| Hydrocarbon condensate and water is often present in the mixed wet gas pipeline.The presence of these substances can cause low liquid multiphase flow rate.The distribution study of multiphase pipeline condensate and water has a high reference valu e on the analysis of pipeline corrosion.Thus,the study of the gas-liquid two phase flow characteristics in wet natural gas pipeline makes great sense.This paper establishes a two-phase flow calculation model for low liquid loading wet gas pipeline in the hilly terrain,for solving the practical problems encountered in the wet natural gas pipeline,and further refines the heat and hydraulic calculation model in a wet natural gas pipeline,and the model validation is performed combined with experiments.The difference between calculation value of pressure drop and liquid holdup based on model with experimental results is small,which verifies the accuracy of the calculation model,and provides the basis and reference for the low liquid loading pipeline design and operation.Combined with the TaLun gas pipeline running data,calculation and analysis of the flow field,liquid holdup and the flow pattern under different operating conditions in the wet gas pipeline in hilly terrain are made with the two-phase flow model established in this paper,to direct the selection of the excavation site on site.The flow characteristics of the whole pipeline and several local pipelines were calculated respectively,the analysis and forecasting are made for corrosive area,and then a sensitivity analysis of both the velocity in tube and pipe dip which two affect the pipeline holdup directly is made.The critical angle of this pipeline is 1.6°under the operating conditions.Location along the pipeline where the dip is larger than this angle may suffer effusions easily,and is the dangerous location of the pipeline operation,and should be focused on increasing the intensity of inspection and cleaning.What's more,elevation mapping of the whole TaLun gas pipeline has been done by using RTK,and the actual angle of the pipeline has been caculated.Then 63 sections of the local pipeline in which the angle is larger than the critical angle is choosen for excavation monitoring.The pipeline corrosion detection is operated by using combination form of RTK+ Magnetic flux leakage detection+ Ultrasonic C-scan+ Ultrasonic thickness.The comparison between actual test data with model calculations and corrosion predictions show a good agreement,and then the conclusion is acquired that in actual production,the operators should focus on monitoring the pipeline corrosion situations from the low-lying location to the front section of the uphill sections where the dip are larger than the critical angle,according to the model calculation results.The comparison between actual test data with model calculations and corrosion predictions show a good agreement,and then the conclusion is acquired that in actual production,the operators should focus on monitoring the pipeline corrosion situations of the low-lying location at the front of the uphill sections where the dip are larger than the critical angle,according to the model calculation results.Following the SY/ T6477-2014 methods,combined with field data of the pipeline,residual strength evaluation has been made.There are a total of 20 defects of the sampling portions of the pipeline can not pass the residual strength evaluation and the pipeline can not be safely used in the current conditions.The pressure of the pipeline needs to be lowered to 1.83 MPa,and the pipeline section of severe corrosion need to be reinforced or replaced as soon as possible.This paper recommends that the pipeline should be increased regular pigging operations,reducing pipeline fluid,weakening corrosive environment,maintaining the ability of the gas pipeline effectively.When conditions changed greatly,the critical angle should be recalculated.The owner should regularly target for pipeline corrosion monitoring,performing predictive maintenance and preventive measures. |
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