The influence of DC stray current on pipeline corrosion

DC stray current can cause severe corrosion on buried pipelines.In this study,firstly,we deduced the equation of DC stray current interference on pipelines.Next,the cathode boundary condition was discretized with pipe elements,and corresponding experiments were designed to validate the mathematical model.Finally,the numerical simulation program BEASY was used to study the corrosion effect of DC stray current that an auxiliary anode bed generated in an impressed current cathodic protection system.The effects of crossing angle,crossing distance,distance of the two pipelines,anode output current,depth,and soil resistivity were investigated.Our results indicate that pipeline crossing substantially affects the corrosion potential of both protected and unprotected pipelines.Pipeline crossing angles,crossing distances,and anode depths,our results suggest,have no significant influence.Decreasing anode output current or soil resistivity reduces pipeline corrosion gradually.A reduction of corrosion also occurs when the distance between two parallel pipelines increases.

Implementation of a Nesting Repair Technology for Transportation Pipeline Repair

Filling methods in the mining industry can maximize the recovery of mineral resources and protect the underground and surface environments.In recent years,such methods have been widely used in metal mines where pipeline transportation typically plays a decisive role in the safety and stability of the entirefilling system.Because thefilling slurry contains a large percentage of solid coarse particles,the involved pipeline is typically eroded and often damaged during such a process.A possible solution is the so-called nesting repair technology.In the present study,nesting a 127 mm outer diameter pipeline in 151 mm inner diameter borehole is considered to meet the repair objective.First,by using the rheological theory,the pipeline transmission resistance and self-flow conveying range are calculated under different working conditions.It is shown that the pipeline transmission resistance is larger when the inner diameter of casing is 80 mm,and the limitflow rate of vertical pipeline self-flow is 120 m^(3)/h;moreover,when the pipeline diameter is 100 mm and theflow rate is 140 m^(3)/h,the self-flow conveying can be satisfied in most of the underground−455 m stage.Accordingly,a plan is presented for the nesting repair strategy,based on the installation of a drill bit under the casing and lowering the casing into the borehole as if it were a drill pipe.Finally,the outcomes of such a strategy are verified.Thefillingflow rate range using the new pipelines is found to be in the range from 188.60 to 224.39 m^(3)/h,and its averagefillingflow rate reaches 209.83 m^(3)/h when conveying 2319.6 m long-distance quarry.

Relationship between microstructure and hydrogen induced cracking behavior in a low alloy pipeline steel

Hydrogen induced cracking（HIC） behaviors of a high strength pipeline steel with three different microstructures, granular bainite ＆ lath bainite（GB ＋ LB）, granular bainite ＆ acicular ferrite（GB ＋ AF）, and quasi-polygonal ferrite（QF）, were studied by using corrosion experiment based on standard NACE TM0284. The HIC experiment was conducted in hydrogen sulfide（H_2S）-saturated solution. The experimental results show that the steel with GB ＋ AF and QF microstructure present excellent corrosion resistance to HIC, whereas the phases of bainite lath and martensite/austenite in LB ＋ GB microstructure are responsible for poor corrosion resistance. Compared with ferrite phase, the bainite microstructure exhibits higher strength and crack susceptibility of HIC. The AF ＋ GB microstructure is believed to have the best combination of mechanical properties and resistance to HIC among the designed steels.