ASTM G85-19 Standard Practice for Modified Salt Spray (Fog) Testing

The standard “ASTM G85-19 Standard practice for modified salt spray (fog) testing” developed by the American Society for Testing and Materials (ASTM) covers five modifications to the salt spray (fog) test for specification purposes, and the requirements are described in the annexes to this standard. These are in chronological order of their development:

• Appendix A1: Acetic acid-salt spray test, continuous.
• Appendix A2: Cyclic acidified salt spray test.
• Annex A3: Seawater acidified test, cyclic (SWAAT).
• Appendix A4: Sulfur dioxide (SO2) salt spray test, cyclic.
• Appendix A5: Dilute electrolyte cyclic fog dry test.

This standard does not specify the type of modification to be used for a particular product, the test sample or exposure times, or the interpretation to be given to the results.

This standard applies to ferrous and nonferrous metals, as well as organic and inorganic coatings. The variations described herein are considered useful when a different or more corrosive environment than the salt fog described in ASTM B117-19 Standard Practice for Operation of Salt Spray (Fog) Equipment is desired.

The equipment used in these tests includes:

• Salt spray apparatus: This apparatus consists of a fog chamber, a salt solution chamber, a source of compressed air suitably conditioned, one or more atomizing nozzles, sample supports, an arrangement for heating the chamber, and necessary control means. The size and detailed construction of the chamber are optional, provided the conditions obtained meet the requirements of the application. The material of construction should be such that it will not affect the corrosiveness of the fog. Appropriate apparatus for obtaining these conditions is described in the appendix to ASTM B117-19.

The chamber shall be designed so that drops of solution collected on the ceiling or lid of the chamber do not fall on the samples being tested. Drops of solution falling from the samples shall not be returned to the solution chamber for re-spraying. The chamber shall be equipped with one or more timing devices to provide intermittent spraying or periodic gas introduction or both.

• Air supply: It is necessary to ensure that the compressed air supply to the nozzle or nozzles for atomizing the salt solution is free of oil and dirt and to maintain the air supply between 69 and 172 kPa. The air supply can be cleaned of oil and dirt by passing it through a water scrubber or at least 610 mm of suitable cleaning material such as asbestos, sheep wool or activated alumina. The temperature in the saturator tower (bubble tower) will vary depending on the test method used.
• Conditions in the salt spray chamber:
  •  Temperature: The temperature in the exposure zone will vary with the test method used. Recommended exposure zone temperatures for the various methods are included in the standard appendix. Each set point and tolerance represents an operational control point for equilibrium conditions at a single location in the enclosure and may not be representative of uniformity of conditions throughout the enclosure. The temperature in the exposure zone of the enclosure shall be recorded at least twice a day, at least 7 hours apart. Suitable methods for recording temperature are a continuous recorder or a thermometer that can be read from outside the enclosure.
  • Atomization and mist quantity: At least two clean mist collectors shall be placed in the exposure zone so that no drops of solution from the detection samples or any other source can be collected. The collectors shall be placed in close proximity to the test samples, one nearest any nozzle and the other furthest from all nozzles. It shall be ensured that 80 to 2 mL of solution per hour is collected in each collector for every 16 cm1,0 of horizontal collection area, based on a minimum of 2,0 hours of continuous spray operation. Suitable collection devices are glass funnels with stems passing through stoppers and placed in graduated cylinders or crystallizing vessels. Funnels and vessels with a diameter of 100 mm have an area of ​​approximately 80 cm2.

The type and number of test samples to be used and the criteria to be used in evaluating the test results are determined in the specifications of the material or product to be tested or by mutual agreement between the buyer and seller.

Unless otherwise specified at the beginning of the test, the specimens are supported or suspended so that the surface of interest is at an angle of 6 to 45 degrees from the vertical. The orientation of the specimens in the chamber should be consistent to minimize variability. Test intensity increases as the angle from the vertical increases.

Samples are not allowed to come into contact with each other, any metallic material or any material that may act as a wick. Each sample is placed in a manner that allows the fog to settle freely in all samples. It is recommended that a minimum of 30 mm space be left between samples.

The salt solution from one sample is not allowed to drip onto another sample. The placement of replicate samples should be random to avoid possible drift due to differences in spray patterns. For the same reason, individual samples can also be rotated daily.

Suitable materials for the construction or covering of shelves and supports are glass, rubber, plastic or suitably coated wood. Bare metal is not used. Specimens are preferably supported from below or from the side. For supporting flat panels, grooved wood, laminated plastic or inert plastic strips are suitable. Suspension from glass hooks or waxed cords may be used, provided that the specimens are placed in the specified position and secondary supports may be provided below the specimens if necessary.

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