I concur Dr Alex - just to clarify, DIN 50021 refers to:
This standard specifies the requirements which corrosion testing apparatuses and corrosive agents must meet in salt spray testing, the aim being to enable identical conditions to be reproduced in all cases in which spray tests are carried out on the basis of standards or agreements. The standard does not deal with the preparation of specimens, the duration of testing, the treatment of specimens after testing, or the evaluation of results. Which of the three methods listed in clause 3 is to be applied in any individual case shall be the subject of agreement between the parties concerned unless specified in relevan standards. The tests described in this standard serve both to characterize the effectiveness of corrosion protection systems and to detect defects quickly. They are not suitable for specifically testing for defects in metallic coatings where the coating is made of a baser metal than the substrate (e.g. zinc or aluminium on steel), since the substrate is in such cases cathodically protected by the coating adjoining the defect.
oops, Tramadol time!