Mechanism of accelerated corrosion in Zircaloy-4 laser and electron-beam welds

The corrosion resistance of a series of Zircaloy-4 laser, electron-beam (EB), and tungsten inert gas (TIG) welds was evaluated in high-temperature water and steam. Corrosion exposures carried out in 633 K water revealed that all welds had excellent corrosion resistance at this temperature. However, corrosion exposures carried out in 673 K steam indicated that the laser and EB welds were susceptible to accelerated corrosion, whereas the TIG welds were not. It is believed that alloy depletion and the resultant loss of high-temperature corrosion resistance can be eliminated or minimized by performing welding operations at a power density such that the metal surface is heated above the melting point, but below the boiling point. 23 refs