PMI (Positive Material Identification) testing is the analysis of materials to determine the chemical composition of a metal or alloy at particular (usually multiple) steps of alloy manufacturing or in-process alloy installation. Knowing the exact composition and grade of an alloy enables suppliers, plant workers, and other responsible parties in the chain of custody of components to match alloy specifications that are chosen for their specific properties such as heat resistance, corrosion resistance, durability, etc. Having the right alloy in the right place is essential in places like petroleum refineries and chemical plants, because the right alloy with the right properties is often all that stands between a safe, efficient operation and lost time and revenue.

Currently most alloy manufacturers, petroleum refineries, and other businesses responsible for alloy grade verification use technology to quickly and easily separate various grades of stainless steel. The most common, portable, and easy-to-use tool for this purpose is a handheld XRF (x-ray fluorescence) analyzer. These instruments are highly accurate at determining the chemical composition of alloys, and thereby their grade. Moreover, they do so within a matter of 5 seconds or less for most stainless steel grades, without significant sample preparation, and safely.