Page 12 - DISS_NYRKOVA

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Cathodic polarization at a potential of -1.45 V, leads to a more rapid

disbondment of artificially aged tape coating as compared to the new one

(disbondment radii, respectively, are  26.9 mm and  9.4 mm). At such a

potential, the disbondment radii of thermosetting coatings of a new generation in

different state differ little (21.9 for the new one and 20.4 mm for artificially

aged polyurethane, 22.9 mm for epoxy coating in both states). Reduction in the

cathodic potential to the level of the minimum protective one contributes to the

preservation of the protective properties of polymeric coatings: new and aged

tape one is by 9.4 and 26.9 times, respectively; new hybrid-epoxy one is by

3.3 times, aged is by 1.7 times; new and aged polyurethane is by 20 times.

For the first time, a procedure for determining potentially corrosion

hazardous sections of main gas pipelines under the cathodic protection was

developed and implemented based on analysing data of designing, executive and

operational documentation and ground technical diagnostics and laboratory

tests, calculation of corrosion cracking probability and ranking the areas as to

the level of a potential corrosion hazard. The probability of corrosion cracking

on the sections of three main gas pipelines in Ukraine was evaluated and it was

shown that on the sections, which were determined as potentially corrosion

hazardous, failures as a result of corrosion cracking were revealed. Therefore,

the developed procedure provides a quite accurate determination of the sections

with an increased corrosion hazard.

For complex anticorrosive protection of a linear part of main gas pipelines

on potentially corrosion hazardous sections, the recommendations were

developed, which have the following main provisions: to supplement the

procedure of technical diagnostics by evaluating the susceptibility of steel to
corrosion cracking in laboratory conditions according to the developed

procedure; to apply protective coatings of very strengthened B type for
protection against corrosion, produced in factory or basic conditions (the main

criterion of their choice is resistance against cathodic disbondment) for the