Measurement of Through-the-Thickness Variations of Mechanical Properties in SA508 Gr.3 Pressure Vessel Steels Using Ball Indentation Test Technique

This collaborative study between the Korea Atomic Energy Research Institute (KAERI) and Oak Ridge National Laboratory demonstrates ABI®'s ability to detect spatial gradients in yield strength, ultimate tensile strength, and flow curve across the thickness of reactor pressure vessel forgings — gradients caused by varying quench rates during heat treatment.

SA508 Grade 3 is the primary forging steel used in pressurized water reactor (PWR) pressure vessels worldwide. During manufacture, the massive thickness of RPV forgings (200–300 mm) means the interior cools more slowly than the surface during quenching, producing measurable through-thickness variations in microstructure and mechanical properties. These gradients are safety-significant because they affect the vessel's resistance to pressurized thermal shock (PTS) — the most severe loading condition a reactor vessel can experience.

The study validated ABI®'s spatial resolution for safety-critical nuclear components by mapping mechanical properties at multiple locations through the forging thickness. Results confirmed that ABI® could detect the property gradients with sufficient resolution to support structural integrity assessments, establishing the technique as a viable alternative to destructive testing for characterizing these critical components.

This paper also represents KAERI's first independent use of Haggag's ABI® system on Korean RPV materials — the start of KAERI's sustained ABI® validation program that would continue for more than a decade.