Nondestructive Testing & Research

Understanding Positive Material Identification (PMI)

Understanding Positive Material Identification (PMI)

At RNDT we are sometimes asked, “what is Positive Material Identification (PMI)?”  PMI is a nondestructive means of determining the chemical composition of metals.  In a global sourcing environment, material can inadvertently become mixed up and cause serious issues while in service.  Missing material certificates or incorrect materials used in a service can increase the risk of a failure, impacting safety, operations, and also maintenance.

When a component material is used in the wrong service it represents a near miss.  PMI will identify the wrong material in service by determining the alloy composition of the materials in use.  RNDT can quickly and accurately determine the chemical composition of many different metals.  RNDT has several Innov-X Alpha Series X-ray fluorescence units, Olympus Delta Element PMI units, and experienced technicians that can provide this service.

X-ray flourescense (XRF) is the emission of characteristic “secondary” (or fluorescent) X-rays from a material that has been excited by bombarding with high-energy X-rays or gamma rays.  The phenomenon is widely used for elemental analysis and chemical analysis, particularly in the investigation of metals, glass, ceramics and building materials, and for research in geochemistry, forensic science and archaeology.

When materials are exposed to short-wavelength X-rays or gamma rays, ionization of their component atoms may take place.  Ionisation consists of the ejection of one or more electrons from the atom, and may take place if the atom is exposed to radiation with an energy greater than its ionization potential.  X-rays and gamma rays can be energetic enough to expel tightly held electrons from the inner orbitals of the atom.  The removal of an electron in this way renders the electronic structure of the atom unstable, and electrons in higher orbitals “fall” into the lower orbital to fill the hole left behind.  In falling, energy is released in the form of a photon, the energy of which is equal to the energy difference of the two orbitals involved.  Thus, the material emits radiation, which has energy characteristics of the atom present.  The term fluorescence is applied to phenomena in which the absorption of a specific energy results in the re-emission of radiation of a different energy (generally lower).

Positive Material Identification allows industrial operators to make informed decisions about critical components, which reduces downtime, improves safety, and mitigates the risk of a catastrophic failure.

RNDT, Inc. is an ISO-17025 accredited commercial nondestructive testing laboratory located in Johnstown, Pennsylvania, that specializes in multiple nondestructive testing applications.

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