The energy of ultrasonic guided waves may be focused in pipes by utilizing a partially loaded excitation. This focusing technique is called "natural focusing", which can be used to improve a defect's sensitivity to ultrasonic guided waves. However, it is possible that there are a few natural focal points within the inspection range at a particular frequency. Consequently, some defects could be missed. The location of the natural focal points, however, changes with frequency. This phenomenon was theoretically predicted and experimentally confirmed. In this paper, the natural focusing inspection technique is investigated. Although a very limited circumferential length might be covered by a naturally focused profile at a single excitation frequency, the entire cross sectional area of the pipe can be inspected when a range of frequencies is employed. Hence, the natural focusing inspection technique can sufficiently inspect the entire pipe with frequency tuning.