Chlorides deposition rate

Average Chloride deposition rate at different exposure conditions... 

Figure 7. Annual average Chloride deposition rate for test station located at the western side of the Cuban Isle depending on exposure conditions and type of atmosphere.

On figure 7 there is represented Average Chloride Deposition rate determined in Cuba for different types of atmosphere and exposure conditions. The results are very similar to those presented on figure 6, particularly respecting outdoor and ventilated shed conditions. Chloride deposition is determined under shelter, that is why it is assumed the same value for ourdoor and sheltered conditions however, it is very well known, the significant influence of precipitations upon outdoor corrosion and its negligible effect under sheltered conditions. In... 

The remarkable difference in the acceleration caused by chloride deposition rate in Havana and Medellin could be due to the considerable difference in the rain regime between both sites. Other characteristic of the environment could also have influence, but rain should play an important role. 

In the presence of a given value of chloride deposition rate, an acceleration of corrosion takes place this acceleration means that corrosion increases with time. At the same time, the acceleration of corrosion caused by chlorides depends on the washing or cleaning effect of rain. Under this condition the following model is proposed ... 

It has been considered that the washing or cleaning effect of rain could be represented by the ratio W/D (amount of rain/frequency of rain). This washing effect could affect the influence of chloride deposition rate on corrosion. 

A good data fit is also obtained for copper. It confirms that the complex chloride deposition rate-rain regime is important for determining mass loss of copper and steel. In this model TOW-ISO has not been used and a good fitness has been obtained. 

It confirms that the acceleration rate caused by chloride ions on atmospheric corrosion of steel and copper depends on the characteristics of rain regime. For a place having high amount and time of rain, a lower acceleration on corrosion rate should be expected for a given chloride deposition rate... 

Cl ] w.c = Chloride deposition rate determined using Wet Candle method [Cl ] D p = Chloride deposition rate determined using Dry Plate method... 

Chloride deposition rate was determined using Wet Candle and Dry Plate methods in the corrosion stations Santiago de las Vegas (rural-urban), Casa Blanca (industrial-marine-urban), Via Blanca (industrial-urban-marine) and Cojimar (marine). 

Figure 9. Changes in annual Corrosion rate of mild steel flat samples, annual average Chloride deposition rate determined by the dry plate method and annual average Sulfur compounds deposition rate determined by alkaline surfaces method in the west side of the Cuban Isle.

Table VII. Average corrosion rate of steel, standard deviation, average Chloride deposition rate, standard deviation and aerage TOW-... 

Table VIII. Average Chloride deposition rate for differents test stations of Campeche...

Test station A Average Chloride deposition rate (mg/ m d) ... 

Chloride ions are easily washed away from the metallic surface by precipitation, while sulfate ions concentration remains more constant. It means that corrosion takes place under very variable concentrations of chloride ions and in the presence of less variable concentration of sulfate ions. Changes in the amount of chloride ions concentration should depend on the particular rain regime of the place. A notable difference has been found between chloride deposition rate determined by collectors protected from liquid precipitations and chloride content in corrosion products. 

In the Cuban Isle, the influence of chloride ions is very significant in determining the corrosion rate. In the coastal territory of the Mexican Gulf, particularly at Campeche, the deposition of Chloride ions is lower. No previous reports have been made about the interaction between chloride deposition rate and rain. The influence of rain seems to be... 

Sulfur Dioxide Category Sulfur Dioxide Deposition Rate, mg/(m day) Chloride Category Chloride Deposition Rate, mg/(m day)... 

Industrial pollution by SO, Airborne salinity chloride deposition rate. mg/inVday... 

Airborne salinity chloride deposition rate, mg/mVday Airbotne salinity chloride deposition rate. mg/mVday Airborne salinity chloride deposition rate, mg/m /day Airborne salinity chloride deposition mg/nr/day... 

Several techniques have been used to monitor chloride in the atmosphere. The wet candle method, ASTM G 140, Method for Determining Atmospheric Chloride Deposition Rate by Wet Candle Method, has been used in marine sites and consists of a fabric-wrapped tube in which the fabric is kept wet with water [12] (Fig. 2). The wet fabric acts as a collector for chloride particulates or droplets. Exposure periods of one week or up to one month have been used. The longer time periods can be a problem because the water source must not be allowed to dry. It is important to protect the wet candle from rain exposure so that wet candle assemblies are usually mounted with a cover over them. With the... 

The second method involves measurement of the temperature, time of wetness, amount of sulfur in the atmosphere, md the amoimt of chloride in the atmosphere. Temperature and hiunidity information can be used to estimate the time of wetness. This estimation is based on the percentage of time that the temperature is above freezing, O C, and the relative humidity is at the same time above 80 %. Once the time of wetness is known, it is then possible to determine a time of wetness class (Table 2). Sulfur dioxide content of the atmosphere can be estimated either by measurement of the concentration in the atmosphere over some period of time or by means of the sulfation plate or candle. This information is then used to develop a sulfur dioxide class or P class (Table 3). The chloride dry plate or wet candle method is used to obtain the chloride deposition rate of the atmosphere that is then converted to a chloride class or S class (Table 3). The corrosion class or C class can be obtained for the time of wetness, chloride, and sulfur dioxide classes (Table 4). Once the corrosion class is known, it is possible to estimate the corrosion damage that will occur in either short-term or long-term exposures for the five metals, steel, weathering steel, aluminum, copper, and zinc (Table 5). The detailed information on this method is discussed in Tables 2-5. 

With respect to chlorides (Cl ), the most widely used procedure is the chloride candle, a gauze wick in a flask of reagent water. The candles tire exposed for a fixed period of time, usually 30 days, then removed. After leaching the exposed gauze into the flask water, the total chlorides are determined analytically, and reported as chloride deposition per unit of exposed area per unit of time (mg/m /day). This method is described in ASTM G 140, Test Method for Determining Atmospheric Chloride Deposition Rate by Wet Candle Method. The other method more recently introduced uses a dry fabric panel, which is also exposed for a predetermined length of time, usually 30 days. Then the chlorides are washed out of the fabric and analyzed. Both procedures are currently described in ISO Standard 9225 however, the dry plate method has been found to produce inconsistent results, and probably will be dropped from the ISO document at its next revision. 

Some studies have indicated that there is a strong correlation between wind speed and the deposition and capture of aerosols. In such a study of saline winds in Spain a very good correlation was found between chloride deposition rates and wind speeds above a threshold of 3 m s or 11 km h" [9]. 

In order to understand the chloride deposition rates in a confined spaces, such as ventilated subfloors in a sea coastal area, a special collecting box shown in Fig. 9.25 was used in which the airborne chlorides were collected on horizontal and vertical filter papers positioned at different locations from the box openings (Fig. 9.26). 

Standard Test Method for Determining Atmospheric Chloride Deposition Rate by Wet Candle Method. Annual Book of ASTM Standards. Philadelphia, Pa. American Society for Testing of Materials. 2002 03(02) G140-02. 

Airborne salinity. Units chloride deposition rate (mg-m -day )... 

The TOW categorization is presented in Table 2.2, and the sulfur dioxide and chloride classifications are presented in Table 2.3. TOW values can be measured directly with sensors, or the ISO definition of TOW as the number of hours that the relative humidity exceeds 80 percent and the temperature exceeds 0°C can be used. The methods for determining atmospheric sulfur dioxide and chloride deposition rates are described more fully in the relevant standards (Table 2.1). 

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