The classical case is when chromium carbide is precipitated at the grain boundaries. The adjacent matrix will be depleted in chromium and a narrow region around the grain boundary may, therefore, be less corrosion resistant than the rest of the material.

In modern stainless steels with lower carbon content, intergranular corrosion is very seldom any problem in practical applications. However, test procedures to detect sensitivity to intergranular corrosion are still used for delivery testing of stainless steels.

The reason is that improper heat treatment can be the gate to "sensitisation" of the steel at a later stage, during welding. The purpose of using a corrosion test method for delivery testing is therefore to check that the steel has been properly manufactured and not the corrosion properties.

The most common test procedures used for delivery tests are described in different national and international standards. The general test methods are the sulphuric acid - copper sulphate test for standard grade steels and the sulphuric acid - ferric sulphate test for special grades. The boiling nitric acid test is also sometimes used, but this is not a general test method and should only be used for special purposes.