Influence of cathodic polarization on the properties of epoxy powder coatings

Issue 24(4) 2019
Pages 7-14

D.N. Zapevalov, Gazprom VNIIGAZ LLC, Moscow region, village Razvilka, Russian Federation

A.Р. Sazonov, Gazprom VNIIGAZ LLC, Moscow region, village Razvilka, Russian Federation

E.V. Sheverdenkin, Gazprom VNIIGAZ LLC, Moscow region, village Razvilka, Russian Federation

A.V. Latyshev, Gazprom VNIIGAZ LLC, Moscow region, village Razvilka, Russian Federation

N.I. Savostina, Gazprom VNIIGAZ LLC, Moscow region, village Razvilka, Russian Federation

Z.P. Semikolenova, Gazprom VNIIGAZ LLC, Moscow region, village Razvilka, Russian Federation


Keywords: main pipelines, epoxy powder coatings, coating defect, shock load, cathodic polarization

http://www.doi.org/10.31615/j.corros.prot.2019.94.4-1

 

The article discusses the effect of cathode polarization on the protective properties of powder epoxy coatings, assesses their operational reliability, statistics of failures and describes the problems found during their operation. 

In the process of applying commercially available pipes with epoxy powder coating on the existing gas pipeline, a not previously manifested defect was observed - the formation of dome-shaped swellings. This led to some restrictions on the use of epoxy powder coatings.
With the advent of a new generation of epoxy materials, as well as in connection with the revision of the regulatory documentation GOST R 51164-98, the issue of removing these restrictions on their use for insulating large diameter pipes (up to 1,420 mm). Without additional protection has become topical.
As a result, it became necessary to estimate the probability of the appearance of defects of this type when using modern powder coatings. We carried out laboratory studies of the effect of cathode polarization on the properties of modern two-layer epoxy coatings after exposure to them of shock loads of a certain size.
The results indicate that the impact of such a mechanical load may cause the appearance of microdefects of the coating, which are not determined by the existing methods of control. Due to the penetration of electrolyte under the coating and the occurrence of certain physicochemical and electrochemical processes that are enhanced by imposing the potential of cathodic protection and increasing the operating temperature, these microdamages can serve as active centers for the formation of a cupola-shaped swelling.