PSI - Issue 81

Roman Dzhala et al. / Procedia Structural Integrity 81 (2026) 98–101

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The use of NCM (Dzhala 2024) makes it possible to carry out integral and differential express monitoring of the condition of the pipelines of various pipeline branches (to identify the least protected sections of the pipeline) and local detailed monitoring in combination with contact methods. 4. Synergy of non-contact and contact methods of UP NDT The measured values and the parameters of the UP ACP determined from them are given in Table 1. Non-contact from the surface above the route, we measure the current J strength flowing along the UP, and the depth h of the pipe in ground. Contactless current measurements J n at different points n of the UP and the distance  z n between them give the values of current consumption  J n at different intervals  z n of the UP length, relative consumption  J n , current attenuation  n along the UP and the transition resistance "pipe-ground" R PG ( z ). On the other side, contact measurements of direct potentials U gg , U mg and alternating electric voltages V gg , V mg give the values of the harmonic coefficient k n and the protective polarization potential U p . At the same time, the combined use of non-contact and contact measurements gives a synergistic effect: in addition to the above parameters (from each separate method) we additionally obtain the soil resistivity  g , metal-soil transition resistance r mg , resistivity of the UP insulating layer r i , cathodic protection current consumption  I n and polarization resistance R p , which can be used to estimate the UP corrosion rate. Table 1. Measurement values and determination of parameters of UP anti-corrosion protection. Dimen sions Parameters of underground pipelines ACP  J n  J n   n R PG ( z )  g r mg r i k n  I n R p U p J n + + + + + + + + h + + +  z + + + + + + V x + + + + + + U x + + + + U mg + + V mg + + + + 5. Example of NDT of the parameters of the UP corrosion protection. Diagnostic examinations of the condition of anti-corrosion protection (ACP) for sections of main pipelines and pipeline networks were carried out using new non-contact and traditional contact electrometric methods, during which the basic NDT procedures were developed. Fig. 1 shows the results obtained by the NCM for determining the distribution along the UP of the transition resistances "pipeline metal - ground" r mg and the insulating layer r i . Two intervals of the UP length with reduced values of transition resistances are visible, which are classified as "insulation damage". Fig. 2 shows the results of contact measurements of the potential difference "pipe-ground" and polarization potential U p of the UP on the same section of the pipeline route. At intervals with damaged insulation of the UP, we have a decrease in potentials. At the same time, at the first insulation damage, we have a protective potential within the normal range (the pipe is protected from corrosion). But at the second damaged insulation, the polarization potential is less than the standard U p < |-0.85| V. This is the most likely place of UP corrosion. To prevent corrosion, it is necessary to repair the insulation or adjust the electrochemical cathodic protection at the second interval of the UP length. Thus, during non-destructive testing of underground pipelines corrosion protection, it is advisable to first control the current distribution non-contact. This shows the distribution of the UP transition resistance (according to the distribution of relative current flows, which are quickly determined during the movement of the equipment along the UP). We identify places of anomalously high current flows, which indicate places of damage to the UP insulation. It is primarily advisable to measure the polarization potentials by contact in these places of high current flows. If cathodic protection is provided in these places, then the UP is protected from electrochemical corrosion and the potentials in neighboring areas can not be measured. This significantly increases the efficiency of the UP ACP NDT and reduces labor costs for diagnostic examinations of the UP.