Non-Destructive Testing Methods: Positive Material Identification (PMI)
Positive material identification (PMI) ensures that the components and welds in a unit are actually the correct materials. Following proper procedures for material ordering, receiving, and traceability should prevent any material mix-ups, but for critical applications, final verification of material is sometimes needed. The most common PMI method uses a hand-held metallographic analyzer that takes advantage of X-ray fluorescence (XRF) to determine the elements that the material is composed of. The analyzer directs a small amount of x-rays into the material. The tested material reflects the radiation from the analyzer which generates energy. Each alloying element has its own atomic structure and will generate a different energy level for each element. The analyzer detects and measures the reflected energy thus identifying the alloying elements, and then identifies the material grade based on the composition. XRF-type PMI analyzers cannot detect some elements such as Carbon, so they cannot distinguish between grades 316 and 316L, for example. Analyzers using the method of optical emission spectroscopy (OES) can detect the amount of Carbon, but these units are significantly larger, more expensive, and slower to operate than XRF-type testers.
Ward has in-house capability of XRF-type PMI verification. Please feel free to contact us if you have any questions about this method.