Koil Energy Solutions Inc. (KLNG)

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As early as the 1930s, the use of X ray began playing an important role in the nondestructive examination of welds. For the first years, fluorescent screens were used as a detector. It was common to use them without much protection since it had not yet been determined that X rays could impair or destroy living cells (Ref. 1). When the health effects of X rays were realized, the use of radiographic films that require exposure and developing became the norm for industrial X ray. The same basic method has now been used in industry for more than 65 years.
Around 1950, the image intensifier was first introduced to the medical field and shortly thereafter also proved valuable for some industrial applications, particularly when moving (real-time) images are useful. Low-resolution linear detector arrays (LDA) were also developed to inspect parts that were continuously moving such as in the field of baggage inspection. While image intensifiers and other nonfilm methods of using X ray have now been used in many industrial applications, the vast majority of X-ray inspections continue to be done with film.


The use of X-ray film carries with it a number of limitations, including the cost and shelf life of the film and chemicals needed to develop it. Darkrooms with processing tanks and tools are required to be near the inspection site and must be stocked and maintained. Film requires taking the exposure with a technique developed through trial and error. There is always a delay between the exposure and the viewing of results, often requiring a series of adjustments to the technique and several revisits to the location for reshooting the exposure.
As various alternatives to X-ray with film have emerged, each has had its own limitations. As with film, most nonfilm alternatives have a fixed format size that is often larger or smaller than the application requires. Typically, nonfilm systems are expensive and lack the portability and durability that many industrial applications demand. Some nonfilm technologies cannot withstand continued use in radiation environments without damage to or eventual degradation of the image quality. Most nonfilm systems are somewhat fragile and temperature sensitive, making their use under typical industrial field conditions difficult and sometimes impossible.

In recent years, other nondestructive methods have been developed to compete with X ray in some weld inspection applications. In particular, advances have been made in ultrasonic equipment and methods; however, X ray continues to offer advantages in that it can detect some types of weld defects that ultrasonics cannot.

In recent years, also, increased emphasis on environmental safety, including concerns for the effects of radiation on workers and the requirement for disposal of the chemicals used to process film, have contributed to the growing need to replace conventional X ray inspections involving long film exposures.

With competition from other inspection methods and the inherent difficulties of conventional X-ray film processing, the X ray method for weld inspection has come to face an uncertain future.

Benefits of CMOS Systems
Enter CMOS (complementary metal oxide semiconductors). In 1995, a small group of NASA engineers invented a way to utilize the same electronic microchip technology used in computer memory to sense light. This discovery paved the way for CMOS detectors for use in digital cameras, document imagers, camcorders, and X-ray detectors.


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Fig. 2 - A CMOS scanner being used on a 48-in. pipeline weld.
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X-ray detectors using these new CMOS sensors have now been developed for the nondestructive examination industry, offering significant benefits over other nonfilm X-ray technologies and avoiding many of the limitations of both film and non-film inspection systems.
Most importantly, an industrial inspection system must be durable and, often, portable. These requirements have been hard to meet with nonfilm X-ray systems until recently. CMOS detector chips are constructed from a metal oxide silicon material making them tolerant to mechanical shock and temperature changes. CMOS detectors take advantage of a new development in electronic chip architecture - thin film transistors (TFT). This TFT architecture means most of the electronics needed to support the detector are located on a microscopic level within the detector. Thus, TFT allows imaging systems made from CMOS to be much more compact and durable than were previous technologies.

These new sensors can be produced in a large range of sizes allowing X-ray detecting panels and line arrays to be matched to the format of the object to be inspected. Imaging sizes from 1 in. C 1 in. to more than 6 ft C 8 ft are now available, overcoming the size limitations of film and other nonfilm alternatives - Fig. 1.

Paralleling the advances that have been made in digital cameras, digital X-ray detectors have improved dramatically in image resolution. In many cases, CMOS X-ray imaging systems can now meet and exceed the resolution provided by X-ray film (see lead photo). This increase in resolution overcomes a significant limitation of previous nonfilm systems. When needed, X-ray sources with microfocus beams can now be used to discover defects of less than 10 microns (0.0003 in.) in size. Rather than using an optical magnifier to view film, the operator simply zooms in on the area of interest to any level desired on the computer display. Like a digital photo camera, the resolution of the X-ray image can be selected by the operator, allowing the image file size to be no larger than necessary, and for the inspection speed to be optimized.

Cost savings from replacing film-based inspection processes with digital systems can be dramatic because consumables are no longer required. CMOS detectors are less expensive to produce than other detectors made from such materials as amorphous silicon or amorphous selenium, allowing the inspection system to cost less to manufacture and repair.

The up-front cost of a CMOS digital system is typically one half to two thirds the cost of earlier nonfilm systems. The up-front cost is often recovered in less than six months through the avoidance of consumables alone. Additional savings are realized through the reduced time required to perform the inspection, lack of need for reshoots, and reduced personnel costs.


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Fig. 3 - A CMOS girth weld scanner.
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Radiation safety for the radiographer and other workers has also been improved through the use of digital X-ray detectors. Because these digital sensors are far more efficient at capturing radiation than film, the exposure time required for most applications is shortened dramatically. Less exposure time means less radiation dosage to the personnel in the area, and faster inspection times. In some applications, CMOS detectors can be used to capture X-ray images in just a fraction of a second, creating so little radiation exposure that it is virtually immeasurable using conventional radiation monitoring devices.
The Future
CMOS systems are now being applied to a broad range of X-ray applications including inspection of pipeline welds during new construction (Figs. 2, 3), tubing welds, castings, agricultural products, medical devices, electronics assemblies, tires, wheels, and many other industrial uses. Because of the advances made in sensitivity, portability, format options, and resolution, these systems can now be used where film and nonfilm X ray were losing out to other inspection methods.

Now, the outlook for X ray is bright. One of the oldest methods in nondestructive testing has found a new life in the future of industrial inspection.

References
1. History of X-ray. YXLON International, Inc., Akron, Ohio. Used with permission.

http://www.aws.org/itrends/06-03/feature.html