Research On Deterioration Of Mechanical Properties Of Buried Metal Pipes By Corrosion And Its Reliability

A majority of pipes are made of metals,e.g.,cast iron and mild steel in China.Due to the material properties and working conditions of metal pipes,problems will inevitably arise after some service time.These problems includes ruptures and structural failures that sometimes lead to insecurities.Among many of the causes of these problems,corrosion effect of burying soil has been believed to be the most significant one.Corrosion by corrosive agents in soil alters the chemical compositions and microstructures of pipe materials,which,in turn,affects the mechanical properties of metal pipes.This corrosion-induced reduction of material mechanical properties will lead to the deterioration of structural resistance,which eventually will result in pipe failure under the same original loads.Yield strength and fracture toughness are the two mechanical factors that are of the greatest significance to the structural resistance of pipelines.However,most researches in this area were dedicated to yield strength rather than fracture toughness.Hence,the intention of this study is to present a comprehensive test program designed to investigate the effect of corrosion on mechanical properties of metal pipes in soil,including both yield strength and fracture toughness.The complete experimental program consists corrosion experiment of two metals in simulated solutions and mechanical test of specimens before and after corrosion experiment.The former part of this program simulate three different working conditions of pipes using simulated soil solutions,while the latter part tests the mechanical properties,namely,the yield strength and fracture toughness of the specimens corroded in different solutions for different time.Corrosion phenomena are analyzed during the corrosion process,based on which,different corrosion types are identified.In addition,deterioration models were developed based on experiment data for the two mechanical properties.Reliability theory has been widely used in the field of structural engineering like pipeline and RC structures.This investigation has also been dedicated to applying structural reliability theory like FOSM and Monte Carlo simulation techniques to pipeline engineering on both failure analysis and service life prediction of pipes.