Study On Technology Of Stray-Current Corrosion Detection On Buried Steel Pipeline Based On Fractal Theory

Pipeline, a secure and economic means of transporting oil and gas in large scale, is more and more widely used in China. Its corrosion problem is attracting more attention, especially the stray-current corrosion which becomes one of the important causation to pipelines detriment. Therefore, to prevent pipelines from detriment and make people's life and property secure, a study on technology of stray-current corrosion detection on buried steel pipeline is imperative. The problem of stray-current corrosion on buried steel pipeline was studied experimentally and theoretically, On the basis of fractal theory and experimentations, a stray-current corrosion model was established and a method of remaining life prediction of pipeline eroded by stray-current was purposed. The main research efforts were as follows:1. The mechanism of stray-current corrosion was discussed preliminarily and the scheme of simulation experimentations was purposed. In experimentations, corrosion rate of test block test affected by the stray-current in different soil environment was researched.2. Images of surface corrosion topography were acquired, and then corrosion characteristics through the technology of digital image processing were obtained. Based on fractal theory, surface corrosion topography has characteristics with fractal and the fractal dimension can be considered as a parameter for describing complexity quantificationally.3. Fractal dimension of test block's surface corrosion topography affected by the stray-current in different soil environment was researched through experimentations. Experimental datum was used to establish a multivariate polynomial model to get relation expression between corrosion rate and fractal dimension in certain condition. In that model, un-significant terms were removed through significant test.4. Three typical corrosion topographies include uniform corrosion, local corrosion, pitting corrosion. Their defect geometric model was established respectively using the formula M V= CR ? S '? t, where M V is metal quality in defect, CR is corrosion velocity, S 'is square of defect and t is corrosion time. Relation expression between corrosion time and fractal dimension was obtained. A new method was presented that using fractal dimension to predict remaining life of pipelines.5. Based on fractal dimension, a life remaining prediction software is developed. Its main functional modules are introduced in detail as well as their implementation techniques. The software is tested in experiments. Results show that the software is convenient to operate and analysis result is reliable, which can meet needs of application.