Materials Performance

JUN 2019

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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22 JUNE 2019 W W W.MATERIALSPERFORMANCE.COM I FEATURE ARTICLE In the oil and gas and power generation industries, carbon steel (CS) pipe is frequently clad with a corrosion-resistant alloy (CRA) to create components with specific properties, such as high-temperature resistance in one area and good corrosion resistance in another. These same CRAs can also be used as filler material for girth welds (Figure 1). These metal interfaces, as well as many other types of dissimilar metal welds, can present challenges during nondestructive testing because of the changes in density and acoustic properties of the materials. Radiography is often used to inspect dissimilar metal welds and interfaces; however, radiography is associated with long exposure times and potentially harm- ful radiation. Because of these difficulties, along with developments in the field of phased array (PA) technology, ultra- sonic PA inspection may be a good alternative for these types of inspections. Conventional ultrasonic testing (UT) is a proven technique for inspecting CS welds. When inspecting a dissimilar weld material, however, several aspects make UT inspection more complex. When a UT beam travels through a component welded with dissimilar metals, both the metal-to-metal interface and the coarse-grained structure of the weld can cause reflection (backscatter) and refraction of the UT waves, which can cause skewing and beam attenuation. In a dissimilar metal weld, each material has its own attenuation factor and can be inhomogeneous and attenuative. This means the attenuation varies along the sound path at different angles and at different depths. Figure 2 illustrates skewing and attenuation of the UT beam at the dissimilar metals' interface when shear waves are transmitted. Because of the need to compensate for varying attenuation, achieving consistent sensitivity throughout a dissimilar material weld and its heat-affected zone can be difficult. Ideally, sensitivity calibration provides the same response for similar indications located at different depths and positions in the weld material. To optimize the inspection of these welds, adequate indication detection can be ensured by reviewing the following: scan planning, calibration, sizing and depth tolerance of indications, and coupling. Nondestructive Testing of Corrosion-Resistant Alloys and Dissimilar Weld Materials A step-by-step overview presents points to consider when conducting ultrasonic phased array testing on dissimilar metal interfaces.

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