Page 15 - DISS_NYRKOVA

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proposed and substantiated: if K  1.60, the steel is prone to corrosion
S

cracking.

2. A new method for evaluating the susceptibility of steel of different

strength categories to corrosion cracking in the conditions of cathodic protection

was substantiated and proposed and the coefficient K was introduced, in which
τ
the change in the length of the areas from the beginning of the destruction of the

sample until its rupture in air as compared to the solution (patent for invention

119578) was taken into account.

о
3. It was shown that at a cyclic change in temperature (from 20 С to
о
50 С) cathodic disbondment of protective coatings from X80 steel occurs more
intensely than from X70 steel: polyurethane one is by 39 %, epoxy one is by

9 %, tape one is by 34 %. Epoxy coating was determined to be the most

resistant against cathodic disbondment.

4. It was experimentally proved that maintaining the protective potential

at the level of -1.45 V leads to a more rapid disbondment of artificially aged tape

coating as compared to the new one (approximately by 3 times). Cathodic

disbondment of new and artificially aged thermosetting coatings of a new

generation (hybrid-epoxy type Polyclad 975 N and polyurethane type Polyclad

777) at the maximum protective potential almost do not differ. Reduction in the

protective potential to a minimum value helps to preserve the protective

properties of polymeric coatings: new and aged tape coating is by 9.4 and

26.9 times respectively; new hybrid epoxy coating is by 3.3 times, artificially

aged coating is by 1.7 times; new and artificially aged polyurethane coating is

more than by 20 times.

5. A procedure for determining potentially corrosion hazardous sections

under the conditions of cathodic protection on existing main gas pipelines in

Ukraine were developed and implemented (brought into force on 01.09.2010 by

the order of SC "Ukrtransgaz" No. 323 of 04.08.2010).

6. The main conclusions, recommendations and proposals of the thesis