Do Haeng Hur

Anodic film properties determined by EIS and their relationship with caustic stress corrosion cracking of Alloy 600

The properties of the anodic films formed on Alloy 600 at different applied potentials in 10 wt.% NaOH solution at 315 °C were studied using in situ electrochemical impedance spectroscopy. Relaxation times for passivation and semiconductivity of the films were determined from EIS measurements. The results were correlated with the stress corrosion cracking (SCC) behavior obtained from the C-ring tests under the same conditions. The changes of the semiconductive properties and the peak of relaxation time were observed around 0.20 V where the SCC rate showed a maximum. These results were also consistent with the prediction parameter for SCC obtained from fast and slow polarization scans.

Inhibition of Stress Corrosion Cracking of Alloy 600 in 10% Sodium Hydroxide Solution at 315°C

Abstract The effect of inhibitors on the electrochemical behavior and stress corrosion cracking resistance of Alloy 600 (UNS N06600) was evaluated in 10% sodium hydroxide (NaOH) solution at 315°C. The specimens, which were of a C-ring type for stress corrosion cracking tests, were polarized at 150 mV above the corrosion potential for 120 h with and without inhibitors such as titanium oxide (TiO2), titanium boride (TiB2), and cerium boride (CeB6). The chemical compositions of the films formed on the crack tip in the C-ring specimens were analyzed using scanning Auger electron spectroscopy. Cerium boride, which was the most effective, was observed to decrease the crack propagation rate by more than afactor of 3 compared with that obtained with no inhibitor. It was found that changes of the active-passive transition potentials and film compositions were related to the resistance to stress corrosion cracking in high-temperature caustic solution.

INFLUENCE OF SIGNAL-TO-NOISE RATIO ON EDDY CURRENT SIGNALS OF CRACKS IN STEAM GENERATOR TUBES

This work presents the influence of noise originating from the tube itself on the detectability and sizing accuracy for laboratory-induced outer diameter axial cracks in nuclear steam generator tubes. The variations of signal amplitude and phase angle of the same cracks were analyzed when increasing the signal-to-noise ratio of the tube itself from 9 to 18. It was experimentally verified that the detectability for small cracks was enhanced by increasing the signal-to-noise ratio. The phase angle also rotated to a value representing the actual position and depth of a crack when increasing the signal-to-noise ratio.

Microchemistry of Ti-Carbonitrides and Their Role in the Early Stage of Pit Initiation of Alloy 600

Abstract The microchemistry of Ti-carbonitrides in Alloy 600 (UNS N06600) was analyzed using transmission electron microscopy and scanning Auger electron spectroscopy. Pit initiation testing was conducted to clarify the preferential pitting sites of Alloy 600 in a deaerated 10,000-ppm chloride solution at 90°C. It was found that sulfur/phosphorus was segregated on the surfaces of the Ti-carbonitrides and that (Mg,Ca)S sulfide particles adhered to them. The pit initiation site was the Ti-carbonitride/matrix interface, which was attributed to preferential dissolution of the (Mg,Ca)S particles and the sulfur/phosphorous-segregated layer, followed by dissolution of the matrix.

Effects of Deposition Potentials on the Morphology and Structure of Iron-Based Films on Carbon Steel Substrate in an Alkaline Solution

The purpose of this work is to investigate the effect of electrochemical deposition potential on the morphology and structure of iron-based films on the carbon steel in an alkaline Fe(III)-triethanolamine solution. The deposition potentials were controlled in the range from −1.05 to −1.23 for 1800 s at 80°C. Total amount of electric charge for electrodeposition process was increased with increasing deposition potential in negative direction. Pure magnetite films with a columnar and defect-free structure were deposited in the potential range from −1.05 to −1.11 . However, petal-like magnetite film containing ferrihydrite and iron was formed at −1.17 . At more negative potential of −1.23 , two distinct layers were observed: a porous outer layer containing ferrihydrite and goethite and a compact inner layer consisting of columnar metallic iron. In the potential range from −1.05 to −1.11 , the pure magnetite films gradually increased the thickness and decreased the surface roughness with an increase of the overpotential. The magnetite film deposited at −1.11 showed the most thick layer and smooth surface state.

Pitting Corrosion and its Countermeasures for Pressurized Water Reactor Steam Generator Tubes

Abstract Pitting corrosion was the primary cause of the Alloy 600 (UNS N06600) steam generator tube degradation in a Korean pressurized water reactor (PWR) plant. Pulled tube examinations and remed...

Sliding Wear Behavior of Steam Generator Tube Materials in Nuclear Power Plants

Wear damage of steam generator tubes of nuclear power plants can cause leakage of radioactive substances. So the evaluation of tubes’ integrity is very important from the viewpoint of nuclear ecocide. In the present study, sliding wear behaviors of Inconel 600 and 690 steam generator tube materials mated with 409 stainless steel commonly used as the support plate were investigated at room temperature in an air environment. For more precise prediction of wear behaviors of steam generator tubes, Archard equation was modified, and the modified wear coefficients were estimated as a function of sliding distance. When using the modified Archard equation, the reliabilities for prediction of wear behavior of Inconel 600 and 690 mated with 409 stainless steel increased from 71.8% to 83.8% and from 60.2% to 85.2%, respectively.

An Automated System for Detection of Through-Wall Cracks in Racks in Steam Generator Tubes

Through-wall axial cracks occurred by primary water stress corrosion are one of the serious defects in steam generator (SG) tubes (made of alloy 600) in pressurized water reactors. Therefore, it is necessary to detect and size them by eddy current testing (ECT) conducted during in-service inspection of SG tubes. To address this issue, it has been recently proposed an effective method, namely „M-shape profile“ approach, which relies on the difference in the amplitude between the pancake and plus point coils in a MRPC probe. Even though the M-shape curve approach is straightforward in principle, it requires time-consuming data processing if performed by human operators. In order to get rid of this tedious task, an automated system is developed in the present work. This paper addresses the principle of the M-shape approach together with the automated system and its performances for the detection of natural axial cracks in SG tubes. The results observed in the present work demonstrate the high potential of the developed system as a very promising tool for detecting through-wall cracks in many practical field applications.

Effects of Hydrogen Contents on Oxidation Behavior of Alloy 690TT and Associated Boron Accumulation within Oxides in High-Temperature Water

The aim of this work is to characterize the oxide layer structure of Alloy 690TT in high-temperature water with different dissolved hydrogen (DH) contents by using an X-ray photoelectron spectroscopy. Under the low DH contents (0.4494–0.8988 mg/kg), the oxide layers were composed of an outermost layer of Ni(OH)2 and Cr(OH)3 enriched in Ni, an intermediate layer of hydroxides and oxides enriched in Cr, and an inner Cr2O3 layer. Outermost NiO coexists with small amount of Cr2O3 layer, while in the inner oxide only Cr2O3 remains. The oxide layers at medium and high DH contents (3.1458– 8.9880 mg/kg) consisted of an outermost layer of Ni(OH)2 and Cr(OH)3 enriched in Cr, an intermediate layer of metallic Ni, hydroxides and oxides enriched in Cr, and an inner Cr2O3 layer. In addition, boron compounds containing B3+ ions were accumulated in the thick and porous NiO layer formed at low DH contents, whereas the accumulation of boron compounds did not occur in the thin and dense polyhedral oxide layer formed at medium and high DH contents.

Simulating Porous Magnetite Layer Deposited on Alloy 690TT Steam Generator Tubes

In nuclear power plants, the main corrosion product that is deposited on the outside of steam generator tubes is porous magnetite. The objective of this study was to simulate porous magnetite that is deposited on thermally treated (TT) Alloy 690 steam generator tubes. A magnetite layer was electrodeposited on an Alloy 690TT substrate in an Fe(III)-triethanolamine solution. After electrodeposition, the dense magnetite layer was immersed to simulate porous magnetite deposits in alkaline solution for 50 days at room temperature. The dense morphology of the magnetite layer was changed to a porous structure by reductive dissolution reaction. The simulated porous magnetite layer was compared with flakes of steam generator tubes, which were collected from the secondary water system of a real nuclear power plant during sludge lancing. Possible nuclear research applications using simulated porous magnetite specimens are also proposed.