nondestructive inspection
EWI is at the forefront of advanced nondestructive inspection techniques.
Ultrasonic Testing
Ultrasonic testing uses high frequency sound waves (>20,000 Hz) to characterize the properties of and detect defects in materials. Sound waves, generated by a piezoelectric transducer, travel through the material. At interfaces such as the back surface or internal defects, sound is reflected back to the transducer where it is received so that it may be evaluated.
Ultrasonic testing is used for inspecting a wide range of materials ranging from thick to thin section welds as well as composite structures and adhesively bonded structures. The method is particularly sensitive to lamination and linear type defects. In addition, the method is routinely used for thickness measurements and corrosion mapping.
At EWI, we have field portable, digital flaw detectors as well as a C-scan system with both large (4x3x1 ft.) and small (6x12x8 in.) immersion tanks.
We have developed or are in the process of developing ultrasonic inspection procedures for a variety of components including:
- Gas pipelines
- Spot welds
- Packaging
- Adhesively bonded joints
- Airbag inflators
Phased Array Ultrasonic Inspection
Phased array techniques make use of an array of several ultrasonic transducers that can be configured in a variety of shapes. The main advantage of this advanced NDE technology is the ability to steer the ultrasonic beam electronically and focus the beam on specific areas within the item being inspected. This provides for faster and more complete scanning of objects with higher sensitivities than with conventional ultrasonics inspection techniques.
Eddy Current Testing
Eddy current testing is a method based on the principles of electromagnetic induction. The method is used to detect surface and near-surface discontinuities, detect changes in material properties, measure electrical conductivity and magnetic permeability, and measure thickness of nonconductive and conductive coatings. The method does not require direct contact with the part being inspected, thus it is truly a nondestructive inspection technique.
A changing magnetic field is generated when an alternating current is passed through a coil. If that coil is placed near a conductive material, the magnetic field causes eddy currents to flow. Eddy currents are affected by the physical and electrical properties of the material. An eddy current instrument senses the resulting changes in the coil’s impedance and displays these changes in a manner that allows an inspector to infer information about the properties and condition of the material.
Conventional and advanced eddy current instruments and probes are used for numerous applications including:
• Surface and subsurface (some limitations apply) flaw detection in nonferromagnetic (e.g. aluminum, stainless steel, inconel and titanium) and magnetic (e.g. carbon and duplex steel) materials
• Weld inspection of nonferromagnetic and magnetic welds.
• Coating and sheet material thickness measurements.
• Metal sorting and conductive material characterization as a function of heat treatment, chemical composition, metallurgical phase content (e.g. ferrite content in duplex stainless steel), fatigue, shot peening and other metal treatments that affect electrical conductivity and magnetic permeability.
• Direct electrical conductivity measurement of nonferromagnetic metals.
EWI has conventional and advanced multipurpose eddy current instruments and probes to address all major applications with little or more customization for the specific task:
Advanced Eddy Current Inspection
New array eddy current technology provides a more intuitive and efficient way to interpret representation of inspection data (C-scan and Isometric view). It is also possible to scan the metal surface and volume using several frequencies simultaneously. Various configurations of active sensor-array groups can be used to improve flaw detection and material property characterization. Multi-frequency scans are extremely useful for examination of heat treatment, structure variations through metal volume (e.g. strain hardening or surfaced stresses), sheet thickness profiling and others. Multi-parameter data is acquired and processed in short period of time and with a minimal number of scans.
Recently, EWI acquired advanced multipurpose array eddy current instrumentation with array and single probes and scanner for flat and curved surfaces. In addition to array- and single-probe eddy current techniques, this instrument can also perform remote field eddy current (RFET) and magnetic flux leakage (MFL) inspections.
Over a period of several years, EWI developed advanced capabilities in computer modeling and simulation of eddy current techniques. Modeling of eddy current inspections for research and practical purposes is strongly supported through analytical and finite-element modeling software packages. Complex inspection areas such as ferromagnetic material (carbon steel) with aluminum alloy coating and multilayer fastener structure have been successfully modeled for the purpose of eddy current surface and subsurface inspections. Simultaneous measurement of metal electrical conductivity and magnetic permeability is also conducted through model optimization.
Radiography
Radiography uses differential absorption of radiation penetrating a test object coupled with recording of an image on film to detect features of the test object that exhibit a difference in thickness or physical density as compared to the surrounding material. The rule of thumb with radiography is that features that exhibit a 1% or more difference in absorption compared to the surrounding material can be detected.
At EWI, we often use conventional radiography (using either an X-ray or gamma ray sources) for our customer’s applications. We also use advanced radiography techniques such as microfocus X-ray when inspecting small joints such as those produced by EWI’s microjoining team.
Magnetic Particle Testing
Magnetic particle testing detects surface and near surface defects in ferromagnetic materials only. Defects in magnetized material will distort the magnetic field causing a “leakage field”. When fine ferromagnetic particles are applied to the surface, they concentrate at the defect by getting caught in the leakage field.
Liquid Penetrant Testing
Liquid penetrant testing is a nondestructive method used to detect surface breaking defects in any nonporous material. Liquid penetrant is applied to the surface and is drawn into defects by capillary action. Once a preset dwell time has passed, excess penetrant is removed and developer applied to draw out penetrant from defects. Visual inspection is then performed.
At EWI, we routinely perform both visible dye and fluorescent dye penetrant inspections.
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Nondestructive
