STRESS-CORROSION FRACTURE OF ELECTRIC-WELDED PIPES IN THE HIGH-AGGRESSIVENESS OILFIELD MEDIUMS

Pipes welded from specially prepared sheet steel, in comparison with the seamless drawn ones, are characterized by the low cost, higher corrosion resistance, and dimensional stability. When ensuring the properties of a welded joint at the base metal level, they can compete with seamless pipes. To start using welded pipes made of new steels, long-term field tests in fields with high aggressiveness of extracted fluids are required. It is necessary to have the comparative results on corrosion resistance of the base metal and welded joints. The paper aimed at obtaining information on the mechanisms and kinetics of stress-corrosion fracture and the operating ability of electric-welded pipes during continuous service. The authors carried out the field (bypass) tests of the electric-welded pipe spools made of 08HMFChA, 13HFA, 09GSF, and 20-KSH steels on the operating oil gathering main of Mamontovskoye oilfield of Western Siberia with the high content of H₂S and CO₂ dissolved gases and bacterial contamination. The study identified the rates of general and local corrosions of base metal, welded joints, and the area of low generating lines of the pipe. The study showed the peculiarities of corrosion fracture initiation and development and change in the rate of general and pit corrosions depending on the chemical composition of steel and its running time. The authors identified the interrelation of the dependence of change in the rate of corrosion fracture with the increase in the running time on the composition and structure of the corrosion products. For the chromic steels (08HMFChA and 13HFA), chromium concentration in the corrosion products is the main factor of surface passivation. The authors proposed the passivation coefficient, in other words, the criterion for evaluation of change in the corrosion rate during running time.

corrosion fracture, carbon dioxide corrosion, bacterial corrosion, corrosion products, welded pipes, welded joint, mechanical properties, oilfield medium, field tests, self-passivation