Tag Penetrant Liquid

In industrial processes where inspection reliability is essential, the choice of penetrant makes all the difference. Metal-Chek FP 91 was developed for water-washable fluorescent penetrant testing, offering clear indications, intense fluorescence, and easy removal – characteristics that directly contribute to more productive and safer inspections.

Classified as Type I, Method A, Level 2, FP 91 is a medium-sensitivity, water-washable fluorescent penetrant, indicated for the detection of surface discontinuities in non-porous materials that require greater sensitivity in the test. Its inspection should be carried out with 365 nm UV-A light, according to the product’s technical instructions.

High sensitivity for more visible indications.

One of the main advantages of FP 91 is its ability to generate sharper indications with an intense fluorescent yellow-green color. In practice, this facilitates the visualization of discontinuities during inspection, especially in controlled environments with adequate lighting, even when using the developer-free technique.

This high detection capability is crucial in applications where small surface flaws can compromise the quality, safety, or performance of the inspected component.

Low background fluorescence: more contrast during inspection.

In addition to the intensity of the indications, the FP 91 exhibits low background fluorescence. This difference contributes to better contrast between the inspected area and any indications, reducing visual interference and facilitating a clearer reading by the inspector.

In fluorescent assays, this point is especially important, as a surface with excessive background can hinder the correct identification of discontinuities.

Washable with water and easy to remove.

FP 91 belongs to Method A, meaning it is a water-washable penetrant. This makes the process of removing excess more practical, as it can be done with a water spray or with clean, dry cloths that are then slightly moistened, according to the technical procedure.

The ease of removal helps optimize the inspection process, maintaining efficiency without compromising test quality. The description also provides guidance on how to avoid excessive washing, preserving the indication of potential defects.

Versatile application in different materials and processes.

The Metal-Chek FP 91 can be used in a wide variety of industrial applications, including materials testing:

• forged;
• laminates;
• fused;
• welds;
• manufacturing steps;
• Maintenance of assembled sets or components.

It can also be applied to ferrous and non-ferrous metals, non-porous ceramics, glass and various types of plastics, provided that the surface is within the temperature range indicated for the test, between 10 °C and 52 °C.

Low material consumption

FP 91 also stands out for its low material consumption, related to less drag during the process and excellent wetting. This factor can contribute to greater product utilization, especially in industrial routines with a high frequency of inspections.

Aerosol version FP 91 HI: practical application.

In addition to larger volume packaging, FP 91 is also available in an aerosol version with hydrocarbon propellant, FP 91 HI. This option is suitable for spray applications, offering practicality for spot inspections, maintenance, and situations where the use of portable packaging facilitates fieldwork.

The aerosol version retains the product’s main characteristics: intense fluorescence, easy removal with water, low background fluorescence, and clear indication of surface discontinuities.

Compliance with recognized standards and specifications.

Another important distinguishing feature of the FP 91 is its compliance with specifications widely used in the industrial market. The product meets requirements such as:

AMS 2644, ISO 3452-2, ASTM E-1417, ASTM E-165, ASME Section V Article 6, PETROBRAS N-2370 and N-1596.

This set of specifications reinforces the suitability of the FP 91 for applications in industrial environments that require technical control, standardization, and traceability of inspection processes.

How does FP 91 contribute to more efficient inspections?

By combining high fluorescent intensity, low background fluorescence, ease of removal, and good durability of indications, FP 91 contributes to a more efficient and reliable assay.

Among the main advantages of the product, the following stand out:

Greater clarity of indications, facilitating the identification of surface discontinuities;

Better visual contrast, due to low background fluorescence;

It is easy to operate because it is washable with water;

Versatile application, in different materials and industrial stages;

Low consumption, contributing to better product utilization;

Aerosol option, ideal for practical and localized applications;

Compliance with technical standards is important for qualified industrial processes.

Metal-Chek FP 91 is an efficient solution for fluorescent penetrant testing on non-porous materials requiring higher sensitivity. Its high revelation capacity, combined with ease of removal and low background fluorescence, makes it an excellent choice for industrial inspections demanding clarity, productivity, and reliability.

For best results, use should follow the applicable inspection procedure, with a properly cleaned surface, adequate penetration time, controlled removal of excess, uniform application of the developer, and inspection under appropriate light intensity.

Excellence in products for those seeking reliable results.

Metal-Chek provides complete solutions for Non-Destructive Testing: penetrant liquids, removers, developers, lighting fixtures 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 our  technical consultants  and find the ideal solution for your process.

Visit our  blog  and check out other technical content.

Discover our complete product line.

Follow Metal-Chek on Instagram, YouTube, Facebook , and LinkedIn.

The reliability of a liquid penetrant test is directly related to the sensitivity of the inspection system, that is, its ability to detect discontinuities of different dimensions.

To guarantee this performance, international standards establish the use of standardized reference blocks, used for sensitivity verification and quality control of the test.

Among these standards, ISO 3452-3 Type I stands out.

What is the ISO 3452-3 Type I standard?

ISO 3452-3 defines requirements for reference blocks used in liquid penetrant testing.

The Type I  standard consists of a metal plate with controlled artificial cracks, used to evaluate the performance of the penetrating system.

This pattern allows you to verify:

• the sensitivity of the assay
• the ability to reveal the indications
• the performance of the system composed of penetrant, remover and developer

Applications of the JIS standard

The ISO 3452-3 Type I standard is primarily used in two situations:

1) Materials acceptance test

Allows you to check the performance of new batches of:

• penetrants
• removers
• developers

This control ensures that the materials meet the expected level of sensitivity.

2) Verification of the test’s sensitivity

Used to confirm that the inspection system maintains adequate performance throughout its use.

JIS Standard Types

The patterns are available with different levels of depth:

• 10 µm
• 20 µm
• 30 µm
• 50 µm

The selection of the standard must be aligned with the level of sensitivity required by the application or as defined in a qualified procedure approved by a Level III inspector.

Relationship to the type of penetrant

The choice of pattern should take into account the type of penetrant used:

• Fluorescent penetrants (Type I)
→ higher sensitivity, typically evaluated with 10 µm or 20 µm standards
• Visible penetrants (Type II)
→ lower sensitivity, typically evaluated with 30 µm or 50 µm standards

This relationship allows for a correct evaluation of the performance of penetrant materials.

Importance of sensitivity control

Verifying sensitivity is essential to ensure the reliability of the test.

The absence of this control can result in:

• Failure to detect relevant discontinuities
• Inconsistency in results
• Loss of process reliability

The use of reference standards allows for the validation of system performance and maintains the repeatability of inspections.

The use of the ISO 3452-3 Type I standard is an essential practice for verifying performance in Liquid Penetrant (LP) testing.

The correct application of these standards contributes to the reliability of the process, meeting regulatory requirements and ensuring the quality of the inspections performed.

Excellence in products for those seeking reliable results.

Metal-Chek provides complete solutions for Non-Destructive Testing: penetrant liquids, removers, developers, lighting fixtures 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 our technical consultants and find the ideal solution for your process.

Visit our  blog  and check out other technical content.

Discover our complete product line.

Follow Metal-Chek on Instagram, YouTube, Facebook , and LinkedIn.

In critical industrial applications, especially those involving materials such as austenitic stainless steels, nickel-based alloys, and titanium, liquid penetrant testing requires not only sensitivity but also rigorous contaminant control.

The presence of elements such as sulfur, chlorine, and fluorine can compromise the integrity of the inspected material.

In this context, ASME BPVC Section V – Article 6, Appendix II establishes specific requirements for controlling these contaminants in the materials used in the test.

ASME V Requirements Art. 6 – Appendix II

Appendix II defines criteria for controlling contaminants in materials used in liquid penetrant testing, especially in sensitive materials.

Normal:

• For nickel-based alloys, the sulfur content must be controlled.
• For austenitic, duplex, and titanium stainless steels, chlorine and fluorine must be controlled.
• The maximum permitted limit for these contaminants is 0.1% by weight.

Furthermore, the standard establishes that:

• Penetrant materials must be analyzed by batch.
• Results must be documented and certificates of analysis issued.
• Certificates must contain batch identification and test results.

Importance of contaminant control

Controlling these elements is essential to avoid undesirable effects during and after the inspection.

Among the main risks associated with the presence of contaminants are:

• Stress corrosion;
• Alteration of material properties
• Surface contamination
• Non-compliance with regulatory requirements

These factors can compromise both the integrity of the component and the validity of the inspection performed.

Critical applications

Contaminant control is particularly relevant in sectors where structural integrity is critical, such as:

• Oil and gas industry
• Aeronautical sector
• Nuclear industry
• Boilers and pressure vessels

Certification and traceability

The standard requires that the materials used in the test have certification with batch traceability.

This documentation should include:

• Results of chemical analyses
• Product batch identification
• Proof of compliance with established limits

Proper selection of consumables

The choice of materials used in liquid penetrant testing should consider not only performance but also compliance with regulatory requirements.

This includes:

• penetrants
• removers
• developers

Using products with contaminant control and proper certification contributes to:

• Preserve the integrity of the inspected material
• Meet regulatory requirements
• Ensure consistency in results

Metal-Chek supplies consumables for liquid penetrant testing developed according to international standards, with contaminant control and batch traceability.

Final considerations

Meeting the requirements of ASME V Art. 6 Appendix II is fundamental in applications involving materials that require contaminant control.

Contaminant control should be considered an integral part of the inspection process, contributing to the safety, reliability, and technical compliance of the tests performed.

Excellence in products for those seeking reliable results.

Metal -Chek provides complete solutions for Non-Destructive Testing: penetrant liquids, magnetic particles, removers, developers, lighting fixtures 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 our  technical consultants  and find the ideal solution for your process.

Visit our  blog  and check out other technical content.

Discover our complete product line.

Follow Metal-Chek on  Instagram ,  Facebook  , and  LinkedIn.

Every day, thousands of industrial structures, equipment, and components operate under severe conditions of pressure, temperature, and mechanical stress.

During manufacturing or throughout the lifespan of these materials, discontinuities can arise and, if not identified in time, can evolve into critical failures, directly impacting safety, operation, and industrial costs.

It is in this scenario that the Non-Destructive Testing (END) Inspector assumes an essential role.

Celebrated on March 27th, Non-Destructive Testing Inspector Day recognizes the importance of this professional who works on the front lines of failure prevention and industrial reliability.

What are Non-Destructive Tests (END)?

Non-Destructive Testing (END) methods are inspection methods used to evaluate materials, components, and structures without causing damage to the parts being analyzed.

These techniques allow for the identification of surface and subsurface discontinuities that can compromise structural integrity, directly contributing to the operational safety and reliability of industrial processes.

They are widely used in activities such as:

• Manufacturing of industrial components
• Weld inspection
• Preventive and predictive maintenance
• Quality control
• Structural integrity assessment

By enabling the early detection of discontinuities, END prevents unexpected failures, reduces operating costs, and increases the safety of operations.

The role of the END Inspector in industrial reliability

The END inspector is the professional responsible for performing, evaluating, and recording the results of inspections carried out using these methods.

Their role requires technical knowledge, mastery of applicable standards, and an understanding of inspection procedures.

Among their main responsibilities are:

• Evaluate the condition of materials and components
• Identify relevant discontinuities
• Interpret indications obtained during inspection
• Record results with technical accuracy
• Ensure compliance with standards and specifications

More than just performing tests, the inspector is responsible for ensuring the reliability of the results, a crucial factor for industrial safety.

Main Non-Destructive Testing methods used in industry

Several methods comprise Non-Destructive Testing. Among the most widely used are Liquid Penetrant Testing (LP) and Magnetic Particle Testing (MP).

Penetrant Testing (PT)

Liquid penetrant testing is used to identify surface discontinuities in non-porous materials.

The method consists of applying a highly penetrating liquid to the surface of the part. After an appropriate interval, the excess is removed and a developer is applied, allowing the indications to be visualized.

It is widely used in the inspection of:

• welding
• machined parts
• cast components
• metallic and non-metallic surfaces

Magnetic Particle Testing (MPT)

Magnetic particle testing is applied to ferromagnetic materials and allows the identification of surface or near-surface discontinuities.

During the test, the part is magnetized and particles are applied. In the presence of discontinuities, magnetic flux leakage occurs, forming visible indications.

It is used in the inspection of:

• welds
• shafts
• gears
• structural components
• parts subjected to mechanical stress

A fast, efficient method that is widely used in the industry.

Qualification and technical responsibility in END testing

Non-destructive testing (END) is not limited to the execution of the method; it also involves the correct interpretation of the observed indications.

Therefore, inspections must follow specific technical standards and procedures defined for each application.

The acceptance criteria, parameters, and procedures are established according to applicable standards and internal procedures of each company, under the responsibility of professionals qualified in the method.

The reliability of the results depends directly on three factors:

• Qualification of professionals
• Correct application of methods
• Proper use of materials and equipment

The role of Non-Destructive Testing in industrial maintenance

Non-destructive testing plays a strategic role in preventive and predictive maintenance, allowing the monitoring of component condition throughout their service life.

With this, it is possible to:

• Plan interventions in advance
• Avoid unexpected failures
• Reduce operating costs
• Increase equipment reliability

Applications of Non-Destructive Testing in major industrial sectors

Non-destructive testing is fundamental in various industrial sectors, especially where structural integrity is critical.

Among the main sectors are:

• Oil and gas industry
• Aeronautical sector
• Automotive industry
• Power generation
• Metal construction
• Industrial maintenance

In these environments, inspection directly contributes to ensuring the integrity of equipment, structures, and operational systems.

The importance of Non-Destructive Testing for industrial safety

Non-destructive testing is an essential part of modern industry, contributing to process reliability and operational safety.

By identifying discontinuities before they develop into critical failures, these methods ensure greater control over the integrity of equipment and structures.

On this Non-Destructive Testing Inspector Day, we reinforce the importance of the professionals who work on the front lines of inspection, ensuring that technical standards and quality criteria are met in every evaluation performed.

Excellence in products for those seeking reliable results

Metal-Chek provides complete solutions for Non-Destructive Testing: penetrant liquids, removers, developers, lighting fixtures 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 our  technical consultants  and find the ideal solution for your process.

Visit our  blog  and check out other technical content.

Discover our complete product line.

Follow Metal-Chek on Instagram, Facebook , and LinkedIn.

Aviation is one of the most stringent industrial sectors when it comes to operational safety. Aircraft are designed to operate under severe conditions of load, vibration, pressure variations, and continuous cycles of structural fatigue over thousands of flight hours.

To ensure that all components maintain their structural integrity over time, the aeronautical industry relies heavily on Non-Destructive Testing (END) .

More than just a verification step, ENDs (Non-Destructive Tests) are part of aviation safety culture. From the manufacturing of structures and components to maintenance programs throughout the aircraft’s lifespan, thousands of inspections are carried out to identify potential discontinuities before they evolve into critical failures.

Every safe flight depends on a series of technical inspections that ensure the structural reliability of the aircraft.

Non-Destructive Testing in the Aeronautical Industry

Non-destructive testing methods are used to evaluate the integrity of materials and components without compromising their future use.

In the aeronautical industry, different methods are applied as required by the aircraft manufacturer’s manual. Among the methods used are:
ultrasound
, radiography
, eddy currents
, liquid penetrant testing
, and magnetic particles.

Each method has a specific function within the inspection programs applied in the manufacturing and maintenance of aircraft.

Among these methods, fluorescent penetrant testing and fluorescent magnetic particle testing are widely used for the detection of discontinuities.

Technical rigor and materials control in aviation

The aeronautical sector adopts extremely rigorous criteria for the products used in inspection processes.

For example, the penetrating materials used in these processes must be qualified in the QPL — Qualified Products List.

Only listed materials may be used in certain aircraft inspection processes, ensuring standardization, traceability, and reliability in the results obtained.

Fluorescent penetrant liquid in aircraft inspection

Fluorescent liquid penetrant testing is widely used in the aeronautical industry to identify extremely fine surface discontinuities.

The method is based on the phenomenon of capillarity, allowing the penetrant to penetrate cracks or discontinuities open to the surface. After removing the excess and applying the developer, the retained penetrant returns to the surface, forming indications observed under ultraviolet illumination.

For aeronautical applications, the penetrants, removers, emulsifiers, and developers used must be properly qualified according to the applicable QPL list.

Metal-Chek offers the Sherwin Dubl-Chek line in Brazil, consisting of penetrant testing systems developed to meet the technical requirements of the aeronautical sector.

Fluorescent magnetic particles in ferromagnetic components

Magnetic particle testing is used to inspect components made from ferromagnetic materials.

The method involves magnetizing the component. When there is a surface discontinuity or a discontinuity near the surface, a distortion occurs in the magnetic field, forming a leakage field that attracts the magnetic particles applied to the part.

In the aeronautical industry, the test is typically performed using fluorescent magnetic particles in an oil-based liquid suspension, which provides greater sensitivity in the formation of indications.

In the context of the Metal-Chek line, fluorescent magnetic particles can be used in the aeronautical sector when applied in oil-based suspension, using the Supermagna OMC 10 MMS vehicle .

This combination allows for the proper formation of the suspension for application of the method, in accordance with the technical requirements adopted in aeronautical inspections.

Inspections throughout the aircraft’s lifespan

Non-destructive testing inspections are not limited to aircraft manufacturing.
These methods are part of ongoing maintenance and structural monitoring programs. Throughout the aircraft’s lifespan, components are periodically inspected to identify potential discontinuities caused by:
• structural fatigue
• repetitive load cycles
• vibration
• thermal variations
• severe operating conditions

This continuous monitoring allows for the identification of potentially critical conditions before they evolve into structural failures.

Air safety built into every inspection

Modern aviation safety is the result of a combination of advanced engineering, rigorous procedures, and reliable inspections.

Non-destructive testing is an essential part of this system, allowing the structural integrity of components to be evaluated without compromising their use.

Each inspection performed represents another level of assurance in the integrity of the aircraft, directly contributing to the safety of passengers, crews, and air operations worldwide.

Excellence in products for those seeking reliable results

Metal-Chek provides complete solutions for Non-Destructive Testing, with products developed according to the main ASTM, ISO, ASME, NM and PETROBRAS standards.

Among its solutions are systems for liquid penetrant testing, magnetic particles, and various consumables used in industrial inspections, contributing to consistent results, operational safety, and technical reliability.

Speak with our  technical consultants  and find the ideal solution for your process.

Visit our  blog  and check out other technical content.

Discover our complete product line.

Follow Metal-Chek on Instagram, Facebook , and LinkedIn.

In an industrial setting, Quality Control is responsible for ensuring that products and processes meet established technical, regulatory, and contractual requirements.

Non-Destructive Testing (END) is an integral part of this Quality Control system. It consists of technical tools used to verify the integrity of materials and components without compromising their future use.

However, in many industrial environments, there is a disconnect between operations and the Quality or END departments.

On one side, those who execute.
On the other, those who inspect.

When this relationship is misunderstood, the perception arises that inspection exists only to point out flaws or interrupt the process. This view generates internal noise and weakens the quality culture.

Operation and END are not competitors. They operate at different stages of the same objective: ensuring the technical conformity and reliability of the final product .

The role of the operation in process integrity

Execution is the foundation of any industrial result.

It is the operational team that applies procedures, controls parameters, performs welding, assembly, and adjustments that determine the component’s performance.

Quality begins in the production process. When execution is consistent and aligned with technical requirements, inspection tends to confirm this conformity.

The operation, therefore, is not merely an executor; it is an active part of the quality control system.

The role of END in technical verification

Non-destructive testing serves to verify whether a product meets integrity criteria.

END does not create discontinuities.
It evaluates what is already present in the material or what is inherent to the manufacturing process.

When a relevant indication is identified, the objective is technical: to prevent an unsuitable condition from progressing in the process or reaching the customer.

Internal inspection reduces major risks, avoids external impacts, and preserves the integrity of the production system.

When conflict arises

Disagreements between operation and quality often arise when inspection is perceived as an obstacle to the pace of production.

However, a nonconformity identified internally represents an opportunity for controlled correction. Conversely, a failure detected externally can compromise contracts, schedules, reputation, and operational safety.

END acts as a validation step within the production flow, not as a barrier, but as a mechanism for technical verification.

When operations and END work as partners

Mature industrial environments exhibit clear characteristics:

• The operational team understands the acceptance criteria applicable to the process;
• The inspector understands the variables and limitations of the production process;
• There is objective technical communication;
• Adjustments are treated as process improvements, not as personal conflicts.

When integration exists:

✔ Rework decreases
✔ Process predictability increases
✔ Approval rate improves
✔ Trust between departments is strengthened

Inspection is now recognized as part of the quality workflow, and not as an impediment.

Quality culture: shared responsibility

Quality is not exclusive to the END sector.

It involves planning, execution, verification, and continuous improvement. When everyone understands their role within the system, the environment becomes more collaborative and technically consistent.

A strong quality culture reduces costs and improves performance indicators in a sustainable way.

Procedures and products as elements of stability

The partnership between operations and END also depends on a solid technical foundation:

• clear and well-defined procedures;
• objective acceptance criteria;
• Standardization of inspection methods;
• Reliable and consistent inspection products.

When parameters are clearly defined and the products used deliver consistent, specification-compliant performance, the process becomes more stable and technically reliable. Consistency in results strengthens trust between departments.

Operation and Non-Destructive Testing operate at different stages of the process, but share the same purpose: to ensure that the delivered product conforms to integrity requirements.

Overcoming the idea that the quality sector is merely a “pointer of errors” is essential to consolidating more mature, cooperative, and efficient industrial environments.

When execution and verification work in an integrated way, the result is a more stable, safe, and reliable production system.

Excellence in products for those seeking reliable results.

Metal-Chek provides complete solutions for Non-Destructive Testing, with products developed according to the main ASTM, ISO, ASME, NM and PETROBRAS standards, contributing to consistent and technically reliable inspections.

– Read more technical content about END on our blog
– Follow Metal-Chek on Instagram: @metalchek and on LinkedIn

Non-Destructive Testing (END) plays a fundamental role in industry. Far beyond a technical inspection step, END is a strategic tool that directly contributes to product quality , operational safety , cost reduction , and the preservation of life .

In an increasingly demanding industrial environment, where failures can result in accidents, unscheduled downtime, and significant financial losses, END (Non-Destructive Testing) acts preventively, allowing the identification of discontinuities before they evolve into critical failures. This control impacts the entire organization, from the purchasing department to senior management, strengthening the industry as a whole.

Non-Destructive Testing: More than inspection, an industrial strategy

Non-destructive testing comprises a set of inspection methods used to assess the integrity of materials, components, and structures without compromising their future use.

Methods such as Liquid Penetrant Testing (LP) , Magnetic Particle Testing (MP) , and Leak Detection are widely applied in manufacturing, maintenance, and operational inspections. They allow for the early identification of discontinuities, defects, or inadequate conditions, ensuring greater reliability in industrial processes. When correctly specified and executed, END ceases to be merely a regulatory requirement and becomes an instrument for quality and risk management .

Strengthening industry and preserving life

One of the main pillars of Non-Destructive Testing is safety. The integrity of equipment, structures, and components is directly related to the protection of people, the environment, and industrial assets.

Undetected defects can result in serious accidents, leaks, structural collapses, and operational interruptions. END (Non-Destructive Testing) acts preventively, significantly reducing these risks by identifying discontinuities in their early stages.

By investing in reliable inspections and appropriate END products, industry strengthens its operations, increases the reliability of its assets, and plays an essential role in preserving life .

Cost reduction and impact on the company’s financial health

Although often viewed merely as an operational cost, Non-Destructive Testing, in practice, represents an investment with a measurable return.

Early fault detection prevents:

• unscheduled stops;
• rework and scrapping;
• catastrophic failures;
• Accidents with human, environmental, and financial impact.

When compared to the cost of an operational failure, the investment in END (Non-Destructive Testing) and quality products becomes small. Companies that adopt routine inspections and structured END programs show greater cost predictability and better financial health over time.

END as a quality inspection and routine tool

Non-destructive testing is widely used as a quality control tool, both in production processes and in maintenance programs.

They act at different times:

• Raw material inspection;
• welding process control;
• verification of manufactured components;
• periodic maintenance inspections.

Routine END inspection demonstrates industrial maturity, enabling traceability, standardization, and compliance with technical standards and contractual requirements. In this way, END directly contributes to the final quality of the product delivered to the customer.

How a quality product in END impacts the entire company

Choosing the right products for Non-Destructive Testing goes far beyond the technical aspects. A low-quality END product can generate hidden costs and compromise the entire inspection system.

The impact is reflected in various sectors of the company:

Purchases and acquisitions

Reliable products reduce rework, internal complaints, and performance variations, facilitating standardization and supplier management.

Maintenance

Consistent results allow for more accurate diagnoses, avoiding unnecessary interventions or recurring errors.

Quality

Reliable testing reduces nonconformities, unwarranted rejections, and increases the credibility of inspection results.

Facilities and operation

The reliability of END (Non-Destructive Testing) ensures operational continuity, safety, and a longer lifespan for assets.

Board of Directors and Management

Risk reduction, cost predictability, and preserving the company’s image directly impact strategic decisions.

Financial health: Fewer failures, fewer accidents, and fewer stoppages result in greater operational efficiency and business sustainability.

Non-Destructive Testing Solutions as a Reliability Factor

For END (Non-Destructive Testing) to fulfill its strategic role, the correct combination of the following is fundamental:

• appropriate test method;
• qualified and approved technical procedure;
• qualified professionals;
• Products developed in accordance with applicable technical standards.

Reliable END solutions contribute to consistent results, operational safety, and regulatory compliance, strengthening the entire industrial chain.

Final considerations

Non-destructive testing is an invisible pillar of modern industry. It protects people, ensures the integrity of assets, reduces costs, and sustains the quality of products and processes.

Companies that view END (Non-Destructive Testing) merely as an obligation miss the opportunity to use it as a strategic tool for management, safety, and sustainability . Conversely, those that invest in reliable inspections, quality products, and technical expertise strengthen their operations and build a legacy of industrial excellence.

Excellence in products for those seeking reliable results

Metal-Chek provides complete solutions for Non-Destructive Testing , with products developed according to the main ASTM, ISO, ASME, NM and PETROBRAS standards, contributing to the quality, safety and reliability of industrial inspections.

👉 Access our blog and check out various technical content about END
👉 Follow Metal-Chek on Instagram: @metalchek and on LinkedIn

In Liquid Penetrant (LP) testing, each step directly influences the effectiveness of the test. After proper surface preparation and adherence to the correct penetration time, the removal of excess penetrant liquid plays a critical role in the inspection process.

Improper removal can mask relevant discontinuities, generate false indications, or hinder the correct interpretation of results. Therefore, this step must be performed with the same technical rigor as the other phases of the test, always in accordance with the qualified and approved technical procedure.

This article discusses the importance of removing excess penetrant fluid, the main errors associated with this step, and its direct impact on the reliability of the liquid penetrant test.

The role of excess removal in the LP assay

The principle of the Liquid Penetrant test is based on capillarity, which allows the penetrant to penetrate discontinuities open to the surface.

After the penetration time, the excess liquid present on the surface must be removed, leaving only the penetrant retained within the discontinuities. This condition is essential for the developer to act correctly, promoting the reverse capillary effect of the penetrant and the formation of visible or fluorescent indications.

Improper removal compromises this balance and directly affects the formation and clarity of the indications.

What characterizes proper removal of excess?

Proper removal of excess penetrant fluid must meet the following criteria:

• to remove the penetrant from the surface without removing it from inside the discontinuities;
• to preserve the sensitivity of the method;
• to enable reliable visual interpretation.

These criteria are not universal and depend on factors such as:

applicable technical procedure.

type of penetrant (visible or fluorescent);

specified removal method;

surface condition;

Methods for removing excess penetrant fluid

Methods for removing excess penetrant may vary depending on the type of penetrant and the application.

Among the most commonly used methods are:

• removal with solvent  (remover);
• removal with water (spray jet);

The choice of method should take into account its compatibility with the penetrant used.

Main mistakes in removing excess penetrant

Excess removal is one of the steps where the most frequent errors occur in the liquid penetrant testing method. Among the main errors are:

Excessive removal

Excessive application of solvent or mechanical action from an intense water jet can remove the penetrant retained in the discontinuities, resulting in:

• loss of relevant indicators;
• reduction in assay sensitivity;

Insufficient removal

Incomplete removal of excess residue leaves it on the surface, promoting:

• difficulty of interpretation;
• emergence of false or irrelevant indications.

Impact of improper removal on the interpretation of indications

The visual interpretation of the indications depends directly on the quality of the excess removal.

When this step is not performed correctly, the following may occur:

• blurred or fuzzy indications;
• difficulty in distinguishing relevant from irrelevant indications;
• Increased risk of improper rejections or undetected failures.

These effects directly impact the reliability of the inspection and technical decision-making.

Metal-Chek solutions for removing excess penetrant

Metal-Chek offers a complete line of removers developed specifically for Penetrant Testing, ensuring efficient and controlled removal of excess product.

These solutions are designed for:

• to preserve the penetrant retained in the discontinuities;
• Avoid blotchy or fluorescent backgrounds;
• ensure compatibility with different LP methods;
• to meet the requirements of the main applicable technical standards.

The choice of the appropriate remover should always take into account the technical procedure and inspection conditions.

Final considerations

Removing excess penetrant fluid is not a secondary step in the test—it is a determining factor in its effectiveness.

When performed correctly, according to a qualified and approved technical procedure, this step ensures:

• proper training of the indications;
• reliable visual interpretation;
• Reducing errors and rework;
• Greater safety during inspection.

In liquid penetrant testing, precision and control at each stage are fundamental to ensuring consistent and technically reliable results.

Excellence in products for those seeking reliable results

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

• Read more technical content on our blog.
• Follow Metal-Chek on Instagram: @metalchek
• Speak with the  Metal-Chek team  and learn about our solutions for non-destructive testing.

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.

Access other technical articles.

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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.