Non-destructive testing of pipes

1. An apparatus for the non-destructive condition assessment of a pipe carrying a fluid, comprising:

a) first and second sensors for detecting an acoustic disturbance propagating past two longitudinally separated points on said pipe; and

b) a processor receiving inputs from said first and second sensors and programmed to:

(i) determine an actual value representative of the propagation velocity of said acoustic disturbance;

(ii) compute a corresponding predicted value for the propagation velocity as a function of at least one wall thickness parameter of said pipe by using a theoretical model for the propagation of acoustic waves in said pipe that assumes said pipe has a finite wall thickness with a predetermined circumferential thickness profile; and

(iii) compute said wall thickness parameter by matching said actual value with said predicted value.

2. An apparatus as claimed in claim 1 , wherein said pipe is a water pipe, and said sensors are mounted on support elements selected from the group consisting of: hydrants connected to said pipe, control valves attached to the pipe, and the pipe wall accessed via manholes or small excavated keyholes in the soil.

3. An apparatus as claimed in claim 1 , wherein said sensors are inserted into the pipe individually or as arrays thru fire hydrants or corporation stops.

4. An apparatus as claimed in claim 1 , wherein said model includes the velocity of propagation of the disturbance in the unbounded fluid or the bulk modulus elasticity of the fluid, the fluid's density, the pipes's internal diameter and wall thickness, and Young's modulus of the material forming the pipe.

5. An apparatus as claimed in claim 1 , wherein said sensors are connected to wireless transmitters, and said processor is connected to a receiver for remotely picking up signals from said sensors; or said sensors are connected to said processor via cable.

6. An apparatus as claimed in claim 5 , further comprising a reference pipe of known wall thickness profile to permit at least one constant in said theoretical model to be back calculated from actual velocity measurements.

7. An apparatus as claimed in claim 1 , wherein said processor is included in a PC or a specially designed device.

8. A storage medium storing coded instructions for instructing a computer to:

accept signals from sensors responsive to an acoustic disturbance propagating along a pipe;

compute an actual value representative of the propagation velocity of said acoustic disturbance by dividing the difference between the distances of said sensors from corresponding acoustic source by the time delay between said acoustic disturbances;

compute a corresponding predicted value for the propagation velocity as a function of at least one wall thickness parameter of said pipe by using a theoretical model for the propagation of acoustic waves in said pipe that assumes said pipe has a finite wall thickness with a predetermined circumferential thickness profile; and

compute said wall thickness parameter by matching said actual value with said predicted value.

9. A storage medium as claimed in claim 8 , further including instructions for instructing said computer to calculate constants for use in said theoretical model from measurements performed on a reference pipe of known wall thickness.

10. A storage medium as claimed in claim 8 , further including instructions to cause said computer to display an input screen for accepting inputs relating to known pipe parameters for use in the computation.

11. A storage medium as claimed in claim 10 , wherein said constants include the velocity of propagation of the disturbance in the unbounded fluid and the bulk modulus of the material forming the pipe.