Study On Buckling Behaviour Of Thin Wall Stainless-steel Lining In Water Supply Pipeline And Its Application

As a new trenchless pipe repair method,the thin-walled stainless steel lining(SSL)is mainly used for the semi-structural repair of water supply pipes.In the operation process,the SSL is subjected to the external pressure caused by groundwater pressure and the negative pressure from the water supply pipeline system.However,there are few studies on the design and buckling performance of SSL.This thesis adopts a combination of theoretical analysis,experimental verification,and numerical simulation to analyze the buckling performance of the thin-walled stainless steel lining installed in the host steel pipe under negative pressure.The main research contents and conclusions of this thesis are as follows:(1)Comparative study on buckling theory model of traditional trenchless rehabilitation liners.Through the analysis and research of ASTM standard model,K parameter model,Glock model,liner buckling model(Boot model)considering the influence of annular gap,ASCE recommended chart model and other traditional liner stability theoretical analysis methods,reasonable liner buckling factors were proposed as the influencing factors of this thesis.The differences between the above traditional models were studied by parameter analysis.The analysis results showed that the ASTM standard design method was the most conservative.The boundary conditions and possible defects of liners were fully considered by the K parameter model,Glock model and Boot model,and the predicted values were significantly different.For the case of thin-walled stainless steel subjected to negative pressure,the above models could not accurately predict the critical buckling pressure.(2)The full-scale tests were carried out for thin-wall stainless steel liners of water supply pipeline.The mechanical properties of thin-wall stainless steel liners material are obtained by a basic performance test.The five groups buckling failure tests of thin wall stainless steel liners of water supply pipeline under negative pressure were carried out,and the instability models of stainless-steel liners controlled by different boundary conditions were studied.Carried out a set of liners full-scale tests under the effect of stiffening,the negative vacuum pressure of buckling stiffening effect was studied on the influence law of thin-walled stainless steel liners failure.The stress-strain,buckling failure pressure,and pressure-displacement curve of the liner monitoring section during negative pressure change were obtained by vacuum negative pressure loading tests.The results of full-scale tests showed that:(1)the critical buckling negative pressure of the thin-walled stainless steel liner was closely related to the wall thickness and diameter of the liner.The smaller the wall thickness of the liner,the smaller the critical buckling pressure;the larger the liner diameter was,the smaller the critical buckling pressure was.(2)Liner buckling usually occurred at the initial defect position;(3)The buckling pressure test values of multiple groups liner tests were significantly different from those of traditional theoretical models,and the existing pipelines have a significant strengthening effect on the liner under negative pressure environment;(4)Adding a stiffening ring inside the inner liner could effectively improve the buckling resistance of the liner,and the stiffening ring should be welded as a whole with the liner.(3)Numerical analysis of buckling behavior of thin-walled stainless steel liners coupled with multiple factors.The initial defect parameters of the thin-walled stainless steel liners were introduced by the lofting method,and a full-scale numerical simulation model was established.The validity of the model was verified by the results of the critical buckling external pressure tests of specimens of different sizes.On this basis,18 groups of negative pressure buckling of flat-wall liners were simulated using initial ellipticity OV,annular gap g and liner DR values as basic variables.Sixteen groups of stiffening liners were numerically simulated by taking the thickness of stiffening ring,inner diameter of stiffening ring,width of stiffening ring,spacing and number of stiffening ring as basic variables.The simulation results showed that:(1)The pre-buckling and post-buckling processes of thin-walled stainless steel could be well simulated by Risk analysis method.(2)For the flat-wall liner,there was a log-linear correlation between the critical buckling pressure P_c and the liner DR value,and the initial defect of the liner determines the values of a and m parameters in the relationship.In addition,the enhancement coefficient K value could also be expressed as a function related to a,m and DR.(3)For the stiffened liners,the greater the stiffness,the greater the critical buckling pressure,and the overall stiffness relationship of the stiffened thin shell liners were the stiffness of the unstiffened part and the stiffness weight value of the stiffened part.The prediction error of stiffening liners stiffness based on the traditional practical length theory of stiffening ring was larger.(4)Research on buckling prediction model of thin-walled stainless steel liners.Based on the experiment and numerical simulation results,the critical buckling pressure prediction model of thin-walled circular shell structure was established.Based on test data,the parametric analysis was carried out.A method for calculating the global buckling critical pressure and the local buckling critical pressure of the thin-walled stiffened shell was proposed.The theoretical criterion of global buckling and local buckling of thin-walled stainless steel liners were formed.Based on the above results,the rehabilitation design method of thin-wall stainless steel liners of pressure pipe was put forward.(5)Application research on thin-walled stainless steel liners rehabilitation design for water supply pipeline.Based on typical thin-wall stainless steel water supply pipeline rehabilitation project of DN 800 mm and DN 1200 mm.This thesis analyzed the external pressure and internal pressure of water supply pipeline during operation and maintenance,provided the liner design process of water supply pipeline under external pressure,internal pressure and negative pressure,and formed the wall thickness selection standard of thin-wall stainless steel liners.And the differences between the present design methods and the proposed methods were compared and analyzed.Further,the key technologies of thin-wall stainless steel liners technology in typical engineering cases were studied,and the corresponding solutions were given.In this thesis,we give the design model and the key techniques of the case-based could provide guidance for related projects.