• Journal of Advanced Marine Engineering and Technology
• /
• v.25 no.2
• /
• pp.345-345
• /
• 2001

This paper was studied on the characteristics of galvanic corrosion and its protection on heat exchanger tube plate in the sea water. In this paper, behavior of pitting corrosion of Ni-al bronze connected with Ti tube was measured af flow velocity of 0 m/s and 2.4 m/s. To protect galvanic corrosion, the protection characteristics of Ni-Al bronze connected with Ti tube by Zn-base alloys galvanic anode and hexagonal nylon insert was investigated. Main results obtained asre al follows: 1) The galvanic corrosion of Ni-Al bronze connected with Ti-tube is more active than single Ni-al bronze. 2) As the circuit resistance increase under the cathodic protection employing Zn-base alloys galvanic anode, Ni-al bronze connected with Ti tube is cathodically unpolarized. 3) The corrosion of Ni-Al bronze connected with Ti tube by nylon insert controls approximately 73% than not nylon insert.

• Proceedings of the Korean Nuclear Society Conference
• /
• 2002.10a
• /
• pp.381.2-381
• /
• 2002

• Journal of Energy Engineering
• /
• v.21 no.4
• /
• pp.362-372
• /
• 2012

The steam generator tubes of nuclear power plants are pressure boundaries, and if tubes are leaked, the coolant with the radioactive materials was flowed out from the primary system to the secondary system and polluted the plant and the air. Recently most crack defects of tubes are stress corrosion cracks and these defects are located in expansion transition area, sludge pile-up region, and U-bend area. The most effective one of crack initiation factors in expansion transition area and U-bend area is the residual stress. According to the experiences of Korea standard nuclear plants(Optimized Power Reactor-1000), they had the stress corrosion cracks at the tube expansion transition area in early operating stage and especially lots of circumferential cracks were occurred. Therefore in this study, the distributions and conditions of residual stresses by tube expansion methods were compared and the dominant reason of a specific direction was examined.

• Journal of the Korean Society of Fisheries and Ocean Technology
• /
• v.20 no.2
• /
• pp.137-142
• /
• 1984

An experimental study has been performed on the heat transfer characteristics of condensation by the injecting steam flow in the tube. The comparison between results of experimental data and available data concerning equivalent Reynolds number has studied. As the result, the followings were obtained. 1. The shear stress of the radial direction in the tube when the injecting steam flow was condensed can be written as root($\tau$sub(0)/$\tau$sub(0v))=1+1.46X sub(tt) super(0.20). 2. The effect of the heat transfer in the injecting steam flow was less than the value of equivalent Reynolds number. The reason are the nonuniform fluid film of the axial and radial direction in the tube. 3. The value of N sub(u) by the heat transfer of condensation can be written as N sub(u)=1.08$\times$[{$\rho$ sub(l) d/$\mu$ sub(l)}/{$\delta$+(2.5/P sub(rl)) ln(y sub(i)/$\delta$)}]$\times${$\tau$ sub(0)/ $\rho$ sub(l)} super(1/2).

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2006.10a
• /
• pp.361-362
• /
• 2006

• Nuclear Engineering and Technology
• /
• v.45 no.4
• /
• pp.513-522
• /
• 2013

The ODSCC detected in the TSP position of Ulchin 3&4 SGs are typical ODSCC of Alloy 600MA tubes. The causative chemical environment is formed by concentration of impurities inside the occluded region formed by the tube surface, egg crate strips, and sludge deposit there. Most cracks are detected at or near the line contacts between the tube surface and the egg crate strips. The region of dense crack population, as defined as between $4^{th}$ and $9^{th}$ TSPs, and near the center of hot leg hemisphere plane, coincided well with the region of preferential sludge deposition as defined by thermal hydraulics calculation using SGAP computer code. The cracks developed homogeneously in a wide range of SGs, so that the number of cracks detected each outage increased very rapidly since the first detection in the $8^{th}$ refueling outage. The root cause assessment focused on investigation of the difference in microstructure and manufacturing residual stress in order to reveal the cause of different susceptibilities to ODSCC among identical six units. The manufacturing residual stress as measured by XRD on OD surface and by split tube method indicated that the high residual stress of Alloy 600MA tube played a critical role in developing ODSCC. The level of residual stress showed substantial variations among the six units depending on details of straightening and OD grinding processes. Youngwang 3&4 tubes are less susceptible to ODSCC than U3 and U4 tubes because semi-continuous coarse chromium carbides are formed along the grain boundary of Y3&4 tubes, while there are finer less continuous chromium carbides in U3 and U4. The different carbide morphology is caused by the difference in cooling rate after mill anneal. There is a possibility that high chromium content in the Y3&4 tubes, still within the allowable range of Alloy 600, has made some contribution to the improved resistance to ODSCC. It is anticipated that ODSCC in Y5&6 SGs will be retarded more considerably than U3 SGs since the manufacturing residual stress in Y5&6 tubes is substantially lower than in U3 tubes, while the microstructure is similar with each other.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2002.11a
• /
• pp.390.1-390
• /
• 2002

In this study, we investigate the plugging effect on the CE type steam generator tube. The natural frequency and mode shape will be changed due to decrease of the effective mass distribution along the tube. We compared the variation of stability ratio for plugged tube with that fur unplugged one. The natural frequency increased because of removing the cooling water inside the steam generator tube, but the stability ratio decreased inversely because of changing the vibrational mode shape. We also investigated the turbulent excitation effect.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.16 no.10
• /
• pp.6641-6646
• /
• 2015

Heat exchanger tube array in a heat recovery steam generator is exposed to the hot exhaust gas flow and it could cause the flow induced vibration, which could damage the heat exchanger tube array. It is needed to establish the characteristics of flow induced vibration in the tube array for the structural safe operation of the heat exchanger. Several researches for the flow induced vibration of typical heat exchangers had been conducted and the nondimensional PSD(Power Spectral Density) function with the Strouhal number, fD/U, had been derived by experimental method. The present study examined the results of the previous experimental researches for the nondimensional PSD characteristics by CFD analysis and the basis for the application of flow induced vibration to the heat recovery steam generator tube array would be prepared from the present CFD analysis. For the previous mentioned purpose, the present CFD analysis introduced circular cylinder tube array and calculated with the unsteady laminar flow for the tube array. The characteristics of lift fluctuation over the cylinder tube array was investigated. The derived nondimensional PSD was compared with the results of the previous experimental researches and the characteristics of lift PSD for circular cylinder tube array was established from the present CFD study.

• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.18 no.12
• /
• pp.52-58
• /
• 2019

This study numerically analyzed the icing process in a U-shaped pipe exposed to the outside by considering the mushy zone of freezing water. Numerical results showed that the flow was pulled outward due to the U-shaped bend in the freezing section exposed to the outside, which resulted in the ice wave formation on the wall of the bended pipe behind. At the same time, the formation of a corrugated ice layer became apparent due to the venturi effect caused by the ice. The factors affecting the freezing were investigated, including the change of the pipe wall temperature, the water inflow velocity, and the pipe bend spacing. It was found that, as a whole, the thickness of the freezing layer increased as the pipe wall temperature decreased. It was also found that the freezing layer became relatively thin when the inflow rate of water was increased, and that the spacing of the pipe bends did not significantly impact the change in the freezing layer.

• Nuclear Engineering and Technology
• /
• v.52 no.5
• /
• pp.889-896
• /
• 2020

The vertically inverted U-tube steam generator (UTSG) is widely used in the pressurized water reactor (PWR). The reverse flow behavior generally exists in some U-tubes of a steam generator (SG) under both single- and two-phase natural circulations (NCs). The behavior increases the flow resistance in the primary loop and reduces the heat transfer in the SG. As a consequence, the NC ability as well as the inherent safety of nuclear reactors is faced with severe challenges. The theoretical models for calculating single- and two-phase flow pressure drops in U-tubes are developed and validated in this paper. The two-phase reverse flow characteristics in two types of SGs are investigated base on the theoretical models, and the effects of the U-tube height, bending radius, inlet steam quality and primary side pressure on the behavior are analyzed. The conclusions may provide some promising references for SG optimization to reduce the disadvantageous behavior. It is also of significance to improve the NC ability and ensure the PWR safety during some accidents.