• Journal of Welding and Joining
• /
• 제33권4호
• /
• pp.30-36
• /
• 2015

Austenite stainless steel(SA213-TP347H) has widely been used for the superheater & reheater tube in USC(ultra-supercritica) coal boiler because of its high creep rupture strength and anti-oxidation. But recently, the short-term failures have happened frequently in heat affected zone for only 4,000~15,000hours of service. Many investigations have been conducted to understand the failure mechanism. The root cause of failure was comfirmed to "strain induce participation hardening crack" or "reheat cracking". This mechanism often occurred due to weld residual stress and precipitation of the Cr, Nb carbides in the stabilized stainless steel such as TP347H. This paper presents an analysis of failure tube and effect of the sample tubes that conducting stabilizing heat treatment in site after 11,380hours & 16,961hours of service. Visual inspection was performed. In addition, microscopic characteristics was identified by O.M, SEM, and hardness test was carried out to find out the heat treatment effects. Failures seem to happen because of being not conducted stabilizing heat treatment in site. And another cause is inadequate weld parameter such as pass, ampere, voltage, inter-pass temperature. Thus, this paper has the purpose to describe that how to prevent similar failures in those weld-joints.

• 한국안전학회지
• /
• 제31권6호
• /
• pp.25-31
• /
• 2016

This paper has analyzed the structure, applicable regulations and the resistance characteristics of insulation ring type of CSST (Corrugated Stainless Steel Tubing for Gas). With the flammability test conducted in accordance with KS C IEC 60811-1-1, the evaluation of insulation resistance, temperature characteristics, and reliability has been conducted. An insulation ring type CSST consists of protective coating, tube, nut, insulation ring, packing, socket, and ball valve. Connecting an insulation ring type CSST to gas tubings for gas appliance is not permitted, moreover, the product shall be installed inside a sleeve pipe in case of buried installation such as the ceiling. Damages on protective coating and tube were detected when fire was applied to the test sample with a portable torch for 60 seconds. The insulation resistance of a normal product was $49.59M{\Omega}$, while that of the product completed the flammability test reduced to $9.21M{\Omega}$. The mean insulation resistance within the confidence Interval of 95% using the mini tap program 17 was $49.59M{\Omega}$ and the mean insulation resistance within the confidence interval reduced to $9.21M{\Omega}$. In the normal distribution analysis of 95% confidence interval, the value-P of the normal product was stable at 0.075 and AD(Anderson-Darling) statistic value was turned out to be 0.063, which is very normal, and the standard deviation was analyzed as 0.2586. The value P of the product completed the flammability test resulted in 0.005, the AD was 1.355 and the standard deviation reduced to 0.07908.

• 대한기계학회논문집
• /
• 제13권2호
• /
• pp.236-242
• /
• 1989

본 연구에서는 주로 보일러의 과열기 및 재열기등의 관재료로 널리 사용되고 있는 304 스테인레스강에 대하여 실제 고온부식현상을 재현한 부식환경하인 630.deg. C, 690.deg. C 및 750.deg. C 3가지 온도범위에서 크리프시험을 실시하고 고온부식이 크리프파단 특성에 미치는 영향을 부식조건이 없는 고온대기중의 실험결과와 비교 검토하였다.

• Journal of Advanced Marine Engineering and Technology
• /
• 제29권5호
• /
• pp.552-559
• /
• 2005

The evaporation pressure drop of $CO_2$ (R-744) in a horizontal tube was investigated experimentally. The experiments were conducted without oil in a closed refrigerant loop which was driven by a magnetic gear pump. The main components of the refrigerant loop are a receiver, a variable-speed pump. a mass flow meter, a pre-heater and evaporator (test section). The test section consists of a smooth. horizontal stainless steel tube of 7.75 mm inner diameter. The experiments were conducted at mass flux of 200 to $500\;kg/m^{2}s$, saturation temperature of $-5^{\circ}C\;to\;5^{\circ}C$. and heat flux of 10 to $40\;kW/m^2$. The test results showed the evaporation pressure drop of $CO_2$ are highly dependent on the vapor qualify, heat flux and saturation temperature. The evaporation pressure drop of $CO_2$ is very lower than that of R-22. In comparison with test results and existing correlations. the best fit of the present experimental data is obtained with the correlation of Choi et al. But existing correlations failed to predict the evaporation pressure drop of $CO_2$. Therefore, it is necessary to develop reliable and accurate predictions determining the evaporation pressure drop of $CO_2$ in a horizontal tube.

• Journal of Advanced Marine Engineering and Technology
• /
• 제31권2호
• /
• pp.145-151
• /
• 2007

The evaporation heat transfer coefficient of $CO_2$(R-744) in a horizontal tube was investigated experimentally. The main components or the refrigerant loop are a receiver, a variable-speed pump, a mass flow meter, a pre-heater and evaporator(test section). The test section consists of a smooth, horizontal stainless steel tube of inner diameter of 4.57 mm. The experiments were conducted at mass flux of 200 to $500\;kg/m^2s$, saturation temperature of -5 to $5^{\circ}C$, and heat flux of 10 to $40\;kW/m^2$. The test results showed the heat transfer of $CO_2$ has a greater effect on nucleate boiling more than convective boiling. Mass flux of $CO_2$ does not effect nucleate boiling too much. In comparison with test results and existing correlations, the best fit of the present experimental data is obtained with the correlation of Jung et al. But existing correlations failed to predict the evaporation heat transfer coefficient of $CO_2$, therefore, it is necessary to develope reliable and accurate predictions determining the evaporation heat transfer coefficient of $CO_2$ in a horizontal tube.

• 대한설비공학회:학술대회논문집
• /
• 대한설비공학회 2009년도 하계학술발표대회 논문집
• /
• pp.1528-1535
• /
• 2009

Characteristics of R-22 and R-134a two-phase vaporization in horizontal small tubes were investigated experimentally. In order to obtain the local heat transfer coefficients, the test was ran under heat flux range of 10 to $40\;kW/m^2$, mass flux range of 200 to $600\;kg/m^2s$, saturation temperature range of 5 to $10^{\circ}C$, and quality up to 1.0. The test section, which was made of stainless steel tube and heated uniformly by applying an electric current to the tube directly, have inner tube diameters of 0.5, 1.5 and 3.0 mm, and lengths of 0.33 and 2.0 m. The effects on heat transfer coefficient of mass flux, heat flux and inner tube diameter were presented. The experimental heat transfer coefficients were compared with the predictions using existing heat transfer coefficient correlations. A new boiling heat transfer coefficient correlation based on the superposition model, with considering the laminar flow, was developed.

• 대한기계학회논문집B
• /
• 제30권6호
• /
• pp.497-504
• /
• 2006

A Coriolis mass flowmeter(CMF), which has U-Shaped unique measurins tube was developed fo. direct mass flow measurement. In order to convert the time difference between two measuring tubes motion into mass flowrate and flow quantity, a signal processing circuit, as a part of CMF, was also developed. The CMF was designed as the 15 mm nominal diameter of pipe connection and the 8 mm stainless steel(sus 316) pipe was used for measuring tube. To maximize the flow signal(time difference) from the measuring tubes, the natural frequency of measuring tube was adjusted as 220 Hz, which is same as the frequency of exciter. The maximum displacement at the end of the measuring tube was measured as 0.05 mm and the maximum time difference between two measuring tubes was observed as $20{\mu}s$, which was proper for discrimination and measuring range of CMF. The developed CMF was tested against the gravimetric flowmeter calibrator in the range of 3 kg/min and 30 kg/min. The results showed that the CMF has good linearity and repeatability in the tested flow range. Large size of CMF base on the current study experience will be developed.

• Archives of Plastic Surgery
• /
• 제35권1호
• /
• pp.73-77
• /
• 2008

Purpose: In case of facial injury, a canalicular injury is common. Many methods and materials have been used for reconstruction of lacrimal canaliculi. Silicone tube is the most widely used material, generally with pigtail probe or stainless steel probe. But it has still many problems. The authors guess that reconstruction using Mini $Monoka^{(R)}$ will reduce those problems and will be more successful. Methods: From July, 2003 to November, 2006 in 24 patients with canalicular injury, 11 cases were recon- structed with former silicone tube and 13 cases were treated with Mini $Monoka^{(R)}$. Results: The mean follow-up period was 3 months. The results of reconstruction were classified into three groups(Normal, Fair, Poor). In 13 cases with Mini $Monoka^{(R)}$ stent, 10 cases were normal, 3 were fair, and no poor cases. But in 11 cases with bicanaliculus silicone stent, 6 cases were normal, 3 were fair, and 2 were poor. Conclusion: Compared with bicanaliculus silicone stent, Mini $Monoka^{(R)}$ stent is fixed well, has no aesthetic problems, makes less foreign body sensation. And the results were successful.

• 설비공학논문집
• /
• 제13권8호
• /
• pp.674-681
• /
• 2001

An experiment is conducted to investigate the effect of the inclination angle on convective boiling heat transfer of a uniformly heated tube. The test section used is a stainless steel tube with10.7mm in inner diameter. The hating length is 3m and is heated directly by an AC current. The test fluid is R-113. Experiment are carried out with mass flow rates of 300, 500 and $700\;kg/m^{2}s$, and heat fluxes varying from 5 to 65 kW/$m^2$. The inclination angles of the tube are $0^{\circ},\;5^{\circ},\;11^{\circ}\;and\;25^{\circ}$. the circumferential temperature variation at low quality region and the location of dryout at high quality region are mainly observed. Circumferential anisothermality occurring at low mass flow rate and low quality conditions is gradually reduced with the increase in the inclination angle and finally disappears at the inclination angle of $25^{\circ}$. Critical quality where dryout is initiated is seriously influenced by the inclination angle. Wall temperature after critical quality is also affected by the inclination angle.

• 동력기계공학회지
• /
• 제11권1호
• /
• pp.63-69
• /
• 2007

The evaporation pressure drop of $CO_2$ (R-744) in a horizontal tube was investigated experimentally. The main components of the refrigerant loop are a receiver, a variable-speed pump, a mass flow meter, a pre-heater and an evaporator (test section). The test section consists of a smooth, horizontal stainless steel tube of 4.57 mm inner diameter. The experiments were conducted at saturation temperature of $-5^{\circ}C\;to\;5^{\circ}C$, and heat flux of 10 to $40kW/m^2$. The test results showed that the evaporation pressure drop of $CO_2$ are highly dependent on the vapor quality, heat flux and saturation temperature. The measured pressure drop during the evaporation process of $CO_2$ increases with increased mass flux, and decreased saturation temperature. The evaporation pressure drop of $CO_2$ is much lower than that of R 22. In comparison with test results and existing correlations, the best fit of the present experimental data is obtained with the previous correlation. But existing correlations failed to predict the evaporation pressure drop of $CO_2$. Therefore, it is necessary to develop reliable and accurate predictions determining the evaporation pressure drop of $CO_2$ in a horizontal tube.