Metal Finishing Guide Book

2012 Organic Finishing Guidebook Issue

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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 solu- tion 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 (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 nec- essary to establish and verify proper condensate collection rates when necessary. Because of the differences in humidity in this test method and the cyclic na- ture of the test, the chamber will need to have a 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 in- dustrial maintenance coatings in- dustry. This test is best suited for the testing of paints on steel. ASTM G 87—Conducting Moist SO2 Tests The ASTM G 87 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 in3 test chamber and does not use a fogging apparatus. The apparatus used to gen- erate the necessary humidity is the same used in the ASTM D 2247 test. The gas introduction apparatus is the same as used in the ASTM G 85 Annex 4 test. Once the test pieces are placed in the chamber 0.2, 1, or 2 L (12, 61, or 122 in3 ) with a purity of 99.9% (liquid phase) is introduced. Then ±12 ) of sulfur dioxide(SO2 the temperature of the chamber is raised to 40 ±°C (104 ±5.4°F) in 1.5 hours and remains at this level for the duration of the test cycle. One test cycle is 24 hours. A test can be run for as many cycles as are agreed and water must be upon between the purchaser and seller; however, the SO2 changed for each 24-hr cycle. The 24-hr test cycles are executed in one of the following ways: 1.Continuous — change of water and SO2 with as little disturbance as possible 2.Alternating Exposure — 8-hr exposure; drying in ambient for 16 hours with 20–30°C (68–86°F) and 75% relative humidity The variations differing from the B 117 practice are that for this test method all test pieces be placed on the same horizontal plane and all test pieces in a giv- 300 Fig. 6. Custom-sized, computer-controlled corrosion test chamber for cyclic testing.

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