Cathodic Protection Performance Improvement For The Buried Gas Pipe Installed By Directional Drilling

Urban gas pipeline installed by directional drilling usually employ anti-corrosioncoatings and sacrificial anode to prevent metal corrosion. Because of the long distanceof the directional drilled pipe and the limited length of the sacrificial anode canprotect, the cathode protection may not meet the required standards. When there isdynamic DC stray current, the cathode protection system is difficult to provideadequate protection.Once the metal corrosiontakes place and form a holeon the buriedpipe, the repair is is difficult and can bring serious disaster.The cathode protection performance improvement for the buried gas pipe installed bydirectional drilling is investigated in the current study based on an actual project Sincethis stray current is mostly dynamic DC interference, and the data are dynamicallychanging, it brings difficulties on impact assessment and improvement for cathodicprotection system. As a new numerical method, Boundary Element Method is basedon the basic solution from a control differential equation of the problem to build aboundary integral equation and obtains the unknown number in the linear equationat the boundary by adopting the discrete means and interpolation, and finally toacquire the desired physical quantities. According to the former testing data, pipelineroutes, the types of sacrificial anodes and subway distribution, this research adoptsboundary element method to build numerical model for the stray currentinterference of subway and cathodic protection system, and via modeling the electricpotential of magnesium anodes and current density, stray current values and theeffect of subway parallel length on the cathodic protection system for cross sections,to get the distribution laws for the electric potential of cathodic protection in crosssections of directional drilling and the protection impact assessment. In accordancewith this assessment results to improve cathodic protection system in directionaldrilling, a primary scheme adopting the combination of polarity drainage and forceddrainage is proposed. At the meantime, a optimizing analysis by using boundaryelement method is carried out for a variety of parameters in this scheme, and theoptimized scheme is used to guide the installation of drainage at the worksite andthe construction and calibration for the forced drainage station. Through the datatesting and impact assessment, the effect of cathodic protection system in crosssections of directional drilling is improved, and meet the criteria for cathodicprotection. Consequently, it provides guarantee for the operating safety of pipelines.