Inspection methods Eddy current

General corrosion control, prevention, and monitoring should be planned for from the onset. To detect and monitor corrosion, various methods must be used, while corrosion protection would be done by the addition of inhibition and use of protection coatings [5]. Visual examination, laser methods, the replication microscopy liquid penetration testing method, magnetic particles testing, the eddy current inspection method, acoustic emission technique, thermal methods of inspection, and nondestructive methods are the various methods to be adopted when monitoring pipeline corrosion [5]. 

Eddy Current Inspection Eddy current inspection is the most widely used of several methods of discontinuity detection for electrically conductive ferromagnetic and nonferromagnetic materials. Both surface and subsurface discontinuities can be detected. 

Eddy current inspection is typically performed in metallic components for cracks or thickness inspections. The method uses a changing magnetic field to create eddy currents in the substrate under test. Those eddy currents create a secondary field back in the eddy current coil. Changes in the substrate that affect the eddy current flow will alter the secondary electromagnetic fields and therefore affect the originating coil... 

Simple shapes such as small-diameter tubing can be tested very rapidly by eddy-current methods. Such methods have been developed and used at ORNL to identify and sort various metals, to determine the thickness of clad or plated layers, to make rapid dimensional measurements of tubing, and to detect flaws in thin metal sections. Because of the large number of ariables which affect eddy-current inspections, the results of these tests must be very carefully evaluated [147]. 

In the intervening years mueh excellent analytical work has been done by Libby, Lord, Dodd, Deeds, Palanisamy and many others which has given us a practical method of understanding eddy current behavior in many applications including nuclear inspection and aerospace where problems of safety and reliability have become so important to us all. 

Progress in mean of modelisation and inverse problem solving [1] let us hope to dispose soon of these tools for flaws 3D imaging in Non Destructive Control with eddy current sensors. This will achieve a real improvement of the actual methods, mainly based upon signature analysis. But the actual eddy current probes used for steam generators tubes inspection in nuclear industry do not produce the adequate measurements and/or are not modelisable. 

When comparing the magnetic particle- and penetrant inspection with other visual methods it appears that our viewing eonditions are not so bad, compared with other methods. In radio-graphie the contrast on the film is mueh lower. In ultrasonies and eddy current the presentation times on the screen is shorter and the contrast is lower. 

Our inspection method is based on an encircling Eddy current coil measuring the structural integrity of the rod, and 8 pancake coils positioned on a typical place over the rods diameter. One inspection block consists of 4 to 6 probe assemblies. 

Sample scan data is a good way to archive the results of an inspection. The inspection could be re-visited later to see how the eddy-current response has changed over time. Random audits of the quality of inspection detection could be monitored. The inspection could also be reviewed if new information becomes known, say from inspection conducted using alternate methods. 

Eddy currents The examination of non-ferrous tubing using external coils is a well-tried and successful inspection technique, owing mainly to the pioneering work of Forster in Germany. The adoption of this method for in-situ inspection of condenser tubes, by mounting eddy-current coils in probes (or bobbins) that can be inserted in condenser tubes, was a logical development of the technique. Suitable apparatus was developed in the immediate post-war period more or less independently by several oil and chemical companies. The principle of operation has been described in the literature... 

The Dow Freeport in-service inspection procedures are similar to those reported earlier in this chapter. The Dow out-of-service (internal) inspection includes ultrasonic thickness measurements at all benchmark locations. Other test methods include shear wave ultrasonics, eddy current, and radiography. Engineers use ultrasonic thickness readings to project the remaining useful life of the vessel and to determine when the next internal inspection should be scheduled. 

Dingwall, P. F., and Mead, D. L. (1976), Non-destructive inspection and volume fraction determination of CFRP using an eddy current method, June 1976, Dept, of Defence, Report RAE-TR-76078. 

Electromagnetic methods such as eddy current, capacitance, microwaves, and terahertz radiation are not traditional inspection methods for composites, but they can be used in some circumstances [36]. Microwaves (300 MHz—300 GHz, 1000—1 mm) and terahertz (300 GHz—3 THz, 1—0.1 mm) are applicable to fiberglass composite inspection and have been successful at the detection of damage and internal features [37—45]. However, electromagnetic radiation at these wavelengths does not penetrate conductive materials. For CFRP, which is mildly conductive, they are only useful for sensing very near the surface. Capacitance measurements can be used to measure dielectric property changes in composites such as moisture uptake or cure condition. 

Degoeje MP, Wapenaar KED, Non-destructive inspection of carbon fiber reinforced plastics using eddy current methods. Composites, 23(3), 147-157, 1992. 

Welds have to be designed so that they can be inspected after manu cture, and throughout the life of the plant. X-ray inspection is normal during manufacture, but during the plant life ultrasonic or eddy-current methods are often easier to deploy. To reduce residual stresses it is normal to heat-treat the welds after manufacture. This is much simpler if the weldment can be heated locally, without imposing stresses on the rest of the tube bundle. The tubes are normally welded to pre-formed spigots machined from the tube plates, which allows both ready inspection and local stress relief during manufacture. 

Several components have been inspected using volumetric techniques. These methods must be qualified in terms of equipment, procedure, personnel and proven on a mock-up. Inspection technology has advanced substantially in recent years. Remote UT EC (Eddy Current) techniques are now available to inspect several internal components involving the top guide, access hole covers, core shroud and shroud head bolts. These techniques include the qualification of procedures for each specific configuration and application. These techniques have been demonstrated to be effective in in-situ inspection testing. 

Eddy-current methods are used to measure a variety of material characteristics and conditions. They are applied in the flaw detection mode for the detection of surface-connected or near-surface anomalies. The test objects must be electrically conductive and be capable of uniform contact by an eddy-current probe. Special equipment and specialized probes are required to perform the inspection. Procedure development, calibration artifacts, and process control are required to assure reproducibility of response in the selected test object. 

In order to reduce the occurrence of rail-defect-related failures, various methods are used to detect rail defects. These methods include visual inspection by the track maintenance staff, ultrasonic defect detection, eddy-current testing, ground-penetrating radar, impedance spectroscopy, and electromagnetic acoustic transducers [16,17]. 

Nondestructive testing. An ultrasonic inspection technique is available for the detection of flaws in plate, piping, and tubing. The water-immersed pulse-echo ultrasound equipment has been adapted to highspeed use. Eddy-current, dye-penetrant, and radiogr.aphic inspection methods are also used as required. The inspected materials have included Inconel, austenitic stainless steel, INOR-8, and the Hastelloy and other nickel-molybdenum-ba.se alloys. 

In addition to the review of general system integrity of the SRS reactors by various review panels, detailed aspects of the UT procedures, inspection work, and examination data have also been reviewed by independent NDE experts. Two recognized experts in the field of nuclear vessel NDE provided independent oversight and conducted random observations of the activities of the UT operation. Both UT and eddy current testing (ET) methods were used for ISI of... 

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