Wet candle method

Airborne salinity can be determined using different methods. In corrosion research the standard method (Wet Candle method) is established in ISO-9225 1992 [33] however, it is not the only method traditionally used. In the case of Cuba it has been widely used the method named as dry plate method, consisting in the employment of a dry cotton fabric of known area exposed under a shed. The amount of chloride deposition on the gauze is determined analytically at the end of the exposure period (two months) and the deposition rate is calculated. 

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

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. 

A number of methods have been employed for determining the contamination of the atmosphere by aerosol transported chlorides, for example, sea salt and road deicing salts. The wet candle method, for... 

In reality, the wet candle method gives an indication of the salinity of the atmosphere rather than the contamination of exposed metal surfaces. The technique is considered to measure the total amount of chloride arriving to a vertical surface and its results may not be truly significant for corrosivity estimates. 

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. 

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). 

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