What Can a Flawed Specimen Teach You? Known flaws aid in training, testing, and technique development Flawed specimens with defects of a known type, size, and location are an invaluable tool for the nondestructive examination (NDE) industry. Regardless of the inspection method or technique, these known flaws provide an accurate and reliable standard for training, testing, and technique development. Flaw manufacturing is a combination of machining, welding, and proprietary special processes. The end goal is to provide a product with “real” flaws that can be used to train or test an NDE technician, develop and prove inspection techniques, or demonstrate equipment capabilities. These flawed specimens can be manufactured to meet the requirements of a specific code or to accommodate a single customer’s unique application. Note that while in actual welds not all discontinuities (such as porosity) are considered flaws or defects, for the purposes of this article all discontinuities mentioned are termed defects/flaws. Defects for Ultrasonic Testing Manufactured defects for ultrasonic testing (UT) comprise possibly the largest portion of the industry need for flawed specimens. These defects typically fall into one of two categories: cracks or weld volume defects. Cracking usually occurs in the weld root, toe, or heat-affected zone (HAZ), and is often a product of cyclic fatiguing. The desired ultrasonic response is a sharp but jagged signal characteristic that displays a Fig. 1 — An example of porosity as viewed in a conventional UT A-Scan display. discernable tip signal for depth sizing. The process used by FlawTech to create these crack-like indications is a combination of mechanical and thermal fracturing and can be controlled with a size tolerance of ±1 mm, when required. Weld volume defects, in the field, are typically a byproduct of the welding process. These defects include, but are not limited to, slag inclusions, porosity, incomplete penetration, and incomplete fusion. There is a reliable and controlled process for intentionally inducing defects in the weld volume, and a tolerance size of ±1 mm with these flaws can be maintained. Each type of weld defect has a unique ultrasonic signature that, coupled with the signal’s location within the weld geometry, the inspector can use to identify the defect type. Figure 1 shows an example of porosity, as viewed in a conventional A-Scan ultrasonic x/y: distance/amplitude display. The pores provide a multifaceted signal that is By Alan Caulder Feature Inspection Trends / Summer 2013 19
Inspection Trends | Summer 2013
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