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.