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Using Dye Penetration Inspection to Ensure Quality

Ensuring the quality of the products that Special Piping Materials sells is of utmost importance and we know that it is also at the top of the list for our discerning clients. As such, we offer a wide range of tests so that you can be sure that your product – whether that’s a flange, pipe or fittings in nickel alloy, stainless steel, 6% Moly, duplex or super duplex – is of high quality and will stand the test of time.

One of the tests that we can carry out in-house across of network of global offices is Dye Penetration Inspection. This popular testing method can be dated back to the 19th Century and is well-regarded in many industries including Petrochemical, Oil & Gas, Nuclear Power and Desalination.

But what is it and how is the process carried out? Read on to find out . . .

What is Dye Penetration Inspection?

Dye Penetration Inspection, otherwise known as Liquid Penetrate Inspection or Penetrant Testing is a widely-used method to check for defects in non-porous materials such as metals, plastics or ceramics.

It is popular due to its relatively low cost, non-destructive process and its ability to detect possible casting, forging and welding surface defects so that the buyer can be assured of the quality of the products they are purchasing. If the Dye Penetration Inspection comes up positive then it could indicate defects such as hairline cracks, surface porosity, incomplete fusion, flaws in joints or fatigue cracks that cannot be seen by the naked eye.

Generally, the test works by either dunking the product into a tank of purple dye or spraying it with the dye. The dye is then cleaned off the surface of the product and a white coat is applied. If there is even the slightest crack or fault in the material, then the dye will seep out of it and will be clearly seen.

What is the process of Dye Penetration Inspection?

Dye Penetration Inspection is based upon the theory of ‘capillary action’ which states that low surface tension fluid can penetrate into clean and dry discontinuities. Once adequate penetration time is given, a developer is applied which works to draw the penetrant out of the flaw in the material and the resultant dye stain will then show where any anomalies lie.

Different penetrants are utilised depending on the material being tested and the sensitivity required. When selecting different penetrant dyes, you must consider many factors such as the surface finish of the product being tested and the size of defect sought. Our qualified Special Piping Materials inspectors will be able to advise you of what process is best for the material you are testing.

The final inspection of the material is performed under either ultraviolet light or white light, depending on whether the penetration dye used is fluorescent or non-fluorescent.

 The method goes as follows:

  1. Cleaning: The surface being tested needs to be free from grease, oils and dirt and therefore wire-brushing or similar pre-cleaning is necessary. Any paint on the material must also be removed prior to testing.
  2. Application: The dye being used is then applied either by dunking or spraying.
  3. Removal: Any excess penetrant is then removed from the surface of the product.
  4. Development: A developer liquid is applied to the product and then it is given time for the dye to seep out of any flaws in the material.
  5. Inspection: A qualified Inspector will then review the product and will be able to determine whether any flaws are present. A deep red or purple line can indicate a crack or fracture whereas dots or ‘splodges’ indicate that there is possible porosity, shrinkage or lack of bond.


The Advantages of Dye Penetration Inspection

There are many advantages of Dye Penetration Inspection, hence why it has become such a popular choice for many companies and many different industries.

These advantages include:

  1. Short timeframe: The test can be carried out very quickly on large volumes of material.
  2. Low-cost: A small amount of equipment is required which keeps costs low, especially if the product is only being tested with a spray can.
  3. High-sensitivity: Relatively small flaws can be detected.
  4. Bespoke: It is suitable for testing products that are of odd shapes and sizes.
  5. Immediate: The results of the test are usually quite conclusive and immediately provide evidence of the type of anomaly present.


As with anything, there is a couple of disadvantages of dye-pen inspection, mainly that the test only works on smooth surfaces like stainless steel or ceramic.

Although the operator of the inspection needs relatively limited training, experience of how to carry out the test and what the results indicate is vital.

How does Special Piping Materials conduct Dye Penetration Inspections?

Special Piping Materials has offices across the world in Australia, Singapore, United Arab Emirates, England, Scotland, America and Brazil and all of these offices can provide portable Dye Penetration Inspections as part of their suite of non-destructive tests.

In our headquarters in Manchester, we can offer an added service as we have the ‘dip tanks’ required for larger products and materials.

At each of our offices, our trained inspectors can carry out the procedures as specified by the customer and they can even work with the customer to advise on what penetrant is most suitable. They will also be able to ensure that the test chemicals are compatible with the sample so that permanent staining or degradation does not occur.

Penetrants are classified by their sensitivity levels and, when selecting a penetrant, factors such as environment under which the test is to be performed, size of defects sought, surface finish and size of test piece are considered.

The inspector then performs a visual inspection under ultraviolet or white light, depending on the type of penetrant used (fluorescent or visible colour contrast), and provides a report back to the customer.

Our methods are robust and proven to be very effective in ensuring that all the materials that we source and supply are of the very highest quality. If any defects are found in the products that we test, then we work with our clients to find an efficient and satisfactory solution.

Contact any of our sales team members today to find out more about our quality assurances, testing capabilities and our unyielding commitment to excellence.

Fast, efficient delivery to your exact specification. Special Piping Materials is as committed to your project as you are.

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