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ASTM B117 Standard Practice for Operating Salt Spray Fog Apparatus

The ASTM B117 standard, also known as the “Standard Practice for Operating Salt Spray Fog Apparatus,” is an essential guideline in the field of corrosion testing. This practice defines the standard conditions for operating salt spray fog apparatus to assess the corrosion resistance of various materials. Complying with this industry-standard ensures accurate and reliable test results. In this article, we will explore the significance of ASTM B117, its application, and the process of conducting a salt spray test according to this standard.

ASTM B117 is a globally recognized standard developed by ASTM International (formerly known as the American Society for Testing and Materials). This standard provides a uniform platform for evaluating the corrosion resistance of materials subjected to salt spray testing. It ensures consistent testing procedures, making it easier to compare results across different laboratories and industries. The ASTM B117 standard serves as a crucial foundation for conducting salt spray tests aimed at assessing corrosion resistance.

By following the guidelines outlined in this standard, manufacturers, researchers, and quality inspectors can consistently evaluate the suitability of materials and coatings for specific applications. Adhering to ASTM B117 ensures accurate and reliable results, enhancing product quality and longevity in corrosive environments. Salt Spray Test Standard, ASTM B117, is an indispensable tool in evaluating material durability, preventing premature failures, and developing reliable corrosion protection strategies. By adopting the ASTM B117 standard, companies demonstrate their commitment to producing high-quality products that can withstand the challenges of real-world corrosion.

ASTM B117 Standard Practice for Operating Salt Spray Fog Apparatus
Equipment Model WEW-YW-90D
Inner Testing Room  900*500*600mm (W*H*D)
Appearance Dimension 1410*1280*880mm (W*H*D)
Laboratory Temperature Neutral Saline Test Method (NSS ACSS) 35C±1C, Acid Saline Test Method (CASS) 50C±1C
Pressure Tank Temperature Neutral saline test method (NSS ACSS) 47C±1C, Acid Saline test method (CASS) 63C±1C
Salt Water Temperature Neutral Saline Test Method (NSS ACSS) 35C±1C, Acid Saline Test Method (CASS) 50C±1C
Laboratory Volume 270L Salt Spray Cabinet
Salt Tank Volume 25L Water Tank
Salt Water Concentration Neutral Saline Test Method (NSS ACSS): Sodium Chloride Concentration 5%; Acid Saline Test Method (CASS); Concentration 5% Sodium Chloride Solution plus 0.26 g Copper Chloride per liter (CuCL2.H20)
Compressed Air Pressure
1.00±0.001kgf/cm2
5.00±1.0011kgf/cm2
Spray Volume 1.0~2.0ml/80cm2·hr (At least 16 hours are collected and the average value is taken)
Laboratory Relative Humidity 85% RH or more
Spray Method Continuous spray (with different controllers for continuous spray and intermittent spray)
Power Requirements AC220V1φ 15A, Salt Spray Cabinet
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 con-struction of the apparatus are optional, provided the conditions obtained meet the requirements of this practice. 4. Apparatus
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 D 1193 (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.
5.1 The type and number of test specimens to be used, as well as the criteria for the evaluation ofthe 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. 5. Test Specimens
6.1 Specimens shall be suitably cleaned. The cleaning method shall be optional depending on the nature ofthe surface and the contaminants. Care shall be taken that specimens are not recontaminated after cleaning by excessive or careless handling. 6. Preparation of Test Specimens
6.2 Specimens for the evaluation ofpaints 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 D 609 and shall be cleaned and prepared for coating in accordance with the applicable procedure of Practice D 609.
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 D 1654, 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.
Note 1: Should it be desirable to cut test specimens from parts or from preplated, painted, or otherwise coated steel sheet, the cut edges shall be protected by coating them with paint, wax, tape, or other effective media so that the development of a galvanic effect between such edges and the adjacent plated or otherwise coated metal surfaces, is prevented.
salt spray testing
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. Position of Specimens During Exposure
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 unencum-bered exposure to the fog.
7.1.4 Salt solution from one specimen shall not drip on any other specimen.
Note 2: Suitable materials for the construction or coating ofracks and supports are glass, rubber, plastic, or suitably coated wood. Bare metal shall not be used. Specimens shall preferably be supported from the bottom or the side. Slotted wooden strips are suitable for the support offl at panels. Suspension from glass hooks or waxed string may be used as long as the specified position of the specimens is obtained, if necessary by means of secondary support at the bottom of the specimens.
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 D 1193 (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 containing anti-caking agents 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. Salt Solution
Table 1 Maximum Allowable Limits for Impurity Levels in Sodium Chloride
8.2 The pH of the salt solution shall be such that when at omized 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 25°C (77°F) using a suitable glass pH-sensing electrode, reference electrode, and pH meter system in accordance with Test Method E 70.
Note 3: Temperature affects the pH of a salt solution prepared from water saturated with carbon dioxide at room temperature and pH adjust- ment may be made by the following three methods:
(1) When the pH ofa salt solution is adjusted at room temperature, and atomized at 35°C (95°F), the pH of the collected solution will be higher than the original solution due to the loss of carbon dioxide at the higher temperature. When the pH of the salt solution is adjusted at room temperature, it is therefore necessary to adjust it below 6.5 so the collected solution after atomizing at 35°C (95°F) will meet the pH limits of 6.5 to 7.2. Take about a 50-mL sample of the salt solution as prepared at room temperature, boil gently for 30 s, cool, and determine the pH. When the pH of the salt solution is adjusted to 6.5 to 7.2 by this procedure, the pH of the atomized and collected solution at 35°C (95°F) will come within this range.
(2) Heating the salt solution to boiling and cooling to 35°C (95°F) and maintaining it at 35°C (95°F) for approximately 48 h before adjusting the pH produces a solution the pH of which does not materially change when atomized at 35°C (95°F).
(3) Heating the water from which the salt solution is prepared to 35°C (95°F) or above, to expel carbon dioxide, and adjusting the pH of the salt solution within the limits of6.5 to 7.2 produces a solution the pH ofwhich does not materially change when atomized at 35°C (95°F).
Note 4: The freshly prepared salt solution may be filtered or decanted before it is placed in the reservoir, or the end of the tube leading from the solution to the atomizer may be covered with a double layer ofcheesecloth to prevent plugging of the nozzle.
Note 5: The pH can be adjusted by additions of dilute ACS reagent grade hydrochloric acid or sodium hydroxide solutions.
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. Air Supply
Note 6: The air supply may be freed from oil and dirt by passing it through a suitable oil/water extractor (that is commercially available) to stop any oil from reaching the Air Saturator Tower. Many oil/water extractors have an expiration indicator, proper preventive maintenance intervals should take these into account.
9.2 The compressed air supply to the atomizer nozzle or nozzles shall be conditioned by introducing it into the bottom of a tower fillwed with water. A common method of introduc-ing 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 in 9.3 of this practice shows the temperature, at different pressures, that are com-monly used to offset the cooling effect of expansion to atmospheric pressure.
Table 2 Suggested Temperature and Pressure Guideline for the Top of the Air Saturator Tower for the Operation of a Test at +35℃ (95℉)
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.
Note 7: If the tower is run outside of these suggested temperature and pressure ranges to acheive proper collection rates as described in 10.2 of this practice, other means of verifying the proper corrosion rate in the chamber should be investigated, such as the use of control specimens (panels of known performance in the test conducted). It is preferred that control panels be provided that bracket the expected test specimen performance. The controls allow for the normalization of test conditions during repeated running ofthe test and will also allow comparisons oftest results from different repeats of the same test. (Refer to Appendix X3, Evaluation of Corrosive Conditions, for mass loss procedures).
10.1 Temperature: The exposure zone of the salt spray chamber shall be maintained at 35°C + 1.1 ~1.7°C . 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 twice a day at least 7 h apart (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. Conditions in the Salt Spray Chamber
Note 8: A suitable method to record the temperature is by a continu- ous recording device or by a thermometer which can be read from outside the closed cabinet. The recorded temperature must be obtained with the salt spray chamber closed to avoid a false low reading because ofwet-bulb effect when the chamber is open.
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 ofsolution 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 cm 2 (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).
FIG 1 Arrangement of Fog Collectors
salt spray fog apparatus
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. Operations shall be so scheduled that these interruptions are held to a minimum. 11. Continuity 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. 12. Period of Exposure
Note 12: 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.
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. Cleaning of Tested Specimens
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.
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. 14. Evaluation of Results
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