LEDs are favored over incandescent and fluorescent bulbs due adequate reliability and lesser safety concerns by general lighting industry. On the other hand, LEDs are used by the nondestructive testing community due to the special lighting conditions and exception caused by fluorescent methods such as liquid penetrant testing and magnetic particle inspection.

With enhancements in NDT passing through the decade and development in LED technology and its manufacturing, UV-A light sources are the perfect key for NDT professionals.

Flexibility is one of the reasons of LED technology used in NDT, therefore it means that more subtleties are required for the perfect presentation of nondestructive testing. In fluorescent penetrant or magnetic particle inspection a lamp is to be effective if the following characteristics are present.

1. PEAK WAVELENGTH AND EMISSION SPECTRUM:

Peak wavelength is the prime factor in choosing LED lamp for fluorescent inspection.

The formula for penetrants and magnetic particle materials was created and at that time the default UV-A source was mercury-vapor, which produces a single UV-A peak at 365.4 nm, the essential discharge line of mercury. Hence, all fluorescent penetrants and magnetic particle materials turn to fluorescent at 365.4 nm.

In LEDs, the peak wavelength is variable and is based on single LED used at the time of manufacturing of UV lamp. To ensure that the penetrant and magnetic particle inspection turn fluorescent with the use of LED UV-A lamp, the LED should have the peak wave length in the range of 360 – 370 nm.

LED has a broad UV-A emission spectrum than the mercury-vapor, therefore emission spectrum is also important. In LED UV-A lamp a deep violet glare is present at the end of the spectrum because it is in the visible light range of above 400 nm. Magnetic particle inspection and fluorescent penetrant are conducted in pitch black condition to strengthen contrast, visible light adulteration will corrupt inspection. For inspections to aerospace specifications, like ASTM E3022, Nadcap AC7114 and Rolls-Royce RRES 90061, this deep violet glare is inappropriate. In this case, any lamp used for aerospace inspection, such as EV6000, should have a UV-A pass filter to stop the visible emission.

Read more about why ASTM E3022 requires a UV-A pass filter.

 

2. BEAM PROFIL AND WORKING DISTANCE:

Lamps can be devised for several application and uses.

Lamps that are made for close-up inspection have a focused intense spot, but have a minor beam spot. The beam zone of a LED UV-A light is the proportion of how a lot of surface is over the base 1,000 µW/cm2 irradiance required for inspection. To accomplish a wide beam region, a variety of LEDs is required.

Area like holes, weld joints and internal surfaces have inspection done with LEDs that have small beam area. Therefore, when used on big surfaces, the small beam makes a “tunnel vision” and the crack/spots can easily slip from the inspector as the beam area is not covering the whole surface.

The lamp with large beam area will help in inspection of the whole surface. So, the it simplifies for the inspector pinpoint and deduce fluorescent indication in the area for closer inspection.

The operating range of an LED UV-A lamp is the least range needed 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 be performed only when the lamp is set at a significant distance than the working distance

Find LED UV lamps for nondestructive testing.

 

3. POWER SUPPLY:

LED UV-A lamp can work on low voltage and on battery power for several hours. This feature makes the lamp mobile and field inspectors can move swiftly.

In this case, there is a drawback of battery-powered lamps because LED intensity is directly connected to supply voltage and current. According the features of a battery, the voltage and current drops when it is used. With LED UV-A lamp, this decreases intensity in that time, dropping it below the minimum 1,000 µW/cm² requirements.

Improved lamps turn off immediately if the intensity goes below the required threshold of 1,000 µW/cm² because the have the constant-current circuits installed in it that keeps track of the intensity. This shows that power supply is also a key factor in UV-A LED lamps.

 

4. CERTIFICATION REQUIREMENTS:

Every industry has its own perquisites for NDT.

In aerospace NDT industry, both fluorescent penetrant and magnetic particle inspection have great requirements on all features of the process. A LED UV-A lamp that is confirmed by the manufacturer to ASTM E3022, similar to the EV6000 hand-held UV lamp, is acceptable for use by all aerospace primes and OEMs, and meets Nadcap audit criteria. Be that as it may, these prerequisites just apply to lamps utilized for final aerospace inspection. Lamps utilized somewhere else all the while, for example, penetrant wash or flush stations, typically don’t require full ASTM E3022 certification.

For non-aerospace industry like welding, energy, pipeline or field inspection have less certification requirements. Progressively rough industrial inspections are frequently done in under ideal conditions so increasingly extraordinary UV-A is expected to make fluorescent indications visible. Therefore, research have shown that UV-A intensities above 10,000 µW/cm² at 15 inches / 38 cm causes the vanish of fluorescent dyes and pigments.

A LED lamp for industrial applications, similar to the recently released EV6500 dual-light UV lamp, ought to incorporate a manufacturer’s certificate of conformance that incorporates the maximum UV-A power, regulated underneath 10,000 µW/cm2.