Risk analysis and maintenance decision making of natural gas pipelines with external corrosion based on Bayesian network

Buried natural gas pipelines are vulnerable to external corrosion because they are encased in a soil environment for a long time.Identifying the causes of external corrosion and taking specific maintenance measures is essential.In this work,a risk analysis and maintenance decision-making model for natural gas pipelines with external corrosion is proposed based on a Bayesian network.A fault tree model is first employed to identify the causes of external corrosion.The Bayesian network for risk analysis is determined accordingly.The maintenance strategies are then inserted into the Bayesian network to show a reduction of the risk.The costs of maintenance strategies and the reduced risk after maintenance are combined in an optimization function to build a decision-making model.Because of the limitations of historical data,some of the parameters in the Bayesian network are obtained from a probabilistic estimation model,which combines expert experience and fuzzy set theory.Finally,a case study is carried out to verify the feasibility of the maintenance decision model.This indicates that the method proposed in this work can be used to provide effective maintenance schemes for different pipeline external corrosion scenarios and to reduce the possible losses caused by external corrosion.

Effect of Chlorine Salt on Durability of Mineral Admixture Concrete under Different Conditions

Mineral admixture concrete is a renewable material.It requires less cement than ordinary concrete and is thus beneficial for economical use of resources and environmental protection.To examine the impact of chloride salt on the durability of mineral admixture concrete under various conditions,in this study,test blocks are divided into two major groups:in one group,the test block is eroded by chloride salt on the interior and by sulphate/magnesium salts on the exterior,and in the second group,the test block is eroded by external chloride/sulphate/magnesium salts.Clean water is considered the control group.Dry-wet alternation tests are carried out to investigate the mechanical properties,mass,macromorphology,and ion content of the concrete.Furthermore,a series of methods,such as XRD,FT-IR,SEM,and EDS,are adopted to examine the phase composition and micromorphology of the concrete.The results show that,for the concrete subjected to the corrosion of internal chloride salt and external sulphate/magnesium salts(0–20 cycles),its mechanical properties improve slowly at the initial stage,but at the final stage(80–120 cycles),it is subjected to more severe corrosion compared to those only eroded by a single corrosive ion,such as the chloride/sulfate/magnesium salts.For concretes subjected to external corrosion of chloride/sulphate/magnesium salts,the concrete durability enhances with the concentration increase of the chloride salt.Mg^(2+)and SO_(4)^(2-)could jointly result in destructive damage to the admixture concrete,main generating corrosion products of ettringite,gypsum,Mg(OH)2,thaumasite,and M-S-H.