Development of New 15Cr Stainless Steel OCTG with Superior Corrosion Resistance

Abstract

New stainless steel OCTG (New 15Cr steel pipe : 0.03C-15Cr-6Ni-2Mo-1Cu) with high strength and superior corrosion resistance has been developed and its capability in oil and gas production environment is shown. The yield strength of the new 15Cr steel pipe was higher than 861 MPa (125 ksi), and good Charpy toughness was obtained in extremely low temperature condition. This material showed remarkably high strength even at high temperature of 200 degree C. The CO2 corrosion resistance was significantly improved so that the critical temperature for the developed pipe was more than 200 degree C at 15 MPa CO2 partial pressure. The superior corrosion resistance for revised the new 15Cr steel pipe was obtained by the higher amount of effective Cr in solution. In addition to this, the new 15Cr steel pipe showed good SSC resistance even in its high yield strength in the mildly sour environment. The good SSC resistance for this developed pipe was obtained by the good pitting resistance, induced from high Cr and Mo addition. Introduction Because of its good corrosion resistance in the high carbon dioxide (CO2) and chloride environment, the field application of API 13% Cr (conventional 13Cr) steel pipe is increasing steadily for Oil Country Tubular Goods (OCTG),. However, the conventional 13Cr steel pipe is susceptible to sulfide stress cracking (SSC) in the sour environment containing hydrogen sulfide (H2S)(3, 4) and less corrosion resistant at elevated temperatures. Furthermore high strength OCTG has been required due to the development of deep wells. A number of modified 13Cr steels with high strength and superior corrosion resistance have been proposed.

DL‐EPR and AFM study of sensitization of a 17%Cr multiphase stainless steel

“…For these applications, high‐strength multiphase stainless steels with 14%–17% Cr were developed recently. [ 1,2 ] These materials contain a higher chromium content than supermartensitic steels, and other important additions, such as nickel, copper, molybdenum, titanium, vanadium, tungsten, and niobium. Nickel is added as an austenitizing element, which also increases the toughness.…”

Correlation between electrochemical properties and stress corrosion cracking of super 13Cr under an HTHP CO2 environment

“…10–12 The corrosion rate of super 13Cr steel is as low as 0.02 mm per year at 150 °C. 13 However, some aspects of material fracture remain unexplained, particularly at high temperature. One aspect that has received little attention is the effect of the complicated metallurgical structure, particularly residual austenite.…”

“…1,12,13,24,28 Most studies have indicated that the temperature limits of 13Cr and super 13Cr are higher than 150 °C and even up to 175 °C; at these temperatures, 13Cr and super 13Cr exhibit no risk of pitting corrosion and cracking. 13 However, few studies have assessed the effects of the HTHP environment with CO 2 and high concentrations of Cl − on the nucleation and development of pitting corrosion. Several studies on pitting corrosion and cracking of 13Cr steel have been conducted under low-temperature and low-Cl − concentration conditions with or without the presence of CO 2 /H 2 S/dissolved oxygen (DO).…”

Slow strain rate tensile test results of new multiphase 17%Cr stainless steel under hydrogen cathodic charging

“…More recently, seeking for higher corrosion resistance, steelmakers studied new grades of steels with higher Cr addition (15 and 17%) [2]. The increase of Cr and other alpha gene elements increased the amounts of ferrite phase in the microstructure.…”

“…A first application of supermartensitic and super-ferriticmartensitic stainless steels is in oil country tubular goods (OCTG) for off-shore oil and gas production [2,3]. The materials can suffer hydrogen attack due to the H 2 S and acidity of the fluids transported, corrosion processes, and also cathodic protection.…”