The National Shipbuilding Research Program. Development of Electromagnetic Acoustic Transducers (EMATS) for Surface/Volumetric Inspection of Welds

Abstract : This report summarizes the results of the National Shipbuilding Research Program (NSRP) Project 7-96-1, ElectroMagnetic Acoustic Transducers (EMATs) for Surface/Volumetric Inspection of Welds. Project 7-96-1 is a continuation of two earlier projects concerning shipyard application of EMATs for surface and volumetric weld inspection. An initial feasibility study (7-91-3) completed for the SP-7 Welding Panel in June, 1994 demonstrated laboratory feasibility for the use of EMAT generated surface waves to replace magnetic particle (MT) and/or liquid penetrant (PT) for surface inspection of welds. A subsequent project funded by Knolls Atomic Power Lab (KAPL) through General Dynamics - Electric Boat (EB) extended the EMAT technology by evaluating shear wave sensors for volumetric weld examination and included system evaluation in the shipyard, comparing the results to conventional inspection methods (MT, PT, ultrasonics (UT), and radiography (RT)). The results of the shipyard evaluation of the surface wave test were positive, while the outcome of the shear wave (SV) investigation for volumetric weld inspection was somewhat inconclusive. These conclusions led to the proposing of additional EMAT evaluations to the SP-7 Welding Panel, resulting in Project 7-96-1, a two year program divided into two phases. Due to the inconclusive results of the diffraction-based approach for volumetric weld inspection, alternate methods of volumetric weld inspection were investigated, and the results of these studies are reported here. Evaluation of the surface wave test is now complete, and the test should be considered ready for implementation by the various SP-7 member shipyards. McDermott Technology, Inc. can assist the shipyards in obtaining EMAT electronics, sensors and support, but the individual yards will need to determine their own requirements for system deployment.