Author: Micro NDT

Penetrant Process : A Developer is applied to bring entrapped penetrant back to the surface by reverse capillary action blotting.
1. A developer, form a uniform coating of fine white powder to create contrast surface for the indication.
2. Developer surface is used for blotting the penetrant out of the discontinuities.
3. Penetrant bleeds and spreads into developer and the indication become easily detectable. The indication may enlarge with time.

Depending on the type of penetrant, excess surface penetrant is removed by one of the following methods,
1. Rinsing with coarse water spray.
2. Emulsifying the penetrant and rinsing with water spray.
3. Rinsing with emulsifier solution.
4. Manually wiping the surface with solvent dampened cloth.

Penetrant Process: Step penetrant may be applied by, spraying, dipping, flooding, brushing.
Important Condition: For penetrant application the part temperature must be within 5 degree cent. to 52 degree cent.
1. Penetrant must be applied to clean dry surface.
2 The entire area to be tested must be covered with a thin layer of
penetrant.
3. Penetrant must not dry during the entire test cycle.
4. A penetration time between 10 to 30 minutes are used. As per applicable LPT
procedure.

1. Surface is cleaned to remove all contaminants to the extent that the interior of the discontinuities are clean and dry.

2. Surface to be cleaned using appropriate cleaning methods such that dirt, oil, grease, scale, rust, paint etc are completely removed.
3. The flaw openings must be clean to allow entry of penetrant.
Following cleaning, the part shall be completely dried.

Discontinuities are detected by a penetrating colored liquid.Indications form directly over the defect. This method detects surface breaking discontinuities only.
This examination process is useful for detection of open to surface discontinuities only.
Applicable to varieties of non porous materials.
Produces enlarged indication for easy detection.
Relative volume of a flaw is indicated by the amount of bleed out.

Penetration materials are classified in two basic types.
Type 1 – Fluorescent Penetrants
Type 2 – Visible Penetrants
Type 3 – Dual penetrants.

The four methods are listed below:

Method A – Water Washable
Method B – Post-Emulsifiable, Lipophilic
Method C – Solvent Removable
Method D – Post-Emulsifiable, Hydrophilic

Pipe Defect: A discontinuity in the centre of the ingot, caused by cavities formed during solidification Becomes elongated in rolling operations Not usually visible on the surface of the article.

Processing Discontinuities

2nd stage of discontinuity

Generated by forming or fabrication operations subdivided into: primary processing discontinuities: Casting, rolling, forging.

Secondary processing discontinuities – Machining, grinding, heat treating, welding, plating.

Primary Processing Discontinuities – Casting

1. Inclusions
2. Porosity
3. Cold shuts
4. Hot tears
5. Shrinkage cavities

Inclusions: Non-metallic impurities, such as sand, slag, oxides, and sulfides that are present in the original ingot. Rolling of raw material into billets or bar stock, these impurities form “stringers”, or lines. When rolled plate it form lamination.

These discontinuity is objectionable, when they occur in critical areas, on highly-stressed surfaces, or in unusual numbers.

Porosity: Gas bubbles being trapped in the material prior to solidification. Bubbles generally round or spherical in shape.

Initial steel making process:

Steps in the Steel making Process.

1. The molten iron from furnace is drawn from the furnace and poured into ingot moulds called “pig iron”
2. Pig iron contains 3-5% carbon; further refining is required to remove the excess carbon and improve the properties of the steel. Iron with less than 2% carbon is typically called a steel.