英高鎳600TT合金管件在蒸汽產生器二次側水質環境之應力腐蝕劣化行為研究

Stress Corrosion Cracking Behavior of TT Inconel 600 Alloy Tubes in Secondary Water Environment of Steam Generator

由於近年來使用英高鎳600TT合金管件之蒸汽產生器陸續發生二次側應力腐蝕劣化後，顯示各電廠之特定運轉條件對劣化行為之發生及成長上扮演重要的角色。因此，以實際之管件試樣探討在特定運轉條件下之應力強度因子對應力腐蝕裂縫成長速率之影響，可提供電廠建立特定維護策略及評估劣化管件壽限之依據。
本研究在氫氧化鈉溶液中進行英高鎳600TT合金管件劣化後，使管件外表面產生應力腐蝕裂縫。將劣化管件置於模擬蒸汽產生器運轉條件及濃縮水質環境系統中使裂縫成長。經過5500小時後，以光學顯微鏡及歐傑電子質譜儀量測管件軸向及徑向之裂縫成長長度。並利用ABAQUS程式進行裂縫應力分析及計算裂縫尖端之應力強度因子，得到應力強度因子對應力腐蝕裂縫成長速率之關係。實驗結果顯示應力強度因子為3.8 ~ 6.3 MPaüm1/2之間時，裂縫沿徑向成長速率為2.6×10-3 ~ 2.5×10-2μm/hr。

The Stress Corrosion Cracking (SCC) degradation of TT Inconel 600 tubes happening in different Steam Generators (S/G) shows that the specific operation conditions of each nuclear plant have played a primary role. Measurement of the crack growth rate by actual tube specimen in specific operation conditions will provide the life prediction of S/G tubes and further establish the maintain strategy.
In this works, cracked TT Inconel 600 tubes, made in NaOH solution, were put in the S/G simulation system to make crack growth. The outside surface of tubes was exposed in concentrated secondary water environment that simulates a specific operation condition. After 5500 hr, axial and radius crack growth of tubes were measured by Optical Microscope and Auger Electric Spectroscope. The configuration factor of crack was built in the ABAQUS finite element analysis code to evaluate fracture analysis by cracks and to calculate the stress intensity factor of crack front. The relationship of the stress intensity factor of crack front and crack growth rate was found. The result shows that the crack growth rate is 2.6×10-3 ~ 2.5×10-2 μm/hr when the stress intensity factor of crack front is in the range of 3.8 ~ 6.3 MPa˙m1/2.