Predicting maintenance with NDT

June 30, 2010
Sheila Kennedy, contributing editor, says examine the integrity of an object, material or system without harming it.

The findings you get from nondestructive testing (NDT) allow maintenance to be predictive, which can be more cost-effective and safer than interval-based or break/fix approaches. Some of the more recent innovations in NDT incorporate electromagnetic, radiographic, ultrasound or thermographic technologies. Following are a few examples.

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Electromagnetic induction: Wire ropes, the workhorse in cranes and other hoisting equipment, are subject to tension, bending, abrasion, corrosion and other conditions that affect their safety and useful life. Visual inspections are unable to detect damage, flaws or other problems in the inner and outer wires and strands, or the inner rope core. Rope replacements that occur at predetermined intervals, regardless of condition, might be too late to prevent an accident or too early to provide a cost benefit.

A proprietary NDT method developed by Konecranes uses electromagnetic-inductive technology to determine the working condition of wire ropes. RopeQ NDT uses permanent magnets to induce a magnetic flux. Once the tool is fastened to wire rope assemblies, it records a series of interior images along the length of the rope. Rope faults cause discontinuities to the measured signal, and the generated diagnostic survey data specifies the locations and degrees of degradation.

Computed and digital radiography: A new NDT option available for inspecting welds on small-diameter steel pipe uses computed radiography to produce digital images from phosphor imaging plates. A computed-radiography reader scans the plate with a laser beam, releasing information as visible light, which is then converted into a digital image. The technology is quicker and consumes less energy and space than industrial x-ray films, which require chemical processing in darkrooms and climate-controlled storage environments for the images.

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A portable computed-radiography scanner from GE Sensing and Inspection Technologies is the first to be qualified and validated by Petrobras to inspect steel pipe as large as 3.5 inches. The CR 50P is capable of scanning different imaging plate formats and sizes, and there’s no wait time between scans because the phosphor imaging plates can be fed simultaneously and continuously, producing a separate image for each plate.

A faster alternative than both computed and film radiography is digital radiography. Like the others, it produces a radiograph to examine an object’s volume for changes, defects or other details, but the digital method reduces radiation exposure time and allows instant image review through a laptop. GE Sensing and Inspection Technologies’ new DXR250V is a compact, portable direct-radiography x-ray detector that provides instant images with GE’s Rhythm software. The 13-pound digital tool makes radiographic NDT accessible to a wider range of applications than previously possible.

Ultrasonic imaging: The introduction of ultrasound imaging cameras, particularly ultra-small, video-style cameras, is making waves. Ultrasound NDT systems send sound waves into an object to analyze subsurface features and faults, such as voids, cracks, delaminations and corrosion. Imperium’s Acoustocam ultrasound video imaging system is powered by the company’s Digital Acoustic Video (DAV) technology. After applying an ultrasound gel to the inspection area, place the Acoustocam probe on the area to capture the x-ray-type video. The image can be viewed and shared in real time over a wireless communication network.

The company’s i600 model was recently introduced as the world’s smallest handheld ultrasound imaging camera for real-time and remote diagnostic inspection. It’s half the size and a third the weight of its predecessor, the i500, and is suitable for inspecting materials such as composites, metals, plastics and microelectronics.

Infrared thermography: Thermography-based NDT methods remotely analyze temperature variations to detect problems in materials or components. A new Line Scanning Thermography (LST) technology from Mistras Group replaces conventional spot ultrasonic readings with infrared automated thickness imaging. The new approach allows large areas of metallic and advanced composite materials to be scanned at a rate of as much as three inches per second.

With LST, large areas of a boiler, for instance, can be mapped, and then as the infrared camera and heat source move across the inspection area, the camera images a region of the sample in real time. By comparison, with conventional flash or pulsed thermography, a large sample can be analyzed only in sections as the surface is heated by a brief light pulse.

E-mail Contributing Editor Sheila Kennedy, managing director of Additive Communications, at [email protected].

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