SEAL 931433 - Caterpillar

Table 20
Crack Inspection Method Advantages vs. Disadvantages
Inspection Method Advantages Disadvantages
Dry Magnetic Particle (MT) - Portable
- Fast/Immediate Results
- Detects surface and subsurface discontinuities - Works on magnetic material only
- Less sensitive than Wet Magnetic Particle
Wet Magnetic Particle (MT) - More sensitive than Liquid Penetrant
- Detects subsurface as much as 0.13 mm (0.005 inch) - Requires Power for Light
- Works on magnetic parts only
- Liquid composition and agitation must be monitored
Table 21
Applicable Crack Detection Standards
Inspection Method Standard Acceptance
Criteria Required
Personnel
Qualifications
Magnetic Particle Testing (MT) EN-ISO 17638
ASTM E709 EN-ISO 23278 - Level 1
AWS D1.1 - Table 6.1 EN-ISO 9712 - Level 2
ANSI-ASNT SNT-TC-1A Level 2 Dry Magnetic Particle Testing (MT)
Refer to Tooling and Equipment Table 3 for part numbers.
Illustration 26 g06085930
(A) Indications shown by magnetic particle testing.
(B) Typical 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.Wet Magnetic Particle Testing (MT)
Refer to Tooling and Equipment Table 3 for part numbers.
Illustration 27 g06085937
(A) Indications shown by magnetic particle testing.
(B) Typical electromagnetic yoke.
(D) UV Lamp used in wet magnetic particle inspection process.
Illustration 28 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 determined by measuring the settling volume by using an ASTM pear shaped centrifuge tube with a 1 mL (0.034 oz) stem with 0.05 mL (0.0017 oz) 1.0 mL (0.034 oz) divisions, refer to Illustration 28. Before sampling, the suspension shall be thoroughly mixed to assure suspension of all particles, which could