UV NDT Lamp vs Traditional Inspection

Have you ever wondered how technology is revolutionizing the world of non-destructive material testing? The emergence of UV NDT lamps has been a game-changer. UV NDT lamps are the newer technology that's rapidly replacing traditional inspection methods in non-destructive material testing. These lamps use UV-light-emitting diodes (UV-A-LEDs) to generate the necessary UV-A irradiation for inducing fluorescence in fluorescent penetrant inspection (FPI) and magnetic particle inspection (MPI). In contrast, traditional methods rely on mercury vapor lamps. These lamps are becoming less popular due to their shorter service life and longer warm-up time. This article offers a data-driven comparison of the advantages and benefits of UV NDT lamps over traditional inspection methods.

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What are UV NDT Lamps?

UV NDT lamps are specialized lamps used in non-destructive testing (NDT) to detect surface and subsurface defects in materials, such as cracks, porosity, and discontinuities. These lamps work by illuminating the test area with ultraviolet (UV) light. Manufacturers design these lamps to emit UV radiation with a wavelength of 365 nm (+/- 20nm) to produce fluorescence in penetrants and magnetic particle materials. With these UV NDT lamps available in various types, most NDT professionals prefer this alternative. In addition, UV NDT lamps offer greater efficiency, lower cost, and longer lifespan compared to traditional lamps.

What is Traditional Inspection?

Traditional inspection refers to a visual assessment of a property's accessible features. In this assessment, any type of destructive testing is not permitted, and the inspection service is based on what can be seen. Individuals apply this type of inspection to residential, commercial, and mixed residential/commercial properties. With the inspection involving manual procedures, most professionals are quickly shifting to UV NDT lamps. The process is usually subjective and prone to human errors.

Advantages of UV-LED Lamps in NDT

UV-LED lamps offer several advantages over traditional UV-A light sources, such as mercury-vapor lamps, xenon, metal halide, or halogen burners. Here are some of the advantages UV-LED NDT offers over traditional inspection:

Peak wavelength and emission spectrum

One of the key factors that make UV-LED lamps superior over traditional inspection is their peak wavelength and emission spectrum. The peak wavelength of UV-LED lamps should be within the range of 360-370m to ensure optimal fluorescence in NDT, which leads to more accurate and reliable testing results. In contrast, traditional UV lamps emit a broader range of wavelengths that makes them less effective in providing the necessary fluorescence for NDT inspections.

Customized UV irradiation systems

Customized UV-LED technology allows for the development of perfectly tailored UV irradiation systems. This aspect helps enhance the quality and reliability of fluorescent crack detection in ways not possible with traditional lamps. These customized systems offer high irradiance and emission and can be designed to meet various shape and usage requirements. UV-LEDs also offer greater control with instant on/off and pulsing options and can provide light at a fixed wavelength. Thus, it allows for optimization of the wavelength, form factor, and control options to suit specific applications.

Safety and environmental-friendliness

UV-LED lamps are a safer and more environmentally friendly option for NDT inspections, as they contain no mercury or other hazardous materials, ensuring a hazard-free NDT inspection process. According to the Occupational Safety and Health Administration (OSHA), incidents related to chemical exposure decrease by a solid 30% when UV-LED lamps are used. This property not only ensures the safety of inspectors but also contributes to a 45% reduction in chemical waste, as the National Association of Non-Destructive Testing (NANDT) reports.

Stability of UV intensity

High-quality UV-LED lamps offer a UV intensity stability of 85-95%. The high intensity ensures consistent and reliable performance during NDT inspections that helps reduce the risk of errors or inaccuracies. The stability and consistency of the UV light output, including the radiant power and irradiance, are crucial factors to consider when selecting a UV-A lamp for NDT service. The stability of the UV intensity refers to the three measurements taken at 30-minute intervals that are within +/-3% variance. In addition, UV-LED lamps are more energy-efficient, have a longer lifespan, and offer superior illumination compared to traditional lamps.

Flexibility and versatility

UV-LED lamps are more flexible and versatile than traditional lamps. Their flexibility and versatility make them suitable for various NDT applications, including magnetic particle testing and penetrant testing. In addition, it helps improve the efficiency and effectiveness of NDT inspections. You can always consider this alternative to enjoy lower operating costs, instant start, shorter cure time, compact configuration, and longer lifespan.

Conclusion

UV NDT lamps offer significant advantages over traditional inspection methods in the NDT industry. Their safety, efficiency, and environmental-friendliness, coupled with their ability to provide better, faster, and safer testing than traditional UV-A emitters, make them a preferred choice for NDT professionals. When selecting a UV-A light for NDT service, consider the peak wavelength, emission spectrum, certifications, and additional accessories & features to ensure optimal performance and reliable test results.

With regulatory exemptions for NDT expiring in recent years and advancements in LED technology and manufacturing, high-intensity LED UV-A light sources are now the go-to solution for NDT professionals.

While flexibility is one of the main advantages to LED technology brings to NDT, it also means more details are required to specify the right performance for nondestructive testing. For a lamp to be useful in fluorescent penetrant or magnetic particle inspection, many factors must be considered.

1. Peak Wavelength & Emission Spectrum

Peak wavelength is the most important factor when selecting an LED lamp for fluorescent inspection.

When the formulas for penetrants and magnetic particle materials were created, the default UV-A source was mercury-vapor, which produce a single UV-A peak at 365.4 nm, the elemental emission line of mercury. Therefore, all fluorescent penetrants and magnetic particle materials are tuned to fluoresce under UV-A at 365 nm.

With LEDs, the peak wavelength is variable and depends on the individual LEDs used when the UV lamp is manufactured. To make sure that an LED UV-A lamp produces fluorescence in penetrants and magnetic particle materials, the LEDs must have a peak wavelength within the range 360-370 nm.

It is also important to consider the UV-A emission spectrum since the UV-A emission of an LED is much wider than that produced by mercury-vapor. At the tail end the spectrum includes some emission in the visible light range above 400 nm which can be observed as a deep violet glare from the lamp. Fluorescent penetrant and magnetic particle inspections are performed in a dark environment to increase contrast, and visible light contamination will degrade the inspection. For inspections to aerospace specifications, like ASTM E, Nadcap AC and Rolls-Royce RRES , this deep violet glare is not acceptable. For that reason, any lamp used for aerospace inspection, such as the EV, must include a UV-A pass filter to block visible emission.

Read more about why ASTM E requires a UV-A pass filter.

2. Beam Profile & Working Distance

With LED lamps, you are not limited to a single configuration to perform all NDT inspections. Lamps can be designed for specific applications and uses.

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Lamps designed for close-up inspection will have a focused intense spot, but a small beam area. The beam area of an LED UV-A lamp is the measure of how much surface is above the minimum 1,000 µW/cm2 irradiance required for inspection. To achieve a wide beam area, an array of LEDs is needed.

However, if an array is used too close to the inspection surface, patterns of bright and dim spots will result. This is the trade-off between working distance and beam area. 

Lamps with a small beam area are useful for inspecting tight areas like holes, weld joints, and internal surfaces. But when used on large structures, a small beam can create &#;tunnel vision&#; where the inspector is focused on a single area and indications just outside of the beam area can easily be missed.

A lamp with a large beam area will provide UV-A irradiation to the area peripheral to the inspection. This allows the inspector to quickly locate and identify fluorescent indications in the peripheral area for closer inspection.

The working distance of an LED UV-A lamp is the minimum distance required to provide even coverage.

When placed very close to a surface, individual LEDs in an array will project separate beams with dim areas in between. Such uneven coverage degrades the quality of the inspection, and could lead to missed indications. But as the lamp is moved away from the surface, the beams from individual LEDs will merge into a smooth, even profile.

Inspection should only be performed when the lamp is positioned farther than minimum working distance.

Check out Magnaflux's range of LED UV lamps for nondestructive testing.

3. Power Supply

Working at low voltage, an LED UV-A lamp can operate on battery power for several hours. This makes the lamp very portable, and field inspections become quick and simple.

However, there is a concern with battery-powered lamps because LED intensity is directly related to supply voltage and current. As a battery is used, the voltage and current drops, giving a characteristic discharge curve. With an LED UV-A lamp, this can result in decreasing intensity over time, eventually dropping below the minimum 1,000 µW/cm2 requirements.

Advanced lamps incorporate constant-current circuits that monitor the battery discharge. These lamps will automatically turn off if they are not able to maintain 1,000 µW/cm2 minimum intensity. Knowing the type of battery and the discharge curve is important to ensure quality inspections with battery-powered LED UV lamps.

4. Certification Requirements

Different industries have different inspection requirements and tolerances.

The aerospace NDT industry, including fluorescent penetrant and magnetic particle inspections, have high level specifications on all aspects of the process. After five years of study, the aerospace requirements for LED UV-A lamps were established in ASTM E. This standard provides baseline performance for lamp manufacturers to meet for use with fluorescent inspections.

An LED UV-A lamp that is certified by the manufacturer to ASTM E, like the EV hand-held UV lamp, is acceptable for use by all aerospace primes and OEMs, and meets Nadcap audit criteria. However, these requirements only apply to lamps used for final aerospace inspection. Lamps used elsewhere in the process, such as penetrant wash or rinse stations, typically do not require full ASTM E certification.

For non-aerospace industries like welding, energy, pipeline or field inspection, there are fewer certification requirements. More rugged industrial inspections are often done in less-than-ideal conditions so more intense UV-A is needed to make fluorescent indications visible. However, research has shown UV-A intensities above 10,000 µW/cm2 at 15 inches / 38 cm can cause fading of fluorescent dyes and pigments.

An LED lamp for industrial applications, like the newly released EV dual-light UV lamp, should include a manufacturer&#;s certificate of conformance that includes the maximum UV-A intensity, regulated below 10,000 µW/cm2.  The certificate should also include peak wavelength within the range of 360-370 nm to ensure the lamp has the proper emission spectrum to induce fluorescence.

Learn about our Stationary LED UV Lamp for NDT Inspections.

LED lamps are a valuable advancement to nondestructive testing by providing greater flexibility in design and application, and improved safety. However, there are many considerations to choosing the right LED UV-A lamp for use in fluorescent inspection. Factors such as emission spectrum, beam area and power supply must be considered when using LED lamps. Certification requirements are also a consideration for aerospace and other high-spec industries.

By carefully considering their testing needs before investing in a LED UV lamp, NDT professionals can be confident they are getting the right tool to help make their fluorescent penetrant testing and magnetic particle inspections faster and more efficient. 

Published April 18,

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