Features of Corrosive Breakdown of Pipe Steel in Gas Condensate

Features of corrosion failure of the inner surface of a pipe extracted from the well of the Denzikul’ field (Uzbekistan) after 256 days of operation are studied. Corrosive environment: gas condensate under a pressure of 6.5–7.5 MPa, temperature of 60°C and density of 826 kg/m³ contained water with a total mineralization of 12.75 g/m³, hydrogen sulfide and carbon dioxide 3.5 and 4.76% (vol.), respectively. A fragment is cut out of the pipe at the inner surface that has through corrosion failure in the form of a triangle, at the base of which, apparently there is a manufacturing macro defect that propagates in the direction of gas condensate movement. Corrosion damage located along the perimeter of the triangle has two characteristic areas: uniform, close to a through hole, and intense corrosion. The width of each of the regions reaches 30 mm in the areas located at the apex of a triangle. The transition from uniform to intense corrosion is accompanied by formation of black protrusions 4–6 mm high and up to 3 mm in diameter, which collapse during transition into the area of general uniform corrosion observed over the rest of the pipe inner surface. The authors attribute features of the nature of corrosion damage observed to interaction of corrosion-active non-metallic inclusions (CANI) with gas condensate and an accelerating effect of hydrogen penetrating into steel on the corrosion process along with appearance and an increase in the level of triaxial tensile stresses in the vicinity of corrosion-active non-metallic inclusions.