Inspection Connection: Radiographic and ultrasonic weld inspection Establishing weld integrity without destroying the component By Tony Anderson, Contributing Writer February 14, 2002 This article outlines the differences in radiographic and ultrasonic weld inspection, the two most common methods if nondestructive testing. It gives an overview of both methods, including how they are used. Radiographic and ultrasonic weld inspection are the two most common nondestructive testing (NDT) methods used to detect discontinuities within the internal structure of welds. The obvious advantage of both of these testing methods is their ability to help establish the weld's internal integrity without destroying the welded component. Radiographic Testing Radiographic testing (RT) usually is suitable for testing welded joints that can be accessed from both sides, with the exception of double-wall signal image techniques used on some pipe. Although this is a slow and expensive NDT method, it is a dependable way to detect porosity, inclusions, cracks, and voids in weld interiors. RT makes use of X-rays or gamma rays. X-rays are produced by an X-ray tube, and gamma rays are produced by a radioactive isotope. The basic principle of radiographic weld inspection is the same as that of medical radiography. Penetrating radiation is passed through a solid object (in this case, a weld rather than part of the human body) onto photographic film, creating an image of the object's internal structure on the film. The amount of energy absorbed by the object depends on its thickness and density. Energy not absorbed by the object causes exposure of the radiographic film. These areas will be dark when the film is developed. Areas of the film exposed to less energy remain lighter. Therefore, areas of the object where the thickness has been changed by discontinuities, such as porosity or cracks, will appear as dark outlines on the film. Inclusions of low density, such as slag, will appear as dark areas on the film, while inclusions of high density, such as tungsten, will appear as light areas. All discontinuities are detected by viewing the weld shape and variations in the density of the processed film. This permanent film record of weld quality is relatively easy to interpret if personnel are properly trained. Only qualified personnel should conduct radiography and radiographic interpretation because false readings can be expensive and can interfere seriously with productivity, and because invisible X-ray and gamma radiation can be hazardous. Ultrasonic Testing Ultrasonic testing (UT) can be used on ferrous and nonferrous materials and often is suited for testing thicker sections accessible from one side only. In general, it can detect finer linear or planar defects than can RT. UT makes use of mechanical vibrations similar to sound waves but of higher frequency. A beam of ultrasonic energy is directed into the object to be tested. This beam travels through the object with insignificant energy loss, except when it is intercepted and reflected by a discontinuity. The ultrasonic contact pulse reflection technique is used in UT. This system uses a transducer, which converts electrical energy into mechanical energy. The transducer is excited by a high-frequency voltage that causes a crystal to vibrate mechanically. The crystal probe becomes the source of ultrasonic mechanical vibration. These vibrations are transmitted into the test piece through a coupling fluid, usually a film of oil, called a couplant. When the ultrasonic waves pulse strikes a discontinuity in the test piece, it is reflected back to its point of origin. Thus, the energy returns to the transducer. The transducer now serves as a receiver for the reflected energy. The initial signal, or main bang; the returned echoes from the discontinuities; and the echo of the rear surface of the test piece all are displayed by a trace on the screen of a cathode-ray oscilloscope. The detection, location, and evaluation of discontinuities become possible because the velocity of sound through a material is nearly constant, making distance measurement possible, and the relative amplitude of a reflected pulse is more or less proportional to the size of the reflector. One of the most useful characteristics of UT is its ability to determine the exact position of a discontinuity in a weld. This testing method requires a high level of operator training and competence and depends on establishing and applying suitable testing procedures. Tony Anderson is a regular contributor to this section and technical services manager with AlcoTec Wire Corporation, 2750 Aero Park Drive, Traverse City, MI

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RFID Drives Up Efficiencies at ABB At its factory in Helsinki, Finland, the manufacturer is using EPC Gen 2 tags to track the production and shipment of the motor drives it makes, resulting in a range of benefits.   By Rhea Wessel  Nov. 25, 2009—ABB a global manufacturer of power and automation equipment for utility and industrial companies, is employing radio frequency identification at its factory in Helsinki, Finland, to better track outbound shipments of approximately 200,000 drives per year. The drives are frequency converters that control the rotational speed of alternating current (AC) electric motors.  ABB implemented the RFID system in order to reduce shipping errors, since such mistakes impact its invoicing process. Without a shipping receipt, the company cannot collect the funds it is owed. In addition, ABB faced a lack of floor space at its Helsinki facility, because production was rising at a rate of roughly 20 percent every year. ABB wanted to have a forwarding operator take over the task of logistics and warehousing, but was hesitant to do so because of its own unreliable, pen-and-paper- based method of manually tracking goods leaving the production area. The company believed that if it could improve its ability to track its goods shipments, it would then have reliable data to compare with that of a logistics partner—thereby reducing the risk involved in outsourcing some of its logistics and warehousing tasks.  RFID readers installed at ABB's loading platforms are used to verify that the correct products are loaded onto trucks. To meet this goal, ABB designed an RFID system to replace its manual shipping processes, enabling it to reduce outbound shipping errors. The company launched its RFID implementation in 2006, used the system in production by 2007 and completed the integration of the technology with its existing SAP system in mid-2009.  "By implementing RFID into SAP, we have reduced our manual work and have a more reliable way of inputting transaction data," says an ABB spokesperson who requested not to be named, in compliance with his company's policy. "Input time for transactions is only seconds, and we generate multiple readings at the same time with RFID—something that is impossible with the bar code."  The SAP implementation was a lengthy process, because ABB had to simultaneously perform a general update of its SAP system. Now, the firm is working to increase the number of fixed readers it uses at its dock doors from three to seven.  The smallest drives that ABB manufactures weigh about 15 kilograms (33 pounds) and are shipped in boxes, while the largest drives weigh up to 400 kilograms (882 pounds) and are transported on pallets. As soon as a drive is manufactured, it is placed in a box or on a pallet, and a worker applies a printed adhesive label containing an EPC Gen 2 UHF inlay to that pallet or box. The drives are then loaded on trucks or trailers for short-term storage or immediate forwarding. RFID tags are interrogated as the goods are moved past fixed gate readers in the loading area near the dock doors. Information about specific goods is linked in the database to the ID number of the truck or trailer, which is entered manually so that ABB knows the loading progress of each vehicle, and has an exact description of the goods it contains.  The system produces a warning error at the gate if a worker attempts to load the wrong products onto a vehicle, and it also notifies employees when a truck's consignment is incomplete. What's more, by outsourcing some of its logistics and warehousing to a partner, ABB was able to free up space at its factory to expand its production capacity.  UPM Raflatac is supplying the tags for the implementation. Vilant Systems, which served as the systems integrator for ABB's RFID deployment, provided the readers, which have a range of 3 meters (10 feet).  Later, ABB hopes its logistics partners will utilize the RFID tags on the pallets and boxes as well, in order to provide it with additional information regarding the status of goods, as well as improve its own services. The company plans to introduce item-level tracking for the components that make up the drives; a large drive may comprise thousands of parts.  In a separate application, ABB has been using RFID in a kanban process involving reusable plywood boxes since December 2005. Both the supplier and ABB read the boxes' RFID tags. When a full box leaves the supplier, its tag is read and an electronic notice is created in SAP. Once an empty box leaves ABB's factory, it triggers a material order from the supplier.  According to ABB, the system has decreased the manpower the company requires to process incoming packages. It has also reduced errors compared with the bar-code system previously used, the firm reports, and provided a return on investment within a few months. In December of this year, ABB plans to implement the same system at a factory in Estonia.  Reference : http://www.rfidjour nal.com/logistic s A S Q

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