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In Liquid Penetrant (LP) testing , the choice between visible penetrants (Type II) and fluorescent penetrants (Type I) is a technical decision that directly impacts the sensitivity of the inspection , the way indications are evaluated , and the reliability of the final result .

Although both types of penetrant are based on the same physical principle, their operational characteristics, inspection conditions, and sensitivity levels differ. This article presents an educational and technical approach , clarifying the main differences between visible and fluorescent liquid penetrants, their applications and limitations, always conditioned by the approved technical procedure .

What is liquid penetrant testing?

Liquid penetrant testing is a non-destructive testing method used to detect surface discontinuities open to the surface in metallic and non-metallic materials, provided the material is not porous .

The method is widely used in industrial inspection due to its versatility and ability to reveal fine discontinuities, provided it is performed in accordance with a specific technical procedure.

Common principle for visible and fluorescent penetrants

Both visible and fluorescent penetrants are based on the physical principle of capillarity , which allows the liquid to penetrate discontinuities open to the surface, even when these discontinuities are extremely small.

After the penetrant is applied and the excess surface product is removed, the product retained in the discontinuities is brought back to the surface by means of the developer, forming indications that will be evaluated during visual inspection.

The difference between the two types of penetrant testing lies not in the operating principle , but in how the indications are visualized during inspection .

Visible Penetrant Testing (Type II): general characteristics

Visible penetrant liquids utilize color contrast , typically red on a white background, to allow for visualization of the indications under adequate white illumination .

General characteristics:

• Inspection performed under visible light;
• indications observed with the naked eye;
• applicable in different industrial environments;
• Widely used in manufacturing inspections.

The reliability of the test depends directly on the intensity of the white light, the uniformity of the developer layer, and the correct execution of the test, respecting the procedure.

Fluorescent Penetrant Testing (Type I): general characteristics

Fluorescent penetrating liquids contain pigments that emit visible light when excited by ultraviolet (UV-A) radiation , allowing indications to be visualized in environments with controlled lighting.

General characteristics:

• Inspection performed under ultraviolet light;
• Indications observed by fluorescence;
• greater visual perception capacity in certain applications;
• Widely used in inspections that require a higher level of sensitivity and reliability.

In this method, the quality of the inspection is directly related to the UV-A lighting conditions, environmental control, and the correct visual adaptation of the inspector and the correct execution of the test, respecting the procedure.

Sensitivity and detection capability

Fluorescent penetrant testing (Type I) is more sensitive than visible penetrant testing (Type II) . However, the most sensitive method is not always the most suitable for all applications.

The choice of penetrant type should consider factors such as the type of discontinuity to be detected , the manufacturing process , the surface condition , the industrial segment , the inspection environment , and the requirements established in the approved technical procedure .

Advantages of the Penetrant Testing Method

In general, the Liquid Penetrant test, in both the visible and fluorescent methods, offers the following advantages:

• a simple and widely used inspection method;
• relatively low operational cost when compared to other END methods;
• Ease of application, provided it is performed according to technical procedure;
• Direct visual interpretation of the instructions;
• good sensitivity for detecting surface discontinuities open to the surface , including fine and small-aperture discontinuities;
• Applicable to parts of different sizes and geometries, provided there is access to the surface to be inspected.

Limitations of the Penetrant Testing Method

Despite its advantages, the Liquid Penetrant test has technical limitations that must be considered:

• It detects exclusively open surface discontinuities and is not applicable to the detection of internal or subsurface faults;
• It is not recommended for porous materials ;
• It requires control of environmental conditions during the execution of the test, including temperature , which must be within the range specified in the technical procedure and applicable standards;
• Inadequate surface or environmental conditions can compromise the reliability of the indications.

Final considerations

The difference between visible and fluorescent penetrants goes beyond the appearance of the indication. It is a technical decision that involves physical principles, required sensitivity, inspection conditions, environment, type of discontinuity, and compliance with the approved technical procedure.

When correctly specified and applied, both methods offer reliable results and contribute to the integrity and safety of the inspected components.

Excellence in products for those seeking reliable results.
Metal-Chek provides complete solutions for Non-Destructive Testing : visible and fluorescent penetrant liquids, developers, removers, and accessories, developed according to the main ASTM, ISO, ASME, NM, and PETROBRAS standards, guaranteeing quality, safety, and technical compliance in every inspection.

Speak with the Metal-Chek team and learn about our solutions for non-destructive testing.

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Liquid Penetrant Testing (LP) is one of the best-known and most widely used methods within Non-Destructive Testing (END) . Simple to perform, yet extremely meticulous in its details, it is fundamental for ensuring quality, safety, and reliability in critical components across various industrial sectors.

Despite its apparent simplicity, inconsistent results are almost always linked to flaws in the preparation, application, or control of test conditions —and not to the method itself. Therefore, understanding its principles is essential for anyone seeking reliable inspections.

What is Penetrant Testing?

The purpose of liquid penetrant testing is to detect discontinuities open to the surface of non-porous solid materials.

Among the most common discontinuities identified by the method are:

• Cracks
• Porosities
• Lack of fusion in welds

One of the great advantages of LP is its versatility . The method can be applied to both magnetic and non-magnetic materials , such as:

• Carbon steels and austenitic stainless steels
• Aluminum and magnesium
• Titanium

Furthermore, LP can also be used, under specific conditions, on ceramics, glass, and some plastics .

Physical Principle of the Liquid Penetration Test: Capillarity

The operation of the liquid penetrant test is based on the physical phenomenon of capillarity .

Capillary action allows a liquid to penetrate open discontinuities on the surface regardless of the orientation of the part , whether vertical, horizontal, or overhead, without depending on the action of gravity.

After applying the penetrant and removing the surface excess, applying the developer promotes the so-called reverse capillary effect , causing the liquid retained in the discontinuities to return to the surface, forming visible or fluorescent indications.

Steps of the Penetrant Testing Process

A reliable LP test follows six fundamental steps :

1. Surface preparation and cleaning
2. Penetrant application
3. Penetration time
4. Removal of excess penetrant.
5. Application of the developer
6. Inspection, recording and final cleaning

Each step must strictly follow the procedure qualified and approved by the Level 3 Inspector , respecting defined standards and parameters.

The Importance of Surface Preparation

The most critical step in liquid penetrant testing is undoubtedly the preparation and cleaning of the surface .

Complete removal of:

• Grease
• Oil
• Carepas
• Oxidation
• Paints and coatings

It is essential for the penetrant to act correctly through capillary action. Poorly prepared surfaces directly compromise the sensitivity of the test .

Types of Products Used in Penetrant Testing

The liquid penetrant test depends on the correct combination of three main groups of products :

1. Removers

Used for:

• Pre-cleaning of the surface
• Removal of excess penetrant, according to the method applied.

2. Penetrating

Classified according to the type of display:

• Fluorescent (Type I) – used under UV-A light.
• Visible (Type II) – observed under white light

And according to the removal method:

• Method A – water washable
• Method B – lipophilic post-emulsifiable
• Method D – hydrophilic post-emulsifiable
• Method C – solvent removable

3. Developers

Used to improve contrast and highlight indications, available in the following forms:

• Dry powder (Form a)
• Aqueous suspension (Form c)
• Aqueous solution (Form b)
• Non-aqueous suspension in solvent (Forms d | e)

Choosing the correct combination depends on the technical procedure , the type of material , and the discontinuity to be detected .

Common Questions about Liquid Penetrant Testing (LP)

Penetration Time: How Long to Let the Penetrating Agent Work?

For Metal-Chek products , the general recommendation is a minimum penetration time of 10 minutes .
In some specific applications, 5 minutes may be sufficient , provided that:

The procedure is qualified.

– Approval from Level 3 Inspector is required.

Can Penetrant Liquid Be Used on Stainless Steel?

Yes. The liquid penetrant (LP) test can be applied to austenitic stainless steel, duplex steel, and titanium , provided that the contaminant levels (Cl + F) indicated in the product’s certificate of analysis are observed.

Is Fluorescent Penetrant Always More Sensitive?

Yes. Fluorescent penetrant (Type I) exhibits greater sensitivity compared to visible penetrant (Type II) .

However, greater sensitivity does not always mean better application . The choice of penetrant type should consider:

• Type of discontinuity
• Manufacturing process
• Surface condition
• Industrial segment
• Applicable procedure

Testing Conditions and Inspector Qualification

The penetrant testing process depends directly on the inspector’s visual ability and the lighting conditions .

Minimum lighting requirements:

• Visible Penetrant (Type II):
  • Visible light ≥ 1000 lux
• Fluorescent Penetrant (Type I):
  • UV-A light ≥ 1000 µW/cm²
  • Visible light < 20 lux

It is necessary for the inspector to periodically undergo visual acuity and color differentiation tests, such as:

• Visual acuity (Jaeger)
• Color differentiation (Ishihara)

Advantages and Limitations of the LP Test

Advantages:

• Simple and low-cost method
• Easy application and interpretation.
• High sensitivity to surface discontinuities
• Applicable to parts of any size and geometry.

Limitations:

• It only detects discontinuities open to the surface.
• Not applicable to porous materials.
• It requires strict temperature control.
  • Typical temperature range: 10 °C to 52 °C

Safety and Applicable Standards

The test should be carried out in well-ventilated environments , with the proper use of Personal Protective Equipment (PPE) .

In fluorescent testing, the use of protective eyewear against UV-A light is mandatory .

Main standards applicable to liquid penetrant testing:

• ASME Section V – Article 6
• ASTM E1417
• ASTM E165
• ISO 3452
• NM 334
• PETROBRAS N-1596
• PETROBRAS N-2370

Conclusion

Liquid penetrant testing remains one of the most efficient tools for detecting surface discontinuities, provided it is performed with technical discipline, reliable products, and well-defined procedures .

Excellence in lead generation lies not in shortcuts, but in the rigorous control of each step of the process .

Excellence in products for those seeking reliable results.

Metal-Chek provides complete solutions for Non-Destructive Testing : penetrant liquids, removers and developers, developed according to the main ASTM, ISO, ASME, NM and PETROBRAS standards , guaranteeing quality, safety and technical compliance in every inspection.

Get in touch and follow the profile @metalchek for more technical content about END.

In non-destructive testing using Liquid Penetrant (LP) and fluorescent Magnetic Particle (MP) methods, the reliability of the inspection depends on a precise combination of factors: quality products, appropriate accessories, UV luminaires within technical specifications, and, most importantly, the correct visualization of the indications .

Within this context, one often underestimated aspect deserves special attention: the inspector’s eye protection . The use of glasses with an appropriate UV-A radiation filter is not only an occupational safety measure, but also a factor that directly impacts the quality of the interpretation of the results .

Fluorescence Assays and UV-A Radiation

Fluorescent END methods are based on the excitation of materials that emit visible light when exposed to type A ultraviolet (UV-A) radiation , generally with a wavelength around 365 nm .

However, continuous exposure to UV-A radiation requires strict control , both from the point of view of operator safety and the reliability of the inspection .

The Human Factor in Test Reliability

Even with:

• highly sensitive penetrating fluorescent lenses,
• fluorescent magnetic particles formulated according to technical standards,
• Even with UV lamps at the minimum required intensity, the test may be compromised if the inspector is not using adequate eye protection .

Vision is the primary tool for interpretation in fluorescent END. Any factor that causes:

• eye strain,
• glare,
• loss of contrast,
• visual discomfort,

It directly impacts the ability to identify, evaluate, and classify indications .

Function of UV-A Filtering Glasses in LP and PM Tests

Safety glasses with specific UV-A filters play a fundamental technical role during fluorescent inspections. Their function goes beyond basic protection.

Key technical benefits:

• Eye protection against prolonged exposure to UV-A radiation.
  Reduces risks associated with continuous exposure during inspection shifts.
• Improved contrast of fluorescent indicators:
  The filter reduces light reflected from the surface and enhances the visualization of the fluorescent glow emitted by the penetrant or particles.
• Reduced eye strain:
  Less eye effort results in more consistent and reliable inspections, especially in repetitive tasks.
• Increased accuracy in interpretation:
  A clearer and more comfortable field of vision contributes to safer technical decisions.

In industrial environments, where residual lighting and reflections can interfere with inspection, this visual benefit is even more relevant.

Integration with Quality Products and Accessories

Metal-Chek develops solutions for fluorescent testing by considering the entire process , and not just the isolated chemical product.

For LP and PM fluorescent methods to achieve their maximum performance, integration between the following is essential:

• Fluorescent penetrants and fluorescent magnetic particles developed in accordance with technical standards;
• UV lamps with appropriate wavelength and intensity compatible with regulatory requirements;
• Appropriate accessories , including safety glasses with UV-A filters compatible with the test’s operating range.

This systemic approach reduces misinterpretations, improves the repeatability of results, and reinforces a culture of quality in inspections.

Safety, Quality and Technical Responsibility

The use of UV-A protective eyewear should be understood as an integral part of good practices in fluorescent testing , aligned with safety guidelines and END reliability requirements.

Conclusion

Reliable fluorescent testing depends not only on high-performance products and equipment, but also on the human factor , particularly the quality of visualization and the inspector’s protection.

The use of glasses with adequate UV-A filter:

• protects vision,
• improves the contrast of the indications,
• reduces fatigue,
• and contributes directly to more accurate and reliable results.

In END, having good vision is just as important as applying the method correctly.

Excellence in products for those seeking reliable results.
Metal-Chek provides complete solutions for Non-Destructive Testing: fluorescent penetrants, fluorescent magnetic particles, UV lamps and accessories, developed according to the main ASTM, ISO, ASME, NM and PETROBRAS standards, guaranteeing quality, safety and technical compliance in every inspection.

Continue deepening your knowledge: explore other technical articles on the Metal-Chek blog.

Contact Metal-Chek.
Follow the profile @metalchek

In Fluorescent Penetrant (LP) and Fluorescent Magnetic Particle (FM) tests , UV-A light is not just an accessory—it is a critical detection tool. The quality of illumination used by the inspector defines what is seen… and what can go unnoticed.

To ensure that the UV-A source truly offers stability, safety, and adequate performance, the industry has adopted ASTM E3022-25, now considered the most rigorous technical standard in the world for UV-A LED luminaires used in END (Non-Destructive Testing).

Why was ASTM E3022-25 created?

ASTM E3022-25 was created precisely to establish minimum and verifiable requirements that define when a UV-A LED light fixture is truly suitable for industrial inspections, especially in critical applications such as:

• Aerospace
• Automotive
• Oil & Gas
• Industrial maintenance
• Welding and structural integrity

In this way , the standard ensures that the luminaire operates within the necessary parameters, guaranteeing that the fluorescence of the penetrants and particles is visible and reliable.

What does ASTM E3022-25 require in practice?

The standard dictates that the luminaire must be tested as a complete unit , not by individual components. This eliminates the possibility of partial tests that do not represent actual performance.

Main requirements that a UV-A luminaire must meet:

* If applicable

This eliminates variations between units and ensures repeatability in the field.

Why is this standard important for safety and for the outcome of the inspection?

A non-compliant light fixture can:

• Reduce the useful inspection area;
• Change the intensity without the operator noticing;
• To utilize a wavelength and have a broad spectrum and reduce fluorescence;
• Increase the risk of undetected failures;
• Generating non-conformities in technical audits (NADCAP, etc.).

For industries that work with critical components — such as structural welds, shafts, bearings, rotors, aeronautical components, and automotive parts — this difference is crucial.

Relationship of ASTM E3022-25 with other END standards

The standard is cited and used as a reference in several technical documents, such as:

• ASTM E1417, ASTM E165 (Liquid Penetrant)
• ASTM E1444, ASTM E709, ASTM E3024 (Magnetic Particles)
• ISO 3059 (Lighting requirements for END)

This reinforces the importance of E3022-25 as a quality base for any UV-A lamp used professionally in END (Non-Destructive Testing).

Final message for inspectors, engineers, and quality managers.

ASTM E3022-25 is not merely a regulatory formality.

It represents a commitment to:

Reliability of the indications

• Operational safety
• Standardization of inspection
• Reproducibility of results
• Compliance with audits

Thus , by using UV-A lamps certified according to this standard, the professional reduces risks, in addition to increasing precision and strengthening the entire quality chain of Non-Destructive Testing.

Stay tuned for updates!

We will soon be presenting important news related to our line of lighting fixtures for END (Non-Destructive Testing).
Follow our blog and social media channels to stay updated on upcoming releases.
Contact our technical consultants .

Excellence in products for those seeking reliable results.

Metal-Chek offers complete solutions for Non-Destructive Testing, developed according to the main technical standards of the sector.
Count on our line of consumables, accessories, and equipment designed to guarantee safety, precision, and compliance in every inspection .

Industrial maintenance is undergoing a silent transformation—and one that is extremely relevant for those working in Non-Destructive Testing (END). UV lamps, essential for Liquid Penetrant (LP) and Magnetic Particle (MP) inspections , have evolved significantly in recent decades, driven mainly by the consolidation of UV LED technology. This change directly impacts the efficiency, quality, and reliability of inspections. More than that, it redefines the role of the inspector, who now has lighter, more durable, and more precise tools to perform critical analyses.

From vapor lamps to UV LEDs: the new era of lighting for END

For many years, mercury vapor-based UV lamps dominated the scene. Although functional, they had clear limitations: intense heating, fragility, high energy consumption, and unstable light.

With the arrival of UV LED lighting , the landscape changed.

Why does UV LED represent a technological leap?

• Stable and instant lighting , with no warm-up time.
• Much longer lifespan , reducing replacements and maintenance.
• Superior energy efficiency , with lower consumption and greater range in battery-powered versions.
• Increased mechanical strength , reducing field failures.
• The absence of toxic materials makes the equipment safer and more sustainable.

For those who inspect welds, critical parts, and structural components, this stability and precision are fundamental.

Portability: real productivity for those who work in the field

The inspector rarely works in comfortable spaces. Most inspections take place in hard-to-reach areas, elevated structures, confined spaces, or extensive pipelines.

The advancement of LEDs has allowed UV lamps to become:

• lighter ,​
• more compact ,
• more ergonomic ,
• more resistant ,
• and with greater operational autonomy .

Direct impacts on the inspector’s routine.

• Less fatigue during long shifts.
• Greater agility in accessing critical points.
• Less reliance on cables or external power sources.
• Greater precision in illuminating the inspected area.
• Reliability even in harsh environments.

Portability is no longer a “plus” but a strategic component of operational efficiency.

Durability and energy efficiency: savings that translate into performance

While traditional light bulbs frequently burned out, high-performance LEDs brought consistency and cost reduction.

Main benefits:

• Less maintenance and less downtime.
• Extended autonomy with long-lasting batteries.
• Reduced overall costs thanks to a longer lifespan.
• Stable UV intensity , ensuring adequate sensitivity in both low-level and mid-life modes.

For ongoing inspections and critical operations, this combination is indispensable.

Regulatory compliance: the importance of ASTM E3022

In END (Non-Destructive Testing), technology alone is not enough: it is necessary to meet the correct standards. ASTM E3022 is the international reference that establishes the minimum requirements for UV LED luminaires used in:

• Magnetic Particle (MP) Testing
• Penetrant Testing (PT)

The standard requires rigorous criteria, such as:

• minimum UV intensity suitable for the method;
• Uniformity of lighting in the inspection area;
• Visible radiation control;
• thermal stability;
• Mechanical strength suitable for industrial use.

Why is this fundamental?

Because lighting failures mean detection failures.
Without compliance with ASTM E3022, there are real risks:

• indications that do not appear;
• Unnecessary rework;
• inconsistent results;
• Problems in audits and certifications;
• security commitments.

The standard ensures that the inspector works with adequate lighting to detect even the most subtle indications.

The practical impact of these advances on the quality of inspections

The evolution of UV LED lighting directly influences:

• The accuracy of discontinuity detection;
• the pace at which inspections are carried out;
• The ergonomics of fieldwork;
• The safety and traceability of the process;
• The reliability of the results delivered.

In sectors such as oil and gas, automotive, aerospace, and metalworking, this translates to lower operational risk and greater control over asset integrity .

UV LED lighting as a protagonist in the new era of END

The combination of portability, energy efficiency, durability, and regulatory compliance has transformed UV LED luminaires into essential tools for modern inspections.

Technology not only makes the inspector’s job easier — it raises the quality of the entire industrial maintenance chain.

Stay tuned for updates!

We will soon be presenting important news related to our line of lighting fixtures for END (Non-Destructive Testing).
Follow the blog and our social media to stay updated on the launch.
Technical lighting, precision, and innovation for those who demand reliable results.

In industrial settings, consumables for Non-Destructive Testing (END) are true allies of reliability. Penetrant liquids, magnetic particles, and developers are formulated to deliver sensitivity , contrast, and stability —three pillars that support the precision of inspections.

One critical point that cannot be overlooked: storage . When done improperly, it accelerates product degradation and directly compromises the test results.

And in industrial inspection, a mistake never comes alone — it translates into rework, costs, and risks.

Therefore, taking care of expiration dates and storage conditions is not just a good practice:  it is fundamental to maintaining the performance and technical compliance required in industrial inspections.

Why proper storage is essential

END consumables undergo rigorous formulations, developed to maintain their properties throughout use. However, factors such as humidity, temperature, and expiration date can compromise them.

• sensitivity in detecting discontinuities,
• contrast of the indications,
• chemical stability
• Repeatability of results .

When exposed to unsuitable conditions, they may:

• to crowd together,
• evaporate,
• change color, odor or viscosity,
• lose sensitivity,
• to generate false indications or mask real flaws.

A degraded product can alter the test results.

Effects of moisture on END consumables

Moisture is one of the main factors that affect the quality of consumables.
When present in excess, it can cause clumping of powdered consumables, changes in product characteristics,  affecting performance and sensitivity.

To avoid these effects, it is important to store the products in dry, well-ventilated places , protected from condensation and sudden temperature changes. In addition, it is recommended to keep the packaging tightly closed , especially in environments with high relative humidity.

Temperature and chemical stability

Temperature has a direct impact on the chemical stability of END consumables. Excessive heat
can alter pigments, cause the evaporation of volatile components, and compromise the performance of penetrants, developers, and magnetic suspensions.
Extreme cold, on the other hand, can cause the crystallization of components , rendering the product unusable.

To ensure optimal stability and sensitivity, it is recommended to store consumables as follows:

• In cool environments , with controlled temperatures between 5°C and 40°C;
• Keep away from heat sources, direct sunlight, and open flames;
• Avoid prolonged exposure to temperature variations.

Validity and usage control

Each consumable has an expiration date defined by the manufacturer , which must be strictly respected.
After this period, there is no guarantee of stability or performance — the product may show changes in color, odor, viscosity, or the formation of residues, indicating degradation of the active components.

In addition to the expiration date, it’s important to check:

• Storage conditions ;
• Label integrity and batch identification .

Good practice includes using the FIFO (first in, first out) principle , ensuring that older products are consumed before new ones.

Good storage practices

1. Store upright to prevent leaks or deformation of the packaging.
2. Avoid stacking cans or aerosols to prevent pressure damage.
3. Keep the products sealed until the moment of use.
4. Do not mix products from different manufacturers — chemical compatibility is not guaranteed.
5. Visually inspect the product before use: changes in appearance indicate loss of stability.
6. Use appropriate storage methods , keeping them away from electrical sources and intense heat.

These measures help preserve the original characteristics of END consumables and ensure testing with maximum repeatability and reliability.

Why follow these guidelines?

Following good storage and expiration date control practices reduces costs, avoids rework, and ensures the integrity of inspection results .
Proper preservation of END consumables is an essential part of quality management in industrial inspections , ensuring that each application maintains the expected performance standard from the first to the last use.

Properly storing and controlling END consumables is an investment in reliability, safety, and durability .
By maintaining ideal temperature, humidity, and shelf-life conditions, inspection ensures consistent results that comply with industry technical requirements.

The inspection begins long before the test is performed — it begins in the warehouse.

Metal-Chek provides complete solutions for Non-Destructive Testing: penetrant liquids, magnetic particles, developers and accessories , developed with cutting-edge technology to offer safety, precision and reliable results in every inspection.

○ Need technical support? Our Metal-Chek consultants are ready to help.

○ Keep learning: explore more technical articles about END on our blog .

○ Join the community of END inspectors and professionals — follow @metalchek .

The reliability of results in Non-Destructive Testing (END) depends directly on the chemical compatibility between the products used. Mixing penetrant liquids, removers, and developers from different manufacturers can compromise sensitivity, generate reading errors, and even invalidate the test.

To ensure consistent performance, traceability, and chemical stability at all stages, it is essential to use complete systems from a single manufacturer—such as the Metal-Chek line—always strictly following the manufacturer’s technical guidelines and applicable procedures.

The Importance of Chemical Compatibility in Non-Destructive Testing

In Non-Destructive Testing (END) , product compatibility is one of the most critical factors in ensuring accurate results.
In methods such as Liquid Penetrant Testing (LP) , each step— pre-cleaning, penetration, removal, and development —depends on a specific and controlled chemical formulation.

Mixing products from different manufacturers, even within the same category, can directly impact the sensitivity of the assay.

All materials used in an assay must be chemically compatible and, preferably, from the same manufacturer .
This standardization ensures the traceability , repeatability , and reliability of the results , as well as guaranteeing that the assembly was developed and tested to operate in chemical equilibrium under controlled conditions.

Risks of Mixing Different Products in Non-Destructive Testing

The use of penetrating fluids, removers, and developers of different brands or chemical compositions compromises the integrity of the process.
Among the main risks are:

• Loss of contrast between the background and the indications;
• Improper removal of the penetrant during cleaning;
• Unexpected chemical reactions between solvents, pigments, and additives;
• Forming false indications in reading;

These factors can lead to false results , rework, and delays, as well as jeopardize the reliability of the inspection and operational safety.

Metal-Chek Line for Liquid Penetrant Testing (LP)

The Metal-Chek line was developed to ensure complete chemical compatibility between all stages of the assay — pre-cleaning, penetration, removal, and development — guaranteeing stable performance, adequate sensitivity, and reproducible results in any industrial application.

Technical Compliance

Metal-Chek products are developed in accordance with applicable national and international standards and must be used in a compatible system by properly trained and qualified personnel .
The combined use of Metal-Chek products ensures uniformity of performance, traceability, and technical compliance , eliminating the risk of incompatibility between stages and guaranteeing accurate and reliable results .

Chemical compatibility is the key factor in ensuring the reliability of liquid penetrant testing.

Mixing products from different manufacturers compromises the chemical balance of the process and can lead to incorrect results, rework, and even inspection failures.

To ensure sensitivity, traceability, and performance in accordance with international standards, it is essential to use all products from the same system and manufacturer , strictly following the manufacturer’s guidelines and applicable procedures .

Compatibility equals reliability — use the complete Metal-Chek system and ensure accurate results.

Continue Learning with Metal-Chek

Explore other technical articles on our blog .Discover our complete line of LP and PM products, developed according to ASTM, ISO, ASME, NM and PETROBRAS standards.Talk to our technical consultants and find the ideal solution for your inspection process.Follow our Instagram page: @metalchek

In Liquid Penetrant Testing (LP), the developer plays an essential role: it is what makes the indications of discontinuities visible. Its function is to form a thin, uniform layer on the clean, dry surface, acting by reverse capillary action —promoting the return of the penetrant retained in the discontinuities to the surface, where the visible indication is formed for evaluation under white/visible light (for visible penetrants) or ultraviolet UV-A light (for fluorescent penetrants), allowing for a clear and reliable assessment.

More than just a product, the developer is a crucial factor in the sensitivity and reliability of the test. Therefore, understanding its variations and applications is fundamental for efficient inspection that complies with technical standards.

Types of Developer and Their Differences

Developers are classified according to their form , and the correct choice depends on the type of penetrant and the inspection environment.

The main categories are listed below:

1. Dry Developer

Dry developer consists of fine powder and forms a light, absorbent film. It is applied to the dry surface after the penetrant has been removed.

• Application: by immersion, dust chamber, electrostatic spray or spraying.
• Advantages: high sensitivity and solvent-free; ideal for fluorescent penetrants.
• Metal-Chek product: D72 Powder Developer , ready to use, non-flammable and easy to remove.

2. Aqueous Developer

Developer prepared in aqueous solution, which forms a uniform white film after drying.

• Application: by immersion or spraying.
• Advantages: homogeneous coverage, easy dispersion, and concentration control.
• Metal-Chek product: D76 Water-Soluble Developer , diluted from 15 to 60 g/L of water, indicated for use with fluorescent penetrants.

3. Non-Aqueous Developer

It consists of fine white particles suspended in solvent, forming an opaque, high-contrast white background . It is the most common type in the field, especially in visible penetrant inspections.

• Application: Apply in a thin, uniform layer by spraying (aerosol or compressed air gun).
• Advantages: quick drying, excellent contrast, and easy removal.
• Metal-Chek product: D70 Non-Aqueous Developer , available in bulk (5L) and D70 (HI) hydrocarbon propellant aerosol versions, both suitable for fluorescent and visible penetrants.
• Operating temperature: 10 to 52 °C.

Good Application Practices (for all types)

• Apply the developer in a thin, even layer , avoiding excess that could mask indications.
• Allow to dry  before inspection.
• Use products within their expiration date and store them according to temperature and ventilation recommendations.
• Inspect under adequate lighting — white light ≥ 1076 lux for visible penetrants or UV-A ≥ 1000 µW/cm² and ambient light ≤ 21 lux for fluorescent penetrants.

Technical Notice

This content is for educational purposes only.The selection of the developer type, application parameters, and operational precautions must follow a qualified procedure approved by a Level 3 Inspector .

Choosing the right developer directly impacts the sensitivity and reliability of penetrant testing.
Each type— dry , aqueous , or non-aqueous —has specific characteristics that must be selected according to the type of penetrant, the inspection conditions, and the required level of sensitivity. The correct choice enhances the quality of the END and ensures more accurate technical decisions.

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The solution for non-destructive testing.

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In industrial inspection, fluorescence in non-destructive testing (END) is a technology that significantly enhances sensitivity and visual accuracy.

Applied in methods such as Liquid Penetrant (LP) , Magnetic Particle (MP) , and Leak Detection (DV) , this technique allows for the identification of minute discontinuities and micro-leaks invisible to the naked eye. The result is greater safety, reliability, and operational performance.

What is fluorescence?

Fluorescence is an optical phenomenon in which certain substances absorb energy from ultraviolet (UV-A) light and re-emit it in the form of visible light .
In non-destructive testing (END), this physical principle is used to enhance the contrast of indications on metallic and non-metallic parts, facilitating the identification of surface or subsurface defects .

When UV-A light (365 nm) strikes the inspected material, the fluorescent particles or dyes react by emitting intense light—typically in shades of green, yellow, or orange. This makes discontinuities clearly visible , even in hard-to-reach areas.
The result is a highly sensitive , precise, and visually clear test that allows for quick and reliable decisions .

Applications of fluorescence in END methods

1. Liquid Penetrant Testing (LP)

The LP fluorescent (Type I) method is indicated for detecting surface-open discontinuities , such as cracks, pores, lack of fusion, and other defects that may compromise the integrity of a component.

After cleaning and applying the penetrant, the excess is removed and the developer is applied. Under UV-A light , the remaining liquid in the discontinuities emits intense fluorescence, clearly revealing the indications.

Among the main advantages is its versatility of application .
The method can be used on metallic and non-metallic materials , whether magnetic or non-magnetic , such as aluminum, magnesium, austenitic stainless steels, and titanium .
It can also be applied to ceramics, glass, and some types of plastics , provided they are non-porous materials .

Metal-Chek Products:

• FP-91 and FP-91 HI – Water-washable penetrants, Type I – Method A, Level 2, ideal for inspections requiring greater sensitivity.

Compatible with D70, D72 and D702 developers .

2. Magnetic Particle Testing (MPT)

In ferromagnetic materials, fluorescence enhances the detection of surface and subsurface discontinuities . Fluorescent magnetic particles
accumulate in regions where the magnetic field escapes, forming visible indications under UV-A light . For magnetic particle testing to be effective, it is essential that the part be magnetized . The application of a magnetic field —circular, longitudinal, or combined—creates magnetic flux lines in the material.

Metal -Chek offers the Supermagna Yoke HMM6 , an alternating current (AC) electromagnetic yoke developed for visible and fluorescent testing. The equipment provides a stable magnetic field and high mobility , making it widely used in industrial, petrochemical, and predictive maintenance inspections.

Metal-Chek Products:

• Supermagna LY 800 – High-sensitivity fluorescent dry-process magnetic particle.
• Supermagna LY 2000, LY 2000 V, LY 3000 and LY 3000 V – Wet-applied fluorescent magnetic powder particles, applicable with OMC 10 MMS (oil) or BC 502 SN + water vehicles .
• Supermagna CLY 2000 VO MMS BP / CLY 3000 O MMS BP / VO MMS BP – Ready-to-use wet (oil) baths with high mobility and contrast.
• Supermagna DLY 2000 – Water-dispersible wet magnetic particle.
• Supermagna CRL 265 AG/SN – Dual concentrate (fluorescent/visible), applicable under visible (white) or UV-A light in environments up to 1000 lx.

3. Leak Detection (Leak Testing)

In leak tests, fluorescent additives allow visualization of micro-leaks in hydraulic, pneumatic, and lubrication systems.
Under UV-A light, even the smallest leaks become visible, enabling immediate repairs and preventing critical failures .

Metal-Chek Products:

• Oil-Glo Ultra SPI Series
  • SPI-OGG (Green) , SPI-OGB (Blue) and SPI-OGW (White) — Fluorescent detectors for oily fluids.
  • Non-flammable, they do not alter the properties of fluids and are NSF certified .
• Water-Glo Ultra SPI Series – Green (WGG) and blue (WGB) fluorescent dyes for aqueous systems.

UV-A Lighting Equipment

For fluorescent testing, it is essential to use UV-A (365 nm) light sources with a minimum intensity of 1000 µW/cm² on the surface being examined, in accordance with END technical standards.
This intensity ensures adequate contrast and accurate reading of the indications.

Benefits of fluorescence in END

The correct application of fluorescence brings significant technical advantages:

• High visual sensitivity , revealing minute discontinuities.
• Greater contrast and clarity of the indications.
• Safe and versatile application in different methods and materials.
• Technical compliance with national and international standards.
• Reduction of rework and operational errors.

Furthermore, fluorescence improves the reliability of results and strengthens quality control in critical inspections.

Fluorescence in non-destructive testing is an essential technology that raises the standard of precision, safety, and reliability in industrial inspections.
By applying this technique in liquid penetrant testing (LP), mechanical testing (PM), and visual diffusion (DV) , enhanced visualization, high sensitivity, and immediate results are obtained , reducing failures and ensuring operational reliability.

With the complete Metal-Chek product line — which includes penetrants and fluorescent particles, leak detection additives, magnetization equipment, and UV-A illumination — your industrial inspection reaches new levels of quality and technical compliance .

See beyond the visible — Metal-Chek fluorescent technology.
Solutions for Non-Destructive Testing.

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In Magnetic Particle (MP) testing , the correct contrast between the surface and the magnetic particles is what guarantees the visibility of the indications and the accuracy of the results .
More than just a product, the Supermagna Contrast 104 Metal-Chek in Magnetic Particle Testing represents the practical application of the contrast concept in visible inspections, meeting the requirements of ASTM E709 , NM 342 and PETROBRAS N-1598 standards .

Function of Supermagna Contrast 104 in Magnetic Particle Testing

The Supermagna Contrast 104 in Magnetic Particle Testing functions to create a uniform white background on the surface of the part or inspection area, upon which colored magnetic particles (visible method, usually black or red) accumulate, making indications of discontinuities more visible under ambient light. The uniform white background increases the visual difference between the part and the particles accumulated over possible surface discontinuities.

Without adequate contrast, subtle indications may go unnoticed, reducing the sensitivity of the assay and compromising the reliability of the results.

In summary, the Supermagna Contrast 104:

• It forms a highly reflective white background , ideal for visible testing;
• It increases the optical contrast between the surface and magnetic particles;
• It facilitates the visual interpretation of the instructions by the inspector;
• It directly contributes to the reproducibility and standardization of PM tests.

When to use Supermagna Contrast 104

Supermagna Contrast 104 is indicated for colored magnetic particle testing (visible method) , conducted under visible illumination with a minimum intensity of 1076 lux , as established by ASTM E709 , NM 342 and PETROBRAS N-1598 standards .

Precautions when applying and removing

In order to guarantee optimal performance and avoid interference with the result, it is recommended:

1. Surface preparation

The area to be inspected must be dry, clean, and free of oil, grease, paint, or mill scale . Prior cleaning with E59 Metal-Chek
is recommended , ensuring a perfectly prepared surface to receive Supermagna Contrast 104.

2. Uniform application

Supermagna Contrast 104 should be applied in a thin, even layer , avoiding excess.
Very thick layers compromise the sensitivity of the assay.

3. Drying

Allow to dry completely before applying the magnetic particles.
The surface should have a uniform, matte, and non-reflective appearance .

4. Removal

After testing, Supermagna Contrast 104 can be removed with a remover such as E59 or TMC 10 Metal-Chek , ensuring thorough cleaning without damaging the surface.

Why choose the Supermagna Contrast 104 Metal-Chek?

The Supermagna Contrast 104 Metal-Chek was developed for professionals seeking precision and performance in magnetic particle testing.

Main benefits:

• High coverage and quick drying , optimizing inspection time;
• An adherent and uniform layer , respecting the thickness limits;
• Intense optical contrast that highlights even the smallest details;
• Compatible with Supermagna BW 333, RW 222, SBW 333/O, SRW 222/O and YD 404 colored magnetic particles .

Technical notice

This content is for educational purposes only. The application of the test methods and parameters must follow a qualified procedure approved by a Level 3 Inspector .

Metal-Chek Excellence

The Supermagna Contrast 104 is more than just a support product:
it is an essential technical element to guarantee quality, sensitivity, and safety in visible magnetic particle testing.

Using the Supermagna Contrast 104 Metal-Chek means investing in standard, precision and reliability , fundamental pillars for those seeking excellence in Non-Destructive Testing .

“Precision is visibility — ensure reliable results with the Supermagna Contrast 104 Metal-Chek.”

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