Papers by Keyword: Steam Generator Tube

Abstract: Inconel alloy such as alloy 600 and alloy 690 is widely used as the steam generator tube materials in the nuclear power plants. The impact fretting wear tests were performed to investigate wear mechanism between tube alloy and 409 stainless steel tube support plates in the simulated steam generator operating conditions, pressure of 15MPa, high temperature water of 290°C and low dissolved oxygen(<10 ppb). From investigation of wear test specimens by the SEM and EDS analysis, hammer imprint, which is known to be an actual damaged wear pattern, has been observed on the worn surface, and fretting wear mechanism was investigated. Wear progression of impact-fretting wear also has been examined. It was observed that titanium rich phase contributes to the formation of voids and cracks in sub-layer of fretting wear damage by impact fretting wear.

Abstract: Steam generator tubes provide the pressure boundary between the primary and secondary regions of a nuclear power plant. Alloy 600 is a tube material with good corrosion resistance; however, tubes of this material have experienced damage, particularly as Stress Corrosion Cracking, under the elevated temperature and pressure environment of a nuclear power plant. These damaged tubes must be repaired to prevent leakage of radioactive material from the primary to the second regions in the nuclear steam generator. In this study, Ni-P-Nano TiO2 and ZrO2 layers were produced by pulse electroplating for steam generator tube repair. These electroplate layers were obtained from Ni sulfamate bath with an added small quantity of H3PO3 and Nano TiO2 and ZrO2 particles with an average size of 20-80nm. Results of TEM analysis in these layers show that Nano TiO2 and ZrO2 particles were uniformly distributed into the electroplated Ni matrix and the tensile strength of these layers at 800-1000MPa was higher than that of alloy 600 with a conventional pure Ni electroplate layer.

Abstract: The bending moment test used by the specimens with partial and circumferential wall thinning was carried out to obtain the AE signal. The time-frequency analysis method for the investigation of the frequency characteristics of the AE signal was applied. The results of the wavelet analysis were compared with those of the bending moment test for the structural integrity of tube. The result of the frequency characteristics by applying wavelet analysis method and dropping ball test was presented similarly to those of bending moment test. It is considered that this simple method with combination of dropping ball test and wavelet analysis is very useful scheme for investigating the structural integrity.

Abstract: Steam generator in a nuclear power plant is huge heat exchanger that transfers heat from reactor to make steam to drive turbine-generator. Failure of the steam generator tubes can result in the release of fission products to the secondary side. Therefore, accurate integrity assessment of the cracked steam generator tubes is of great importance for maintaining the safety of the nuclear power plant. This paper provides limit loads for circumferential through-wall cracks in steam generator tubes under combined internal pressure and bending loads. Such limit loads are developed on the basis of three dimensional finite element analyses assuming elastic-perfectly plastic material behavior. As for the crack location, both the top of the tubesheet and U-bend regions are considered. The analysis results can be directly applied to the practical integrity assessment of cracked steam generator tubes, because the comparison between experimental data and FE results shows a very good agreement.

Abstract: Generally rupture of steam generator tubes occurs accompanying significant plastic deformation. In this study, the burst pressure of a damaged steam generator tube is calculated from the plastic instability analysis using the finite element method. Two wear types, flat and circumferential types are considered. An equation for the burst pressure is proposed by using the concept of strength reduction factor and the Svensson equation. The analysis results are also compared with the experiment data from published references and they show a good agreement with the experiment data.

Abstract: Fretting wear generated by flow induced vibration is one of the important degradation mechanisms of steam generator tubes in the nuclear power plants. Understanding of tube wear characteristics is very important to keep the integrity of the steam generator tubes to secure the safety of the nuclear power plants. Experimental examination has been performed for the purpose of investigating the impact fretting. Test material is alloy 690 tube and 409 stainless steel tube supports. From the results of experiments, wear scar progression is investigated in the case of impact-fretting wear test of steam generator tubes under plant operating conditions such as pressure of 15MPa, high temperature of 290
C and low dissolved oxygen. Hammer imprint that is actual damaged wear pattern, has been observed on the worn surface. From investigation of wear scar pattern, wear mechanism was initially the delamination wear due to cracking the hard oxide film and finally transferred to the stable impact-fretting pattern.

Abstract: A statistical assessment model for structural integrity of steam generator tubes with axial cracks at the top of the tubesheet was proposed using Monte Carlo method. In the model, a method for estimating the number of "real cracks" from in-situ inspection (ISI) data was used. Based on the estimated "real cracks", the number of newly detected cracks and growth of cracks during arbitrary operating period were simulated using the Monte Carlo method. The flaw growth rate used in the simulation was statistically calculated from the periodic in-service non-destructive inspection data. The number of cracks, the probabilistic distribution of crack sizes at the end of next operating interval and the probability of burst during operation were calculated from numerously repeated simulations using the proposed model.

Abstract: Signals acquired from a Combo calibration standard tube used to calibrate for inspection and evaluation of motorized rotating pancake coil probe signals from steam generator tubes. So, Combo tube signals should be consistent and accurate since they have strong influence on evaluation procedure of signals. However, motorized rotating pancake coil probe signals are very easily affected by various factors so that they can distort amplitudes and phase angles which are quantitative terms for signal evaluation. To overcome this problem, we explored possibility of using numerical simulation as a practical calibration tool for the evaluation of real field signals. In this study, we investigated the characteristics of a motorized rotating pancake coil probe and a Combo tube. And then we used commercial software to produce a set of calibration signals and compared to the experiments. Using simulated Combo tube signals, we evaluated deliberated single circumferential indication defects, and these results were compared with experimental signal evaluation results.

Abstract: During the past couple of decades, several limit load solutions have been proposed to resolve steam generator (SG) tube integrity issue. However, for estimation of specific load carrying capacity under different conditions, these solutions have to be modified by using lots of experimental data. The objective of this paper is to introduce a new burst pressure estimation scheme based on fracture mechanics analyses for SG tubes with a crack. In this context, closed-form equations were derived to get relevant parameters from three dimensional elastic-plastic finite element analyses and, then, a series of structural integrity analyses were carried out using the predicted J-integrals from the equations. Finally, in comparison with the experimental data as well as corresponding estimation results from conventional limit load solutions, it was proven that the proposed estimation scheme can be used as an efficient tool for integrity evaluation of cracked SG tubes.

Abstract: In the present study, the synthetic signals from the combo tube are simulated by using commercial electromagnetic numerical analysis software which has been developed based on a volume integral method. A comparison of the simulated signals to the experiments is made for the verification of accuracy, and then evaluation of five deliberated single circumferential indication signals is performed to explore a possibility of using a numerical simulation as a practical calibration tool. The good agreement between the evaluation results for two cases (calibration done by experiments and calibration made by simulation) demonstrates such a high possibility.