More manufacturers are turning to nondestructive testing and evaluation methods to meet the challenges created by increasingly complex machinery designs and greater demand for component reliability, according to two recently released studies.

The average manufacturer now spends more than $67,000 annually on NDT equipment and services, according to a new study released by Quality magazine, and conducted by BNP Market Research Division (Troy, MI).

According to the survey, a Nondestructive Testing Study, in which more than 1,000 quality professionals were polled and 262 responded, more than one-fourth of respondents spend between $10,000 and $50,000 on NDT equipment and services annually, and 16% spend $100,000 or more. Of the types of nondestructive testing performed by respondents, the vast majority-78%-perform visual and optical testing; 45% perform liquid-penetrant testing and 43% perform leak tests.

More than one-third of respondents are from companies that manufacture fabricated metal products. Other industries represented include electric and electronic equipment (21% of respondents), transportation equipment (15%), primary metal industries (14%), rubber and miscellaneous plastic products (8%), nonelectronic machinery (5%), and instruments and related products (2%).

"Nondestructive tests help detect variations in structure, physical discontinuities, dimensions, metrology, and the physical and mechanical properties of materials," says Leo O'Connor, research director for Technical Insights, a division of consulting firm Frost & Sullivan (San Jose, CA), who released an analysis of the NDT market in May. "These tests also help check their composition, chemical analysis and, most importantly, stress and dynamic response."

New products

New types and uses of products are cited as reasons for the increased use of NDT technology. According to the Frost & Sullivan study, the rising cost of advanced materials has necessitated a reduction in the size and weight of components while increasing the workload on them. NDT improves safety levels by helping develop

damage-tolerant designs.

As a part of a safe-life design, sophisticated techniques using ultrasonics, eddy currents, X-rays, dye penetrants, magnetic particles and other forms of interrogating energy are used to detect and remove components with macroscopic structure defects from service.

"Today, quantitative descriptions of NDT performance, such as the probability of detection, are integral to statistical risk assessment," O'Connor says. "NDT is an accepted failure-related engineering discipline, and rapid advances in digitization and computing are changing data-processing capabilities."

By far, the most popular testing devices are microscopes and thickness gages, with 74% of respondents in the Quality survey using microscopes and 70% using thickness gages. Other popular equipment includes dye penetrant inspection (46%), X-rays (28%), magnetic particle inspection (28%) and eddy current testing (27%).

Making waves

One technology making significant strides is ultrasonics. Quality-control practitioners have long relied on ultrasonic techniques as a way to nondestructively gage the thickness of manufacturing materials. In the early days, these measurements often required a series of complex calculations by the users of ultrasonic measuring devices. But in recent years, miniaturization in digital computing power has led to portable, user-friendly ultrasonic instruments that allow near-instantaneous readings of material thickness, while also providing on-board data-logging and networking capabilities.

Now the field of ultrasonic NDT is taking another step. Because of advances in digital-signal processing software, new portable ultrasonic devices are emerging that can-for the first time-provide simultaneous thickness measurements of multiple material layers in a test piece. Additional advances enable precise gaging of extremely thin multilayers not previously measurable by ultrasonic instrumentation.

These capabilities are being developed to meet quality control needs for a growing range of manufactured products and components. As a result, ultrasonic thickness gaging is likely to find increasing application on the factory floor by industries ranging from automotive and aerospace to appliances, packaging and pharmaceuticals.

Conventional ultrasonic thickness gaging works by measuring the round-trip transit time of a high-frequency sound pulse as it travels through a material. An ultrasonic transducer that generates bursts of sound energy is coupled to one side of the test piece. Sound waves traveling through the material reflect off the far side and return to the transducer. The gage precisely measures how long it takes for the echo to return, and then, using programmed information on the speed of sound in the test material, it calculates and displays the thickness of the part.

This approach works well in the majority of gaging applications involving common engineering metals, plastics and ceramics, as well as in rubber, fiberglass, composites, and even liquid and biological materials. However, in a growing number of cases, manufacturing quality control requires measurement of thin material layers that cannot be read by conventional ultrasonic gages. It is in these cases that newly developed approaches involving frequency-domain analysis or use of high-test frequencies may offer a convenient solution.

Other NDT systems gaining in popularity include leak testing and eddy-current testing. Leak testing is a form of NDT that finds leak sites and measures the quantity of material passing through these sites. When testing a part with pressure and performing a pressure decay test, it is referred to as pressurizing the part. When testing a part with a vacuum and performing a vacuum-decay test, it is referred to as evacuating the part.

Eddy-current testing relies on a probe with an electrical-test coil that produces alternating magnetic fields. When the probe is moved close to an electrically conductive material to be tested, the probe induces circulating electrical currents, or eddy currents, within the test piece. The eddy currents in turn create magnetic fields that interfere with the magnetic field of the coil, changing its electrical signal. Interruptions in the eddy current flow caused by imperfections such as cracks in the test piece can then be detected with instrumentation that monitors the test-coil electrical signal.

Moving forward

New applications for quantitative nondestructive evaluation (QNDE) are being explored to improve the productivity of manufacturing processes. QNDE can improve productivity by reducing the development cycle time and creating in-line measurements for process control.

The engineering applications of NDE are increasing throughout the product lifecycle. Globalization is leading to the development of uniform practices and, as a result, emphasis is expected to increase on NDE standards, enhance educational offerings and simulations that can be communicated electronically.

"As technologies improve, service requirements increase and machines are subjected to wider extremes of all kinds of stress," O'Connor says. "NDT will prove crucial in developing stronger materials." NDT