Temperature And Pressure Drop Analysis And Its Application In CO₂ Corrosion Evaluation Of Subsea Pipeline

The submarine pipeline is becoming an indispensable transport tool in the subsea oil development process. Temperature/pressure drop analysis and CO2 corrosion evaluation has always been the focus in pipeline engineering. The pipeline temperature/pressure drop analysis is interacting with CO2 corrosion rate calculation. The comprehensive consideration should be put on the link among those three factors in pipeline design. However, the friction coefficient is often obtained by iterative calculation in traditional design method, which makes it difficult to establish a comprehensive link between the pipeline temperature/pressure drop and induce some deviation in the pressure drop calculation result finally. At the same time, there is some inaccuracy in CO2 corrosion rate calculation, which will cause the design result conservative by using the temperature and pressure drop calculation results. Based on the above problem existing in the traditional design method, explicit friction coefficient formula is established using the crude oil test data, which will link the pipeline temperature and pressure drop calculation together. The CO2 corrosion rate calculation is carried out on that basis, which improve the accuracy of the CO2 corrosion rate calculation and pipeline design process.Firstly, the control equations for pipeline temperature and pressure drop calculation is established combined with operating characteristics of the submarine pipeline. The general form of the explicit friction coefficient formula is summarized and given by reading the relevant literature and material. The explicit friction coefficient formula, which is suitable for the test crude oil, is established by using the test data. A comparison is carried out, which is shown that the calculation results of the formula given in this thesis have consistent accuracy with the classical C-W implicit formula, while the calculation workload can be reduced and improve the design efficiency of the pipeline。Secondly, the pipeline temperature and pressure drop calculation is carried out using the explicit friction coefficient formula established in the above. The accuracy of this thesis's calculation result is proved by comparing this thesis's results with the traditional design method calculation results and monitor data. The comparing results is also showing that the pipeline pressure drop calculation accuracy can be improved if the link between the temperature and pressure drop analysis is been taken into comprehensive consideration. The parameter sensitivity analysis is carried out to determine the effect of the design parameter, on the temperature and pressure calculation results.Finally, the CO2 corrosion rate has been calculated on the basis of the temperature and pressure drop analysis results. A comparison is carried out among the common corrosion prediction models, the reason why those models will produce different results is analyzed and the prediction model using in this thesis is determined. The accuracy of corrosion rate calculation can be improved by taking the link between temperature and pressure drop calculation into consideration, which is proved by comparing this thesis's calculation result with the traditional design method result. The parameter sensitivity analysis is made to determine the effect of the parameter on the corrosion rate calculation result.