.ndt test
.non destructive testing
Nondestructive testing (NDT) is the process of inspecting, testing, or evaluating materials without destroying the serviceability of the part
Visual inspection inspect for high splatter, undercut, bad stop start point, surface crack.
1) Surface inspection
- Magnetic particle
- Liquid penetrant
a) Magnetic particle
- Testing magnetic fields to locate surface discontinuities in magnetic materials.
- When the magnetic field encounters a discontinuity, the flux lines produce a magnetic flux leakage
- Because magnetic flux lines don’t travel well in air, magnetic particles are applied to the surface of the part will be drawn into the discontinuity,
- Use of a Yoke to generate magnetic field
b) Liquid penetrant test
Step 1 – Precleaning of the Surface
The 3 spray cans (aerosol) are provided for this test. First one is named cleaner. The technician sprays the cleaner to the test object and then cleans the surface with non-used rag or cloth.
Step 2- Application of Penetrant
In the second step, the technician applies penetrant spray can to the surface which is in sharp red color. The technician needs to wait for 5 to 15 minutes depends on test procedure.
Step 3- Removal of the Excess Penetrant Liquid
In the third step, the technician removes penetrant liquid from the surface by rag or cloth and uses back and forth rubbing to clean the surface. No red color should be visible after cleaning.
Step 4 – Application of Developer
In the fourth step, the technician takes the developer spray can and agitates it and then sprays to the surface. Then he waits for 10 minutes. In this time, the defect will be visible
Step 5 – Evaluation / Interpretation
In the fifth step inspector evaluates the test result
2) Internal inspection
- Radiography
- Ultrasonic most frequently used test methods
a) Radiographic method
- Exposing a test object to penetrating radiation so that the radiation passes through the object being inspected and a recording medium(film) placed against the opposite side of that object.
- With both, the radiation passing through the test object. causing an end effect of having darker areas where more radiation has passed through the part and lighter areas where less radiation has penetrated.
- Use of x-ray or gamma ray
b) Ultrasonic method
- Ultra-high frequency sound is injected into the part being inspected and if the sound hits a material with cracks, discontinuity some of the sound will reflect to the sending unit and can be presented on a visual display.
- By knowing the speed of the sound through the part and the time required for the sound to return to the sending unit, differences shows place of crack.
- Thus, able to find likely area of discontinue by the darker area