Guest Editorial -For Plateworld.com                                                 

 Don Baudrand, Don Baudrand Consulting,   e-mail:donwb@tscnet.com

 

Corrosion Testing

The standard "there is usually not a direct relation between salt spray resistance and resistance to corrosion in other media." Since conventional salt spray testing seldom correlates with actual performance in service, a variety of cyclic cabinet tests have been developed to predict corrosion resistance. The purpose of the symposium that forms the basis of this STP was to promote understanding of cyclic cabinet corrosion tests and other alternatives to the salt spray test. The goal was to establish correlations between these tests and actual corrosion resistance in service environments and to promote standardization of these tests.

CASS Test -- Copper-Accelerated Acetic Acid Salt Spray (Fog) Test (ASTM B368, B117)

This test is performed according to ASTM Test Method B368. It is performed using a standard ASTM B117 salt fog cabinet, but the fog solution is mixed and acidified with acetic acid to a pH between 3.1 and 3.3. Copper chloride is then added to the salt solution. The solution is atomized as a fog into the cabinet which is maintained at 120° F (49° C). This test is used to determine corrosion resistance of various aluminum alloys.

Solution composition: Atomized solution of 3.8 liters 5% NaCl + 1g CuCl2.2H2O, acidified to pH = 3.2 with CH3COOH

Test conditions: According to ASTM B368

Result from test: Corrosion resistance in severe industrial atmosphere. Read this

.2 This method is applicable to evaluating the corrosive performance of decorative copper/nickel/chromium or nickel/chromium coatings on steel, zinc alloys, aluminum alloys, and plastics designed for severe service. It is also applicable to the testing of anodized aluminum. The suitability of this test and correlation of results with service experience should be determined before it is specified for coating systems or materials other than those mentioned in this paragraph.

Corrodkote (Topic 11122)

Solution composition: Paste of 0.99 g Fell…6H20 + 0.21 g Cu(NO3)2…3H2O + 6,0 g NH4Cl+ 180 g Kaolin + 300 ml H2O

Test conditions: According to ASTM B380, paste applied to surface. Coated specimen placed in 100% humidity

Result from test: Resistance to under deposit corrosion. Read this

Controlled humidity test: there are fifteen ASTM standards relating different variations of creating and controlling fog and humidity in cabinets for corrosion testing of a broad spectrum of products, from decorative electrodeposited coatings to the evaluation of the corrosivity of solder fluxes for copper tubing systems. The basic humidity test is most commonly used to evaluate the corrosivity of materials or the effects of residual contaminants. Cyclic humidity tests are conducted to simulate exposure to high humidity and heat typical of tropical environments. The cabinet performing such tests should be equipped with a solid-state humidity sensor reading the current humidity condition and a feedback controller. The mechanism used to control the humidity moves chamber air via a blower motor and passes it over a heater coil in the bottom of the chamber with an atomizer nozzle fogging into this air stream.

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