Objective During the operation of pipeline systems, pressure fluctuations inherent to the pipeline transportation environment generate background noise. As pressure increases in these systems, the magnitude of pressure fluctuations changes, subsequently affecting the intensity of the background noise. In the process of detecting pipeline defects, background noise interferes with the normal operation of ultrasonic in-line detectors, resulting in reduced detection accuracy. Horizontal straight pipeline segments make up the majority of oil and gas pipeline systems. Therefore, studying their noise characteristics provides a scientific foundation for analyzing noise in other pipeline segments. From this perspective, it is crucial to analyze background noise during the operation of ultrasonic in-line detectors in straight pipeline segments.

Methods A simulation experimental platform for ultrasonic in-line inspection was established to collect pressure and echo signal data from a pipeline system operating under varying pressures and flow rates. The positions of the operating detector were collected according to the pressure variation law of pipeline systems. The pressure fluctuation ranges and the pressure variation rates within the pipeline system during the operation of an ultrasonic in-line detector in the straight pipeline segments were analyzed. The intensity of background noise caused by pressure fluctuations was investigated through frequency domain analysis to clarify its influence on the echo signals. Additionally, the effect of background noise generated by pressure fluctuations of the transported media on the flaw detection accuracy of the ultrasonic in-line detector was quantified by calculating wall thickness and associated errors based on the transit time method.

Results During the operation of the ultrasonic in-line detector in the straight pipeline segments, the transported media caused pressure fluctuations, ranging from 0.093 MPa to 0.196 MPa. In most experiments, the pressure variation rates were below 0.531 MPa/ms; however, a maximum rate as high as 17.792 MPa/ms was recorded. Analysis of the frequency domain characteristics of the pressure signals revealed that the noise amplitude was narrow between 3 MHz and 7 MHz. The noise signals at 5 MHz and 6.929 MHz increased due to the influence of pressure variation rates, with maximum increase rates of 415.023％ and 1,240.825％, respectively. Nevertheless, the maximum increase in noise amplitude was only 0.881, indicating a minimal impact on the performance of the ultrasonic in-line detector. Further analysis of the ultrasonic echo signals showed that background noise caused changes in the amplitude and peak sampling points of these signals, thus impacting the accuracy of wall thickness calculations. The variations in background noise amplitude had little effect on the wall thickness calculations, with error rates ranging from 0.128％ to 4.324％.

Conclusion The influence of background noise generated by pressure fluctuations of transported media on flaw detection by ultrasonic in-line detectors is negligible in engineering applications. The findings of this study provide a theoretical reference for flaw detection using ultrasonic in-line detectors operating in straight pipeline segments.