Literature/@iso 18069 2015

• title: Corrosion of metals and alloys
• authors:
• year:

Method for determination of the uniform corrosion rate of stainless steels and nickel based alloys in liquids

4 Principle

4.1 This method involves immersion of the material in the intended liquid after the required temperature has been reached. Mass measurements are carried out before and after each of three sequential periods, 24 h, 72 h, and 72 h of immersion. Period 1: 24 h of immersion in the liquid. When exposed to acid, the passive layer will change composition during this period. In addition, contaminations on the specimens will be removed during this period. For this reason, the first period is normally not accounted for when evaluating the corrosion rate. Period 2: 72 h of immersion in the liquid. This period determines the corrosion rate. Period 3: 72 h of immersion in the liquid with activation of the specimens. This period determines the corrosion rate of a specimen with an active surface and the ability to repassivate in the specific liquid. 4.2 The weight, before and after each period, is measured, the mass loss during each period is calculated, and the average corrosion rate is determined for periods 2 and 3. 4.3 In the beginning of the third period, the specimens shall be activated, according to the procedure described in 8.5, to investigate whether the material has the ability to repassivate in the specific conditions. 4.4 Activation by a potentiostat or zinc shall be used, except in strongly oxidising solutions, such as nitric acids or ferrous sulfate where a hydrochloric acid solution shall be used. 4.5 The test involves immersion of specimens in a test liquid, which is in open air. This implies that the oxygen in the aerated liquid can maintain the passive layer and the result shall therefore not be compared with results obtained in deaerated liquid.