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areas, on which pipes from steels of an increased strength (580 MPa and higher)

are laid, to maintain polarization potentials at a level not lower than -1.10 V

(relative to c.s.e.).

The results of the work were implemented during the development of the

main provisions of SOU 60.3-30019801-070, DSTU N B A.3.1-29, changes

No. 1 to DSTU 4219.

Scientific novelty of the obtained results.

1. For the first time a new scientific approach to the study of the influence

of different factors on the regularity of the process of corrosion cracking of steel

pipe assortment (on the example of X70 steel) was developed, which is based on

modeling the peculiarities of their action in laboratory conditions, which are

identical to the conditions of the main pipeline operation, which allowed

evaluating the susceptibility of the steel to corrosion cracking under such

conditions.

2. A set of factors was revealed, that cause degradation of polymeric

coatings (in particular, of a tape one) applied to pipe steel during cathodic

protection, namely: presence of defect in the coating, its contact with a corrosive

environment and cathodic polarization. It was shown that an increase in

о
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temperature from 20 С to 50 С accelerates this process, which continues its
development over time. After 2.5 months of contacting with the environment,

the primer layer of tape coating is exposed to degradation, which is confirmed

by the appearance of bands of inorganic fillers – calcium carbonate and talc in

the infrared spectra. The properties of polyethylene tape do not change during

the mentioned period. Presence of destruction products of the primer layer in the
test solution improves the susceptibility of X70 steel to corrosion cracking.

3. It was for the first time determined, that under the conditions of a long-
term action of metal deformation in a model soil electrolyte at a cathodic

polarization at a potential of -1.0 V, for X70 steel subsurface corrosion is
inherent, and for X80 intergranular fracture is typical, caused by the hydrogen

penetration into the metal. The rate of propagation of corrosion cracking in X80