Crystallization Behavior of Ammonium Chloride in High-Pressure Heat Exchanger of Hydrotreating Unit

In view of the corrosion failure of a high-pressure heat exchanger in a diesel hydrogenation unit, the formation mechanism of ammonium chloride in a multiphase flow system is investigated in this article. Numerical simulation is carried out by user defined function (UDF) on the process of adding source of mass transfer in computational fluid dynamics (CFD) solvers. The distribution characteristics of ammonium chloride are illustrated by the parameters including crystallization temperature of ammonium chloride, volume fraction of ammonium chloride, and mass transfer rates of NH3 and HCl, and the causes of corrosion cracking in the U-shaped bend of the heat exchanger are discussed. The results show that there is a great risk of ammonium chloride deposition in the heat exchanger from 4.5 m away from the outlet of the second pass. The crystallization area in the tube gradually expands from the wall to the center along the flow direction, and the crystallization rate is higher near the tube wall. The field sampling test results show that the corrosion cracking is hydrogen-induced cracking, which is due to the existence of large amount of hydrogen, high impacting force, excessive flow rate, and the risk of ammonium chloride particle erosion at the U-bend. In order to alleviate the corrosion of ammonium chloride deposition, some improvement measures are put forward, such as raising the inlet temperature of the tube side to 215 °C and increasing the water injection by 30%, which play an important role in decreasing the formation of ammonium chloride in the heat exchange system.

A Field Study of Atmospheric Corrosion of Carbon Steel after Short Exposure in Pelabuhan Ratu, West Java Province, Indonesia

The investigation of atmospheric corrosion of mild carbon steel as representative of offshore infrastructure has been carried out in the marine tropical of Pelabuhan Ratu, West Java, Indonesia. They are exposed up to 76 days of periods, and their corrosion rates are determined according to ASTM G1-03. The surface morphology, the elemental compositions and compounds were observed using a scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD), respectively. The environmental parameters of the test site are monitored during exposure, such as air temperature, relative humidity (RH), airborne salinity and dew temperature. Based on the results, the corrosion rates of steels were 2.79 and 2.8 mpy within the 27 and 76 days exposures, respectively. The presence of chloride deposition on the surface of steel can increase the severity of corrosion. Moreover, the detrimental effect of chloride was observed in rust product, which was covered by an oxygen element. The main phases of rust products present were magnetite (Fe3O4) and hematite (α-Fe2O3.H2O). Several cracks were observed in the rust layer, which tended to exfoliate and lose adherence and protectiveness from further corrosion attack. HIGHLIGHTS The presence of chloride deposition on the surface of steel can increase the severity of corrosion. The severity of corrosion attack mainly depends on the exposure time and some climatic parameters, such as relative humidity (RH), air temperature and chloride airborne. The uniform distribution of the chloride tends to increase the production of ferrous chloride in high RH condition and the aqueous layer deposited on carbon steel. There are two phases on corroded carbon steel such as hematite (α-Fe2O3.H2O) and Magnetite (Fe3O4) after exposure GRAPHICAL ABSTRACT

Zinc-nickel alloy coatings: electrodeposition kinetics, corrosion, and selective dissolution. A review

A review of the literature is devoted to the patterns of the electrodeposition of zinc-nickel alloys including the kinetics of cathodic reduction of zinc, nickel, and zinc-nickel alloys in ammonium chloride, sulphate, and glycinate deposition electrolytes. We studied the data on the effectiveness of the corrosion resistance of zinc-nickel coatings and summarised the principal patterns of selective dissolution of the Zn-Ni alloys. The role of the addition of glycine to an ammonium chloride deposition electrolyte was determined in the modification of the morphological and anticorrosive properties of the coatings.

Quantitative Analysis Methods of Chloride Deposition on Silver for Atmospheric Corrosion Monitoring in South Korea

The chloride deposition rate is one of critical factors affecting the atmospheric corrosion of metals, which can be monitored by exposing Ag specimens and analyzing their surfaces using various ways. Although a coulometric reduction method can provide an absolute chloride deposition rate, new and alternative methods can be pursed, i.e., methods using typical surface analysis tools (scanning electron microscopy-energy dispersive X-ray spectroscopy, SEM-EDS; X-ray diffraction, XRD; and X-ray photoelectron spectroscopy, XPS). Since the surface analysis tools can only provide relative values, a correlation between the coulometric reduction and surface analyses should be developed. To develop the correlation between them, Ag specimens were prepared by exposing them to the atmosphere at 12 locations in South Korea for one year. Surface analysis of retrieved Ag specimens yielded correlations for the chloride deposition rates between the coulometric reduction method and typical surface analysis tools. Each correlation showed a fairly linear relationship, especially ones obtained from SEM-EDS and XPS. The developed correlations can be used when estimating the chloride deposition rate by using surface analysis tools as an alternative to the coulometric reduction method.

Particularities of indoor atmospheric corrosion of steel inside electric boxes in the tropical climate of Tabasco, Mexico

Indoor corrosion inside electric boxes is important for the reliability of electric and electronic instruments. A parallel evaluation of indoor/outdoor atmospheric corrosion of steel, pollutants and meteorological parameters was made at two sites, i.e. a rural site and a coastal site of the Tabasco State, Mexico. Two exposure conditions were evaluated: outdoors and inside electric boxes. Very low levels of sulphur compounds have been observed at the two exposure sites and two exposure conditions. As expected, corrosion of steel in an open atmosphere is higher than indoors (electric boxes). The difference between corrosion outdoors and inside electric boxes is higher at the coastal site due to the influence of chloride deposition. Significant differences have been observed in the morphology of corrosion products formed on steel. The influence of sun radiation, rain, dew and fog causes the formation of more compact corrosion products. The influence of Time of Wetness outdoors is in some extent equivalent to the influence of relative humidity inside electric boxes. Commonly, chloride deposition is very low indoors, showing low influence on corrosion. However, in particular conditions of Tabasco coastal tropical climate, its role is significant indoors. Reliability of electric and electronic instruments could be affected.

Assessment of effective infiltration in the deep arid vadose zone of the Negev, Israel

<p>The Israeli national site for radioactive waste is situated in the Yamin Plain, within the Negev desert. Estimation of  water recharge to the ~500 m deep vadose zone underlying the site  is crucial for assessing risks related to contaminants transport. However, estimation of water fluxes in deep arid vadose zones is a challenging task because of their small magnitude and the lack of a direct measurement technology. Studies conducted in a deep arid vadose zone in Nevada, USA point to complex transient flow dynamics, in which the direction of water flow in the top of the vadose zone is upward while in the rest of the section water flows downwards to the water table.    </p><p>            In this study we present a combination of techniques which are used to obtain an initial evaluation of the water dynamics in this environment. These techniques include direct and continuous measurements of water content at the upper 5.5 m of the vadose zone through a vadose zone monitoring system which contain FTDR water content sensors; profiles of water content, leachable chloride and soil texture; and numerical modeling.</p><p>            The monitoring of the upper 5.5 m of the vadose zone during the years 2014-2018 indicates that even after extreme rain events of ~ 50 mm (constituting more than a half of the annual rainfall) there is no water infiltration to the lower parts of the section. These results exemplified the need for an alternative method to detect low water fluxes that characterize this arid area. We therefore use an inverse modeling approach where numerical solutions of water movement in the vadose zone are fitted to measured profiles of chemical and physical parameters from two shallow boreholes in the Yamin Plain. The water content of both boreholes revealed an extremely dry environment, with low saturations and high pore-water chloride concentrations, above 15,000 mg/l, in certain depths. Peak chloride concentrations did not coincide in the two boreholes, raising the question whether these peaks are connected to water fluxes or to changes in soil texture, which can inhibit water infiltration.</p><p>             Numerical simulations were then used to solve water flow and solute transport. Input parameters, including chloride deposition rate, precipitation rate, and surface run-off fraction were varied to fit the measured chloride profiles. Results indicate very small water fluxes of less than 1 mm/yr in the bottom of the vadoze zone. The simulations also show that the mass of chloride in the profile is less than the one expected based on estimated chloride deposition rate and published records of paleo-rain. These results suggest either a delayed climate shift to dry conditions compared to previous estimates for the region (8000 yr BP), and/or a partial input of the 4 g/m<sup>2</sup>/yr of deposited chloride, possibly due to runoff.</p>