Modification of Bbituminous Coatings to Prevent Stress Corrosion Cracking of Carbon Steel

Stress corrosion cracking (SCC) is the most dangerous kind of pipelines corrosion. The SCC appears on the stressed metal due to contact with aggressive media through the rupture of polymer coating. Inhibition of the SCC is one of the urgent tasks of corrosion protection of underground pipelines. The research reports the method of inhibiting the SCC of pipe steels by modification of polymer protective coatings.

With help of slow strain rate test (SSRT) the effect of general corrosion inhibitors and surfactants on the propensity X70 pipe steel to the SCC in aggressive electrolytes has been investigated. The vinyl-containing silane (VS) is shown to be an effective inhibitor of SCC of steel.

The VS has been proposed as a modifying additive to a bitumen coating (DEKOM-GAZ type). Modification of coating should provide both satisfactory adhesion and exit of the SCC inhibiting compounds to electrolyte under film and their adsorption onto the metal surface in the case of mechanical damage or loss of adhesion.

Peel shear test at an angle 90° away from steel plate has been used for evaluation of adhesive properties of modified coating. It has been shown that the additive of the VS does not impair the adhesion of the protective coating. Using FTIR microscopy output of the inhibitor molecules from the polymer matrix to solution and their adsorption onto the metal surface was evaluated. The aqueous extract obtained by exposure of the polymer coating with the addition of the VS in contact with water for 30 days has been investigated. IR-spectra analysis showed that predominantly the VS goes from the coating into solution and adsorbs on the metal surface.

Thus the modified polymer coating, the use of which will prevent the development of SCC of carbon steel, has been developed.