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

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 ofK _1ssc 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 ofK _1ssc 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 (K _1ssc increases by 29–50%). Alloying with 0.5% Co and 0.05% Zr results in the formation of nonequilibrium structures. In this case,K _1ssc is close to those of welds made with carbon steel electrodes. On alloying with 0.2% V, the fine structure forms, andK _1ssc decreases by 20–30%. Alloying with vanadium in these amounts is inadmissible. Preference should be given to complex microalloying. Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 35, No. 1, pp. 95–102, January–February, 1999.     

Evaluation of the resistance of corrosion-proof steels to corrosion cracking in hydrogen sulfide solutions

We study the tendency of corrosion-proof steels of the martensitic, martensite-ferritic, austenitic, austenite-martensitic, and ferrite-austenitic classes to corrosion cracking in hydrogen-sulfide-containing media. We have established that austenitic chromium-nickel-molybdenum (08Kh17N15M13T and 10Kh17N13M2T) and ferrite-austenitic (12Kh21N5T and 02Kh22N6AM3 steels are the most resistant to fracture: the threshold stresses in NACE solution (5% NaCl solution + 0.5% CH₃ COOH saturated with H₂S, 20±2°C, pH ∼ 3) are not less than 90% of the yield point. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 41, No. 6, pp. 103–107, November–December, 2005.     

Corrosion-mechanical resistance of pipe steel in hydrogen-sulfide containing media

We investigate the resistance to hydrogen-sulfide stress corrosion cracking and hydrogen-induced cracking of ASTM A333 steel intended for the oil and gas industry. On the basis of the results obtained for seven meltings of this steel supplied for the Tengiz gas-processing plant, we established that all meltings satisfy specifications of the NACE MR0175-96 standard in their chemical composition and strength characteristics (S < 0.005%. P < 0.025%, HRC < 22, etc.). For two of the seven investigated meltings, resistance to hydrogen-sulfide stress corrosion cracking is not high (threshold stresses < 0.8Σ^min _0.2) and one melting has a low resistance to hydrogen-induced cracking (coefficient of the length of regions of crack formation > 6% and coefficient of the width of regions of crack formation > 3%). Therefore, complete (100%) incoming control over the corrosion-mechanical resistance of all materials of equipment operating in hydrogen-sulfide-containing media must be carried out. Translated from Fizyko-Khimichna Mekhanika Materialiv. Vol. 36, No. 3, pp. 93–97, May-June. 2000.     

Serviceability of nickel alloys and some types of steel in hydrogen-sulfide-containing media

We analyze the sensitivity of 36NKhTYu, 36NKhTYuM5, 40NKKhTYuMD, and 75NKhTYuB nickel alloys and 17G1S and 08Kh17N15M3T steels to the action of hydrogen sulfide according to the criteria of threshold stressesK _Iscc by the method of tension with low strain rates. We study the electrochemical characteristics of the indicated materials and show that 75NKhTYuB and 36NKhTYu alloys are unsuitable for application in the oil and gas industry. The parameters of 40NKKhTYuMD alloy and 17G1S steel must be improved. The best operating characteristics are exhibited by 36NKhTYuM5 alloy and 08Kh17N15M3T steel (produced by the “Dneprospetsstal” plant). These metals can guarantee the required level of serviceability of equipment used in the oil and gas industry and operating in contact with hydrogen-sulfide-containing media. Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 33, No. 3, pp. 102–108, May–June, 1997.     

Corrosion cracking of cast Cr—Ni—Mo ferritic—austenitic steels

We study two-phase cast steels in aggressive media most extensively encountered in industry and nature, namely, chloride, alkali, and hydrogen-sulfide media. Unlike austenitic cast steels, two-phase cast steels prove to be promising structural materials for the operation in hot concentrated alkali media and chloride solutions of low concentrations. In the case where the concentration of chlorides may increase, working stresses can be found according to their threshold values. The two-phase cast steels are unsuitable for operation in hydrogenating media. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 41, No. 5, pp. 106–110, September–October, 2005.     

Investigation of the Serviceability of Tubing Strings Made of Steel of Strength Group K

The resistance of steel of strength group K to corrosion, hydrogen-corrosion, and stress-corrosion fracture is analyzed for hydrogen-sulfide-containing media of the Lokachi gas field and in the NACE solution. It is shown that the indicated type of steel is not susceptible to hydrogen-induced cracking, its resistance to sulfide fracture σ _ssc ≈ 0.8 σ_{0.2 min}, and the rate of corrosion is much lower than the dangerous threshold value. This enables us to conclude that the tubing and casing strings made of this type of steel can be safely exploited at the Lokachi gas field.__________Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 41, No. 1, pp. 109–110, January–February, 2005.     

Requirements to Crack Resistance of Materials of Oil and Gas Equipment Operating in Hydrogen-Sulfide Media

We investigate the crack resistance of low-alloy pipe steels, their welds, and nickel and titanium alloys in air and in a hydrogen-sulfide solution NACE. We determine the stress intensity factors in the course of testing in air K _c and in hydrogen sulfide K _Issc as well as the coefficients of medium influence B _Issc = K _Issc /K _c. We establish minimum admissible values K _Issc ^min and B _Issc ^min that ensure high serviceability of structural materials of oil and gas industry. We obtain that K _Issc ^min 33MPa· for low-alloy steels and welds, K _Issc ^min 70MPa· for nickel alloys, and K _Issc ^min 50MPa· for titanium alloys. The criterion B _Issc ^min 0.6 is the same for various materials. We recommend to include the criteria of crack resistance K _Issc ^min and B _Issc ^min in the corresponding standards, specifications, etc.     

Influence of Hydrogen Sulfide on Serviceability of Materials of Gas Field Equipment

We analyze basic types of corrosion, corrosion-hydrogen, and corrosion-mechanical fractures of steels in hydrogen sulfide-containing media. We propose a new concept based on the chemical interaction of atomic hydrogen with thermodynamically unstable inclusions and carbides of steel, which results in the formation of microvoids on metal–inclusion boundaries. This is the main reason for hydrogen sulfide corrosion cracking and hydrogen-induced cracking of steels.     

Workability of Tubings and Casings in Hydrogen Sulfide Media

We studied the corrosion resistance, hydrogen-induced cracking, and hydrogen sulfide stress corrosion cracking of specimens taken from tubings and casings made of steels D, L, S-75, and R-105, in both standard hydrogen sulfide NACE solution and stratal water of the Lokachi gas field (Ukraine). We established that the corrosion rate of the steels in the stratal water is 5–7 times less than that in the NACE solution, that hydrogen-induced cracking does not occur, and that steels S-75 and D are resistant to hydrogen sulfide stress corrosion cracking under stresses equal to 0.8 of the minimally allowable yield strength. In the NACE solution, steels D and L were subjected to blistering, and the resistance of steels S-75 (casing), S-75 (tubing), D, L, and R-105 to hydrogen sulfide stress corrosion cracking is equal to, respectively, 0.8, 0.75, 0.5, 0.4, and 0.38 of their minimally allowable yield strength.