Bubble Defect Analysis And Safety Measures Of The Zhu-Qu Natural Gas Pipeline

Due to the high content of hydrogen sulfide,Gathering pipelines in High-sulfur gas field are suffered electrochemical corrosion,hydrogen blistering and delamination,hydrogen induced cracking(HIC),hydrogen embrittlement and sulfide stress corrosion cracking(SSC),then the risk of safety and environmental protection of the pipeline system is greatly increased.ZhuQu line transport wet gas with sulfur capacity 7.2g/m3 for long-terms.Many bubbling defects is found on pipe wall inside by intelligent detect and site excavate.Experimental analysis and theoretical study are conducted to ensure the pipe's safety.Based on the material of the pipe,the blistering defects formation mechanism and influence factor is analyzed.Finite element model and reliability evaluation model are established.According to the burst test data,the correctness and adaptability of the evaluation method is proves,and then reasonable and effective security management measures of the pipeline are put forward.Combine intelligence test data and on-site inspection of ZhuQu line,bubbling defects in the inner wall of the pipeline are analyzed in shape,size,and distribution.Blistering occurred at the wall thickness of 6.5mm,half of the original wall thickness.Bubbling defects distribute randomly along the pipeline inside wall,sizes,Diameter is less than 40mm and height less than 20 mm,and the shape likes hemisphere.Physical and chemical experiments of ZhuQu line are conducted on pipe sections,in order to comprehensive analysis pipeline bubbling defects' failure mechanism and influencing factors.Because of the low level of early technology in steel rolling,segregation exit in the center of pipe evidently,MnS banded exit accordingly.Central segregation become the nucleation of hydrogen to permeate and accumulate,when the hydrogen pressure reaches a certain level,the pipe wall is plastically deformed outward bulge bulbs.The formation of bubbling defects is influenced by H2S concentration,pH,temperature,anion and cation,stress and material organization,processing property.Based on the hydrostatic test,the blasting tests are conducted on pipe sections.The destruction pressures are obtained directly,as basic parameters provided for finite element analysis of bubble defects of pipeline and reliability evaluation.Experiments show that,bubble defects weaken the strength of pipeline.According to the experiment and field ZhuQu line's detection results,a geometric model of single bubble and bubble,adjacent to the 3D finite element model,and calculated by ANSYS software.Bursting pressure of the pipeline is calculated based on the fourth strength theory and failure criterion,and is compared with the experimental burst pressure,to validate the finite element model and calculation.The actual pressure in bubbles is get from explosion pressure,and also the safe operation pressure of pipe,which is 4.7MPa.The analysis showed that,bubble defects lead to stress concentration.The maximum stress is located at the edge of the bubbling adjacent.With the bubbling increasing,the maximum Von Mises stress deereases rapidly,rendering index fell law.The axial distribution bubbling defects has the largest stress concentration factor,followed by 450 distribution.The smallest is circumferential distribution bubbling defects.Burst pressure is relevant with the bubble size,bubble pressure and bubble spacing.On the basis of reasonably determining pipes' yield strength,blasting pressure,Mises stress levels,the deviation coefficient of Mises stress is introduced,and a reliability evaluation model based on a normal distribution function is established,to determine the minimum reliability coefficient under pipe yield strength,which is 1.67.Safety level is low.According to the pipeline's characteristics,combined with defect detection,finite element evaluation,reliability,reasonably determine the management of safety production,including controlling opeanalysisrate pressure,exchanging pipes,encryption inspection and evaluation cycle,they are suitable for the actual situation at the scene,can effectively improve the level of safe in operation of ZhuQu line.