Layer | Fill | Outline |
---|
Map layers
Theme | Visible | Selectable | Appearance | Zoom Range (now: 0) |
---|
Fill | Stroke |
---|---|
Collaborating Authors
Results
ABSTRACT: SSC resistance of 110 ksi sour grade low alloy steel OCTG was evaluated in highly pressurized H2S environments assuming the application to High Pressure/High Temperature (HPHT) oil and gas fields. The DCB test was selected to numerically evaluate the environmental severity in view of SSC. Effects of H2S pressure and temperature on KISSC values were investigated. Test results showed that the increase in H2S pressure from 0.1 to 1.5MPa decreased KISSC values. KISSC values increased with increasing testing temperature over the range from 24 to 65oC. SSC mechanism in the high pressure H2S environments was discussed in view of corrosion weight loss, structures or chemical compositions of corrosion products formed on the steel surface, and atomic hydrogen absorption and its stability in the steel. INTRODUCTION: High Pressure/High Temperature (HPHT) oil and gas fields are being actively developed for the world-wide energy demand. Higher strength oil country tubular goods (OCTG) are required for the HPHT well applications to withstand the high total pressure and the deadweight. However, recent developments of HPHT wells are often faced with higher levels of H2S, for example in the Middle East, China or Caspian Sea fields. It is widely recognized that high strength steels suffer from Sulfide Stress Cracking (SSC), one of degradations of steels caused by absorbed hydrogen from wet H2S environments. Therefore, high strength low alloy steel OCTG with the good resistance to SSC are required for the HPHT casing applications. Test solution specified in NACE TM 0177-2005 saturated with H2S at ambient pressure has been used for the SSC evaluation of low alloy steel OCTG. The standard test environment is useful for quality assurance testing. Additionally, fit-for-purpose testing has recently been employed to qualify materials for specific well environments, less or more severe than the NACE standard test environment. There are numerous studies on environmental factors affecting SSC, such as temperature, pH, H2S partial pressure at ambient pressure. Furthermore, the effect of high total pressure on SSC has recently been discussed1)-3). Thermodynamic calculations show that the H2S solubility in aqueous solution pressurized with high pressure CH4 will be significantly reduced at a given H2S partial pressure compared to ambient pressure values1). That suggests current laboratory tests at ambient pressure may be excessively severe than actual oil and gas fields with high total pressure2)-3). However, there is a limited number of studies on the effects of high pressure H2S beyond ambient pressure which HPHT well development often encounters. Ikeda et al. investigated hydrogen absorption into linepipe steels and the susceptibility to Hydrogen Induced Cracking (HIC) in solutions saturated with high pressure H2S. They reported HIC susceptibility and absorbed hydrogen content increased with the increase in partial pressure of H2S. They showed that the solution saturated with the mixed gas of 1MPa H2S and 1MPa CO2 might be more severe than the standard NACE solution. Kimura et al. reported test results on hydrogen permeability and susceptibility to HIC of a linepipe steel in NaCl solutions saturated with high pressure H2S gas6).
- Asia (0.86)
- North America > United States (0.46)
Application Limits For 110Ksi Strength Grade Super 13Cr Steel In CO2 Environments Containing Small Amounts Of H2S
Takabe, Hideki (Sumitomo Metal Industries, Ltd) | Ueda, Masakatsu (Sumitomo Metal Industries, Ltd) | Martin, John William (BP Exploration, Exploration and Production Technology Group) | Nice, Perry Ian (StatoilHydro)
ABSTRACT: 110ksi strength grade modified 13Cr steels, that are categorized as "13-5-2" in ISO13680, have been developed and widely used as an OCTG tubing material for CO2 environments containing small amounts of H2S. However, the application limits are not clear due to the complex interaction of the environmental-related factors, such as chloride concentration, pH and H2S partial pressure, on the sulfide stress cracking (SSC) and high temperature stress corrosion cracking (SCC) resistance. A 110ksi strength grade super 13Cr steel, UNS S41426, was evaluated for its SSC resistance in accordance with Method A of NACE TM0177-96. The SSC-resistance domains for 110ksi grade super 13Cr steel are proposed as a function of Cl- concentration, pH and H2S partial pressure. The influence of Clconcentration was larger for the lower pH or higher H2S partial pressure environments. The SCC resistance was evaluated by the four-point bent beam test technique. The SCC-resistance domain in 0.001MPa H2S environment at 175oC was influenced by Cl- concentration and pH. Super 13Cr steel suffered from SCC at low pH and high Cl- ion concentration even within the SSC-resistance domain. From these test results, it is suggested that the cracking resistance should be evaluated at the maximum service temperature, as well as at 25oC, when evaluating the application limits for super 13Cr steels. INTRODUCTION: Modified 13Cr steels, that are categorized as "13-5-2" in ISO13680, have been developed as materials with improved SSC resistance over conventional 13Cr martensitic stainless steel (AISI420) of a similar strength.1 Some modified 13 Cr steels are registered as downhole tubular component materials and their application limits, such as H2S partial pressure, pH and temperature are listed in NACE MR0175/ISO 15156-3.2 However, there are no specific application limits for a 110 ksi strength grade in the standard, although this has been widely used for CO2 environments containing small amount of H2S. SSC and SCC test results for 110ksi grade modified 13Cr steels have been reported and the effect of Clcontent, pH and H2S partial pressure on SSC resistance discussed.3,4,5,6 Hashizume et al reported that SSC susceptibility increased when the pH of the test solution was less than the depassivation pH (pHd)10 and high temperature cracking (SCC) has occurred at 160oC in high Cl- concentration environments.5 Nice and Martin pointed out that the SSC resistance of modified 13Cr steel bar materials was strongly influenced by Cl- concentration6. Furthermore, high temperature SCC in high density clear brine with high Cl- concentration is becoming a problem for modified 13Cr downhole tubulars.7 Therefore, not only SSC evaluation at room temperature, but also SCC evaluation in high Cl- concentration environments at elevated temperatures should be considered in order to establish the application limits of this alloy class. In this work, SSC tests of 110ksi grade super 13Cr steel, UNS S41246 were carried out under different environmental test conditions, with chloride concentrations ranging from 1,000 to 211,000 mg/l, pH levels from 2.8 to 5.5 and H2S partial pressures from 0.0001 to 0.1 MPa.