Metal Finishing Guide Book


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dard is that all the cycles during the test period be equal in length. Introducing SO2 into the exposure zone on a periodic basis requires additional apparatus. The chamber can be equipped with a device that will disburse the SO2 evenly throughout the chamber without directly impinging on any test pieces. The SO2 supply source attached to the chamber must have a regulator, flow meter, and timer to allow for accurate introduction of SO2 in accordance with any set cycle. It is imperative to address all safety issues: equipment, personnel, apparatus, and procedures prior to testing with SO2, since it is a very hazardous highly toxic gas. Note that the primary changes to the chamber are to allow for the correct introduction of the SO2. All parts of the chamber that come into contact with the SO2 must be made of materials that are inert to SO2 gas. Annex 5—Dilute Electrolyte Cyclic Fog/Dry Test For this test the electrolyte solution contains 0.05% sodium chloride and 0.35% ammonium sulfate in 0.60% by mass of ASTM D1193 Type IV water. This solution is much more dilute than the standard salt spray (fog) test and is run using 2-hr cycle times comprised of 1-hr fog at ambient 24°C ±3°C and relative humidity below 75%, followed by 1-hr dry off at 35°C. That is, the test pieces are exposed to 1 hour of spray fog at controlled "room" temperature, then 1 hour dry-off time at 35°C Fig. 6. Custom-sized, computer-controlled corrosion test chamber for cyclic testing. (95°F). The collected condensate shall have a pH within the range of 5.0 to 5.4. Because of the cyclic nature of this test, a separate 16-hr salt fog test is necessary to establish and verify proper condensate collection rates prior to starting the cyclic test. Because of the differences in humidity in this test method and the cyclic nature of the test, the chamber will need to have a separate air line and valve to allow the atomizing air to bypass the humidifying tower and timing apparatus to control the cycle times, temperature changes, spray, and airflow. This test is a modification of the British Rail "Prohesion" test developed in the 1960s for the industrial maintenance coatings industry. This test is best suited for the testing of paints on steel. ASTM G87—Conducting Moist SO2 Tests The ASTM G87 standard is an adaptation of the sulfur dioxide tests used in Europe and is particularly effective in producing easily visible corrosion on metals as would be observed in an industrial or marine environment. This test requires 2 ±0.2 L (122 in3 ±12 in3) Type IV water in the bottom of the test chamber and does not use a fogging apparatus. The apparatus used to generate the necessary humidity is the same used in the ASTM D2247 test. The gas introduction apparatus is the same as used in the ASTM G85 Annex 4 test. Once the test pieces are placed in the chamber 0.2, 1, or 2 L (12, 61, or 122 in3 ±12 in3) of sulfur dioxide (SO2) with a purity of 99.9% (liquid phase) is introduced. Then the temperature of the chamber is raised to 40 ±°C (104 ±5.4°F) in 1 ½ 543

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