Research On Leak Detection Technology For In-Service Pipeline

With the development of industry, pipelines are widely used in ship, major equipment, oil and gas transport system. Ship pipe path includes fuel pipe, lube pipe, cooling water pipe and so on, and the leak of any pipe may cause related equipments unable to use, even influence the safe use of main and auxiliary engines; pipelines in major equipments are usually oil pipe and water pipe, taking utility boiler for example, the accident of "four-tube" crack in boiler has always been one of the major problems in power plant, which baffles the unit operation safely and economically; the leak of oil and gas pipeline causes not only large resource waste and huge environmental pollution, but also threatens people's lives and property. Therefore, it has important significance in research and engineering application to study on leak detection technology for in-service pipeline.In this paper, a pipeline leak detection testing system had been developed, a series of pipeline leak detection testing research were carried out, and error analysis of pipeline leak detection testing system had been completed. Follows are the main works:(1) The fundamental principle of common pipeline leak detection methods are simply introduced, negative pressure wave method and flow method are combined to detect and locate pipeline leak, wavelet analysis is chose as signal processing method of pipeline pressure and flow, in which, wavelet denoising method is used to filter away noise from original pressure and flow signals and wavelet singularity analysis is used to detect catastrophe points of pipeline pressure and flow signals, so pipeline leak detection and location can be implemented.(2) A pipeline leak detection synthetical testing platform was built in the laboratory to simulate normal operation and leak condition of liquid delivery pipeline, and a set of pipeline leak detection testing system was developed by Virtual Instrument LabVIEW, which based on negative pressure wave and flow. This system can not only monitor operation condition of the pipeline real-time, detect and locate leak in time, but also replay history data by query time. Based on the testing platform, a variety of leak detection testing research can be carried out under different leakage rate, different pipeline transportation condition such as steady transportation condition and unsteady transportation condition and different pipeline layout such as horizontal transport pipeline and vertical transport pipeline.(3) On the basis of the testing platform, when pipe flow is under steady transportation condition, factors having influence on leak location precision were discussed. Leak detection tests were carried out for a section straight pipe and a section complicated pipeline which has elbows and layout of beam line changes. The test plan was developed by orthogonal test design method. Through the variance analysis of testing results, we can get conclusions as follows: for a section straight pipe, the small pipeline transport flux, the better the leak location precision is, and leakage rate has little influence on leak location precision; for a section complicated pipeline, pipeline transport flux and leakage rate have influence on leak location precision, and the more elbows in pipeline, the worse leak location precision is.(4) On the basis of the testing platform, pipeline leak detection tests when flow is under unsteady transportation condition were carried out. On pumps start-up, the liquid pressure oscillation is comparatively large; flow is under unsteady transportation condition at this time. Under four kinds of different conditions, pressure fluctuation is divided into three degrees, we can find that leak location precision is better when pressure fluctuation is small, and by analyzing testing data of different pressure fluctuation degree, a set of modified value were provided, leak location precision had been improved.(5) Error sources of pipeline leak detection experimental system had been analyzed. Random error was caused by various interference noises, including common mode interference, series mode interference and signal channel interference. Systematic error includes temperature error, nonlinear error and sensitive error of sensors, sampling error and analog-digital conversion error in data acquisition, computer calculation error, displaying error and data processing error of virtual instrument software. Error constitution formula of pipeline leak detection system had been summarized, and several methods were provided to amend and restrain errors.