Abstract: A method for determining if deterioration in structural integrity of a pressure vessel, having both sensor and oscillator affixed to or embedded in said exterior surface thereof. An electrical current is provided to the oscillator so as to cause said oscillator to oscillate and produce a mechanical disturbance to the exterior surface and cause a detectable natural frequency response of said pressure vessel. The resultant natural frequency response is detected and recorded. After a period of elapsed time, the natural frequency response is again obtained. It is compared with the recorded natural frequency response first obtained, and if there be a difference therebetween, such as a shift in the frequencies at which the natural resonances occur, or a decrease or increase in the amplitude of one or more of the natural frequency resonances, then a flag is raised. An apparatus for determining if deterioration in structural integrity of a pressure vessel, and a pressure vessel, is further disclosed.