高溫注氫純水環境下採行抑制性被覆304不銹鋼之腐蝕行為研究

Corrosion Behavior of Type 304 Stainless Treated with Iinhibitive Coatings in High Temperature Hydrogen Water Chemistry Environments

蔡春鴻(C. H. Tsai) ； 葉宗洸(T. K. Yeh) ； 鄭宇翔(Y. S. Cheng)

《防蝕工程》 17卷4期 (2003/12) Pp. 331-340

https://doi.org/10.6376/JCCE.200312.0331

摘要

隨著沸水式反應器(Boiling Water Reactor, BWRs)運轉時間的增長，反應器組件材料遭受沿晶應力腐蝕龜裂(Intergranular Stress Corrosion Cracking, IGSCC)以及輻射促進應力腐蝕龜裂的機率也逐漸提高。近年來，許多擁有BWR的電廠均已採用於飼水中添加氫氣的加氫水化學(Hydrogen Water Chemistry, HWC)技術,藉以防制IGSCC與IASCC的發生。文獻資料顯示，HWC確實對沸水式反應器主冷卻迴路中的部分組件，具有防蝕保護的效果。然而，HWC技術的應用並非完美無缺，在較高飼水注氫量下（通常在0.6ppm以上），它具有提昇管路輻射計量的副作用；且對於壓力槽內部接近爐心出口附近的組件，如爐心上方空間和爐心側版上部等過氧化氫濃度偏高的區域，不能有效抑制IGSCC的發生。因此，為達到在HWC狀態下進一步保護爐心出口附近若干區域之目的，甚至在無注氫狀態下達到全面防制組件發生IGSCC的目標，我們選擇抑制性被覆進行BWR組件之防蝕可行性研究。
本研究以氧化鋯(ZrO2)、氧化鈦(TiO3)及二硝酸基氧化鋯[ZrO(NO3)2]等化合物做為試藥，在模擬BWR水化學循環迴路中，針對150℃被覆處理後之304不銹鋼，進行電化學腐蝕電位(Electrochemical Corrosion Potential, ECP)量測與慢應變速率拉伸測試，藉以了解此一材料在不同被覆狀態下，於高溫注氫純水環境中的腐蝕行為。研究結果發現，經過氧化鋯、氧化鈦或二硝酸基氧化鋯被覆處理後的試片，在相同水化學環境中其ECP值皆比預長氧化膜試片來的低，且在注氫環境中其ECP值較未注氫時低，注氫量增加和抑制性被覆處理均會使ECP值下降，兩者同時進行對降低ECP值有加成效果。在慢應變速率拉伸實驗的部分，我們發現隨著注氫量提高被覆與未被覆試片的IGSCC比例皆有降低的趨勢，並有較大的伸長量與較長的斷裂時間；在相同水化學環境中預氧化膜試片出現IGSCC比例較覆模試片低但差異不大，且有較小的伸長量與較短的斷裂時間，顯示試片IGSCC起始的時間確實因抑制性被覆處理而延長，得到較長的斷裂時間、斷裂最大應力值、伸長量與數量較少的二次裂口，對抑制IGSCC有正面成效。

關鍵字

沿晶應力腐蝕 ； 抑制性被覆 ； 氧化鋯

並列摘要

Incidents of intergranular stress corrosion cracking (IGSCC) and irradiation-assisted stress corrosion cracking (IASCC) of stainless steel components in the primary coolant circuits of boiling water reactors (BWRs) are occurring with increasing frequency as the power reactors age. In the past decade, the HWC technique has been widely adopted as a measure for mitigating IGSCC and IASCC in BWR vessel internal components. However, this technique is not without problems. Along with the application of HWC is a shortcoming of exerting a high man-REM cost on the operator due to elevated radiation fields. Furthermore, it is not at all clear that HWC is effective in protecting some components against IGSCC, particularly for protecting in-vessel components that are exposed to high gamma and neutron fields. Therefore, new technologies, such as inhibitive coatings, were brought into consideration to enhance the effectiveness of HWC. In this study, experiments were conducted to investigate the effects of inhibitive coating with TiO2, ZrO2, and ZrO(NO3)2 by chemical immersion at 150 oC on Type 304 SS. Measurements of electrochemical corrosion potential (ECP) and slow strain rate tensile(SSRT)tests in simulated BWR circulation loop to investigate the efffects of inhibitive coating with zirconium oxide and with a compound containing zirconium oxide on Type 304.Testresults showed that the treated SS specimens exhibited lower ECP than the pre-oxidized specimen, and the specimens exhibited lower ECP in higher than in lower hydrogen consumption. Increasing hydrogen concentration and treating IPC both can reduce ECR. In the SSRT test results, all tested specimens showed less IGSCC in higher hydrogen concentration, and had the longer elongation and fracture time. In the same water chemistry environments, preoxidized one had less IGSCC, the lowest elongation and the shortest fracture time. The results indicated that IPC did prolong the crack initial times to get longer fracture times, larger maximum fracture stress, and less second cracks. That can provide protection against IGSCC.

並列關鍵字

Intergranular Stress Corrosion Cracking ； inhibitive coating ； zirconium oxide