PSI - Issue 16

Roman Dzhala et al. / Procedia Structural Integrity 16 (2019) 218–222 4 Roman Dzhala , Vasyl’ Dzhala, Roman Savula, Oleh Senyuk, Bohdan Verbenets’ / StructuralIntegrity Procedia 00 (2019) 000 – 000

221

nc n n n J J J l /    , m

-1 ,

( 6 )



 1 2

where – the average value of current in pipeline at n -th interval. The relative linear density of current leakage δ J n is proportional to the electrical conductivity of insulation coatings and is considered as damage indicator of UP insulation: the maximum value of δ J n indicate the location with the least TR of the protective coatings. nc n n J J    J

4. Special contact measurements of polarization and ohmic potentials

Polarization and ohmic potentials, both constant and alternating voltages, are measured simultaneously (Dzhala at al. (2017)), which gives additional information and has significant advantage compared with known methods (DSTU 4219-2003). A copper sulfate reference electrode is located along axis of UP. The constant difference between potentials U mg and alternating voltage V mg between UP and reference electrode located in the medium, and potential difference U gg and alternating voltage V gg between two electrodes (reference and auxiliary) on the earth were measured. Then polarization potential is calculated by the formula as: / p mg mg gg gg U U V U V    . (7) For the implementation of the described method a special device for measuring polarization and ohmic potentials VPP (Dzhala at al. (2018)) was developed. Measurements of constant and variable voltages are used to find damages of UP insulation using known Pearson and transverse gradient methods. Analysis based on the measured value of U P enables controlling efficiency of anticorrosion protection of metal in conductive medium.

5. Determination of the components of transitional resistance of UP

The insulation resistance of a certain area (interval) of UP using low frequency alternating current can be considered as active, it means its reactive component can be neglected (Dzhala at al. (2018)). Then resistance of insulation under real conditions (saturated with moisture, with pores and defects) can be determined by the formula:

in n in R V j /  ,   m 2 ,

(8)

where density of alternating current flow j n in this section is determined using CMC. The alternating voltage on the insulation V in is determined by measurements of voltage V mg between the pipe metal and the comparison electrode, located on the earth surface above UP, and of V gg on the earth surface between two electrodes (reference and auxiliary) spaced at a distance x . It was demonstrated by Dzhala at al. (2018) that if the distance x is chosen taking into account the depth and diameter of the UP by the formula 2 2 1 . h x h D         , (9) then the measured voltage on the earth surface above the UP V gg = V x equals the voltage drop V G in the soil above the UP V gg = V G . Then, to determine the insulation resistance, the electric voltage on the insulation should be obtained: V in = V mg – V gg . (10)

If direct current is applied, the transition resistance of the section metal – soil is determined by the ratio