Corrosion and fracture characteristics of low-alloy steels for power plants

Kim, Seonhong Sungkyunkwan university 2018 국내박사

The alloying effect of Cu for a flue gas desulfurization materials was investigated using the electrochemical methods in the modified green death solution and surface analyses. The test results demonstrated that the densely formed rust layer with high metallic Cu content improves the corrosion resistance of Cu-containing steel in the FGD environment. Because the free standing Cu2S precipitates had the insoluble characteristic in highly acidic solution, it produced the relatively porous Cu-enriched layer on the high Cu-containing steels surface. In addition, the degradation mechanism of the Cu-contianing steel in the green death solution was investigated. After 30 min of immersion, the steel surface was covered with a Cu-enriched film. Improvement of the film properties and the corrosion resistance were realized for the immersion time up to 6 h due to the development of the Cu-enriched layer. However, the Cu particle was formed in the Cu-enriched layer for the immersion time beyond 6 h. Since the formation of the Cu particle generated a Cu-depletion region, micro-galvanic corrosion between the Cu particle and the Cu-depletion region leads to the localized film breakdown on the surface film. The localized film breakdown, which decreased the corrosion properties of the Cu-containing steel, was accelerated by the continuous formation of Cu particles in the rust layer. The inhibition effect of the molybdate on the microbiologically influenced corrosion (MIC) behaviour of the cooling water pipeline under the incubation of the iron oxidizing bacteria (IOB) condition was examined. The decreased Fe2+ ions activity caused by the IOB metabolism increased the metal dissolution reaction and decreased the anodic inhibition reaction of the phosphate. As the molybdates injected into the IOB incubation environment, the growth of the IOB cells was suppressed and the deterioration of the protective film on the steel surface decreased. These results are due to the formation of the molybdenum oxides on the steel surface under the IOB incubation condition. In addition, the molybdate addition was effective on the corrosion behaviour of the steel with the previously formed IOB biofilm as well as the fresh steel under the IOB incubation condition. To identify the effects of the stress concentration at the pit on the fracture of the district heating (DH) pipeline, the stress increase with the wall thickness reduction was formulated. The formula includes the stress intensity factor with the propagation of pitting corrosion. As the result of the application of the DH pipeline condition to ASME B31.3 code formula and the corrosion test, the interplay with only uniform corrosion and the stress due to the internal pressure can not be an immediate reason for the DH pipeline. Furthermore, the thickness loss due to both uniform and localized corrosion exceeded before KI reaches the fracture toughness (63 MPa√m) of the pipeline steel (ASTM A106 Gr.B) under all of the studied conditions. The stress concentration at the pit was not sufficient to cause the pipeline fracture except that other factors affect the fracture of pipeline.

초임계 수산화 공정에서 페놀과 2, 4-Dichlorophenol의 분해에 관한 연구

이상영 연세대학교 대학원 2003 국내석사

본 연구는 초임계수 산화공정에 있어서 할로겐화 화합물의 처리시 발생되는 산에 의한 반응기의 부식 문제와 에 의한 Fouling이나 Scaling 문제를 해결하고자 “Floating type"이라고 불리우는 내부식성 반응기를 사용하였다. Phenol과 2, 4-Dichlorophenol(DCP)의 반응 생성물을 GC-MS로 분석한 결과 1차 반응 생성물이 형성되고 이러한 중간 생성물을 거쳐 다시 형성된 2차 생성물이 산화 반응을 일으켜 최종 생성물인 H₂O와 CO₂, HCl로 전환됨을 알 수 있었다. 이것은 반응 생성물의 색 변화를 통하여서도 확인할 수 있었다. Phenol의 경우 2, 4-DCP의 예비 실험으로 시행하였는데 산화제의 양을 양론비의 200%, 300%의 과량으로 투입하였을 때 완전히 전환되었음을 알 수 있었다. 2,4-DCP(Dichlorophenol)의 경우 저농도에서는 일정량(양론비의 100%)을 이상을 첨가하였을 때 전환율의 변화를 볼 수 없었다. 또한 온도가 높을 때, 농도가 낮을 때, 유속이 느릴 때, 압력이 높을 때 보다 높은 전환율을 나타내는 것을 볼 수 있었다. 이는 residence time의 변화와 반응성에 기인하였다. 또한 체류시간이 3∼4초로 매우 짧음에도 79%이상의 높은 전환율을 보여줌으로써 빠른 반응성을 확인할 수 있었다. 부식을 방지하기 위하여 사용된 "floating type" 반응기의 경우 장시간의 실험 후에도 산에 의한 반응기의 부식이나 중화제에 의한 염의 생성 문제가 발생하지 않았다. 이를 통하여 “floating type" 반응기가 할로겐화 화합물을 처리하는 데 있어서 효과적임을 알 수 있었다. This study was carried about the destruction of the Phenol and 2,4-Dichlorophenol in supercritical water oxidation(SCWO). In this study, anti-corrosive SCWO system named "Floating type" reactor was designed and was used to control of corrosion by acid formed in the treatment of halogenated hydrocarbon and fouling by counter-agent for neutralization of acid. The objectives of this study were to investigate the correlation of parameter effects on phenol and 2,,4-DCP oxidation, and the application of "Floating type reactor" in supercritical water oxidation. In order to confirm the intermediate of 2,4-DCP oxidation, The results of GC-MS analysis shows that 1^st and 2^nd reaction intermediate dimer were found, and then, finally, convert to H₂O, CO₂ and HCl. It was able to confirm the degree of destruction using the sensual methods such as odor and color. Before investigating the corrosion by halogenated compound, 2,4-DCP, Phenol was used for the test of the effect of H₂O₂ on destruction of refractory organics. Complete conversion was showed at the condition over the excess of stoichiometry amount of 200% H₂O₂. In the case of 2,4-DCP, we can't see the change of the conversion rate at low concentration(300ppm) and over the certain amount(stoichiometry 100%) of oxidant. And also, conversion increased with increasing temperature and pressure, and with decreasing concentration and flow rate. This is caused by the change of the residence time and reactivity. In spite of 2-4sec residence time, conversion was over 79%. It shows that oxidation rate in SCW is very rapid. In "Floating type" reactor, corrosion and fouling problems were not founded with long term operation. In this results, the "Floating type" SCWO reactor was very efficiency anti-corrosive system for the treatment of halogenated hydrocarbon.

Effects of Cu, Sb and welding microstructure on the galvanic corrosion of steel weldment in sulfuric and hydrochloric acid solution : 황산 염산 복합환경에서 용접재의 갈바닉 부식에 미치는 구리, 안티모니 및 용접조직의 영향

장승익 성균관대학교 일반대학원 2015 국내석사

This study examines the effects of Cu, Sb and welding microstructure on the galvanic corrosion of weldment using two types of filler metals in sulfuric and hydrochloric solution. Cu, Sb improved the corrosion resistance of weldment by the formation of protective layer and suppressed the anodic dissolution of the substrate. The welding microstructure affected the corrosion resistance by influencing the reaction at electrolyte/metal interface and the stability of protective layer. These factors lead to different galvanic corrosion behaviour of two weldments with time.

Effects of Cu, Sb and welding microstructure on the galvanic corrosion of steel weldment in sulfuric and hydrochloric acid solution

Jang, Seungik Sungkyunkwan University 2015 국내석사

Characterization of metal corrosion and degradation by aqueous amino acid salts for the capture of CO2

안승연 Graduate School, Yonsei University 2010 국내석사

In this study, we investigated the absorption ability of potassium salts of amino acids solutions for carbon dioxide and compared the results to MEA. The corrosion and degradation behavior were investigated in a CO2 absorption process using aqueous potassium salts of glycine and taurine. The experimental parameters varied were the concentration, amino acid type, temperature, CO2 loading, piperazine, and the presence of corrosion inhibitors. The corrosion characteristics of carbon steel were measured with potassium glycinate and potassium taurate solutions over a wide range of concentrations (1.5 to 5.0 M) and temperatures (313.15 to 353.15 K). The corrosion rate was calculated using a weight loss method averaging the results of four specimens. The degradation of aqueous amino acid salts is measured concentration 30 wt% and at 393.15 K. The experimental results indicate that increases in the concentration of the aqueous amino acid salts, solution temperature, CO2 loading, and piperazine concentration accelerate the corrosion rate. In addition, corrosion inhibitors were proven to be effective in controlling corrosion. Also the potassium salts of amino acid solutions were confirmed using continuously at 393.15 K. From the results of this study, the potassium glycinate solution was beneficial at high concentration and adding NaVO3. The potassium taurate solution was advantageous at low concentration and adding the piperazine.

산성비에 의한 강재부식의 실험적 연구

정의열 상지대학교 대학원 2008 국내석사

강구조물은 철강기술의 향상과 국가경제의 발전에 따라 점차 그 사용빈도가 증가하는 추세이나 주변 환경에 의한 도장이나 피막에 열화손상이 발생한 경우 부식의 영향을 받기 쉬운 단점이 있다. 부식은 시간의 경과와 더불어 축적되는 성질의 것이며, 강교의 물리적 수명을 지배하는 중요한 열화요인이다. 대기 중에 노출된 교량은 여러 부식원인 중에서도 산성비에 의한 부식이 큰 비중을 차지한다. 이처럼 산성비에 의해 도막이 열화 되고, 강재에 부식이 발생하게 되면 부재의 단면이 감소하므로 강도 및 강성이 저하되고 더욱이 국부부식이 발생하는 경우에는 부식개소에 응력집중이 일어나 피로강도가 저하되며 구조물의 물리적 수명을 지배하는 중요한 열화요인이 될 수 있다. 최근 우리나라에서는 이러한 열화 손상된 교량이 급증한 데 따라 사회적으로 교량의 안전성에 대한 관심이 높아지고 있는 실정이며 효과적이고 경제적인 유지관리가 무엇보다 중요한 과제가 되고 있다. 이러한 합리적인 유지관리를 위해서는 공용기간의 경과에 따른 열화와 손상정도의 파악 및 그 원인에 대한 적절한 대책이 강구되어야 할 것이다. 따라서, 부식의 진행에 따른 강재의 기계적 성질 변화에 대한 정량적인 자료는 설계자나 진단자에게 매우 중요한 자료가 될 것으로 판단된다. 본 연구에서는 산성환경에서 시간의 경과에 따른 교량용 강재(SS 400)의 부식특성을 인장시험을 통하여 항복강도, 인장강도 등을 대기상태와 염수분무시험 후의 값을 비교분석 함으로써 산성비에 의한 강재의 부식이 모재의 기계적 특성에 미치는 영향을 실험을 통하여 알아보았다. Structural steel has been used more and more as steel technology and a national economics has been developed. However, structural steel has its shortcomings: It is vulnerable to corrosions caused by degradation damages in painting or coating. Corrosion tends to be accumulate over time, and also is a major degradation factor to determine physical life of steel bridges. Corrosion by acid rains is one of the most devastating degradation factors of bridges that are exposed to open air. When the coating is degraded by acid rain, in turn, cross-section of bridge materials is decreased, which result in decrease in strength of a structure. Especially, when a localized corrosion takes place, a stress concentration takes place at corrosion point, which results in the decrease of fatigue strength and becomes a major factor of physical life of steel structure. These days, the safety of bridges is brought to a public attention, as the numbers of bridges suffer from degradation damages sharply increases, which makes the effective and economic way of bridge maintenance an important issue in this country. Therefore it is required to evaluate the state and causes of degradation damages as service life of bridges passes, and come up with appropriate measures to control the damage. Therefore, I discern the quantitative data about changes in the mechanical characteristics as the corrosion progresses to become a very important data to the designer or an examiner. In this study, I have tested the SS400 used in bridges under acidic environment in tensile test to observe the effects of acid rain on the corrosion of the material. In this I have utilized the tensile test to measure, compare and analyze the values of the yield point stress, and the stress levels before and after the salt water spray test to evaluate the effects of the acid rain on the corrosion of SS400 mechanical characteristics.

Thermal stability and material assessment of HFO-1234ze(E) as a working fluid for supercritical organic Rankine cycle (SORC)

Miqdar, Zulfikar Irriyanto Sungkyunkwan university 2020 국내석사

초임계 유기랭킨사이클 (Supercritical Organic Rankine Cycle, SORC)는 산업계 또는 지열 등 비교적 낮은 열원을 회수하여 전기를 전기를 생산하는 유망한 기술이다. HFO-1234ze(E) (trans-1,3,3,3-tetrafluoroprop-1-ene)는 온난화 지수가 낮기 때문에 SORC 시스템에 사용하기에 유망한 작동 유체 중 하나이다. 본 연구에서는 폐열을 이용하여 발전하기 위해 설계된 SORC loop의 온도와 압력 조건에서 HFO-1234ze(E)의 열분해를 평가하였고 kinetic model을 수립하였다. 5.0 MPa에서 433.15–473.15 K 범위의 온도에서 장기 분해 시험 (최대 6 개월)에서 잔류 HFO-1234ze(E) 농도의 정량적 측정에 의해 1st order kinetic model식을 확립하였다. Kinetic model은 SORC 시스템에 최적의 온도를 선택하기 위한 조건을 제공할 수 있다. SORC loop에서 고온 영역 (열교환기, 터빈)의 온도가 423.15K 일 때, HFO-1234ze(E)의 분해 속도는 50 년 연속 사이클 가동에서 단지 1.25 %였으며, 이는 작동 유체로서 HFO-1234ze(E)의 높은 열안정성을 나타낸다. 고온 영역에서 온도가 20K 및 40K 증가하면 50년 사이클링 후 각각 5.24% 및 18.40%의 분해가 발생하여 온도에 대한 열분해율의 민감도가 존재하였다. 작동유체와 SORC 루프를 구성하는 다양한 종류의 재료에 대한 호환성을 조사하기 위해서, HFO-1234ze(E)를 알루미늄, 철 기반, 니켈 기반 및 구리 기반 합금의 부식 거동을 ㅇ녀구하였다. SEM, EDS, XPS 및 SIMS와 같은 표면 분석 방법을 활용하여 냉매 노출 후 각 금속의 다른 거동이 발생하는 것으로 나타났습니다. 일예로 알루미늄의 경우 HFO-1234ze(E)에 노출시켰을 때 보호 MgF2층을 형성함으로써 알루미늄 합금 저항에 중요한 역할을 한다. 한편, 니켈계 합금으로서의 인코넬 718은 표면에서 생성 된 다수의 조밀한 산화물 층으로 인한 냉매 오염이 가장 적었으며, 스테인레스 스틸 외부 표면은 산화물이 붕괴됨으로써 노출되었다. 구리계 합금에서 알루미늄의 존재는 음극 보호 층으로서 작용 하였다. Supercritical organic Rankine cycle (SORC) has been considered a promising technique to generate electricity by recovering low-to-medium heat resources. Because of its low grobal warming potential, HFO-1234ze(E) (trans-1,3,3,3-tetrafluoroprop-1-ene) is one of promising working fluid for use in the SORC system. In this work, a simple kinetic method was proposed to evaluate the thermal decomposition of HFO-1234ze(E) under the temperatures and pressures that were examined for the SORC loop. By quantitative measuring of remained HFO-1234ze(E) concentration at the long-term decomposition test (up to six month) at temperatures in the range of 433.15–473.15 K at 5.0 MPa, a kinetic equation was established based on the first order kinetic model, which can provide impactful guidance to select optimum temperatures for SORC system. When the temperature of high-temperature region was 423.15 K, the decomposition rates of HFO-1234ze(E) was only 1.25% for 50-year continuous cycle running, indicating high thermal stability of HFO-1234ze(E) as the working fluid. The increase of the temperatures by 20 K and 40 K at the high-temperature region resulted in 5.24% and 18.40% decomposition, respectively, after the 50-year cycling running, suggesting that the high sensitivity of the thermal decomposition rate to the temperature in the SORC loop. The compatibility of HFO-1234ze(E) towards various kind of material was investigated by examining the corrosion behavior of aluminum, iron-based, nickel-based, and copper-based alloy. The weight change measurement and surface analysis such as SEM, EDS, XPS, XRD and SIMS revealed that different behavior of each metal occurred after the refrigerant exposure. The formation of protective MgF2 layer played an important role to aluminum alloy resistance. Inconel 718 as nickel-based alloy suffered the least refrigerant contamination due to multiple and dense oxide layer generated in the surface while stainless-steel outer surface was exposed due to oxide spallation. In the other case, the presence of aluminum in copper-based alloy acted as cathodic protective layer.

Control of Corrosion and Biofouling in Seawater Pipe

Kim, Mun Su 한국해양대학교 대학원 2019 국내석사

In the present-day society, with the emergence of sophisticated technologies, shipbuilding and marine industries have been developed in a rapid and broad manner. This requires that ships and marine structures, such as offshore plants and power plants have not only high value, but also a long life-expectancy. In the case of the marine infrastructures including vessels, their system should be obligatorily cooled to navigate vessels and operate facilities in order to avoid system being overheated. Therefore, most facilities have used seawater as coolant. However, along with the advantages of using seawater as coolant, such as cost-efficiency and resource abundance, there are also disadvantages, including corrosion and biofouling. Thus, in the field of vessels and energy plants, a disaster-defined as the inability to navigate, stop of generating power, and malfunction of plant facility-could occur either due to poor cooling or pitting caused by corrosion. Nevertheless, what aggravates the situation is that an effective and efficient technique that would enable control of corrosion and biofouling in seawater pipes is still lacking. Among relevant pipeline corrosion protection technologies, there is the method that is the inner surface coating of the pipe. However, the shortcoming of this method is that it is no longer effective when the coated surface is cracked. In addition, in thermal power and nuclear plants, a widely used technique that enables restricting the growth of marine organisms is electrochlorination. However, the limitation of this technique is that it is manually operated and adjusted by non-experts. Depending on the amount of current, marine organisms would evolve too much in the pipe or HClO produced by electrochlorination devastates ecosystem. In this context, it is obvious that a thorough investigation of effective ways to control corrosion and biofouling in seawater pipes is urgently needed. In the present study, cathodic protection and electrochlorination were experimentally tested for their effectiveness in the control of corrosion and biofouling. As a result of the cathodic protection in the pipes, when inspecting the surface of specimen and pipe, we observed that the studied specimens were properly protected. Furthermore, as shown by the results of measuring hypochlorous acid produced by electrochlorination, the lower cathodic protection potential was maintained, the higher increase of the HClO concentration was observed. In addition, when adjusting additional current in the electrochlorination facilitiy, we were also able to adjust the total HClO concentration, which could decimate marine organisms. From these results, we observe that the control of corrosion and biofouling would be possible by using cathodic protection and electrochlorination. 최근 기술의 발달로 해양 관련 산업은 급속한 성장을 거듭하고 있다. 이에 따라 선박, 해양플랜트 및 발전소와 같은 설비는 고부가가치화, 장수명화가 요구되고 있다. 이러한 설비들은 운항 및 시스템 가동을 위해서 해수를 냉각수로 사용하고 있기 때문에 배관 내부에 부식문제와 해양생물의 번식에 의한 냉각 불량 문제가 생긴다. 부식과 해양생물의 번식이 냉각계통에 영향을 미치면 결과적으로 선박의 운항 불능, 플랜트 설비의 시스템 중단과 같은 사태가 발생한다. 그럼에도 불구하고, 해수 배관 내면에서의 방식 및 방오 기술과 관련된 연구개발은 미비한 상태이다. 배관 내면의 부식방지 기술에는 코팅하는 방법이 사용되고 있으나, 이는 결함이 생기면 부식이 진행되는 것을 막을 수 없다. 또한 해양생물의 번식 억제 기술로 해수 전해설비를 사용하고 있으나 비전문가에 의해 운용되어 전류량에 따라 해양생물의 번식을 억제하지 못해 냉각관이 막히거나 고농도의 배출수에 의해 배수구 주변 생태계가 파괴되는 문제가 발생하고 있다. 따라서 배관 내면의 부식을 예방함과 동시에 해양생물의 부착을 억제하기 위한 연구개발이 필요한 상황이다. 본 연구에서는 음극 방식과 해수 전해를 배관 내면에 적용하여 배관 내부에서 발생하는 부식을 막고, 동시에 해양생물을 사멸하는 산화제인 차아염소산의 농도를 조절하는 실험을 수행하였다. 배관 내면의 음극 방식 실험결과 청수보다 해수에서, 정지중인 환경보다 유속이 존재하는 환경에서 높은 방식 전류가 공급되었고 탄소강 시험편과 배관의 표면 확인 시, 방식을 시행한 시험편은 표면의 보호가 이루어짐을 확인하였다. 음극방식을 하면서 만들어지는 차아염소산 농도의 측정 결과, 낮은 방식전위를 유지할 수록 방식전류에 의해 생성되는 차아염소산 농도가 증가하는 것을 확인하였다. 또한, 해수전해설비에서 전류를 추가적으로 제어할 경우 해양생물을 사멸시킬 수 있는 차아염소산 농도범위로 조절이 가능함을 확인하였다.

배연 탈황설비 덕트 재료의 부식 특성에 관한 연구

함정완 연세대학교 대학원 2000 국내석사

Application of acid neutralisation capacity to predict the risk of steel corrosion in concrete under chloride environments

정민선 Graduate School, Yonsei University 2012 국내박사

The durability assessment for concrete structures under a chloride attack mainly consists of chloride transport and corrosion resistance. The chloride threshold level for steel corrosion can be expressed in free chloride concentration, ratio of [Cl-]:[OH-], and total chloride content, which may not reflect the aggressiveness of corrosion factors and inhibitive natures, leading to the variation in the values depending on the detection methods. Thus, it seems required to define a single, dominant value for the threshold level. In this study, acid neutralisation capacity (ANC) of cement matrix was used to evaluate the corrosion resistance. Additionally, the influence of chloride binding capacity together with ANC on corrosion behaviour was determined to provide a single value of chloride threshold level. As a result, it was found that the threshold value was strongly dependent on the binder type, corrosion detection techniques. In particular, there was no clear-cut relation between binding of chloride ions and corrosion resistance, whilst the ANC strongly affected the threshold level. Thus, the threshold level could be represented by the molar ratio of [Cl-]:[H+] to reflect both the aggressiveness of chloride ions and inhibition effect of hydration products. Moreover, the ANC technique is more applicable, since only small amount of concrete fragment is used to define the ANC of concrete and all the procedures are relatively very simple. Likewise, the ANC technique provides a more convincing representation of the threshold level, irrespective of binder and concrete quality, thereby being very applicable to examine the durability of concrete structures at the resistance of chloride-induced corrosion.