentration that will allow application to the test surface by spraying.
Concentration:
The concentration of the suspended magnetic particles shall be as specified by the manufacturer and be checked by settling volume measurements.
Concentrations are