Abstract: B-type sleeve is usually applied for pipeline reinforcement when cracks generate in the girth weld of oil and gas pipelines. However, the evolution of the cracks especially longitudinal cracks of circular welds under the coverage may become great concerns for pipelines´ safe operation. A technique based on guided wave inspection was applied here to evaluate depth change of those longitudinal cracks. Two circular arrays consisting of piezoelectric wafers were designed to inspire and receive certain optimal selected guided mode in certain frequency, to ensure more energy flux pass through the original pipeline rather than the sleeve thereby carrying more information about girth weld defect. The wafer thickness could be optimized and the signal truncation window was determined by compromising the consideration on signal amplitudes and signal characterization parameters. The finite element model was further applied to get signal database corresponding to varying crack depths and locations in pitch catch mode of piezoelectric wafer arrays. Finally, when actual signal was used to correlate with the database, the recovery of crack location and depth information can then be expected. Preliminary experimental results showed that this scheme could achieve circular artificial crack depth estimation under the sleeve coverage.