Apparatus
4.1 The apparatus required for salt spray (fog) exposure consists of a fog chamber, a salt solution reservoir, a supply of suitably conditioned compressed air, one or more atomizing nozzles, specimen supports, provision for heating the chamber, and necessary means of control. The size and detailed construction of the apparatus are optional, provided the conditions obtained meet the requirements of this practice.
4.2 Drops of solution which accumulate on the ceiling or cover of the chamber shall not be permitted to fall on the specimens being exposed.
4.3 Drops of solution which fall from the specimens shall not be returned to the solution reservoir for respraying.
4.4 Material of construction shall be such that it will not affect the corrosiveness of the fog.
4.5 All water used for this practice shall conform to Type IV water in Specification D1193 (except that for this practice limits for chlorides and sodium may be ignored). This does not apply to running tap water. All other water will be referred to as reagent grade.
Test Specimens
5.1 The type and number of test specimens to be used, as well as the criteria for the evaluation of the test results, shall be defined in the specifications covering the material or product being exposed or shall be mutually agreed upon between the purchaser and the seller.
Preparation of Test Specimens
6.1 Specimens shall be suitably cleaned. The cleaning method shall be optional depending on the nature of the surface and the contaminants. Care shall be taken that specimens are not recontaminated after cleaning by excessive or careless handling.
6.2 Specimens for the evaluation of paints and other organic coatings shall be prepared in accordance with applicable specification(s) for the material(s) being exposed, or as agreed upon between the purchaser and the supplier. Otherwise, the test specimens shall consist of steel meeting the requirements of Practice D609 and shall be cleaned and prepared for coating in accordance with the applicable procedure of Practice D609.
6.3 Specimens coated with paints or nonmetallic coatings shall not be cleaned or handled excessively prior to test. 6.4 Whenever it is desired to determine the development of corrosion from an abraded area in the paint or organic coating, a scratch or scribed line shall be made through the coating with a sharp instrument so as to expose the underlying metal before testing. The conditions of making the scratch shall be as defined in Test Method D1654, unless otherwise agreed upon between the purchaser and the seller.
6.5 Unless otherwise specified, the cut edges of plated, coated, or duplex materials and areas containing identification marks or in contact with the racks or supports shall be protected with a suitable coating stable under the conditions of the practice.
Position of Specimens During Exposure
7.1 The position of the specimens in the salt spray chamber
during the test shall be such that the following conditions are
met:
7.1.1 Unless otherwise specified, the specimens shall be supported or suspended between 15 and 30° from the vertical and preferably parallel to the principal direction of flow of fog through the chamber, based upon the dominant surface being tested.
7.1.2 The specimens shall not contact each other or any metallic material or any material capable of acting as a wick.
7.1.3 Each specimen shall be placed to permit unencumbered exposure to the fog.
7.1.4 Salt solution from one specimen shall not drip on any other specimen.
Salt Solution
8.1 The salt solution shall be prepared by dissolving 5 6 1 parts by mass of sodium chloride in 95 parts of water conforming to Type IV water in Specification D1193 (except that for this practice limits for chlorides and sodium may be ignored). Careful attention should be given to the chemical content of the salt. The salt used shall be sodium chloride with not more than 0.3 % by mass of total impurities. Halides (Bromide, Fluoride, and Iodide) other than Chloride shall constitute less than 0.1 % by mass of the salt content. Copper content shall be less than 0.3 ppm by mass. Sodium chloride that has had anti-caking agents added shall not be used because such agents may act as corrosion inhibitors. See Table 1 for a listing of these impurity restrictions. Upon agreement between the purchaser and the seller, analysis may be required and limits established for elements or compounds not specified in the chemical composition given above.
8.2 The pH of the salt solution shall be such that when atomized at 35°C (95°F) the collected solution will be in the pH range from 6.5 to 7.2 (Note 3). Before the solution is atomized it shall be free of suspended solids (Note 4). The pH measurement shall be made at 23 6 3°C (73 6 5°F) using a suitable glass pH-sensing electrode, reference electrode, and pH meter system in accordance with Test Method E70. pH measurement shall be recorded once daily (except on weekends, or holidays when the salt spray test is not interrupted for exposing, rearranging, or removing test specimens or to check and replenish the solution in the reservoir. The maximum interval between pH measurements shall not exceed 96 h). Only diluted, reagent grade hydrochloric acid (HCl) or reagent grade sodium hydroxide (NaOH) shall be used to adjust the pH.
Air Supply
9.1 The compressed air supply to the Air Saturator Tower shall be free of grease, oil, and dirt before use by passing through well-maintained filters. (Note 6) This air should be maintained at a sufficient pressure at the base of the Air Saturator Tower to meet the suggested pressures of Table 2 at the top of the Air Saturator Tower.
9.2 The compressed air supply to the atomizer nozzle or nozzles shall be conditioned by introducing it into the bottom of a tower filled with water. A common method of introducing the air is through an air dispersion device (X1.4.1). The level of the water must be maintained automatically to ensure adequate humidification. It is common practice to maintain the temperature in this tower between 46 and 49°C (114–121°F) to offset the cooling effect of expansion to atmospheric pressure during the atomization process. Table 2 shows the temperature, at different pressures, that are commonly used to offset the cooling effect of expansion to atmospheric pressure.
9.3 Careful attention should be given to the relationship of tower temperature to pressure since this relationship can have a direct impact to maintaining proper collection rates (Note 7). It is preferable to saturate the air at temperatures well above the chamber temperature as insurance of a wet fog as listed in Table 2.
Conditions in the Salt Spray Chamber
10.1 Temperature—The exposure zone of the salt spray chamber shall be maintained at 35 6 2°C (95 6 3°F). Each set point and its tolerance represents an operational control point for equilibrium conditions at a single location in the cabinet which may not necessarily represent the uniformity of conditions throughout the cabinet. The temperature within the exposure zone of the closed cabinet shall be recorded (Note 8) at least once daily (except on Saturdays, Sundays, and holidays when the salt spray test is not interrupted for exposing, rearranging, or removing test specimens or to check and replenish the solution in the reservoir)
10.2 Atomization and Quantity of Fog—Place at least two clean fog collectors per atomizer tower within the exposure zone so that no drops of solution will be collected from the test specimens or any other source. Position the collectors in the proximity of the test specimens, one nearest to any nozzle and the other farthest from all nozzles. A typical arrangement is shown in Fig. 1. The fog shall be such that for each 80 cm2 (12.4 in.2 ) of horizontal collecting area, there will be collected from 1.0 to 2.0 mL of solution per hour based on an average run of at least 16 h (Note 9). The sodium chloride concentration of the collected solution shall be 5 6 1 mass % (Notes 9-11). The pH of the collected solution shall be 6.5 to
7.2. The pH measurement shall be made as described in 8.2 (Note 3). Both sodium chloride concentration (measured as specific gravity) and volume of condensate collected (measured in mL) shall be recorded once daily (except on weekends, or holidays when the salt spray test is not interrupted for exposing, rearranging, or removing test specimens or to check and replenish the solution in the reservoir. The maximum interval between these data collection measurements shall not exceed 96 h).
10.3 The nozzle or nozzles shall be so directed or baffled that none of the spray can impinge directly on the test specimens.
Continuity of Exposure
11.1 Unless otherwise specified in the specifications covering the material or product being tested, the test shall be continuous for the duration of the entire test period. Continuous operation implies that the chamber be closed and the spray operating continuously except for the short daily interruptions necessary to inspect, rearrange, or remove test specimens, to check and replenish the solution in the reservoir, and to make necessary recordings as described in Section 10.
Period of Exposure
12.1 The period of exposure shall be as designated by the specifications covering the material or product being tested or as mutually agreed upon between the purchaser and the seller. NOTE 13—Recommended exposure periods are to be as agreed upon between the purchaser and the seller, but exposure periods of multiples of 24 h are suggested.
Cleaning of Tested Specimens
13.1 Unless otherwise specified in the specifications covering the material or product being tested, specimens shall be treated as follows at the end of the test:
13.1.1 The specimens shall be carefully removed.
13.2 Specimens may be gently washed or dipped in clean running water not warmer than 38°C (100°F) to remove salt deposits from their surface, and then immediately dried.
Evaluation of Results
14.1 A careful and immediate examination shall be made as required by the specifications covering the material or product being tested or by agreement between the purchaser and the seller.
Salt Spray Tester
Salt Spray Tester is used to test the anti-erosion quality of the surface of all materials after the rust-proof painting, coating, electroplating, anodizing, and rust-proof greasing .anti corrosion treatment for a variety of materials, corrosion resistance of their products.
Salt Spray Tester is an accelerated corrosion test that produces a corrosive attack to the coated samples in order to predict its suitability in use as a protective finish. The appearance of corrosion products (oxides) is evaluated after a period of time. Test duration depends on the corrosion resistance of the coating; the more corrosion resistant the coating is, the longer the period in testing without showing signs of corrosion. Different coatings have different behavior in salt spray test and consequently, test duration will differ from one type of coating to another.
