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This is one of our most basic inspection techniques, but it’s also one of our most effective non-destructive testing methods. Contact us right now for dependable results and knowledgeable guidance from a friendly engineer. We provide coverage throughout the United Kingdom.

A penetrating dye solution is applied to the required surface area of the investigated structure. Following that, the dye is removed from the surface, with any further staining indicating abnormalities in the substance under inquiry.

This type of NDT is commonly used to detect surface flaws due to its dependability and effectiveness as a form of quality control. It ensures that any indications that components should be fixed or replaced are detected and documented.

ASTM E165 Liquid Penetrant Testing also serves as a resource: a means of determining the adequacy and thoroughness of a liquid penetrant examination technique advocated or mandated by various organisations.

Process standards and techniques for liquid penetrant testing of components and materials are developed. Every customer who requires penetrant testing is strongly advised to sign a contract. All aspects of this procedure may be agreed upon by the competent engineering organisation and the supplier.

To organise liquid penetrant testing facilities and staff.

This discipline includes methodologies for material penetrant examination. Surface discontinuities such as cracks, seams, laps, cold shuts, shrinkage, laminations, through leaks, or lack of fusion are detected by non-destructive testing procedures like as penetrant testing. It is suitable for in-process, final, and maintenance inspections. It may test nonporous, metallic, ferrous, and nonferrous metals, as well as non-metallic materials such as nonporous glazed or completely densified ceramics, nonporous polymers, and glass.

This practise neither provides nor suggests criteria for assessing penetrant testing indications. However, if signs are found, they must be reviewed or categorised before they may be analysed.

There must be a particular regulation, standard, or formal agreement in place to specify the kind, size, position, and direction of permissible and prohibited indicators.

 

It is difficult to find surface fractures on a non-porous substance with the naked eye. This is where tools like a fluorescent penetrant system and custom NDT equipment are useful. The techniques are used to find flaws in objects made of ceramic, metal, and plastic, including leaks and cracks. The steps you must follow to find flaws in any non-porous material are listed below.

Cleansing initially

When doing fluorescent penetrant examination, pre-cleaning or initial cleaning of the material is the first and necessary step (FPI). In order to leave the surface exposed, this step guarantees that all liquids, oils, grease, and paints are removed. In this manner, the outcomes are flawless and free of contaminants. It also makes it simple for you to spot the surface flaw.

Deep-cutting use

The penetrant application process begins once the material is prepared and clean. After gently immersing the surface, the penetrant is allowed to work for a while. The time frame relies on the material being used and the kind of flaw you believe could be visible at first glance. A good amount of material exposure to the penetrant frequently yields excellent results, as any seller of NDT supplies would also concede.

Taking away extra penetrant

In a controlled setting, the extra penetrant must be removed next. That way, all surface-based penetrants will be eliminated, leaving just the penetrant on the alleged flaws. If the extra penetrant isn’t removed, flaws are probably going to result.

Applications from developers

The surface is coated uniformly with a thin layer after the material has been cleaned of extra penetrant. The developer is known by this name. By separating the penetrant from the fault, it is responsible for providing an ideal indication or visibility. Stains that are coloured will reveal any potential flaws.

Surface examination

Inspecting the surface is the final stage when utilising the custom penetrant system. After 10 minutes, you need to finish. For the surface to blot and produce outstanding results, that amount of time is sufficient. The outcomes could be unreliable if you wait too long. Because of this, be careful to time everything correctly. low ambient light, and UV radiation are all used throughout the examination as per the necessary equipment. With such, it will be simple for you to see the flaws.

That brings us to the current list of the five crucial actions you must complete while using the fluorescent penetrant system. For precise and simple-to-read results, each step should be properly completed. Any error produced might result in sounds, which frequently make it challenging to spot the flaws.

The term “liquid penetrant inspection,” or “LPI,” also refers to dye penetration testing. One of the non-destructive inspection methods most frequently employed is dye penetrant examination. It may be utilised in a huge range of product applications and sectors. This approach is employed in metalworking facilities, the aerospace industry, the production of electrical energy, and any procedure that makes use of a metal joining technique like welding. It is applied to pipe inspection and weldment verification in the petrochemical sector. The purpose of these tests is to look for any surface breaking faults. These tests have several applications. Typically, they are used to ceramics, non-porous materials, metals, and plastics. The non-destructive procedures and low cost of the test have made it famous. It is required to undergo dye penetration testing if a new product is to be developed. It locates any potential cracks and leaks caused by fatigue.

Dye-Penetrating Fluorescent Inspection Principle

This assessment is focused on the dye’s ability to penetrate, as implied by its name. Any surface discontinuities and flaws will absorb the dye when it is forced to flow through the material. As a draw penetrant, the dye is also known. The most frequent methods for applying it are brushing, dipping, and spraying. Developer is used after the penetrant has been removed from the surface. Visual inspection is performed by the developer. An excellent tool for identifying anomalies is the liquid penetrant examination system. The durability of the material may also be guaranteed using them. Although liquid penetrant testing may be used on any non-porous, clean material, whether metallic or not, it is not recommended for use on surfaces that are extremely unclean or rough. The penetrant testing method must include surface cleaning. A manual, semi-automatic, or completely automated process can be used. It is typical to use continuous manufacturing lines, penetrant examination, and time-cycled cleaning, dipping, washing, and drying of the specimens.

Liquid Penetrant Inspect Advantages

Sensitivity: The test can detect even minute surface imperfections. It is well known for being extremely sensitive. Industries are frequently looking for testing techniques that may detect contaminants that are both small and irregularly distributed. This type of testing satisfies both of these demands.

Flexibility: Several materials may be tested using the liquid penetrant method. It encompasses both conductive and non-conductive items, metallic and non-metallic surfaces, and even magnetic and non-magnetic surfaces. These materials can all be tested without failure.

• Testing aids in visualising the issue for engineers. Directly drawn on the surface are the indicators.
• The exam is affordable. All the test materials were economically viable on their own.

Various use cases to start, this method of testing may be used to a wide range of geometric forms. The test doesn’t require an even surface because it relies on the amount of absorption. Even if the surface’s form is complex, imperfections will nevertheless allow liquid to get through. When faults are present, they will eventually be visible on the surface.

Chemicals utilised in these tests are exceedingly compact, in contrast to those employed in many other testing procedures. They may be easily stored and used throughout the examinations.

 

We’ve all been waiting, we heard it was coming. And many of those affected will now know that its arrived, what are we talking about?

It’s called ISO9712-2022 the International standard for qualification and certification of NDT personnel affective for General engineering sectors and manufacturing.

There are several factors to address which may have impact on organisations from large to small and even the Independent contractor, but it all needs to begin with small steps.

From the top down and the bottom up, the Implementation of a plan and awareness is key at an early stage.

 

• Firstly if your certification is reliant upon ISO9712 schemes or PCN, you may already be aware of certain changes from BINDT, Inform your employer QA-department to the new changes.
• QA-managers who employ NDT personnel are expected to conduct a risk based assessment or GAP-Analysis from 2012 to 2022 requirements.
• QA-managers and companies who have contractual obligations by design or legal binding requirements are expected to conduct a risk based assessment of needs, and how do 2022 requirements affect their operations.
• Assessments and analysis would be expected to adopt Plan-Do-check-Act methodologies consistent and ISO9001 certification.

 

Advisory points:

The new 2022 standard Introduces the need for companies to adopt a Company written practice procedure outlining the requirements for how to certify personnel and the scope of certification needed for your company.

Even though your company has a design or contractual need for NDT, have you audited your supplier to review if their company written practice meet the needs of your company?

All companies differ in the qualification and certification requirements and should not be overlooked. If needed your Level-3 NDT technician or Notified body can offer advice.

British standards online offer guidance documentation and standards to advise uses of the changes to requirements, please see the links below for more Information:

BS EN ISO 9712 Non-destructive testing. Qualification and certification of NDT personnel | BSI (bsigroup.com)

 

The PSM-5 simulated defect panel has become the industry standard for repeated function of a company’s Liquid penetrant process, utilised commonly with fluorescent systems monitoring daily performance and aiding to fault find the defective element of the system wherever monitoring would fall below an established baseline.

The PSM-5 panel is manufactured from stainless steel sheet material, chromium plated and Impressed from the rear of the panel with 5 Brinell hardness indents in a controlled manner to crack the layer of chromium of the panels test side. You’ll also note that on the (right) test side the panel has an aluminium oxide media blasted surface, this roughness creates a surface for washability tests called out by your specifications or national standard.

One common misconception is that the TAM is used to measure sensitivity by the number of stars you can achieve. This thinking is only a crude estimation, more realistically this is a measure of the manufacturer’s formulation, viscosity, pigmentation, and fluoro-optical properties.

This guide and recommended practice are recommended for new and experienced users. With the passage of time many people will have troubles with there simulated defect monitoring panel, but by experience it always comes back to best practices. There are a multitude of cleaning options (not all best for use with your panel) and with some effective pointers and tips you should experience trouble free use for many years.

Storage: Store your panel by immersion in a fast evaporating solvent. Acetone is suitable and easy to obtain. Just make sure its in a well-sealed container to stop any evaporation losses.

 

Operation:

• Remove your panel from storage and wipe the panel area with a clean lint free wipe before the solvent evaporates away. You don’t want any residual streaks staining your testing area.
• Preferably dry your panel in an air circulated drying oven at 60-70oC for 15 mins prior to the application of penetrant materials, but if your liquid penetrant system doesn’t utilise this a compressed air blast (<25psi) will accelerate evaporation. The panel may appear to be dry after point-one but without this stage starburst 5 (smallest crack) may become difficult to replicate.
• After removal from your drying oven, allow the surface to cool <38^oC is recommended. You don’t want to accidently dry the penetrant on the surface of your panel or increase the penetrant viscosity.
• Apply your penetrant and process in a typical manner to that of your production parts. Recommendable to process daily with your first batch production run. (For ease of description a process control chart of operation sequences is recommended).
• Following development evaluate and view your panels results to that of BASELINE calibration that was created when first established, The comparison will be to a 1:1 scale colour photograph replica.
• After completion remove the developer residues with a lint free cloth and return your panel to storage in solvent.

Common faults:

I can’t find Starburst 4 or 5 (dependent chosen penetrant): As described earlier, most cases come down to poor pre-processing. If you don’t fully evaporate or dry the panel before applications, you’ll still hold an amount of solvent residue in the tight Indications. This will reduce effective penetration, may dilute your penetrant constituents in the flaw reduce detectability.

A second reason could be your developer application layer. Has there been a difference in application time compared to the BASELINE or is the developer chosen In-affective? If this has happened and you try to Isolate the developer, apply a thin layer of non-aqueous developer to see if there is penetrant in the flaw itself. (don’t do this more than once) repeated wipes will remove any penetrant you try to locate.

Discrepancy between multiple operators can have an outcome on results obtained, the practices here will help but recommended to develop a process control chart or data card to standardise the processing of the test panel…. this way you achieve repeatable results.

Penetrant Colour and Fluorescence

The colour of the penetrant material is of obvious importance in a visible dye penetrant inspection, as the dye must provide good contrast against the developer or part being inspected. Remember from the earlier discussion of contrast sensitivity that generally the higher the contrast, the easier objects are to see. The dye used in visible dye penetrant is usually vibrant red but other colours can be purchased for special applications.

When fluorescent materials are involved, the effect of colour and fluorescence is not so straightforward. LPI materials fluoresce because they contain one or more dyes that absorb electromagnetic radiation over a particular wavelength and the absorption of photons leads to changes in the electronic configuration of the molecules. Since the molecules are not stable at this higher energy state, they almost immediately re-emit the energy. There is some energy loss in the process, and this causes photons to be re-emitted at a slightly longer wavelength that is in the visible range. The radiation absorption and emission could take place a number of times until the desired colour and brightness is achieved. Two different fluorescent colours can be mixed to interact by a mechanism called cascading. The emission of visible light by this process involves one dye absorbing ultraviolet radiation to emit a band of radiation that makes a second dye glow. Since the human eye is the most used sensing device, most penetrants are designed to fluoresce as close as possible to the eyes’ peak response.

Penetrant Brightness

Fluorescent brightness was erroneously once thought to be the controlling factor with respect to flaw detection sensitivity. Measurements have been made to evaluate the intrinsic brightness of virtually all commercially available penetrants and they all have about the same brightness. Intrinsic brightness values are determined for thick liquid films, but the dimensional threshold of fluorescence is a more important property. The measurement of fluorescent brightness is detailed in ASTM E-1135, “Standard Test Method for Comparing the Brightness of Fluorescent Penetrants.”

The penetrant materials used today are much more sophisticated than the kerosene and whiting first used by railroad inspectors near the turn of the 20th century.  Today’s penetrants are carefully formulated to produce the level of sensitivity desired by the inspector.  To perform well, a penetrant must possess several important characteristics. A penetrant must:

• Spread easily over the surface of the material being inspected to provide complete and even coverage.
• Be drawn into surface breaking defects by capillary action.
• Remain in the defect but remove easily from the surface of the part.
• Remain fluid so it can be drawn back to the surface of the part through the drying and developing steps.
• Be highly visible or fluoresce brightly to produce easy to see indications.
• Not be harmful to the material being tested or the inspector.

All penetrant materials do not perform the same and are not designed to perform the same. Penetrant manufactures have developed different formulations to address a variety of inspection applications.   Some applications call for the detection of the smallest defects possible and have smooth surfaces where the penetrant is easy to remove.  In other applications, the rejectable defect size may be larger, and a penetrant formulated to find larger flaws can be used.  The penetrants that are used to detect the smallest defect will also produce the largest number of irrelevant indications.

Penetrant materials are classified in the various industry and government specifications by their physical characteristics and their performance. Aerospace Material Specification (AMS) 2644, Inspection Material, Penetrant, is now the primary specification used in the USA to control penetrant materials.  Historically, Military Standard 25135, Inspection Materials, Penetrants, has been the primary document for specifying penetrants but this document is slowly being phased out and replaced by AMS 2644.  Other specifications such as ASTM 1417, Standard Practice for Liquid Penetrant Examinations, may also contain information on the classification of penetrant materials but they are generally referred back to MIL-I-25135 or AMS 2644.

Penetrant materials come in two basic types. These types are listed below:

• Type 1 – Fluorescent Penetrants
• Type 2 – Visible Penetrants

Fluorescent penetrants contain a dye or several dyes that fluoresce when exposed to ultraviolet radiation.  Visible penetrants contain a red dye that provides high contrast against the white developer background. Fluorescent penetrant systems are more sensitive than visible penetrant systems because the eye is drawn to the glow of the fluorescing indication.  However, visible penetrants do not require a darkened area and an ultraviolet light to make an inspection. Visible penetrants are also less vulnerable to contamination from things such as cleaning fluid that can significantly reduce the strength of a fluorescent indication.

Penetrants are then classified by the method used to remove the excess penetrant from the part.  The four methods are listed below:

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

Water washable (Method A) penetrants can be removed from the part by rinsing with water alone.  These penetrants contain an emulsifying agent (detergent) that makes it possible to wash the penetrant from the part surface with water alone.  Water washable penetrants are sometimes referred to as self-emulsifying systems.   Post-Emulsifiable penetrants come in two varieties, lipophilic and hydrophilic.  In post-emulsifiers, lipophilic systems (Method B), the penetrant is oil soluble and interacts with the oil-based emulsifier to make removal possible.  Post-Emulsifiable, hydrophilic systems (Method D), use an emulsifier that is a water soluble detergent which lifts the excess penetrant from the surface of the part with a water wash.  Solvent removable penetrants require the use of a solvent to remove the penetrant from the part.

Penetrants are then classified based on the strength or detectability of the indication that is produced for several very small and tight fatigue cracks. The five sensitivity levels are shown below:

• Level ½ – Ultra Low Sensitivity
• Level 1 – Low Sensitivity
• Level 2 – Medium Sensitivity
• Level 3 – High Sensitivity
• Level 4 – Ultra-High Sensitivity

The major US government and industry specifications currently rely on the US Air Force Materials Laboratory at Wright-Patterson Air Force Base to classify penetrants into one of the five sensitivity levels.  This procedure uses titanium and Inconel specimens with small surface cracks produced in low cycle fatigue bending to classify penetrant systems.  The brightness of the indication produced is measured using a photometer. The sensitivity levels and the test procedure used can be found in Military Specification MIL-I-25135 and Aerospace Material Specification 2644, Penetrant Inspection Materials.

An interesting note about the sensitivity levels is that only four levels were originally planned.  However, when some penetrants were judged to have sensitivities significantly less than most others in the level 1 category, the ½ level was created.  An excellent historical summary of the development of test specimens for evaluating the performance of penetrant materials can be found in the following reference.

The following is a non-exhaustive list of some of the defect types which can be found during the non destructive testing process.

 

CASTING DEFECTS

The following defects are present in the material before any further processing operations such as forging, or rolling have begun.  All casting defects are therefore inherent.

Porosity

This is formed by gas which is insoluble in the molten metal.  The gas is trapped within the metal when if solidifies and remains in the form of spherical or tubular cavities.

Airlocks

A cavity formed by air which has been trapped in the mould by the metal during pouring.

Blowholes

These are small holes in or on the surface of the casting.  They are caused by gas evolution from the decomposition of grease, moisture etc., but not from the mould itself.

For example, during the sand casting operation, moisture from the mould produces steam, this is normally forced through the mould due to the absorbent nature of the sand but sometimes the steam cannot get through to the outside and is forced back into the casting, blowing holes in the casting surface.

Non-metallic inclusions

Non-metallic inclusions are impurities such as slag, oxides, and sulphides, which exist in the molten metal and finally the solidified metal.

Pipe/shrinkage defects

This is a cavity in the centre of the ingot/casting caused by shrinkage during solidification.  A primary pipe is surface breaking; secondary pipes are those which exist sub-surface.  The top of an ingot casting is removed to get rid of the primary pipe.

Other shrinkage defects may occur in steel castings where there is a localized variation in section thickness.  Shrinkage defects are not normally associated with gas, but a high gas content will magnify their extent.

Interdendritic shrinkage: very small shrinkage cavities associated with dendrite solidification.

Segregation

Segregation is chemical heterogeneity, or the non-uniform distribution of the alloys or impurities.  Pure metals do not exhibit segregation.

In carbon steels, the elements which segregate are those that are either insoluble or form lower freezing point complexers, e.g., sulphur, phosphorus, carbon, manganese, and silicon.

 

 

Cold shuts

A cold shut is an area of lack of fusion which may be surface breaking or sub-surface in a casting.  Cold shuts may result from splashing, surging, interrupted pouring, or the meeting of two streams of molten metal coming from different directions.

Hot tears (cracks)

Cracks caused by non-uniform cooling resulting in stresses which rupture the surface of the metal while its temperature is still in the brittle range.  They appear as ragged lines of variable width and numerous branches.  The tears may originate where stresses are set up by the more rapid cooling of thin sections that adjoin heavier masses of metal, which are slower to cool.  Curved surfaces and corners tend to promote hot tearing

A wrought product is a worked product, primarily produced by hot working, e.g., forging or rolling, although cold working is possible in some areas.

As the nature of penetrant testing is to locate surface breaking defects this means that the preparation of the surface is one of the most critical parts of the entire penetrant testing operation.

With this in mind many specifications and end users feel the need to specify pre penetrant etching of parts which have been subject to operations which could potentially smear or otherwise peen the surface of the parts.

These operations include but are not limited to Sand, grit, vapour, plastic or other media blasting, burnishing, lapping or honing surface finishing by tumbling, vibration or grinding.

During these operations and others with similar features softer metals such as aluminium and titanium can have small parts of their surface peened which could potentially lead to a section of material being pushed over the top of the open surface of a surface breaking defect, should this occur and be left in this condition it would essentially stop dye penetrant from entering the open surface of the defect which would render the test unable to locate the defects.

Due to this the parts must be etched prior to the dye penetrant testing process.

The process of etching is a chemical operation using a suitable chemical to remove a pre determined quantity of the material from the surface of the component.

An example type of this operation would be the pre penetrant etching of aluminium for Airbus UK. The common method to carry this out is via the use of a deoxidiser such as Henkel 6/16 deoxidiser in nitric acid, in this process an etch rate is first determined by submerging a 2024 aluminium test plate in the etching solution for a pre determined length of time and performing stock loss and weigh measurements in order to calculate a removal rate of the material.

Once the removal rate has been calculated by an approved member of staff they are then ready for the etching of production parts.

For Airbus UK parts the total amount of material that shall be removed from the surface prior to the penetrant testing operation is 5 μm (0.0002 inches).

Once the parts have be submerged in the etching solution for the correct amount of time to remove this amount of material the parts are then thoroughly dried usually at an elevated temperature for a minimum of 45 minutes before being moved on to the dye penetrant testing process.