Fig. 2 — An example of a linear crack indication manufactured to be located at one of the typical stress points along a bolt shank. distinguishable from other defects, as well as weld geometry. As ultrasonic inspection technologies have advanced over the years, from analog signals on oscilloscopes to today’s automated phased array systems, the ability of end users to evaluate the implanted defects, as well as the balance of the weld volume, has required manufacturers of flawed specimens to place nearly as much focus on maintaining an ultrasonically signal-free balance of the weld as on manufacturing the defects themselves. The goal is for no unintended defects from the welding process to confuse the inspector in finding and quantifying the implanted flaws. This is an overarching challenge for manufacturing defects across all inspection methods: ensuring that no unintentional defects are present that will affect the usability of the specimen for testing or training. Specimens for Magnetic Particle and Penetrant Testing Defects for magnetic particle testing (MT) and penetrant testing (PT) are typically manufactured and classified together. When manufacturing defects for MT and PT, surface condition is critical. The presence of any unintentional indications on the weld area surface or on the surface of a machined or forged part can affect the usability of a specimen, and also cause confusion during training or testing. The majority of defects manufactured for MT and PT applications are linear, crack-like indications. In machined or forged parts, these defects are placed in the areas of stress most likely to exhibit cracking in a typical industrial application. As with any flawed specimen, the more realistic the defect appearance and location, the better a tool it is for the NDE technician. See Fig. 2 for an example of a linear crack indication at one of the typical stress points along a bolt shank. Defects manufactured for MT and PT in welded specimens typically are located in the weld or HAZ, and may orient transverse or longitudinally. These defects are most often linear, but also encompass welding defects such as porosity or overlap. Defects in the weld root area are typically located along the root or in the associated HAZ. Defects for Visual Inspection Manufacturing defects for visual inspection may be the most challenging endeavor in this industry. They are, of course, visible, and are difficult to manufacture in both an intentional and realistic manner. The processes to create these defects, such as overlap, undercut, and surface porosity have been refined over the years. The American Welding Society has used FlawTech’s manufactured defects for visual inspection for Certified Welding Inspector (CWI) testing, and many other companies and industries have used them as well. These defects are often used in a “show and tell” manner to provide a visual and portable representation of what a technician may find in the field. When held to the appropriate tolerance, these visual defects are also a great tool for testing technicians’ knowledge of metrology and their ability to determine if a certain flaw is acceptable or rejectable according to the applicable code. Defects for Radiographic Inspection Defects are also available for radiographic testing (RT). This inspection technique is a great tool for identifying weld defects that may or may not be readily detectable by UT. The focus of this method is typically flaws in the weld volume, but with the proper film sensitivity, cracks may also be detected. Specimens for RT feature the appropriate flaw types, such as slag inclusions and porosity. These specimens can train the technician in appropriate shot setup, as well as film interpretation. Radiographic film interpretation is a submethod in itself. There are customers who, for film interpretation training purposes, do not need an actual specimen, but only need film that shows typical known flaws, as well as film processing defects. These film processing defects can train a technician to identify when there are issues with the inspection technique, rather than with the part being inspected. A set of films can be provided that contains typical flaws as well as processing defects, such as lack of density and double exposure, to support the need for film interpretation training. Specimen Design Understanding specific defects and being able to reliably reproduce them is the basis of flawed specimen manufacturing, but another critical component is combining defects of the right size and type with the correct material and geometry to end up with a part that is correctly designed for the specific application. Typically, flawed specimens fall into three categories: 20 Inspection Trends / July 2013
Inspection Trends | Summer 2013
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