INFLUENCE OF INSULATION DEFECTS SIZE ON PIPELINE AC CORROSION

L. Ya. Poberezhny, V. S. Tsykh

Abstract


Due to the growing needs of both the population and industry, in a significant amount of natural gas and an increase in electricity consumption, it is not always possible to differentiate the corridors of the parallel leakage of alternating current and pipelines or to maintain the distance specified by the regulatory documents. To determine the likelihood of corrosion alternating current induced voltage indicator only and not be taken into account other factors such as current density, or the ratio between the values of the AC and DC. Such a criterion for estimating the risk of corrosion by alternating current as the alternating current density is more accurate and takes into account a greater number of factors (soil resistance, defect area) that affect the course of corrosion processes. The regularities of increasing the level of alternating current density in soils with low, medium and high values of corrosion activity are established in the paper. The method of calculation is to determine the current density on the defect of the circular coating, since according to the results of surveys, defects of protective coating of round shape or punctures with a diameter of 0.005 m are most common. In the normative documentation, the area of the standard defect in the insulation coating is equal to 6,25 × 10-4 m2 (d = 0,0282 m), in foreign standards, the area of the defect was adopted 1 · 10-4 m2 (d = 0,0112 m). With a constant diameter of the defect in the protective coating, the density of the alternating current will be higher, the less the electrical resistance of the soil. Appropriate calculations have been made to establish the relationship between the level of the UPS, the defect size and the induction current density. The voltage range of the induced alternating current is selected in the range from 1 to 120 V (1, 5, 10, 15, 20 and further in step 10 V), and the dimensions of the defects are selected as follows: 0.005; 0.011287; 0.02; 0.0282; 0.05 and 0.1 m. An area nomogram relationship between the defect in the protective coating and the largest current density in the range induced voltage. At constant current density and soil resistance small defects exposed to corrosion rather than defects in large area, since the current density on a smaller defect will increase. The smaller the defect in the protective coating, the greater the likelihood of corrosion by alternating current. The obtained data will allow to determine the areas of pipelines with high risk of electric shock with an alternating current and to prevent the emergency situations in a timely manner.


Keywords


AC corrosion; induced current density; corrosion activity; electrical conductivity of soil

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References


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DOI: https://doi.org/10.15421/40270524

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