“…Because the E rp enhancement is attributed to the effect of MSs, it should disappear at high potentials. These predictions are consistent with the experimental results reported by Hinds et al [125] For the duplex stainless steel (Figure 17), in the moderateand high-chloride concentration (>0.03 molal), the presence of H 2 S enhances localised corrosion by decreasing E rp values. Both E rp for 1 and 100% H 2 S are largely parallel to the line of nitrogen and shift to more negative direction successively.…”
Section: Modelling Localised Corrosionsupporting
confidence: 92%
“…These predictions are consistent with the experimental results reported by Hinds et al. [125] Figure 16 Model (lines) vs. experimental results of repassivation potential for 13Cr–5Ni–2Mo martensitic stainless steel. All results are at 85°C [123].…”
Section: Critical and Corrosion Potentials For Sccsupporting
confidence: 91%
“…The effect of H 2 S on increase in corrosion potential arises from two mechanisms: the decrease in pH and the direct cathodic reduction of dissolved H 2 S [124]. The combination of decrease in repassivation potential and increase in corrosion potential due to H 2 S would be expected to result in localised corrosion above a critical chloride concentration in the presence of H 2 S. This is indeed consistent with experimental results [124,125].…”
Corrosion-resistant alloys (CRAs) are employed in severe oil and gas production environments that operate at high pressures and temperatures and contain chlorides, CO 2 , and H 2 S. They exhibit high resistance to uniform corrosion in these environments due to their passivity. However, they can suffer from different forms of environmentally assisted cracking (EAC), depending on the environmental and metallurgical conditions. This paper reviews the recent literature of EAC in CRAs and presents an overall framework for evaluating the SCC based on electrochemical modelling of corrosion and repassivation potentials for localised corrosion. The modelling is supported by experimental data on crack growth as a function of environmental variables, alloy content, and potential.
“…Because the E rp enhancement is attributed to the effect of MSs, it should disappear at high potentials. These predictions are consistent with the experimental results reported by Hinds et al [125] For the duplex stainless steel (Figure 17), in the moderateand high-chloride concentration (>0.03 molal), the presence of H 2 S enhances localised corrosion by decreasing E rp values. Both E rp for 1 and 100% H 2 S are largely parallel to the line of nitrogen and shift to more negative direction successively.…”
Section: Modelling Localised Corrosionsupporting
confidence: 92%
“…These predictions are consistent with the experimental results reported by Hinds et al. [125] Figure 16 Model (lines) vs. experimental results of repassivation potential for 13Cr–5Ni–2Mo martensitic stainless steel. All results are at 85°C [123].…”
Section: Critical and Corrosion Potentials For Sccsupporting
confidence: 91%
“…The effect of H 2 S on increase in corrosion potential arises from two mechanisms: the decrease in pH and the direct cathodic reduction of dissolved H 2 S [124]. The combination of decrease in repassivation potential and increase in corrosion potential due to H 2 S would be expected to result in localised corrosion above a critical chloride concentration in the presence of H 2 S. This is indeed consistent with experimental results [124,125].…”
Corrosion-resistant alloys (CRAs) are employed in severe oil and gas production environments that operate at high pressures and temperatures and contain chlorides, CO 2 , and H 2 S. They exhibit high resistance to uniform corrosion in these environments due to their passivity. However, they can suffer from different forms of environmentally assisted cracking (EAC), depending on the environmental and metallurgical conditions. This paper reviews the recent literature of EAC in CRAs and presents an overall framework for evaluating the SCC based on electrochemical modelling of corrosion and repassivation potentials for localised corrosion. The modelling is supported by experimental data on crack growth as a function of environmental variables, alloy content, and potential.
“…Moreover, Hinds et al also used the Gumbel function to estimate the pitting potential for different area specimens. 43 The pitting potential follows the extreme distribution well by proper conversion of the Gumbel function. Since the pitting potential has a negative correlation with the pit depth, the same as for CPT, it is suitable to describe the variation of CPT with specimen areas by the Gumbel extreme function.…”
Section: Establishment Of the Model Of Cpt For Large-scale Specimens-mentioning
Critical pitting temperature (CPT) of 316L stainless steel with different specimen areas in 3.5 wt% NaCl solution was investigated by the potentiostatic method. The results showed that the CPT exhibited a decreasing tendency with the increase in specimen areas, which was attributed to the higher probability for large-scale specimens to attain a large pit depth than small specimens. Therefore, stable pitting is easier to form, resulting in a lower CPT. Subsequently, a Gumbel extreme function was applied to establish a model correlating CPT with the specimen area. The CPT was linear with the double logarithm of the specimen area and could be accurately predicted for large-scale specimens.
“…9,39 Therefore, a comprehensive set of new E rp data has been obtained in this study for a 13-Cr supermartensitic stainless steel (UNS S41425, commonly referred to as S13Cr) to elucidate the interplay of Cland H 2 S in localized corrosion. 9,39 Therefore, a comprehensive set of new E rp data has been obtained in this study for a 13-Cr supermartensitic stainless steel (UNS S41425, commonly referred to as S13Cr) to elucidate the interplay of Cland H 2 S in localized corrosion.…”
A model has been developed for predicting the localized corrosion repassivation potential (E rp ) for alloys in environments containing chloride ions and hydrogen sulfide. The model has been combined with E rp measurements for a 13-Cr supermartensitic stainless steel (UNS S41425) at various concentrations of Cland H 2 S. The model accounts for competitive adsorption at the interface between the metal and the occluded site environment, the effect of adsorbed species on anodic dissolution and the formation solid phases in the process of repassivation. The effect of H 2 S is complex as it may give rise to a strong enhancement of anodic dissolution in the occluded environment and may lead to the formation of solid metal sulfide phases, which compete with the formation of metal oxides. H 2 S can substantially reduce the repassivation potential, thus indicating a strongly enhanced tendency for localized corrosion and stress corrosion cracking. However, exceptions exist at lower H 2 S and Clconcentrations, at which H 2 S may lead to the inhibition of localized corrosion. The model accurately reproduces the measured repassivation potentials for alloy S41425 and limited literature data for alloy CA6NM (J91574), thus elucidating the conditions at which H 2 S increases the propensity for localized corrosion and those at which it does not. Since the repassivation potential defines the threshold condition for the existence of stable pits or crevice corrosion, the model provides the foundation for predicting localized corrosion and stress corrosion cracking in environments that are relevant to oil and gas production.
INTRODUCTIONCorrosion behavior of corrosion-resistant alloys (CRAs) in the oil and gas industry has been attracting significant attention over the past two decades due to a marked trend towards increasing severity of corrosive environments in terms of temperature, pressure, and aggressive species. This trend, coupled with increasing scrutiny of production systems by regulators and the public, is expected to continue in the future and provides impetus to a reexamination of approaches to materials selection.At present, materials specification is based on a combination of standard tests (e.g., NACE TM-01-77 1 ), fit-for-purpose testing, and experience. The empirical knowledge is embodied in standards, such as ISO 15156, 2 guidance documents and company specifications. The boundaries of acceptable performance of CRAs are often specified in terms of empirically determined ranges of H 2 S and CO 2 partial pressures. However, such approaches may not be satisfactory because the performance of CRAs depends on many other factors such as temperature, acidity, chloride concentration, elemental sulfur, etc., which in turn may depend on complex chemical and phase equilibria in downhole environments.Furthermore, the relationship between accelerated laboratory tests and the actual field environment is often not quantified. Essentially, the performance of a given material needs to be understood in terms of its reliability in a ...
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