The paper introduces a numerical internal corrosion rate prediction method into the internal corrosion direct assessment (ICDA) process for wet gas gathering pipelines based on the back propagation (BP), the genetic algorithm (GA) and BP, and the particle swarm optimization and BP artificial neural networks (ANNs). The basic data were collected in accordance with the terms established by the National Association of Corrosion Engineers in the Wet Gas Internal Corrosion Direct Assessment (WG-ICDA) SP0110, and the corrosion influencing factors, which are the input variables of the ANN model, are identified and refined by the grey relational analysis method. A total of 116 groups of basic data and inspection data from seven gathering pipelines in Sichuan (China) are used to develop the numerical prediction model. Ninety-five of the 116 groups of data are selected to train the neural network. The remaining 21 groups of data are chosen to test the three ANNs. The test results show that the GA and BP ANN yield the smallest number of absolute errors and should be selected as the preferred model for the prediction of corrosion rates. The accuracy of the model was validated by another 54 groups of excavation data obtained from pipeline No. 8, whose internal environment parameters are similar to those found in the training and testing pipelines. The results show that the numerical method yields significantly better absolute errors than either the de Waard 95 model or the Top-of-Line corrosion model in WG-ICDA when applying the approach to specific pipelines, and it can be used to investigate a specific pipeline for which the data have been collected and the ANN has been developed in WG-ICDA SP0110.

This study developed a theoretical model for predicting the downstream temperatures of high pressure high temperature condensate gas flowing through chokes. The model is composed of three parts: the iso-enthalpy choke model derived from continuity equation and energy conservation equation; the liquid-vapor equilibrium model based on the SRK equation of state (EoS); and the enthalpy model based on the Lee-Kesler EoS. Pseudocritical properties of mixtures, which are obtained by mixing rules, are very important in the enthalpy model, so the Lee-Kesler, Plocker-Knapp, Wong-Sandler and Prausnitz-Gunn mixing rules were all researched, and the combination mixing rules with satisfactory accuracy for high pressure high temperature condensate gases were proposed. The temperature prediction model is valid for both the critical and subcritical flows through different kinds of choke valves. The applications show the model is reliable for predicting the downstream temperatures of condensate gases with upstream pressures up to 85.54 MPa and temperatures up to 93.23 °C. The average absolute errors between the measured and calculated temperatures are expected for less than 2 °C by using the model.

Waxy, high pour point and high viscosity oil is transported by the heated oil pipeline. The power and fuel cost account for large proportion in total cost. Long distance heated oil transportation pipeline contains many pump stations and heating stations. In the condition of satisfying transportation amount required, the operators can formulate many operation schemes which are composed of different hydraulic and thermodynamic parameters. Determine optimal scheme is important to improve the economic returns and social benefits. Aimed at minimum power and heating cost, this paper proposes a heated oil pipeline operation optimization model with consideration of thermodynamic constraints, hydraulic constraints, pipeline strength constraints, pump characteristic constraints, temperature and pressure constraints at outlet and inlet of pump stations and heating stations along the pipeline. The model is solved by the combination of linear approximation method and simplex method. Based on theory research, computer program is developed. Finally, the practical application shows energy saving of the optimal operation scheme obtained is significant. The method and program are of widespread usage.

In view of the hydraulic transient problem in heated oil pipeline, an unsteady flow simulation model is built in this paper. The characteristic method and Newton-Raphson method are utilized to solve the model. According to the phenomenon that the light oils would release from the liquid and form void fraction when the pressure is over lowing, the model considers the relationship between the gas release and pressure variation. Then the concentrated cavitations model is utilized to deal with the problem. Based on the model, the computer program is developed to simulate the hydraulic transient. Ultimately, this paper analyses the hydraulic transient behavior at the high-point place which is in front of the middle pump station of certain heated oil pipeline when the pump stopped. The study suggests that it is necessary to consider the cavitations and liquid-column separation in order to ensure the simulation results' accuracy. At the same time, the study shows that analyzing the liquid-column separation phenomenon is also necessary to ensure the oil transport pipeline's operation safety.

Third-party damage does not only depend on the own conditions of gas pipes, but also is directly affected by the external environment, the operation and management conditions. As the law of overall failure of third-party damage in Sichuan-Chongqing region is in accord with Europe, according to the related failure data provided by the Europe Gas Pipeline Incident Data Group, pipeline failure probability model of third-party damage is established by linear regression analysis, scoring system and weight determination method of risk assessment. The model is modified after synthetically considering the historical failures of pipelines, environmental and operation condition of Sichuan-Chongqing region. Failure probability of 10 pipelines is calculated by Visual Basic programming. The calculation results show that the pipe diameter, wall thickness and cover depth are the main factors to the failure probability of gas pipelines. The model can be used as quantitative index of third-party damage, the quantification of the failure probability can provide the basis for the operation, maintenance and detection of gas pipelines.

In view of the problem that how to select the natural gas pipeline's optimization regulation schemes, the analysis method is utilized to select the pipeline's regulation schemes evaluation indexes which include the pipeline's flow rate, operation income, risk and gas storage capacity. According to the emphasis points of the regulation schemes, the AHP method is adopted to calculate the indexes' weights. The gas pipeline's operational database and the optimal operation scheme are constructed in this paper. Based on the grey relational analysis method, a multi-objective comprehensive evaluation mathematical model which considers the indexes is established. The model measures the degree by which various regulation schemes approach the optimal one. Then the priority order of multiple schemes is determined. The computer program is developed to evaluate a pipeline's regulation schemes. The study shows that the model and algorithm discussed in this paper are feasible.