PMI is abbreviation for Positive Material Identification.PMI is actively applied in the oil and gas industry.Purpose of PMI includes:1) Check the correctness of material used for making a certain equipment.2) Check the content of alloying elements for a specific type of steel.3) Check the type of steel used, e.g. Stainless Steel 316, Stainless Steel 304, Stainless Steel 410, Duplex Stainless Steel 22% Cr, Super Duplex Stainless Steel 25% Cr.
How to do PMI?
PMI can be done using XRF or OES methods.
XRF is X-Ray Fluorescence. XRF can be done using a portable analyzer or a desktop analyzer. Desktop XRF analyzer is suiable for test samples and small-sized products, tested in a lab or office environment. Portable XRF analyzer is suitable for products as well as test samples, tested anywhere. That's the beauty of portable XRF analyzer; it can be easily carried around for testing to be done anywhere, i.e. at site, at plant, at platform, at vendor's warehouse, at vendor's factory.
OES is Optical Emissions Spectroscopy. OES is often used in test labs. OES have an advantage over XRF, because OES can detect and measure Carbon (C) and Nitrogen (N). Disadvantage is OES will create a "burn mark" on product tested, so it is not truly non-destructive.
ExxonMobil does not permit PMI using OES for testing the real products.
PMI for Valves
PMI is often used for checking the valve materials used, especially for the body and bonnet. PMI is often used as a Quality Control practice if the body/bonnet material is made of stainless steel, duplex stainless steel, or super duplex stainless steel.
