Which materials are commonly used for steam generator tubing and what degradation concern is most prominent?

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Multiple Choice

Which materials are commonly used for steam generator tubing and what degradation concern is most prominent?

Explanation:
Steam generator tubing in pressurized water reactors is typically made from nickel-based alloys in the Alloy 600 family (such as 600 and 690). These alloys were chosen for their combination of strength and corrosion resistance in the high-temperature, high-purity primary-water environment. The most prominent degradation path for these tubes is primary water stress corrosion cracking. The operating conditions—tensile stresses from fabrication and bending, plus the mildly oxidizing, borated water—favor crack initiation and slow growth along grain boundaries in these nickel alloys, which can progress to through-wall cracks. Alloy 690 offers improved resistance due to higher chromium content, so it is favored in newer tubes. Other materials and degradation modes mentioned in the alternatives don’t reflect the common tubing material or the dominant failure mechanism in this setting.

Steam generator tubing in pressurized water reactors is typically made from nickel-based alloys in the Alloy 600 family (such as 600 and 690). These alloys were chosen for their combination of strength and corrosion resistance in the high-temperature, high-purity primary-water environment. The most prominent degradation path for these tubes is primary water stress corrosion cracking. The operating conditions—tensile stresses from fabrication and bending, plus the mildly oxidizing, borated water—favor crack initiation and slow growth along grain boundaries in these nickel alloys, which can progress to through-wall cracks. Alloy 690 offers improved resistance due to higher chromium content, so it is favored in newer tubes. Other materials and degradation modes mentioned in the alternatives don’t reflect the common tubing material or the dominant failure mechanism in this setting.

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