Apparatus and method for non-intrusive pressure measurement and early identification of solids formation using selected guided ultrasonic wave modes

A method of measuring a pressure of a fluid inside a pipe or vessel, comprising:

• attaching a transducer to an outer wall of the pipe or vessel;
• transmitting a signal from the transducer at a characteristic frequency via a plurality of guided wave modes, the characteristic frequency being a frequency at which the plurality of guided wave modes are separated in time when detected, wherein the characteristic frequency is in a range between 50 kHz and 1 MHz, or 10 kHz to 2 Mhz, and wherein the plurality of guided wave modes comprise at least one of
• a circumferential shear horizontal (C-SH) wave traveling in the wall,
• a circumferential Lamb type (C-LT) wave traveling in the wall, and/or
• a cavity acoustic (CA) wave that travels through the fluid in the pipe or vessel;
• detecting the plurality of guided wave modes after travel in or through the wall a predetermined number of times, each of the plurality of guided wave modes having a signal receipt time after said predetermined number of times;
• and
• calculating the pressure of the fluid using the signal receipt times by correlating the signal receipt times with a pressure at the characteristic frequency.