Research On Trenchless Detection And Protection Of Buried Steel Pipelines In Karst Environment

With the construction of urban subways and underground power grids,it accelerates local perforation and spalling of area anti-corrosive coating were happened in buried steel,then led to leakage of gas pipeline and pollution of soil environment and other potential risk problems,Thus it causes the people’s lives and property caused immeasurable loss.In this paper mainly,The stray current corrosion mechanism of buried steel pipeline,stray current corrosion under special environments and the flexible protection technology to buried steel pipeline is studied are mainly studied.This paper mainly includes three parts,the concludes are as follows:Firstly,the corrosion failure mechanism of buried steel pipeline is studied combined with ANSYS finite element simulation and actual measurement of the potential gradient.The concrete content includes the formation and spread of stray current in the soil,the mechanism that stray current effects to the pipeline and the process of pipeline corrosion,etc.The results show that :(1)In the same soil properties,the greater the intensity of stray current,the greater of the impacted region,and At the same the intensity of stray current,the lower of soil resistivity,the greater of the impacted region;(2)when the pipe has no anti-corrosion coating or the coating is damaged,The stray current will flow into the pipe and outflow from the pipe in the point where the soil resistivity is relatively lower,thus accelerate pipe corrosion;when coating of pipe is intact,the stray current will flow along with the pipe,the stray influence is very small.(3)In the study of pipeline cathodic protection,the result of ANSYS simulation is very close to actual measurement,the average error and maximum error are within 10%,it shows that the ANSYS simulation could used to the pipeline cathodic protection.Secondly,with the platform of the ANSYS WORKBENCH14.0,the stray current corrosion types of Karst environment which includes the stray current interference caused by cathodic protection,heterogeneous soil,and metal materials with different properties,The results show that: for the parallel pipes,the potential distribution of affected pipe is graduallyincreasing from both ends to the middle,the end’s effect is the maximal;for the intersected pipes,the potential distribution of affected pipe is gradually decreasing from the middle to ends,and the crossing point suffered the greatest impact.one pipe run through beyond 2 kinds of soil,pipe will accelerate corrode at the junction of soils,pipeline with different features exposed into the same soil(e.g.,the old and new pipelines connected),because of different potential,the new line as anode will be corroded faster than the old,especially in the welding place.Last but not least,the study about trenchless flexible protection of buried steel pipeline in the Karst environment.On the one hand,the traditional flexible anti-corrosive measures were optimized :By properly increasing the voltage,20 m pipes can be protected by 1.7m flexible anodes,at the same time,“the ends” and “Ring-Arc” laying concept of flexible anodes in special conditions was put forward and verified by experiments,in this way pipeline protection could avoid obstacles to realize pipeline protection.On the other hand,for the case of multiple pipes laid in the same ditch,using the grounding device of the cathodic protection system as the only anode,and the multiple pipes as the cathodic of the electrochemical cell to realize the joint drainage of pipe group.And in the contrast experiment of buried pipeline joint drainage protection,the advantages of flexible anode material such as convenient installation,energy conservation and environmental protection is confirmed.