• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.27 no.2
• /
• pp.99-104
• /
• 2017

Refractories used in low-rank coal gasification reactors are usually exposed in a highly corrosive $H_2S$ gas at less than $1000^{\circ}C$, and their mechanical properties such as erosion resistance and fracture strength decline with the exposure time. However, the cause of the degradation of the mechanical properties has little reported yet. In this paper, two kinds of castable refractories with different refractoriness had been exposed in a $H_2O/N_2/H_2S$ mixed gas with high $H_2S$ content for 100 hours at $900^{\circ}C$, and the changes of microstructure, crystalline phases and erosion resistance were compared before and after the corrosion test. The weight of the refractories decreases due to the elution of silica in the specimens after the corrosion test. The capillary porosities of the samples are reduced, but the erosion resistance of the samples is fatally weakened after the corrosion test. There also are changes in constituent phases; dmitryivanovite ($CaAl_2O_4$) and amorphous silica ($SiO_2$) disappear, and gypsum ($CaSO_4{\cdot}2H_2OS$) and kaolinite ($Al_2Si_2O_5(OH)_4$) newly appear after the corrosion test. It is obvious that the phase change from dmitryivanovite that works as a binding agent in the castable refractory to gypsum is the main reason of the degradation of the erosion resistance, because the mechanical properties of gypsum are much poorer than those of dmitryivanovite.

• Journal of Ocean Engineering and Technology
• /
• v.4 no.1
• /
• pp.88-100
• /
• 1990

Among the test methods to evaluate stress-corrosion cracking(SCC) on the basis of fracture mechanics, constant displacement(bolt) loading method using modified-WOL specimen is practically convenient. In this test method, compliance formula is generally required to calculate load(consequently $K_{ISCC}$). There are many problems in using the analytic compliance formula to calculate $K_{ISCC}$, so we had proposed the experimental $K_{ISCC}$ evaluation technique in the previous report. This study has employed the slightly altered configuration of modified-WOL specimen made of weldable structural stee(BS360-50D). With these specimens, stress-corrosion tests have been performed in $H_2S$ gas saturated 20% HCl solution. Through the test, the problems as mentioned earlier have been discussed again, and the proposed evaluation technique has been verified. And the stress-corrosion cracks and hydrogen blisters have been investigated in the initiation step with the aids of metallurgical micrographs, SEM fractographs, and EPMA analysis. The inclusions segregated in the mid-thickness region traps hydrogen to produce the hydrogen blistering. The applied or residual stress does not contribute the occurrence of the blister. Hydrogen absorbed into the mid-thickness region is consumed to produce the blistering so that stress-corrosion crack could hardly be detected at that region. The stress-corrosion cracks initiate from the inclusions and propagate in radial pattern. And the initiation site is remote from the crack tip and is inclined from the crack plane, which is assumed to be caused by the triaxial stress and the amount of the absorbed hydrogen.

• Journal of the Korean institute of surface engineering
• /
• v.56 no.2
• /
• pp.125-136
• /
• 2023

Recently, ammonia has emerged as an alternative energy source that can reduce carbon emissions in various industries. Ammonia is used as a fuel in internal combustion engines because it contains no carbon in its components and does not emit any carbon when burned. It is also used in various fields such as fertilizer production, refrigeration, cleaning and disinfection, and drug manufacturing due to its unique characteristics, such as high volatility and easy solubility in water. However, it is highly corrosive to metals and is a toxic gas that can pose a risk to human health, so caution must be exercised when using it. In particular, stress corrosion cracking may occur in containers or manufacturing facilities made of carbon-manganese steel or nickel steel, so special care is needed. As ammonia has emerged as an alternative fuel for reducing carbon emissions, there is a need for a rapid response. Therefore, based on a deep understanding of the causes and mechanisms of ammonia corrosion, it is important to develop new corrosion inhibitors, improve corrosion monitoring and prediction systems, and study corrosion prevention design.

• Journal of Aerospace System Engineering
• /
• v.8 no.2
• /
• pp.33-39
• /
• 2014

Feathering spindle is one of the critical parts of the rotor system in the Smart Unmanned Aerial Vehicle(SUAV) that it was manufactured with special material, Maraging C300. During the initial ground and tie-down flight tests of the SUAV, surface of the feathering spindle contacting to the needle-roller bearings showed excessive wear and dent due to high vibrating loads transferred from the rotating blades. Gas nitriding process was applied to the bearing contact surface of the feathering spindle to increase surface hardness so as to improve the surface defects. This paper briefly presents the gas nitriding process adopted and the spindle quality improvements including wear and corrosion resistance.

• Journal of the Korean institute of surface engineering
• /
• v.31 no.6
• /
• pp.307-316
• /
• 1998

The effects of surface roughness on chromate conversion coating and the corrosion behavior of galvanized steel sheets were investigated. Surface roughness was differently given to the galvanized steel sheets tested and these were then chromated. Accelerated corrosion test was conducted under the condition of $30^{\circ}C$, 90%RH with flowing 200ppm $SO_2$ gas. The galvanized steels were also exposed to urban environment for 5 weeks. The corrosion rates were measured by weight gain method. The distribution of chromate film and corrosion product on the coating were examined which SEM/EDS. The chromate film formed preferentially at the convex sites rather than at the concave sites on the surface. The corrosion products were found at the concave sites where the chromate film formed rarely. The corrosion product on the coating were found at the concave sites where the chromate film formed rarely. The corrosion rates increased slightly with the surface roughness in accelerated corrosion test but significantly in field test.

• Corrosion Science and Technology
• /
• v.6 no.3
• /
• pp.112-119
• /
• 2007

This paper presents the importance of corrosion control and protection technology with a real case study of heater tube rupture damaged by High temperature H2S-H2 corrosion in the refinery. The heater was operated at the Hydrocracking unit and the operation temperature and pressure was $340^{\circ}C$ and $18kg/cm^{3}$ respectively. Top side of the convection tube was thinned by high temperature hydrogen sulfide and hydrogen gas as a uniform corrosion and finally ruptured under operation pressure. Damaged area (Convection tube zone) was blocked by protection wall, so it was impossible to inspect with conventional nondestructive examination. Instead the elbow area which is out of the protection wall was inspected regularly to evaluate the corrosion rate of convection tube indirectly. However the operation temperature and the phase of the process stream was different between inside the chamber and outside the chamber. As a result, it caused severe corrosion to the horizontal convection tube inside the chamber comparing to the elbow outside the chamber. Finally convection tube was corroded more rapidly than the elbow and ruptured after 13 years operation. Because of the rupture, the heater was totally burned and the operation was stopped for 3 months until it has been reconstructed. To prevent this kind of corrosion problem and accident, corrosion control should be strengthened and protection technology should be improved.

• Proceedings of the Korean Institute of Surface Engineering Conference
• /
• 2015.05a
• /
• pp.128-129
• /
• 2015

Al-rich coatings were prepared on hot rolled low carbon steel by hot dipping method in molten Al-bath to investigate the corrosion resistance with the possible outcomes and defects of aluminized coatings in air and $Ar-0.2%SO_2$ mixed gases. Coating microstructure was composed of an inner Al-Fe intermetallic layer and outer Al-rich layer. Aluminum oxidized preferentially to the thin, outer, protective ${\alpha}-Al_2O_3$ layer, without forming the nonprotective iron/sulfur-oxide layer after heating at $800^{\circ}C$ for 20 h, in both the gases and provided the resistance against corrosion.

• Proceedings of the Korean Institute of Surface Engineering Conference
• /
• 2015.05a
• /
• pp.122-122
• /
• 2015

Al-rich coatings were prepared on hot rolled low carbon steel by hot dipping method in molten Al-bath to investigate the corrosion resistance with the possible outcomes and defects of aluminized coatings in air and $Ar-0.2%SO_2$ mixed gases. Coating microstructure was composed of an inner Al-Fe intermetallic layer and outer Al-rich layer. Aluminum oxidized preferentially to the thin, outer, protective ${\alpha}-Al_2O_3$ layer, without forming the nonprotective iron/sulfur-oxide layer after heating at $800^{\circ}C$ for 20h, in both the gases and provided the resistance against corrosion.

• Proceedings of the Korean Institute of Surface Engineering Conference
• /
• 2013.05a
• /
• pp.114-115
• /
• 2013

$Ti_3AlC_2$ was corroded between 800 and $1100^{\circ}C$ in an Ar-0.2% $SO_2$ gas atmosphere according to the equation: $Ti_3AlC_2+O_2{\rightarrow}rutile-TiO_2+{\alpha}-Al_2O_3$ + (CO or $CO_2$). The scales that formed on the $Ti_3AlC_2$ were thin and rich in ${\alpha}-Al_2O_3$, whose growth rate was exceedingly slow. The $TiO_2$ was present either as the outermost surface scale or a mixture inside the ${\alpha}-Al_2O_3$-rich scale. In the $Ti_3AlC_2$, the activity and diffusivity of Ti were low, whereas those of Al were high. This was the main reason for the superior corrosion resistance of $Ti_3AlC_2$ over TiAl.

• Journal of the Korean institute of surface engineering
• /
• v.21 no.2
• /
• pp.53-67
• /
• 1988

The high temperature corrosion of Fe-C alloys were studied at I atm SO gas in the temperature range 500~80$0^{\circ}C$ by means of a thermogravimetric analysis. The Na2SO4 induced high tempwrature corrosion rate was also measured at atm O2 gas under above the temperature renge. The reaction products were identified with the aid of X-ray diffraction technique, and micostruction of the alloy/scale interface was observed with a optical microscope and SEM. The experimental results were disussed by the themodeynamic calcutions. Under above the experimental condition. the reaction rates decrbon with increasing carbon content. The transfer of Fe ion was limited by a residue of carbon precipitated at alloy scale interface due to the oxidation of Fe-C alloys at alloy surface. The effect of cold working on reaction rate was different between the Fe containing low carbon and Fe-C Alloy containing carbon above 0,73 wt%. In a cold worked iron containing low carbon content, the crystallization of metal surface leads to the poor adherence between the alloy and the cavity formed between the alloy and scale. The outward diffusion of ion through the scale is estimated to be hindered by the cavity formed between the scale, consequently decreasing reaction rate. In the case Fe-C containing carbon above 0.73 Wt% alloy, the reaction rate was little affected by cold working, because the effect of content on reaction rats is greater than the effect of cold working.