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51318-11256-Elevated Pressure Tests in Single Phase Aqueous Solutions on Low Alloy Steel SSC Resistance

This paper summarizes an experimental program that studied the impact of aqueous solutions containing various concentrations of H2S at varying total pressures established by the pressurization of the single aqueous phase.

Product Number: 51318-11256-SG
Author: Brian D. Chambers / Manuel Gonzalez / Nirmal Tatavalli-Mittadar / Sytze Huizinga / Raymond French
Publication Date: 2018
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Sour well design is often limited by susceptibility to H2S-related cracking mechanisms.

Recent experimental evidence has demonstrated that in high pressure systems, parameters such as dissolved H2S concentration or H2S activity or related fugacity govern the tendency of carbon steels to resist sulfide stress cracking (SSC). A particular implication of utilizing these parameters is that the H2S fugacity will increase as pressure increases in a liquid-full system as can be illustrated through, for example, Ensemble Henry’s Law. This ‘beyond bubble point’ risk has been identified in recent changes to NACE MR0175 / ISO15156 but has yet to be experimentally validated.

This paper summarizes an experimental program that studied the impact of aqueous solutions containing various concentrations of H2S at varying total pressures established by the pressurization of the single aqueous phase. The intent was to assess whether the increased H2S fugacity associated with an increase in pressure of a liquid-only system would result in decreased SSC resistance of carbon and low alloy steels.

The findings of the experimental program were unanticipated from what appears to be a strong effect of total pressure on test specimen resistance to SSC. Hypotheses attempting to explain these findings are presented and discussed.

Sour well design is often limited by susceptibility to H2S-related cracking mechanisms.

Recent experimental evidence has demonstrated that in high pressure systems, parameters such as dissolved H2S concentration or H2S activity or related fugacity govern the tendency of carbon steels to resist sulfide stress cracking (SSC). A particular implication of utilizing these parameters is that the H2S fugacity will increase as pressure increases in a liquid-full system as can be illustrated through, for example, Ensemble Henry’s Law. This ‘beyond bubble point’ risk has been identified in recent changes to NACE MR0175 / ISO15156 but has yet to be experimentally validated.

This paper summarizes an experimental program that studied the impact of aqueous solutions containing various concentrations of H2S at varying total pressures established by the pressurization of the single aqueous phase. The intent was to assess whether the increased H2S fugacity associated with an increase in pressure of a liquid-only system would result in decreased SSC resistance of carbon and low alloy steels.

The findings of the experimental program were unanticipated from what appears to be a strong effect of total pressure on test specimen resistance to SSC. Hypotheses attempting to explain these findings are presented and discussed.

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