Effect of the chemical composition of welds of pipelines on their resistance to crack propagation in hydrogen-sulfide environments

Abstract

We investigate the influence of the chemical composition of a weld metal on the long-term crack resistance under static loading in NACE hydrogen-sulfide solution. The effect of C, S, P. Mn, Si, Ni, Cu, V, Zr, Co, B, and Mo on corrosion-mechanical properties of welds is established. Welds containing about 0.11–0.14% C are shown to have the highest crack resistance. The optimum concentrations of manganese (∼0.6%) and silicon (∼0.3%), at which the maximum values ofK1ssc are obtained, are found. The admissible manganese and silicon contents are 0.39–1.0% and 0.2−0.5%, respectively. The susceptibility to cracking increases with sulfur and phosphorus contents. The highest values ofK1ssc were obtained at a sulfur content of 0.004 to 0.014% and at a phosphorus content of 0.014 to 0.023%. The adverse influence of these elements in welds is manifested to a lesser extent than in the rolled metal. Alloying with boron is inexpedient and dangerous. Joint alloying with 0.4–0.54% Cu and 0.1–0.3% Ni improves the crack resistance. The influence of molybdenum is analogous (K1ssc increases by 29–50%). Alloying with 0.5% Co and 0.05% Zr results in the formation of nonequilibrium structures. In this case,K1ssc is close to those of welds made with carbon steel electrodes. On alloying with 0.2% V, the fine structure forms, andK1ssc decreases by 20–30%. Alloying with vanadium in these amounts is inadmissible. Preference should be given to complex microalloying.