tailieunhanh - INSPECTION, EVALUATION AND REPAIR OF HYDRAULIC STEEL STRUCTURES Episode 6

Tham khảo tài liệu 'inspection, evaluation and repair of hydraulic steel structures episode 6', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | EM 1110-2-6054 1 Dec 01 e. Ultrasonic testing UT . UT inspection is a nondestructive method in which high-frequency sound waves are used to detect surface and internal discontinuities. The sound waves travel through the materials to be inspected and are reflected from surfaces refracted at interfaces between two substances and diffracted at edges or around obstacles. The reflected sound waves are detected and analyzed to define the presence and location of discontinuities. Cracks laminations shrinkage cavities pores and other discontinuities that act as metal-gas interfaces can be easily detected. Inclusions and other nonhomogeneous defects in the metal can also be detected. UT inspection is usually performed with longitudinal waves or shear waves . angle beam . Most UT inspections for discontinuities are performed using angle-beam technique. The pulse-echo method with A-scan is most commonly used for inspection of welds. The most commonly used frequencies are between 1 and 5 MHz with sound beams at angles of 0 45 60 and 70 degrees. During application of the method all surfaces of the part to be examined should be free of weld spatter dirt grease oil paint and loose scale. Applicable guidance documents include ASTM A435 A435M ASTM A577 A577M ASTM E114 ASTM E164 ASTM E214 ASTM E1316 ANSI AWS and ANSI AWS . 1 Advantages. UT provides near-instantaneous indications of discontinuities. It is not hazardous to personnel nor does it have adverse effects on materials. The method is very accurate. It has superior penetrating power allowing the detection of discontinuities deep in the part is highly sensitive permitting the detection of small discontinuities and provides good accuracy in determining the size position and shape of discontinuities. 2 Disadvantages and limitations. Manual operation and interpretation of results require experienced technicians. Even with experienced personnel reference standards are needed for calibrating the equipment and for .