High precision ultrasonic corrosion rate monitoring

Abstract

The invention relates to very precisely measuring changes in thickness of pipe walls to determine corrosion rate prior to any significant corrosion loss. The thickness is determined by ultrasonic testing where many measurements of the wall thickness are taken at the same spot by a fixed sensor and errors associated with noise and temperature changes are substantially eliminated. A highly sensitive receiver converts each reflected pulse to waves that are averaged with other pulse measurements. The resulting average wave is analyzed so that each waveform is analyzed to identify the extrema and inflection points of each reflected pulse. The resulting analysis provides a far more accurate determination of the time between reflected pulses. As a result, a far more accurate picture of corrosion at the location of the wall of the pipe can be determined within weeks with a high degree of confidence.

1 . A process for precisely determining corrosion rate of a metal wall of a vessel or pipe where the process comprises:
 a) installing an ultrasonic sensor to a location of the wall where the ultrasonic sensor includes an ultrasonic source disposed to provide an ultrasonic pulse into the wall, and ultrasonic receiver disposed to receive reflections of the ultrasonic pulse from the opposite surface of the wall material, a temperature sensor and analytical circuitry to receive and collect temperature data from the temperature sensor and waveform data from the receiver;   b) measuring the temperature of the wall;   c) emitting a series of pulses from the ultrasonic source into the wall;   d) receiving at least a first and second reflection of each pulse from the wall that has crossed the thickness of the wall with a receiver to create a wave and collecting the wave forms into a Sample Collection;   e) measuring the temperature of the wall at the beginning and end of the collecting of the data;   f) determining that the temperature has remained substantially constant during the collecting of the Sample Collection and eliminating the Sample Collection if the temperature has not remained substantially constant during the collecting of the Sample Collection;   g) aligning the waveforms of the Sample Collection;   h) averaging the set of aligned waveforms within the Sample Collection to create a Representative Waveform for the Sample Collection;   i) identifying at least first and second echo sets within the average waveform representing the first reflection from the material and second reflection from the material, respectively;   j) determining the extrema and inflection points of each echo;   k) determining the “centers” of each echo using the characteristic points;   l) calculate the elapsed time between sequential echoes through the difference in their “centers”;   m) calculating a coefficient of thermal velocity expansion for the metal wall by collecting a number of Sample Collections at different temperatures performing a regression analysis for the various thickness measurement at the temperature of the respective Sample Collections to find a coefficient of thermal velocity expansion for the metal wall;   n) determining a temperature corrected wall thickness of the material based on the precise calculated time for an ultrasonic sound wave to travel through the wall along and the coefficient of thermal velocity expansion; and   o) collect further Sample Collections over time to measure the wall thickness at subsequent times and compare the subsequent temperature corrected wall thickness measurements to determine a corrosion rate for the wall.   
     
     
         2 . The process for precisely measuring the thickness according to  claim 1  further including the step of maintaining the temperature of the analytical circuitry within a range of one degree Fahrenheit for all measurements. 
     
     
         3 . The process for precisely measuring the thickness according to  claim 1  wherein the ultrasonic receiver disposed to receive reflections of the ultrasonic pulse from the opposite side of the material provides a signal to the analytical circuitry comprising data of the first and second reflection of each pulse received from the material and wherein the analytical circuitry further includes an amplifier for amplifying signal and a digitizer for digitizing the signal and the process further comprises maintaining the temperature of the amplifier and digitizer within a range of one half of one degree Fahrenheit for all measurements.