Effect of Cooling Rate on Sulfide Stress Cracking Resistance of a Q345 Pressure Vessel Steel Subject to Hydrogen Sulfide

As an important equipment for the separation, store, and transport of the oil and natural gas in energy industry, the pressure vessels are subjected to harsh service environments of sulfide stress cracking (SSC). In this work, the effect of the cooling rate on the SSC susceptibility of a Q345 pressure vessel steel is studied. A pronounced distinction in microstructure is presented as the cooling rate is increased from ≈1 to ≈15 °C s −1 . At ≈1 °C s −1 , the microstructure is consisted of polygonal‐like ferrite and distinct banded pearlite. At ≈5 °C s −1 , the microstructure is consisted of polygonal‐like ferrite and faintly banded pseudo‐pearlite. At ≈15 °C s −1 , the microstructure is acicular ferrite with a complete elimination of banded structure. The cooling rate decides the level of the banded structure. As the cooling rate increases, the banded structure becomes relatively slight and even disappears. Strength in sort ascending is ≈1, ≈ 5, and ≈15 °C s −1 . The SSC failure happens at ≈1 and ≈5 °C s −1 , while does not happen at ≈15 °C s −1 . The strength is not the only dominant factor responsible for the SSC failure. The SSC is preferentially generated at the banded structure. The elimination of the banded structure is necessary to improve the SSC resistance of the Q345 pressure vessel steel.