Corrosion resistance of welded tubing of L80 strength group of different chemical composition

Abstract

In previous publications, it was shown that the use of low-carbon steels with bainite hardenability alloyed with chromium, molybdenum and other carbonitride-forming elements is promising for the production of cold-resistant and SCC (sulfide stress corrosion cracking)-resistant electricwelded tubing (tubing). Tubing is often operated in CO2-containing corrosive environments, therefore, determining the steel resistance to this type of corrosion is an urgent task. It is known that the addition of chromium to steel increases not only its hardenability, but also its resistance to CO2 corrosion. Influence of other alloying elements is not obvious. For the laboratory experiment, nine variants of the chemical composition of steels for the production of welded tubing were developed. The rolled test steels were investigated. Results of the studies of corrosion resistance of these steels are shown and compared. The authors made an assessment of influence of the main alloying elements on resistance to CO2 corrosion. The steels with different contents of Cr, Mo, V, Mn, Zr were studied for resistance CO2 corrosion at different temperatures. It has been established that the steel chemical composition and the test conditions determine the composition of CO2 corrosion products, affect the process of formation and growth of corrosion products, thereby affecting corrosion resistance. Decrease in the corrosion rate of chromium-alloyed steels can be associated with the protective properties of the corrosion products formed during testing. Laboratory corrosion tests for resistance to CO2 corrosion at an elevated temperature of 65 °C and subsequent studies of the formed corrosion products revealed a positive effect of chromium and molybdenum on the rate of general corrosion by mechanism of formation of dense corrosion products that perform a protective function.