دانلود رایگان مقاله خوردگی الکترولیتی سیستم خط لوله آب در فاصله از راه دور

Abstract

Case study of corrosion failure of urban water supply system caused by the harmful effects of stray currents was presented. The failure occurred at a site distant from the sources of these currents namely the tramway and railway traction systems. Diagnosis revealed the stray currents flow to pipeline over a remote distance of 800/1000 m from the point of failure. At the point of failure stray currents flowed from the pipeline to the ground through external insulation defects, causing the process of electrolytic corrosion of the metal. Long distance between the affected section of the pipeline and the sources of stray currents excludes the typical protection against stray currents in the form of electrical polarized drainage. Corrosion protection at this point can be achieved by using the earthing electrodes made of magnesium, which will also provide cathodic current protection as galvanic anode.

5. Summary

Failure diagnosis made on the case of pipeline corrosion showed that in places of external insulation leaks occurred an electrolytic corrosion process. Metal oxidation was caused by the out-flow of stray currents from pipeline to soil. These currents in-flow to the pipeline in the area of the crossing under railways and tram, where both tractions run parallel to each other within a short distance. The flow of currents through pipeline takes place on the significant distance from traction. Out- flow of stray currents from the pipeline to the ground at the point of failure favored the configuration of the traction and the water supply system and the associated electric field distribution in the ground. Elimination of the risk of water supply system electrolytic corrosion in the area of the point of failure can be achieved by using magnesium sacrificial anodes. They served also as the earthing electrodes through which stray currents can flow from the water supply system to the ground (instead of through the interface metal/electrolyte), and will be a source of cathodic protection current performed by means of sacrificial anodes.