• 한국해양공학회지
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• 제22권3호
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• pp.82-88
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• 2008

The diesel engine of the merchant ship has been aperated in severe environments more and more, because the temperature of the exhaust gas of a combustion chamber is getting higher and higher with increasing use of heavy oil of law quality, due to the significant increase in the price of oil in recent some years. As a result, the degree of wear and corrosion between exhaust valve and seat ring is more serious compared to other engine parts. Thus the repair welding of exhaust valve and seat ring is a unique method to prolong the life of the exhaust valve, from an economical point of view. In this study, the corrosion property of both weld metal and base metal was investigated using electrochemical methods such as measurement of corrosion potential, cathodic and anodic polarization curves, cyclic voltammogram, and polarization resistance in 5% H2SO4 solution. The test specimen was a part of an exhaust valve stem being welded as the base metal, using various welding methods. In all cases, the corrosion resistance as well as hardness of the weld metal zone was superior to the base metal. In particular, plasma welding showed relatively good properties for both corrosion resistance and hardness, compared to other welding methods. In the case of DC SMAW (Shielded metal arc welding), corrosion resistance of the weld metal zone was better than that of the base metal, although its hardness was almost same as the base metal.

• 대한공업교육학회지
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• 제31권1호
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• pp.200-210
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• 2006

초기 응력부식균열에 대한 감수성 평가 시험법인 C링 시험법(C-ring Test)은 용접부의 후열처리 균열감수성을 평가하는 시험법으로 적합하다고 알려져 있다. C링 시험법은 실제 용접부 열영향부에 노치를 제작하여 잔류응력이 열영향부에 미치는 영향을 평가할 수 있다는 장점을 가지고 있다. 따라서 본 연구에는 C링 시험법을 이용하여 원자력 발전소 압력용기에 사용되는 Co-Mo강의 용접부 결함 발생 현상을 검토 하고자 Co-Mo강에 대하여 후열처리를 실시하였으며, C링 시험법을 통하여 용접 열영향부의 후열처리 균열을 평가하고자한다. 결론은 다음과 같다. 바나듐 모디파이 합금(AMAX 3Cr-1Mo­-0.1V, JSW 3Cr-­1Mo-­V-­Ti-­B 및 JSW $2\frac{1}{4}Cr$-1Mo-­V-­Ti-­B강)은 Berkeley $3Cr-1\frac{1}{2}Mo-\frac{1}{2}Ti$ 및 $2\frac{1}{4}Cr$-­1Mo합금강보다 후열처리 균열에 대한 감수성 보다 높게 나타났다. C-ring 시험에 있어서 바나듐 모디파이 합금은 2종의 후열처리조건과 3종의 응력조건에서 모두 균열을 나타냈으나 Berkeley $3Cr-1\frac{1}{2}Mo-\frac{1}{2}Ni$강과 Luken $2\frac{1}{4}Cr-1Mo0.1C$재료는 690MPa와 더 이상의 응력조건에서 2종의 후열처리를 실시하는 조건에서도 균열이 발생하지 않았다. C-ring 시험결과, 균열깊이는 바나듐 모디파이 재료인 경우, 낮은 후열처리온도와 비교해서 높은 후열처리온도인 경우가 감소하고 있다. C-ring 시험에 대한 SEM분석결과 균열은 오스테나이트 결정 입계를 따라 파괴되는 파괴양상을 나타내고 있으며 연성파면은 나타나지 않았다.

• Journal of Advanced Marine Engineering and Technology
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• 제15권4호
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• pp.22-28
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• 1991

The crevice corrosion behavior on austenitic AISI 304 and 316L stainless steel welded by TIG, MIG, $CO_2$ and SMA was studied. The results are as follows : In 10% $FeCl_3$ solution and natural sea water sampled near Mokpo port, the base metal of 304 stainless steel showed small amount corrosion, whereas 316L stainless steel did not showed any corrosion in the test periods. The weight loss caused by crevice corrosion increased with increasing weld heat input and residual .delta. ferrite formed in welded part. The corrosion resistance of the welded part was in the order of TIG, MIG, $CO_2$ and SMA. From this tendency, it is proved that the smaller heat input gives the better corrosion resistance.

• Journal of Welding and Joining
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• 제22권5호
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• pp.58-64
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• 2004

Although leakage at a low carbon steel pipe made by electrical resistance welding (ERW) was reported due to grooving corrosion, the cause for the corrosion has not yet been cleared. In order to clarify the main cause, failure analysis on the leaked pipe was carried out, followed by metallographic investigation and corrosion test for the various ERW pipe made with different welding heat input. The microstructure, particularly inclusion content, of the weldment is dependant on the welding heat input applied. For an improper low heat input, the amount of inclusion at the weld was high. High inclusion content accelerated grooving corrosion at the weld. It is therefore that welding heat input should be controlled based on the carbon content of the pipe in order to improve the corrosion resistance of the ERW pipe.

• Journal of Welding and Joining
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• 제18권3호
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• pp.97-105
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• 2000

The stress corrosion cracking(SCC) and hydrogen embrittlement cracking(HEC) characteristics of a weathering steel weldment were investigated in aerated acid-chloride solution. The electrochemical properties of weldment were investigated by polarization test and galvanic corrosion test. Weathering steel did not show passive behavior in the acid-chloride solution. Galvanic corrosion between the weld metal and the base metal was not observed because the base metal was anodic to the weld metal. The slow-strain-rate tests(SSRT0 were conducted at a constant strain rate o 7.87×{TEX}$10^{-7}${/TEX}/s at corrosion potential, and at potentiostatically controlled anodic and cathodic potentials. The weldment of weathering steel was susceptible to both anodic dissolution SCC and hydrogen evolution HEC.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.666-669
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• 2003

Electrical resistance welded steel pipes showed leakage failure within 5 years usage. Microstructural analysis and hardness test were carried out, whose results gave no evidences about the reason of failure. For the analysis, 3 kinds of ERW pipes with different heat inputs were produced. Microstructural differences according to the different heat inputs were detected. Differences of the amount of inclusion in the weld line were observed. It is concluded that the difference of heat input during ERW pipe production caused the microstructural changes which resulted in the leakage failure.

• 대한기계학회논문집A
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• 제32권9호
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• pp.770-781
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• 2008

In nuclear power plants, ferritic low alloy steel components were connected with austenitic stainless steel piping system through alloy 82/182 butt weld. There have been incidents recently where cracking has been observed in the dissimilar metal weld. Alloy 82/182 is susceptible to primary water stress corrosion cracking. Weld-induced residual stress is main factor for crack growth. Therefore exact estimation of residual stress is important for reliable operating. This paper presents residual stress computation performed by 6" safety & relief nozzle. Based on 2 dimensional and 3 dimensional finite element analyses, effect of welding variables on residual stress variation is estimated for sensitivity analysis.

• 설비공학논문집
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• 제25권10호
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• pp.568-572
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• 2013

The main components, such as a reactor vessel, in commercial nuclear power plants have been welded to pipes with dissimilar metal in which Primary Water Corrosion Cracking (PWSCC) has been occurred. PWSCC has become a worldwide issue recently. This paper addresses the results of experimental and numerical analysis to prevent PWSCC by changing the stress profile that is tensile stress to compressive stress at interesting regions with plastic deformation generated by mechanical pressure. Based on the results of experimental and numerical analysis with a 6 inch pipe and dissimilar metal welded pipes, compressive stress 68~206 Mpa is generated at all locations of inner surface in the heat affected zone.

• Journal of Welding and Joining
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• 제15권5호
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• pp.124-133
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• 1997

Corrosion behavior of welded SWS400 steel used for bridges was studied in a range of the acid-rain environment using immersion, potentiodynamic polartization, polarization resistance, and galvanic corrosion tests. The SWS400 steel exhibited active corrosion behavior in the range of acid-rain environment, i.e. no passivation. As the results of immersion corrosion test, Tafel extrapolation method, and polarization resistance measurement, the average corrosion rats of the steels were 0.31-0.72 mm/year in the pH of 4-5, and 0.17 mm/yera in the pH 6, respectively. The steel showed a resistance to corrosion in the pH 6. The observed active behavior of SWS400 steel in chloride-containing environment indicated that the chloride ions exerts a detrimental influence on the formation of passive films. Galvanic corrosion was observed between the weld and the base metals because the weld is anodic to the base metal.

• Journal of Welding and Joining
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• 제31권2호
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• pp.49-56
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• 2013

We have investigated traits of clad metals in hot-rolled clad steel plates, sensitization and mechanical properties of STS 316 steel plate and carbon steel(A516). Clad steel plates were butt-weld by SAW+SMAW, and with the time of heat treatment as the variable, heat treatment was conducted at $625^{\circ}C$, for 80, 160, 320, 640, 1280 minutes. As a way to evaluate it, sectioned weldments and external surfaces were investigated to reveal the degree of sensitization by mechanical property, etching and those of EPR test, results were compared with it. In short, the purpose of this study is suggesting some considerations in developing on-site techniques to evaluate the sensitization of stainless steels.