鎳基600TT合金應力腐蝕裂縫起始與成長之研究

Initiation and Growth of Stress Corrosion Cracking on Inconel 600TT Alloy

銹垢形成濃縮的二次側水質環境堆積在蒸汽產生器管板（Tube Sheet）與管支撐板（Support Plate）處是使熱交換管外表面產生應力腐蝕裂縫之主要肇因。本研究之目的在於探討鎳基600TT合金試樣置於濃縮模擬二次側水質環境中，應力腐蝕劣化起始和環境參數之關係；以及管件試樣上已有應力腐蝕裂縫存在時，在模擬蒸氣產生器之運轉條件下，觀察裂縫成長行為及量測裂縫成長速率。實驗結果顯示在濃縮模擬二次側水質中，鎳基600TT合金會產生IGA／SCC的現象。至於降溫運轉對延緩劣化起始之效果有限。已存在應力腐蝕裂縫之管束在百萬倍濃縮模擬二次側水質環境中，測試5504小時後，以渦電流檢測及顯微檢查，都發現有裂縫成長的現象。裂縫沿管束表面成長之速率大約為7.3 x 10-3～4.9 x 10-2 µm /hr。此外，以歐傑電子質譜儀（Auger Electric Spectroscope AES)）確認裂縫深度成長長度，初步估算出裂縫成長率在4.2 x 10-3～1.3 x10-2 µm /hr之間。將進行更多的裂縫檢測以確認正確的數據。

The piling up of sludge between heat exchange tube and Tube Sheet or Tube Support Plate is one of the primary root causes for Outside Diameter Stress Corrosion Cracking (ODSCC) on steam generator tubings. Examination of crack initiation time and measurement of crack growth rate of Stress Corrosion Cracking (SCC) for the Inconel 600TT alloy are conducted in the condensing simulation secondary side water environments. The Intergranular Attack/Stress Corrosion Cracking (IGA/SCC) is found on the surface of samples. The result show that the benefits is quite low to reduce the crack initiation time while lowing operation temperature. In the mean time, degraded tubes are tested for 5504 hours in a condensed environment of which concentration factor 106 times applied to calculate the simulated water condition according to the analysis result of hide out return. The crack growth rate for crack length on tube surface by OM and ECT inspection is from 7.3 x 10-3 µm/hr to 4.9 x10-2. The evaluation of crack growth rate for crack depth by AES examination is in the range of 4.2 x 10-3 to 1.3 x10-2 µm/hr. It will be verified by more examinations.