PMI Testing, also known as 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 parties in the chain of custody to match alloy specifications for specific properties such as heat resistance, corrosion resistance, durability, etc.
Having the right alloy in the right place is essential in industries such as the petroleum and chemical industries, because the right alloy with the right properties is often all that stands between a safe, efficient operation and lost time and revenue.
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Stainless steel grades differ by chemical composition. The key differences between the various grades are mainly the amount of Fe (iron), Cr (chromium), Ni (nickel), Mo (molybdenum), and Cu (copper) present. Some grades are very different from each other with differing properties; for example, 400 series stainless steels are magnetic whilst 300 series stainless steels are not. Other grades are more similar and it is much harder to tell the difference between them without the aid of technology. For example, 304SS consists of 18-20% Cr and 8-10.5% Ni, whereas 316SS consists of 16-18% Cr and 10-14% Ni.
Although these alloys are very close in composition, they respond differently to corrosive chemicals and higher temperatures making it necessary to be certain you are using the correct alloy for the job intended.
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.
A handheld XRF PMI gun like the Bruker S1 TITAN can analyze, identify and display the grade and composition of a material in less than 5 seconds without creating any marks on the material or destroying the sample in any way
PMI machines are highly accurate at determining the chemical composition of alloys, and thereby their grade as well as their solder composition. Moreover, they do so within a matter of 5 seconds or less for most stainless steel grades, without any need for sample preparation. XRF guns pay for themselves in terms of reducing materials mix-ups and ensuring the best prices for scrap identification, and they do not require any advanced training to operate. An operator can be trained to use a system within a few hours.
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XRF, or X-Ray Fluorescence, involves measuring the energy emitted from a sample after its exposure to an X-ray. In XRF instruments, an X-ray tube is used to generate the X-ray. . The energy emitted from the sample results from electrons being displaced from atom orbits within the stainless steel sample.
This emission occurs due to the primary x-ray beam's energy, which knocks electrons out of inner orbits. These displaced electrons leave vacancies that are filled by electrons from higher orbits, releasing fluorescent energy that is characteristic (i.e. unique) for each element.
Detected by the XRF instrument's detector, this energy indicates the elemental composition of the sample. Distinct fluorescent energies for each element enable the instrument to identify the elements present and their quantities, facilitating reference against known alloy compositions. For instance, a composition of 17% Cr, 12% Ni, and 2% Mo signifies 316 SS, which XRF analysis can confirm.
Users do not however have to understand the theory fully to use one of our PMI testing guns - operation of the instrument happens using a simple point and scan mechanism and the in-built software does all of the work, providing a simple readout on the screen.
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Positive Material Identification (PMI) plays a crucial role in various industries, enhancing material reliability, safety, and compliance with industry standards:
Petrochemical Industry and Refineries: Ensuring materials' heat resistance, corrosion resistance, and durability for safe and efficient operations
Aerospace and Defense: Verifying materials' grade and composition for reliable and safe aircraft, rockets, and military equipment
Manufacturing and Construction: Ensuring compliance with quality standards, detecting counterfeit materials, and preventing mix-ups during fabrication
Power Generation: Identifying materials that can withstand extreme conditions in power plants and energy production facilities
Oil and Gas Pipelines: Ensuring pipeline integrity and preventing failures caused by corrosion through regular PMI inspections
Pharmaceutical and Food Processing: Using compatible materials for equipment to maintain product quality and safety
Automotive and Transportation: Verifying material quality for safe and durable vehicle components and structures
Recycling and Scrap Sorting: Identifying and sorting different metals and alloys for efficient recycling processes