"An assessment has been made of ultrasonic techniques developed to date for nondestructive evaluation of SiC heat-exchanger tubes. The results suggest that ultrasonic inspection is a useful and valuable technique for inspecting these tubes, including ceramic butt joints. However, this method alone is currently not sufficiently effective to detect all critical flaws because of (a) the difficulties in following the surface of an out-of-round tube; (b) the high velocity and thus the large angle of refraction of sound in SiC, which for small-diameter tubes loads to significant beam distortion; and (c) insufficient resolution, relative to the small critical flaw size in ceramics, at conventional ultrasonic testing frequencies. The experiments show that higher frequencies (up to 35 MHz) are required for effective wall-thickness measurements and detection of laminar-type flaws. While acoustic microscopy techniques for flaw and material characterization and holographic interferometry for crack sizing can be used for pre service inspection, in-service inspection of heat-exchanger tubes will probably be limited to ultrasonic inspection from the bore side. A new 22-MHz ultrasonic bore-side probe has been assembled. This probe is built to tighter tolerances than earlier versions to reduce mirror wobble, is designed for easy exchange of ultrasonic mirrors, and has a magnetic coupling to rotate the mirror (this prevents water damage of the mirror motor, a problem encountered with previous probe designs). Circumferential EDM notches as small as 125 um deep x 250 um long were readily detected. Axial notches as small as 500 um deep x 1250 um long were also detected. Natural flaws of the order of hundreds of um in size were readily detected. Calculations have shown that effective detection of axial flaws with this probe will be possible only for tubes with essentially circular cross sections (i.e., out-of-roundness limited to about plus or minus 1% variation in inner diameter). A special 20-MHz surface-wave probe was also tested and proved sensitive enough to detect a 125-um-deep outer-surface notch. Acoustic microscopy (for flaw and material characterization) and holographic interferometry (for crack sizing), although not adaptable to bore-side inspection, were shown to be effective as complementary or confirmatory techniques when used in conjunction with conventional ultrasonic testing. Preliminary results employing the micro focus radiography technique have indicated that his method is more sensitive than conventional radiographic techniques for ceramic butt joint assessment."