The development of microalloyed pipeline steels for applications in hydrogen sulfide environments has been focused on increasing the yield strength, however the microstructure remains as the main feature that modify the susceptibility of thes e steels to sulfide stress corrosion cracking in sour environments. Sulfide stress cracking (SSC) is a mode of degradation that appears when a hydrogen sulfide environment is present combined with a local state of stress. In this work, the role of the micr ostructure and the yield strength were investigated using pipeline steels API 5L grades X - 52, X - 65, and X - 80, in order to correlate the susceptibility to pressurized sour environments. The susceptibility to SSC was investigated using Linear Elastic Fractur e Mechanic (LEFM) on compact samples (MWOL specimens), loaded in all cases to 50% of yield strength. The steel with higher resistance is prone to hydrogen embrittlement and shows a transgranular crack path. Also, the steel with lower resistance shows a dra stic corrosion in the fracture surfaces exposed to the environment with a transgranular crack path. In the samples with a banded microstructure the stress corrosion cracking susceptibility is evident and seems to be affected by hydrogen diffusion. In the s teel samples with a homogeneous microstructure as the X65, there is evidence that the crack growth observed is only by dissolution bulbs.
Keywords: Stress corrosion cracking, sulfide stress cracking, anodic dissolution, hydrogen embrittlement, microalloye d steel