LIQUID PENETRANT TESTING

2.2.1        LIQUID PENETRANT TESTING:-

Penetrant solution is applied to the surface of a precleaned component. The liquid is pulled into surface breaking defects by capillary action. Excess penetrant material is carefully cleaned from the surface.

A developer is applied to pull the trapped penetrant back to the surface where it is spread out and forms an indication. The indication is much easier to see than the actual defects

MAIN USES OF PENETRANT TESTING

It is used to locate cracks, porosity and other defects that break the other surface of a material and have enough volume to trap and hold the penetrant material.

LPT is used to inspect large areas very effectively and will work on most nonporous materials.

Equipment’s used:

1.      Developer

2.      Penetrant

3.      Cleaner

Procedure:

1.      Cleaning (remove oil and dust )

2.      Application of penetrant (red or violet)

3.      Remove of excesses penetrant (dwell of 10 min ) by thinner

4.      Apply developer (white color) dwell 10 min.

5.      Evaluation of the indication

6.      Remove of residual or developer

7.      Application protective coating

Advantages of LPT:

1.      Large surface areas or large volumes of parts or materials can be inspected rapidly and at low cost.

2.      Parts with complex geometry are routinely inspected.

3.      Indications are produced directly on surface of the parts providing a visual image of the discontinuity.

4.      Equipment investment is minimum.

Disadvantages of LPT:

1.       The defects are only surface breaking defects.

2.       Surface preparation is critical as contaminants can mask defects

3.       It requires relatively smooth and nonporous surface

4.       Post cleaning is necessary to remove chemical