ultrasonic testing

ultrasonic testing

Ultrasonic testing of welds. UT is now a primary means of NDE . Of the big five NDE methods, only UT and RT can reveal flaws which are substantially subsurface: Because the propagation of US is essentially a mechanical phenomenon, it is especially suited to determining characteristics of Engg. Materials.The major NDE applications includes:flaw detection thickness measurement, and metallurgical characterization The principal advantages are: 1. Its ability to penetrate to greater depths. 2. Its ability to test from one surface 3. Its sensitivity to detect minute flaws 4. Its comparative accuracy in determining flaw size and location 5. Its electronic operation for rapid and automated inspection.The principal disadvantages are: 6. Technicians’ considerable native ability, training, experience,and motivation, 7. Good coupling, surface roughness, geometry Ultrasonic testing of welds. Selection of Probe angle: Based on grove angle. Probe angle θ = 90- α/2 where α is the grove angle. Common practice of selection of angle: 1. Based on grove angle 2. As per AWS 0-30 mm thick 70 degree 3. 30-40 mm “” 60 “” 4. > 40 mm “”” 45 “” 5. Finally as per approved procedure Selection of Frequency: 1. Depends on job thickness and beam path 2. Surface roughness, & grain size 3. Size of discontinuity sought. 4. In practice the following is the most suited frequency range: 2.25 to 4.0 M.Hz 5. 2.25 M.Hz is the most ideal as it detects the discontinuities comparable to calibration standard, without producing very fine indications which are of not interest for acceptance or rejection,greater penetration,good S/N ratio. The Procedure 1. Study the weld details- process, edge ppn, backing strip, grove angle, 2. Remove all loose scales, loose paints, spatter, 3. Scan the entire surface intended for angle beam probe’s travel up to the weld with normal beam for possible lamination and other gross discontinuities. 4. Study the procedure for UT inspection. Selection of equipment scanning range: 1. Calculate the HSD & FSD and HBP & FBP HSD (OA) =t tan θ: FSD(OB) = 2t tan θ; HBP(AO’) = t/cos θ and FBP(BA’O)= 2t/cos θ 2. Set the range to approx. to 1.25 times of FBP= 1.25 BA’O B A O A’ O’ Defect sizing & reference blocks In UT the relative size of the defect is compared with a known artificial flaw or reflector.There are many methods of sizing in practice, and the common most methods are DGS SCALES, AND a reference block with a SDH hole. DGS STANDS FOR DISTANCE, GAIN, & SIZE ASME BPV CODE AND API, AWS THE SIZE IS ESTIMATED WITH SDH ASME REFERENCE BLOCKS FOR WELD DEFECT SIZING A DAC CURVE IS DRAWN WITH A KNOWN SIZE OF SDH. THE SAME HOLE SERVES AS A REFERENCE REFLECTOR AT DIFFERENT PATH SHOWING REDUCED AMPLITUDE AT INCREASED BEAM PATH. DAC CURVE. ON A CRT SCREEN [...]... impedance mismatch 2 The orientation of discontinuity w.r.t to the direction of US beam 3 The surface profile of the discontinuitysmooth and plane, irregular or curved 4 The size of the discontinuity Ultrasonic testing of off-shore platform structures: RP 2X OFF-SHORE STRUCTURES REQUIRE EXTENSIVE USE OF T,K,Y TUBULAR MEMBER INTERSECTIONS US IS THE BEST MTHOD TO INSPECT THE WELDED AREA RT IS THE MOST SENSITIVE... API RP2-X WELD PROFILES: RP-2X TRANSFER LOSS CORRECTION REFERENCE BLOCKA C B D 0 0 TRANSFER LOSS -CONTD ON THE JOB SURFACE; A A ON REFERENCE BLK BB ON JOB THE DIFF IN dB is transfer Loss in fig A B A B Ultrasonic reject criteria API RP2X LEVEL A – WORKMANSHIP QUALITY-NOT INHERENTLY RELATED TO THE COMPONENTS’S FITNESS FOR PURPOSE- BUT BASED ON THE QUALTIY OF WELD THAT WELDER SHOULD BE ABLE TO ACHIEVE . Ultrasonic testing of welds. UT is now a primary means of NDE . Of the big five. experience,and motivation, 7. Good coupling, surface roughness, geometry Ultrasonic testing of welds. Selection of Probe angle: Based on grove angle. Probe