The Remaining Life Prediction Of Gather Lines In Oil Fields

Recent years pipeline integrity and safety assessment, remaining life prediction of corroded pipeline have attracted more and more attention. When corroded pipeline is on operation, blowout or leakage would probably happen, which would cause terrible accident and bring tremendous loss. However, blind replacement of pipeline would waste great maintenance expenses. The remaining life prediction of corroded pipeline would be useful in the safe operation of a corroded pipeline and would be an effective way to cut down maintenance and operational costs. Furthermore, it could give the engineers a reasonable estimate as to the decision whether to abandon or maintain a corroded pipeline.The corrosion types of oil pipeline were discussed in the paper, and their mechanisms and configuration was presented. The corrosion configuration was classified and described by geometry model. The soil corrosion is one of the main forms of gather lines corrosion in oil fields, which was discussed in the paper. The soil's physical and chemical characters and corrosion rates around gather lines in an oil field were explored, Such as conductivity of soil 0.9～93.1?.m, water content 5%～30%, pH 8～11, total salt content 0.02%～0.5% and corrosion rates 0.01～0.36 mm/a. The physical and chemical characters and corrosion rates around gather lines in an oil field change enormously, that leads great change of soil corrosiveness around gather lines. The influence of the physical and chemical characters upon soil corrosiveness and correlation of them were also analyzed. The most important factor of soil corrosiveness around gather lines in an oil field is total salt content. Two kinds of methods were studied to predict the remaining life of corroded pipeline. One is based on reliability theory and probabilistic statistics, another is based on extreme distribution. The technique procedure and the main processes of pipeline life prediction were described in this paper. The data of pipeline life prediction and method of measurement is expounded. The applied condition was also discussed. The inspect data obtained from an oil field is analyzed in the paper. The whole data accords with weibull distribution and the maximal corroded value of the pipeline location corrosion accords with extreme distribution. The maximal possible corroded wall-thickness value of the whole pipeline was estimated basing on the bivariate extreme distribution theory. Based on extreme distribution and the power exponent formula of local corrosion growth, a deterministic model of life prediction is finally developed on the inspect data obtained from an oil field.