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DIN Standards Committee Materials Testing

Overview

As an alternative to the continuous salt spray test methods of ISO 9227, intermittent salt spray test methods may be used. The results of such tests provide a better correlation with the effects of exposure in environments where there is a significant influence of chloride ions, such as from a marine source or road de-icing salt. Accelerated corrosion tests to simulate atmospheric corrosion in such environments should include cyclic exposure under the following conditions: a) A phase of controlled cyclic humidity conditions, where the test object is subjected to an environment which alternates between high humidity and comparative dryness; b) A wet phase, during which the test object is repeatedly subjected first to a spray of aqueous salt-containing solution then to a wet "stand-by" period during which residual wetness remains on the test object. A prolonged period of continuous exposure to wetness, extending over several hours, results. These two phases should be cycled for an appropriate number of times. The test method described in this International Standard conforms with these requirements, as follows: The major part of the test cycle consists in an exposure in two steps at 95 % relative humidity at 35 °C and 50 % relative humidity at 45 °C. To simulate the wet phase of the cycle, the humidity level has been set close to the condensation limit, but at a level at which test conditions can be satisfactorily controlled. Introducing 100 % humidity conditions inevitably results in loss of control of the amount of salt deposited on a test object. In the first (wet) phase of exposure, the test objects are sprayed for 15 min with a 1 % (mass fraction) aqueous solution of sodium chloride acidified to pH 4,2, to simulate the rather acidic precipitation present in industrialized areas, followed by a 1 h 45 min period of wet "stand-by". This sequence is repeated three times to give a total of 6 h exposure to wetness. The "wet" phase is repeated twice a week. If spraying is carried out more frequently or a more concentrated solution of sodium chloride is used during this phase, results may appear that are seldom experienced in the field, for instance severe diffusion blocking byred rust or excessive dissolution of zinc. The test method described in this International Standard is mainly intended for comparative testing and the results obtained do not permit far-reaching conclusions on the corrosion resistance of the tested metallic material under the whole range of environmental conditions within which it may be used. Nevertheless, the method provides valuable information on the relative performance of materials exposed to salt-contaminated environments similar to those used in the test. See Annex A. This International Standard defines an accelerated corrosion test method to be used in assessing the corrosion resistance of metals in environments where there is a significant influence of chloride ions, mainly as sodium chloride from a marine source or road de-icing salt. This International Standard specifies the test apparatus and test procedure to be used in conducting the accelerated corrosion test to simulate, in a very controlled way, atmospheric corrosion conditions. Within the framework of this International Standard, the term "metal" includes metallic materials with or without corrosion protection. The accelerated laboratory corrosion test applies to: - unalloyed steels, zinc-coated steel, aluminium and their alloys; - metallic coatings (anodic and cathodic); - chemical conversion coatings; - organic coatings on metals. The method is especially suitable for comparative testing in the optimization of surface treatment systems. This document (FprEN ISO 16701:2013) has been prepared by Technical Committee ISO/TC 156 "Corrosion of metals and alloys", the secretariat of which is held by SAC (People's Republic of China), and has been adopted within the framework of the Vienna Agreement by CEN/TC 262 "Metallic and other inorganic coatings", the secretariat of which is held by BSI (United Kingdom). The responsible German committee is Working Committee NA 062-01-77 AA "Korrosionsprüfung" ("Corrosion testing") of the Materials Testing Standards Committee (NMP).

Document: references other documents

Responsible national committee

NA 062-01-77-01 GAK - Joint Working Group NMP/NAB: atmospheric corrosion protection tests  

Responsible european committee

CEN/TC 262 - Metallic and other inorganic coatings, including for corrosion protection and corrosion testing of metals and alloys