PSI - Issue 16

Roman Dzhala et al. / Procedia Structural Integrity 16 (2019) 218–222 2 Roman Dzhala , Vasyl’ Dzhala, Roman Savula, Oleh Senyuk, Bohdan Verbenets’ / StructuralIntegrity Procedia 00 (2019) 000 – 000

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proper anticorrosion protection, as was shown by Dzhala at al. (2018), Nykyforchyn at al. (2009), Strizhevsky at al. (1981) and others. However, it is known that pipelines with identical insulation coatings operated in soils with different resistivity have different transient resistance. Therefore for proper diagnostics it is necessary to determine components of TR of UP. The practical importance of TR and the difficulty of its measure in real conditions is considered in many researches; and a number of methods are proposed for determination of TR (DSTU 4219-2003, Strizhevsky at al. (1981)). For UP examinations, contact electrometric methods are traditionally used, the main disadvantages of which are complexity and insufficient informativeness. They can be eliminated by the usage of contactless measurements of currents (CMC) in combination with a new method of polatisation potential measurement (PPM), which enables improving significantly the efficiency of diagnostics of UP (Dzhala at al. (2018)). The purpose of the work is to develop the method for determining the TR components of underground pipeline on the basis of the known regularities of electromagnetic field distribution of UP and using the new methods and means of CMC and PPM in order to eliminate disadvantages of known contact methods. Resistance of input (output) of electric current from environment to a metal pipe – transient resistance R mg is the main parameter of passive protection against corrosion damaging in an electrically conductive medium. The main components of R mg are: contact resistance R c at the metal – environment boundary, resistance of isolation R i and resistance to current flux in soil R g . These components are necessary for designing, adjusting and control of corrosion protection and diagnostics of the technical condition of underground and underwater metal structures. TR R mg on surface with an area S is defined (Nykyforchyn at al. (2009)) as R mg = U mg S / ΔI, Ω·m 2 , (1) where U mg – potential difference metal – soil; Δ I – current flow in this area. A quality of UP insulation is mainly characterized by TR of insulation ((Dikmarova and Kornienko (2002), Nykyforchyn at al. (2009), Strizhevsky at al. (1981), DSTU 4219-2003). In particular, if R i > 10 000 Ω·m 2 – the insulation is good, the damage are small and single; if R i < 500 Ω·m 2 – insulation is poor, the damage is large and significant. The resistance to current flux R g depends on the electrode geometric parameters (diameter and depth of a pipe) and electrical conductivity of soil  g , which is considered as an indicator of corrosive aggressiveness (Dzhala at al. (2018)). Polarization resistance R pol is related to the electrophysical processes on the boundary metal – medium and can be used for an evaluation of corrosion rate (Dzhala at al. (2018), Herasymenko at al. (2017), Mansfeld (1976), Zvirko et al. (2017)). The complexity of the determining R mg of protective coatings of UP at a certain site of pipeline is due to large length of UP and lack of access to its surface. One of the most used local methods of control is the method of "wet" contact (DSTU 4219-2003, Strizhevsky at al. (1981)). For its implementation, access to pipeline surface and the special band-electrode for passing current to the metal are required. TR is determined by the formula (1) based on the measured difference in potentials. The main disadvantages of this method are: a need for shurfing (excavation of the site UP); limited (local) control zone; violation (removal of soil) of the pipe surrounding conditions. The method enables determining only resistance of isolation R i . It should be noted that physical and chemical properties of insulation can be changed by wet contact and can be different than that of UP. This method should be considered as an additional only, since sample estimations have a random character and do not have reliable results on a state of protective coatings adjacent sections of the UP. The method of the leakage current (Dzhala at al. (2018)) assumes determination of current density i pg , which flows from UP surface into soil surrounding the certain section of pipeline, and measurement of potential difference U PG of pipe – earth. The ratio of the measured parameter values gives the integral value of TR of protective coatings of UP with a diameter D according to the formulas: 2. The physical essence of transition resistance and analysis of methods for its determination