Re: creep charecterisation by ultrasonics Structural Integrity Associates, Inc.(SI) has worked extensively over the past weveral years with the Materials Proeperties Council (MPC) to develop and implement ultrasonic procedures for creep damage assessment. These studies were performed on samples removed from service and containing various levels of creep damage, from random cavitation, through aligned cavitation, micro-cracking, and finally macro-cracking. We have found that time-of-flight diffraction (TOFD) plays an important role in a comprehensive inspection regimen. TOFD can identify more advanced stages of creep including macro-cracking, most often micro-cracking, and under certain conditions even relatively dense, aligned cavitation. Equally important, TOFD can be used to sort out fabrication flaws reliably. It is a very complex situation, and the degree to which TOFD can identify creep damage often depends on the overall weld quality, density of fabrication flaws, etc. Therefore the detection threshold can vary dramatically from one weld to the next. To reliably characterize cavitation and its level, we have found that we must utilize a very tightly focused beam. We use an annular phased array approach in which we create a tightly focused beam using conventional focusing lenses, and then utilize the phasing to vary the focal depth. The latter technique is applied on a selective basis at specific locations to provide a statistical characterization of cavitation. These thechniques have been successfully applied by SI in hundreds of power plants throughout the US for detection and characterization of creep damage in seam welded high energy piping systems over the past 5 or so years. For more information, please see the SI web site (www.structint.com).