英高鎳600管件表面應力腐蝕裂縫製作探討

The Production of SCCs on External Surface of Inconel 600 Tubings

壓水式反應器核能電廠的蒸汽產生器管束是電廠重要的壓力邊界，而管束狀態的掌握是電廠老化管理重要的一環，因此必須定時執行非破壞檢測；然而現階段在電廠普遍應用的渦電流檢測法，尚有其檢測的門檻值和評估裂縫深度的不準度。為了提昇渦電流檢測的技術，必須於實驗室利用嚴苛的環境，於管件表面製作應力腐蝕裂縫，以為比對裂縫深度之用。在此實驗中應用不同的構想和組裝，使英高鎳600管件試樣表面分別有較大之圓周向或軸向負荷，以便在嚴苛的環境中分別產生軸向或圓周向之應力腐蝕裂縫。所使用的腐蝕環境為280℃的40% NaOH + 300 g/l Cu2O 混合溶液。測試結果顯示裂縫生成的數目、裂縫長度和測試時間並沒有一定的關係，然最深裂縫深度和時間有成正比例之關係。但因所生的裂縫並非在特定位置，且在同一位置處並非唯一之裂縫，因此渦電流檢測信號會產生干擾的現象。在此利用PTFE塗覆的有無，可以成功的解決所遭遇的問題。

Since steam generator tubings is a primary pressure boundary for PWR reactor, so that their service status is an important factor for aging management of power plant, especially for aging ones. Nondestructive inspection intermittently being conducted is a necessary measure to provide enough and valuable information to keep them intact through taking appropriate actions. However, eddy current inspection, currently most popular and effective method, could not provide good inspection reliability and sizing accuracy. For improving inspection techniques, defected tube with stress corrosion cracking on the outer surface should be prepared from laboratory by means of severe caustic environments. Therefore, the correlation of inspection signal and configuration of cracking will be established. In this study, in order to produce both axial and circumferential SCC on external surface of Inconel 600 tubings, an appropriate setup or facility, which offers high enough circumferential or axial stress to tube specimens, is required. In here, a severe caustic environment of 40% NaOH + 300 g/l Cu2O was used. Test results showed that the produced cracking, such as their numbers, length or even their depth, did not establish any correlations with testing periods. But the maximum depth of produced cracking, irrespective axial or circumferential SCC, was proportion to testing time. However, the produced cracks are not located at one specific region and are too concentrated to identify each specific parameter using eddy current inspection, then the improvement of production of one crack at a definite region is developed. The coating of PTFE on outside surface of tube specimens can overcome this problem.