Very low tolerable partial pressures of H2S (⁠pH2S) have been reported for duplex stainless steels in sour environments. However, such steels resist stress corrosion cracking (SCC) in sour environments even at substantial pH2S. values.

To assess the limits of applicability, SCC tests should include an environment of reasonably accelerated severity. It is also important to take practical experience into account.

Slow strain rate testing (SSRT) is considered to put unrealistic mechanical demands on the material, since the stress can reach the ultimate tensile strength (UTS) and the strain rate is controlled to give maximum SCC sensitivity. Constant-strain and constant-stress tests are more relevant to practical conditions.

The actual environment is always more complex than the plain H2S/Cl or H2S/CO2/Cl environments used in the majority of laboratory tests. Bicarbonate ions are most often present, and by increasing the pH value, they reduce the aggressiveness of the environment.

Duplex stainless steels have been used for many years in applications with significantly higher pH2S than many laboratory tests have indicated to be possible.

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