To evaluate thermal aging of primary pipe for nuclear power plant in life time, accelerated thermal aging experiments of weld of primary pipe made of 316LN stainless steel were performed at 325, 365 and 400℃ for 15000h. Charpy impact energy and nanohardness of ferrite phase of weld were tested for different thermal aged time. Taking the nanohardness as the standard of thermal aging embrittlement, the thermal aging activation energy for weld of 316LN,93.1 kJ/mol was obtained by Arrhenius Formula. Meanwhile, taking the Charpy impact energy of weld at room temperature as the prediction parameter of thermal aging embrittlement, the equation for prediction of thermal aging embrittlement of weld was obtained by fitting method. Finally, the Charpy impact energy of the weld during 60 operation years at actual operation temperature was estimated by thermal aging activation energy and the prediction equation. The experimental results indicate that the nanohardness of the ferrite phase in the weld increases quickly, and the impact toughness decreases sharply with increase of thermal aging time. The predicted results show that the toughness of the weld decreases fast in the early 15 years, and then decreases slowly.
Key words
316LN weld /
Thermal aging /
Charpy impact energy /
Nanohardness
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