PSI - Issue 16

220 Roman Dzhala et al. / Procedia Structural Integrity 16 (2019) 218–222 Roman Dzhala , Vasyl’ Dzhala, Roman Savula, Oleh Senyuk, Bohdan Verbenets’ / Structural Integrity Procedia 00 (2019) 000 – 000 3 i pg = Δ I / π DL , A / m 2 , R PG = U PG / i pg , Ω· m 2 . (2) In the method of the signal attenuating (Dzhala at al. (2018)) the patterns of voltage and current distribution in long pipeline are used. Additional line parameters are needed, including longitudinal resistance R LP of pipeline. R PG = π DL 2 · R LP / ln 2 ( U 2 / U 1 ), Ω· m 2 . (3) The method of input resistance uses the ratio of measured voltage and current values at the site of a homogeneous long pipeline with its longitudinal R LP and transverse R PG resistance: Control of the TR of UP protective coatings during operation is recommended by the DSTU 4219-2003 to be carried out by the integrated estimation method on the basis of measurements of parameters of electrochemical protection. The main disadvantages of the method are incorrect determination of current density i and difficulty of a finding the current emission resistance in soil because of needed parameters of soil and metal are sometimes unknown. In addition, according to the method (DSTU 4219-2003), length L of the action zone of the cathodic protection installation (CPI) can be incorrectly determined, since it is unknown which part of current of CPI flows into the UP under so-called "end zone"(Nykyforchyn at al. (2009)). Consequently, the method gives some value of insulation TR, averaged over the entire zone of action of CPI (for tens of kilometers). This value may differ significantly from the actual values TR for certain sections (parts of this zone). This makes it impossible to use it to control the distribution of insulation resistance along the route and to find insufficient UP insulation. Thus, the known methods for determining TR of protective coatings have some disadvantages. As shown below, these disadvantages are eliminated by a usage of CMC developed by Dzhala at al. (2018). For diagnostics of underground pipeline the theoretical bases of the CMC method, systems of component and modular primary transformers were developed (Dzhala at al. (2018)). A new method of CMC with azimuthal and radial orientations of observation sites was proposed. New equipments such as BIT-3, BIT-K, BVC for contactless UP examinations were developed and implemented at examinations of aboveground and underground gas and water pipelines (Nykyforchyn at al. (2009)), which validated the contactless method. The methods for determining parameters of insulation and electrochemical anticorrosion protection of steel of UP were developed, and the technology of contactless integral, differential and local inspection of corrosion protection of UP for CMC using contact electrometry was proposed (Dzhala at al. (2017)). The proposed methodology for usage of contactless integral, differential and local inspection consists in the following. As a source of probing current, CPI is used, which supplies a stable pulse current to the pipeline under inspection. In the absence of CPI, an alternating current generator of low (<1.5 KHz) frequency can be used. In the non-contact method a value of the current J p (Dzhala at al. (2018)) is measured, which flows through the UP at the points n = 0, 1, 2, ..., spaced along the UP. The next step is determining length of intervals l n as a distance of each subsequent measuring point of current from the previous one along pipeline. For small changes of current along the pipeline (with good insulation) the interval l n is increased. For large changes of current the interval is reduced to values which are proportional to a depth of occurrence of UP. The current loss at each interval l n of UP, located in one shoulder zone of the source of sounding current is determined: U 0 / J 0 = ( R LP · R PG / π D ) 1/2 . (4) 3. Methods and means of contactless measurements of the UP currents

1     n n n J J J , А.

( 5 )

The relative linear current density (relative current consumption per length unit of pipeline) is calculated: