• Tribology and Lubricants
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• 제25권3호
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• pp.171-175
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• 2009

One of the critical issues associated with the 40mm long hollow cylinder's development and maintenance is the prediction of cylinder erosion. The actual firing test is the most accurate method to measure the cylinder erosion rate. But it costs a great deal and requires a long measurement time. Hence many empirical methods have been proposed to predict the erosion rate and life span of long hollow cylinders. An EFC formula is calculated. An approximate erosion formula for the ammunition type A is derived to interpolate 16 observation values up to 4,000 rounds. A new erosion equation and muzzle velocity formula are also suggested. Several numerical results are presented.

• 한국지반공학회논문집
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• 제20권8호
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• pp.89-96
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• 2004

흐르는 물의 침식유발능력과 지반의 침식저항능력을 동시에 고려할 수 있는 새로운 교량세굴해석 모델을 개발하기 위한 많은 연구가 진행되었으며, 이러한 노력의 일환으로 지반의 침식율을 정량화할 수 있는 세굴률 시험기가 개발되었다. 본 연구에서는 세굴률 시험기를 이용하여 3종의 재성형 점토에 대해 세굴률 실험을 실시하였다. 재성형 점토의 세굴률 실험을 통해 성형하중의 변화에 따른 세립토의 침식특성을 분석하였으며, 또한 토성치와 침식율의 상관관계 분석을 시도하였다. 실험과 해석을 통해, 토질정수 중 특히 단위중량과 전단강도는 지반의 침식특성에 큰 영향을 미치는 것으로 나타났다.

• 한국표면공학회지
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• 제34권6호
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• pp.575-584
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• 2001

Erosion due to abrasive particles contained in gas streams from boilers has been emerged as a significant problem in the coal fired power plants. Particle erosion accounted for approximately 50% of boiler failures and especially flyash erosion was responsible for 20~30% of emergency boiler shutdowns. Particularly, because of the high ash loading and high velocity, most erosion occurs in the boiler tubes and economiser tube bank where the direction of the gas stream changes to $180^{\circ}$ .In this study, a high temperature particle erosion tester was used to evaluate erosion rate in a simulated environment. The erosion parameters such as erosion temperature, particle impact angle, particle velocity and various particle size were changed. Flyash is the combustion product of the pulverized coal, where size is ranging from 1 to $200\mu\textrm{m}$. Flyash composed of mainly SiO$_2$, $A1_2$$_O3$, and $Fe_2$$O_3$has dense spherical particles and irregular particles containing numerous pores and cavities. From the erosion tests at various conditions, the maximum erosion was experienced at impact angles of $30^{\circ}$ to $60^{\circ}$ In addition, erosion rate increased in proportional to velocity and temperature. And from the observation of the eroded surfaces, it was also concluded that 304 stainless steel was mainly eroded by extrusion-forging at high impact angle ($90^{\circ}$) and by microcutting mechanism at low impact angles ($30^{\circ}$ and $45^{\circ}$).

• Corrosion Science and Technology
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• 제18권6호
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• pp.292-299
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• 2019

The hull material of a high-speed ship may cause erosion damage from fluid impact. When physical erosion and electrochemical corrosion combine, erosion corrosion damage occurs. The aluminum ship is vulnerable to erosion corrosion because it can be operated at high speed. Thus, in this study, Al5052-O and Al6061-T6 aluminum alloys for the marine environment were selected as experimental materials. The erosion corrosion resistance of Al5052-O and Al6061-T6 aluminum alloys in seawater was investigated by an erosion test and potentiodynamic polarization test at the various flow rate (0 m/s, 5 m/s, 10 m/s, 15 m/s, 20 m/s). Erosion corrosion characteristics were evaluated by surface analysis, 3D analysis, SEM analysis, and the Tafel extrapolation method. The results of surface damage analysis after the erosion test showed that Al6061-T6 presented better erosion resistance than Al5052-O. The results of the potentiodynamic polarization test at the various flow rate, corrosion current density by Tafel extrapolation presented lower values of Al6061-T6 than Al5052-O. Al5052-O showed more surface damage than Al6061-T6 at all flow rates. Consequently, Al6061-T6 presented better erosion corrosion resistance than Al5052-O. The results of this study are valuable data for selecting hull material for an aluminum alloy vessel.

• Journal of Mechanical Science and Technology
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• 제17권1호
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• pp.114-121
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• 2003

Water droplet erosion is one of major concerns in the design of modern large fossil steam turbines because it causes serious operational problems such as performance degradation and reduction of service life. A new erosion model has been developed in the present study for the prediction of water droplet erosion of rotor blades operated in wet steam conditions. The major four erosion parameter : impact velocity, impacting droplet flow rate, droplet size and hardness of target are involved in the model so that it can also be used for engineering purpose at the design stage of rotor blades. Comparison of the predicted erosion rate with the measured data obtained from the practical steam turbine operated for more than 90,000 hours shows good agreement.

• 수산해양기술연구
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• 제28권2호
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• pp.171-183
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• 1992

In this paper, the behaviour of cavitation erosion, influence of corrosion and corrosion control on slide bearing metals for internal combustion engine were investigated, and this experiment was done by the vibratory cavitation erosion tester. The main results obtained are as follows: 1. With decreasing the space between horn and specimen, the weight loss and its rate increased step by step. But the weight loss and its rate of 0.2mm space decreased conversely more than that of 0.4mm space at early stage. 2. The weight loss and its rate with change of pH were appeared to the order of pH2>pH12>pH7>pH4. And the weight loss and its rate at pH 4 decreased at best. 3. The weight loss and its rate by cavitation erosion for bearing metals were shown to the order of W.M7>W.M1>K.M4. 4. There appeared mainly small pit hole at pH2, and appeared the pit of netting thread type at pH12 by the results of the damaged surfaces at pH2 and pH12 environments that were sensitive to cavitation erosion. 5. With increasing the viscosity of lubricating oil, the weight loss rate by cavitation erosion became dull at the space below 0.5mm. 6. The protective efficiency of cavitation erosion-corrosion is superior inhibitor of chormate(25 ppm) to cathodic protection.

• Tribology and Lubricants
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• 제34권5호
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• pp.175-182
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• 2018

Accumulation of coal ash at the boiler wall reduces combustion and fuel efficiency. The design of a wall blower is important to effectively remove coal ash. We present numerical results for the removal of coal ash from boiler walls of domestic coal-fired power plants, associated with the computational fluid dynamics for the flow from spray nozzle to boiler wall. The numerical model simulates an erosion process in which the multiphase fluid comprising saturated vapor and fluid water is sprayed from the nozzle, and the water particles impact the boiler wall. We adopt the Finnie erosion model for water particles. We obtain the erosion rate density as a function of nozzle angle and its injection angle. As excessive coal ash removal usually induces damage to the boiler wall, the removal operation typically focuses on a large area with uniform depth rather than the maximum removal of coal ash at a specific location. In order to estimate the removal performance of the wall blower nozzle considering several functionality and reliability factors, we evaluate the optimal injection and nozzle angles with respect to the biggest cumulative and highest erosion rates, as well as the widest range and lowest standard deviation of the erosion rate distribution.

• Journal of Pharmaceutical Investigation
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• 제30권4호
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• pp.295-297
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• 2000

A new method to evaluate erosion of biodegradable polymer, polyanhydrides, was developed. The polymer devices were prepared with the melt-casting method and weight loss was accurately measured after agitating the devices in buffers (pH 1-9), and removing the device at selected time intervals and freeze-drying the device. The erosion rate was estimated from the plot of the weight loss(%) of device as a function of time. The freeze-drying technique used in this study is particularly useful for estimating the erosion rate of biodegradable polymer.

• 한국지형학회지
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• 제20권3호
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• pp.41-53
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• 2013

이 연구는 안면도 둔두리 해식애를 대상으로 주기적인 현장조사를 통해 침식율을 산정하고, 침식형태를 분류하였다. 침식기준목을 이용한 현장 측정결과, 해식애의 연간 침식율은 지점별로 약 25~102cm/yr 정도로 추정되었다. 침식율은 봄에서 여름까지 점차 증가하다가 가을에 다소 감소하는 경향을 보였다. 특히, 6~7월 사이의 침식율이 다소 감소하는 추세를 보이다가 7~9월 사이에 급격히 증가하였다. 이러한 원인은 연구지역에 직접적인 영향을 끼친 여름 집중호우 및 태풍으로 발생한 폭풍해일에 의해 해식애의 침식이 다른 기간에 비해 급격하게 진행된 것으로 판단된다. 그 후 해식애의 침식율은 가을철이 되면서 점차 감소하다 12월에서 1월이 되면 다시 증가세를 보이는데, 이는 겨울철 해식애의 기반암이 동결 융해작용을 반복하면서 기계적풍화가 활발히 진행되었기 때문인 것으로 판단된다. 둔두리 해식애의 침식 형태별 유형은 세 가지 유형으로 구분이 된다. 첫 번째 Type A의 경우 동일한 기반암 혹은 경암층으로 이루어진 해식애에서 관찰되는 유형이다. 두 번째, Type B의 경우 동일한 기반암 혹은 경암층으로 이루어진 해식애 면에 토양을 포함한 풍화물질이 형성되어 있는 비교적 Type A에 비해 경사가 완만한 해식애에서 관찰되는 유형이다. 마지막으로, Type C의 경우 경암층과 연암층이 혼재되어있는 해식애에서 관찰되는 유형으로, 강우나 파랑에너지에 의해 연암층이 먼저 붕락 및 침식되고 노출된 경암층이 추가적으로 붕락이 이루어지는 유형이다.

• Corrosion Science and Technology
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• 제19권6호
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• pp.310-317
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• 2020

This study investigated the damage to the specimen due to liquid droplet impingement erosion corrosion, which improved the corrosion resistance and durability via hard anodization of 5083-H321 aluminum alloy, which is widely used for small ships and marine structures. The experiment combined liquid droplet impingement erosion and electrochemical equipment with the flow rates in natural seawater solution. Subsequently, Tafel extrapolation of polarization curves was performed to evaluate damage due to the liquid droplet impingement erosion corrosion. The damaged surface was observed using a 3D microscope and a scanning electron microscope. The degree of pitting damage was measured using the Image J program, and the surface hardness was measured using the micro-Vickers hardness tester. The corrosion current density, area, depth, and ratio of the damaged areas increased with the increase in flow rate. The grain size of the damaged area at a flow rate of 20 m s-1 showed fewer and minor differences in height, and a smooth curved shape. The hardness of the damaged surface tended to decrease with increase in flow rate.