Risk Assessment Method And Software Development For Girth Welds Of High-Grade Steel Pipes

The pipeline failure data in recent years show that the failure modes of high-grade steel(X70 and above)pipelines and other steel-grade pipelines are quite different,especially the failure of girth welds.In the failure accident of high-grade steel pipeline,the failure of girth weld accounts for about 1/3.Therefore,in order to reduce the number of failures of girth welds and ensure the safe and efficient operation of pipelines,it is necessary to conduct risk assessment on girth welds.This paper establishes a comprehensive girth weld risk evaluation system and develops risk evaluation software by analyzing the accident cause,index weight,failure probability,and failure consequence value,combined with girth weld failure data and failure characteristics.The main research contents are as follows:(1)By analyzing the historical failure data of the girth weld,the main reasons for the failure are obtained,and the failure fault tree diagram is established.Dematel method was used to optimize the fault tree structure,and the core index was extracted according to the centrality threshold,and the optimized girth weld failure index system was obtained.(2)Use the AHP to get the importance weight of the core index relative to the superior index.Due to the mutual influence and dependence between the indicators,the Dematel method is introduced to calculate the degree of influence and the influence weight.Combining importance weight and influence weight,the final weight of the failure index is obtained,which is used in the subsequent risk assessment.(3)Due to the small amount of data and known information of girth weld failure records,the grey clustering method,which does not require a large amount of data but can reduce the degree of ambiguity,is used to calculate the failure probability.By referring to relevant national and enterprise standards,a failure consequence evaluation model is established.(4)According to the characteristics of large number of indicators and complex data types,the risk assessment software Risk AST was developed by using Matlab App designer.The failure data of a girth weld is imported for verification,and the evaluation results are consistent with the actual failure situation,which proves that the risk assessment model can accurately evaluate the risk of girth welds.Finally,compared with the Kent method,the results show that the risk assessment model based on grey clustering is more consistent with the actual situation in predicting the failure of girth welds.