Role of water chemistry and microstructure in stress corrosion cracking in the fusion boundary region of an Alloy 182-A533B low alloy steel dissimilar weld joint in high temperature water

Stress corrosion cracking (SCC) in the fusion boundary (FB) region of an Alloy 182-low alloy steel (LAS) dissimilar weld joint in 288 °C water was investigated by experiments and finite element simulation. Creviced bent beam and crack growth rate (CGR) experiments showed that, while the FB was a barrier to SCC growth, further crack growth into LAS was activated by a combined effect of sulfate and dissolved oxygen in water. Finite element simulation suggested that a positive gradient of hardness as the crack approached to the FB in dilution zone caused decreased CGR. Role of microstructure and water chemistry in SCC was discussed.

► Hardness gradient in the high hardness zone adjacent to fusion boundary in dilution zone.
► Combined effect of dissolved oxygen and sulfate concentration on crack growth in fusion boundary region.
► 400-ppb Sulfate in water for reactivating crack growth at fusion boundary at K = 30 MPa√m under normal water chemistry.
► Decreased crack growth rate in the high hardness zone is expected due to the hardness gradient.
► Reactivation of crack growth from the pitting at fusion boundary by preferential oxidation along the grain boundary.