Non-destructive testing (NDT) can be simplistically described as a method used to conduct an inspection without moving or breaking the item or surrounding area under examination. Although not limited to medicine, aerospace, and industry, these three large sectors are particularly dependent on non-destructive inspection methodologies. One of the most helpful tools for NDT is the Ultraviolet (UV) lamp. Let’s take a brief look at the presence of UV lamps in NDT settings.
Non-destructive testing is a broad field
The definition of NDT can be quite broad unless one limits its description to a test, evaluation, or inspection, in a particular field of engineering or medicine. As well, the type of inspection that is required also comes from a long list of possibilities.
Fluorescent Magnetic Particle Inspection (FMPI or MT) and Fluorescent Penetrant Inspection (FPI or PT) are strongly associated with the use of fluorescent lighting and NDT.
Let the light come in
UV light is longer than X-rays, and shorter than visible white light, placing it into the 10 to 400 nm wavelength range. Known as black light, non-visible UV light can be harmful. The shorter UV-C rays, up to 290 nm, however, rarely reach the earth, and this is fortunate. Also be wary of UV-B rays, which are responsible for sunburns. The longer rays of UV-A, between 320 and 400 nm, are the least dangerous to humans.
In the past, magnetic particle penetrants used a mercury base, which became fluorescent with a UV-A light of 365.4 nm. This led to the requirement of today’s UV light sources for NDT. The standard requirement for a peak wavelength is between 360 – 370 mm.
The UV lamp advantage
One aspect of UV lighting that gives it the edge is that it provides visibility into the area under inspection where otherwise, there is none. The magnetic particles or penetrants that are applied to the surfaces of the areas to be inspected become fluorescent, providing visibility into the tiniest of flaws, such as cracks, breaks, and positioning changes.
What to look for in a UV lamp
There are UV lamps and then there are UV lamps. To achieve the most efficient, successful, and safe examinations, it is important to choose the correct UV lamp for the task at hand.
LED illumination
UV LED lamps are highly recommended for non-destructive testing. In fact, for the most part, LED lamps have replaced incandescent and fluorescent lamps, which may not be easily available in the near future.
However, some legacy UV lamps can be modified to accept LED bulbs. UV LED lamps are lighter, making them very manageable. The bulbs are long-lasting, not prone to fading, and can be housed in cooler casings.
Handheld or stationary
The advantage of handheld UV LED lamps is, of course, their portability and their low energy consumption. However, unlike their predecessors, the mercury vapor bulbs, they do not offer the intensity and the wide beams that are required in some inspections.
Meeting the challenge, some UV lamp producers are using LED lighting to create stationary overhead lamps with intense, wide beam coverage, and adaptable frames, allowing easy vigilance over production in assembly lines. This is a low-cost alternative to frequently-replaced fluorescent bulbs.
The importance of a filter
With a peak wavelength between 360 – 370 nm, violet tail emissions of visible light above 400 nm can mask flaws and cracks with light glare. A filter improves visibility by providing more contrast.
Additional considerations
Science and engineering are always in flux. Similarly, developments in the field of non-destructive testing brings with it much to consider.
- With the introduction of LED bulbs in UV light sources, dangers resulting from potential accidents in non-invasive fault-seeking, are no longer concerns. Burns resulting from filaments in mercury vapor are becoming a thing of the past. With less electrical demands from LED bulbs, power supplies can be lightweight, making the lamp easier to handle in tough conditions.
- Just the fact that mercury will no longer be needed is enough of a cause for celebration.
- Visibility with LED lamps is instantaneous.
- For some conditions, a narrower beam is required. NDT requirements must lead the way when determining the lamp’s specifications for a particular type of inspection.
- One challenge that designers are working on is the emission of heat flux at the emitters of UV LED lamps. This is a result of smaller technology with increased energy levels.
Non-destructive testing has broadened its scope over the years, giving rise to compliance standards for specific NDT applications. The most well-known compliance standard to look for in UV-A lamps for NDT with FMPI and FPI, is the ASTM E3022 standard. Whatever the standards of compliance are for a particular industry, non-destructive testing and its reliance on dependable lighting for inspections, is now an important branch of engineering in its own right.
