INVESTIGATION OF THE CORROSION BEHAVIOR OF ALUMINIUM 1980T1 IN SEAWATER AND DRILLING MUD BY ELECTROCHEMICAL METHODS

Abstract

The main methods of corrosion protection of equipment and metal structures of offshore drilling platforms are considered. The corrosion resistance of the high-strength 1980T1 aluminium alloy used for the manufacture of the riser in seawater and drilling mud, the effectiveness of its protection with zinc-rich coatings using the methods of polarization resistance, potentiometry, as well as appearance assessment studied. In seawater at 20 and 40 °C, alloy 1980T1 refers to resistant materials - 3-4 (6 grade according to GOST 5272- 90), intense pitting formation is observed, in drilling mud the corrosion rate (Km) increases more than 10 times refer to seawater (low-resistance, 6 grade), which is due to the alkaline nature of the medium. There is intense continuous corrosion, large pitting, ulcers on the seam and its border. In seawater at 20 °C, the Km of aluminium and coatings are comparable. In the drilling mud at 20 °C, the coatings provide a 2,5…4-time reduction in Km. After 30 days of exposure in seawater and drilling mud at 20 °C, the zinc-polyurethane coating detached to40…70%, intense pitting of base observed. Bubbles all over the surface of zinc-epoxy coating observed. Zinc-silicate and zinc-polyurethanalkyde coating with a high concentration of zinc had only small delamination in the weld area. In seawater at 20…40 °С and drilling mud at 20 °C zinc-silicate coating has the greatest tread capacity, the zinc-polyurethane, zinc-polyurethanalkyde and zinc-epoxy coatings are insignificant. Additional protection of welds and pipe surfaces in seawater achieved using insulated, metallized, protective coatings and cathode protection, in drilling mud it is also necessary to study the possibility of pH reduction and the use of effective corrosion inhibitors.