This part of ISO 3651 specifies methods for the determination of the resistance to intergranular corrosion of ferritic, austenitic and ferritic-austenitic (duplex) stainless steels in media containing sulfuric acid. It also specifies the purposes which may be assigned to the test. The test methods included are: — method A: the 16 % sulfuric acid/copper sulfate test (Monypenny Strauss test); — method B: the 35 % sulfuric acid/copper sulfate test; — method C: the 40 % sulfuric acid/ferric sulfate test. The methods are applicable to stainless steels supplied in the form of cast, rolled or forged products and tubes and intended for use in a mildly oxidizing acid medium (for example, sulfuric acid, phosphoric acid). Unless specified in the product standard, the method to be used, A, B or C, shall form the subject of an agreement between the interested parties. Annex A gives examples of application of the three methods on stainless steels. NOTE— It is important to note that the result of the corrosion test is only strictly valid for the corrosive medium used in the test. It constitutes a basis for estimating the resistance to intergranular corrosion but may not be used to check resistance to other forms of corrosion (general corrosion, pitting, stress corrosion, etc.). It is necessary for the user to adapt the specified corrosion test to the use which will be made of the alloy. These test should, in no case, be considered as an absolute criterion of the quality of the metal.