Test organic coatings

Various conditions of accelerated corrosion testing are summarized in Table 1.10. According to ISO 14993 [85], water condensation on the test specimens should not occur under wet conditions. The methods of testing organic coatings on metallic materials according to ISO 11997-1 under cyclic corrosion conditions include condensation of water on the test surface during the period of humidity [87]. 

Where changes in appearance are of paramount interest, as in the case of metallic and organic coatings on steel or other metals, visual examination is most desirable. To facilitate ratings on such a basis, photographic standards have been employed, as, for example, in tests on chromium-plated steel undertaken by ASTM Committee B-8 on Electrodeposited Metallic Coatings . These ratings are supplemented by a shorthand description of the nature of the deterioration observed. 

Thus, both the proper conduct of the testing programme and the valid use of the data depend on an understanding of the nature of organic coatings and of the forces through which they are degraded. 

D 2803 1982 (1987) Test method for filiform corrosion resistance of organic coatings... 

One costly form of degradation is corrosion of metallic objects and structures. Organic coatings are widely used to protect these objects from corrosion. No completely acceptable and predictive methods exist for the evaluation of corrosion protection. Since corrosion is an electrochemical phenomenon, electrochemical testing may provide the evaluation tools which are wanting. 

The aluminum spill tests in water led to effective plant preventative schemes wherein organic coatings were placed on all solid surfaces which, in the event of an accident, might be in contact with molten metal and water. Use of such coatings has greatly diminished the frequency of thermal explosions. 

Strong hammer blows on the outside of the vessel wall often initiated explosions even in cases where organic coatings covered the bottom. There was a threshold energy for an explosion to result for the Alcoa test scale, it was about 19 m kg (137 ft lb) although only about one-half of this energy probably reached the water. Such an impact would lead to overpressures less than 0.5 bar. 

In all shock-initiated tests, the probability of a violent incident increased with an increase in the temperature of the aluminum. In many instances, explosions could be obtained even in g/ass-bottomed vessels or vessels with an organic coating. The eiluminum on the bottom would explode violently with completion in about 600 jusec. (There may, however, have been a 1- to 2-msec delay after the detonation of the explosive charge before the large explosion.)... 

Organic coatings are commonly evaluated using salt water immersion, salt fog or spray, modified salt exposure tests (e.g., salt fog with added SO2), and various cyclic exposure tests. Humidity exposure and water immersion, and, for many applications, physical resistance tests (adhesion, impact resistance, etc.) are widely used preliminary tests. Standard methods for most of these tests are given in compilations of standard tests such as the Annual Book of ASTM Standards (16). Test methods have been extensively reviewed (e.g., 17-23). 

Metallic corrosion is an electrochemical process associated with the flow of current between surface sites having a difference in electrochemical potential. The assessment and evaluation of organic coatings to prevent metal corrosion has traditionally been accomplished through salt fog testing (ASTM B-117) and long term exposure tests in particular service environments. Electrochemical techniques have often been considered (, but are not routinely employed in practice. 

Khrushchev (1957) considers that the need to measure the force T has not been sufficiently well substantiated, nor has a sufficiently precise and easy in service hardness tester been developed yet for determinations of this type. However, he appreciates the usefulness of scratch hardness tests, especially at low loads, as a non-destructive technique. He recommends these methods as very useful for hardness determination of metallic layers or of materials exposed to abrasive wear under operating conditions (plastics, organic coatings, such as varnishes and paints, etc.). Scratch methods are especially important in tests of anisotropic materials where a change in scratch width is the measure of anisotropy. In static indentation methods, the indentations obtained in anisotropic materials are misformed, varying... 

Requirements and tests for Pyroxylin type NC are described in Specs listed here as Refs 51 52 and for Technical NC(for use in organic coatings) in Ref 53. Several US std tests are described in Ref 55. In Ref 49 is described detn of N content of NC by IR spectrophotometry and in Ref 55 detn of NC by chromous chloride reduction. One of the latest methods on detn of N content in NC by ferrous-titanous titration is described in Ref 44. This test will be included in the next edition of US Military Standard Spec... 

ASTM D 1653 - 03, Standard Test Methods for Water Vapor Transmission of Organic Coating Films, 100 Barr Harbor Drive, P.O. Box C700, West Conshohocken, PA 19428-2959. 

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