Why are dissimilar metal welds a focus for PWSCC mitigation?

• A. Residual stresses and differing electrochemical properties at the weld interface increase cracking risk in primary water
• B. They are cheaper to weld
• C. They always have identical thermal expansion
• D. They reduce corrosion resistance uniformly

Answer: (A)

Dissimilar metal welds are a focus because the weld zone combines two key factors that drive PWSCC: tensile residual stresses from the welding process and a galvanic, electrochemical mismatch at the metal interface. The heat-affected zone and weld metal carry tensile stresses that persist during operation, while the two metals (and the filler) have different electrochemical potentials and corrosion behaviors. In the reactor’s primary water, this creates a localized environment where anodic dissolution and hydrogen-related processes can initiate and propagate cracks along the weld interface, especially in susceptible alloys. This combination—mechanical stress and electrochemical heterogeneity at the weld boundary—significantly elevates cracking risk, which is why these dissimilar metal welds are targeted for mitigation. The other statements don’t fit the mechanism: cost or the idea of identical thermal expansion don’t capture the causal role of residual stresses and electrochemical differences, and the notion of uniform corrosion reduction isn’t accurate for PWSCC.