When the variable variation range is not too large, the prediction accuracy can be much higher than the previous example. In addition, for some specific conditions, there are the following simpler methods of discrimination. Newly-built or short-lived pipelines can assume that the membrane resistance R0 is zero, and determine L and k according to the binary linear equation. In general, the membrane resistance causes a small IR drop, such as RD = 1m2, i = 20mA / m2, IR drop = 20mV. The following are considered as ignoring RD. 2 Newly-built or better-quality coatings, assuming that the defects are small (for example: d for a single thin coating and many defects, if the defect path item is negligible compared with the size item. Then the IR drop mainly depends on the defect size d, That is: (IR / i) = 0711d (9) As above, suppose i and value, then when d according to the above example, assuming that the known defect path parameter is 87cm, introduce the defect size correction factor P, the value of which is shown in Table 2. The corresponding IR The descending discriminant is: (IR / i) = 00872P (10) 5 In the formula, the current density can refer to the design value of cathodic protection, or it can be determined on site by the cathodic polarization experiment on bare steel test pieces.
In the soil and water environment, the current density of steel to establish cathodic protection is 1mA / m2200mA / m2. Stray interference currents can exceed this range, making IR drop prediction more difficult. This article discusses the relationship between IR drop and soil resistivity and defect size at normal current density. The graph can easily determine the magnitude of IR drop measured by cathodic protection potential under specific current density, soil resistivity and defect size.
Three kinds of current density are given: 20mA / m2 represents the normal protection current density; 1mA / m2 represents the lowest value, and 200mA / m2 represents the highest value. Exceeding this value generally only occurs in chemical media, or the presence of stray currents in the soil. The area enclosed by the curve (lower right) represents the negligible IR drop (the IR drop in cathodic protection potential measurement is a function of factors such as soil resistivity, coating defect size, and current density flowing into the coating defect; the IR drop is always equal to The current density i is proportional to the definition of (IR / i) as the IR drop resistance factor to simplify the calculation. The near reference method cannot effectively eliminate the IR drop error under extremely high soil resistivity conditions.
Pipeline coating defects are the main factors causing IR drop, which can be divided into membrane resistance, defect path resistance and stray current resistance. 4 Various simplified methods for estimating IR drop in engineering are proposed.
Atv Vehicle,All Terrain Vehicle,All Terrain Farming Vehicle,Racing Quad Atv
Binzhou Daowang Power Co.,Ltd , https://www.dwutv.com