Fluorescent Penetrant Inspection

When your standard requires a surface free from cracks, inclusions, porosity or other surface flaws that cannot be detected with a visual inspection, Fluorescent penetrant inspection will allow detection of such indications on most non-porous materials.

We start with surface preparation to ensure all surfaces are free of contaminants that could prevent the penetrant from entering discontinuities. We then apply a level 3 high sensitivity fluorescent penetrant by submerging the component and allowing the component to drain dwell for a sufficient amount of time to allow the penetrant to be drawn into any possible discontinuities by capillary action. We then use a manual coarse water spray to remove the excess penetrant from the surface.

The components are then placed into a temperature controlled oven to ensure adequate dryness of the component. Once the component is dry, a thin uniform layer of dry developer is applied for the length of time necessary to allow the penetrant to be drawn back to the surface and provide a contrasting background allowing the detection of the discontinuities under black light.

The component is then interpreted and evaluated to each customer’s requirements. Upon completion of the inspection the component is cleaned to remove developer and any other examination material residues that may be detrimental to the subsequent operations.

Below are the main steps of Liquid Penetrant Inspection:

1. Pre-cleaning:

The test surface is cleaned to remove any dirt, paint, oil, grease or any loose scale that could either keep penetrant out of a defect, or cause irrelevant or false indications. Cleaning methods may include solvents, alkaline cleaning steps, vapor degreasing, or media blasting.

2. Application of Penetrant:

The penetrant is then applied to the surface of the item being tested. The penetrant is allowed to soak into any flaws. As expected, smaller flaws require a longer penetration time.

3. Excess Penetrant Removal:

The excess penetrant is then removed from the surface. The removal method is controlled by the type of penetrant used. Water-washable or solvent-removable or hydrophilic post-emulsifiable penetrants are the common choices. Emulsifiers represent the highest sensitivity level, and chemically interact with the oily penetrant to make it removable with a water spray. 

4. Inspection:

The inspector will use visible light with adequate intensity (100 foot-candles or 1100 lux is typical) for visible dye penetrant. Ultraviolet (UV-A) radiation of adequate intensity (1,000 micro-watts per centimeter squared is common), along with low ambient light levels for fluorescent penetrant examinations. Inspection of the test surface should take place after 10- to 30-minute development time, depends of product kind. This time delay allows the blotting action to occur. The inspector may observe the sample for indication formation when using visible dye. It is also good practice to observe indications as they form because the characteristics of the bleed out are a significant part of interpretation characterization of flaws.

5. Post Cleaning:

The test surface is often cleaned after inspection and recording of defects, especially if post-inspection coating processes are scheduled.

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