PMI

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If a material certificate of purchased material is missing or it is not clear what the composition of a material is, then PMI offers the solution. Moreover, The most frequent cause of industrial accidents is failures in mechanical integrity due to usage of incorrect materials and insufficient strength of welded joints. Positive Material Identification (PMI) is one of the more specialized nondestructive testing methods that is used to analyze and identify the material grade and alloy composition for quality and safety control.

PMI is

  • rapid,
  • non-destructive method,
  • can be performed on a wide range of components and assets, and
  • provides semi-quantitative chemical analysis.
  • It is used for both material verification and identification.


 
PMI analyzers come in a variety of shapes and sizes, from mobile to handheld, and allow operators to verify the safety of their equipment, or the exact composition of the materials they make use of with complete confidence.
 

PMI can:

  • Ensure products/components have been manufactured using the correct alloy
  • Find potentially mixed-up alloys
  • Identify if the wrong material has been used
  • Ensure material conforms to the correct standard and specification (both customer and industry)
  • Ensure welded components have used the correct filler material

Positive material identification is performed using either of the two techniques below:

  • X-ray Fluorescence (XRF) analyser
  • Optical Emission Spectroscopy (OES)

X-ray Fluorescence (XRF) analyzer :

it is a non-destructive analytical technique used to determine the elemental composition of materials. XRF analyzers determine the chemistry of a sample by measuring the fluorescent /secondary  X-ray emitted from a sample when it is excited by a primary X-ray source. Each of the elements present in a sample produces a set of characteristic fluorescent X-rays (“a fingerprint”) that is unique for that specific element, which is why XRF spectroscopy is an excellent technology for qualitative and quantitative analysis of material composition. However, it cannot detect carbon and some lighter elements and is not suitable for identification of pure carbon steel materials.

X-ray Fluorescence (XRF) analyzer
X-ray Fluorescence (XRF) analyzer
Image Credit: Olympus Scientific Solutions

Typical working principle of X-ray Fluorescence (XRF) analyzer
Typical working principle of X-ray Fluorescence (XRF) analyzer
Image credit: https://www.xos.com/

Caution: During the analysis, the analyzer emits a directed radiation beam when the tube is energized, care must be taken to always point a handheld XRF analyzer directly at the sample and never at a person or a body part.

safety tips while using XRF analyzer:

  1. Provide radiation safety training to operators
  2. Never aim the device at yourself or others when the primary beam (x-ray on) lights are illuminated
  3. Never hold samples during analysis
  4. Be aware of primary beam indicator lights
  5. Handle and use with respect
  6. Store securely – obey local storage requirements
  7. If you have a Safety Emergency, notify your Radiation Safety Officer (RSO) and analyzer vendor

XRF is used in industries

  • Oil and gas
  • Metal fabricating
  • Automotive & aerospace
  • Scrap metal recycling
  • Precious metal recycling
  • Mining & exploration
  • Construction & environmental engineering

Optical Emission Spectroscopy (OES):

This method can detect almost all types of elements including carbon and lighter elements and carbon steel. Although not as portable as XRF analyzers, the equipment can be transported to sites and used at high elevations with proper lifting arrangements.

Optical emission spectrometry involves applying electrical energy in the form of spark generated between an electrode and a metal sample, whereby the vaporized atoms are brought to a high energy state within a so-called “discharge plasma”. These excited atoms and ions in the discharge plasma create a unique emission spectrum specific to each element, as shown in images below. Thus, a single element generates numerous characteristic emission spectral lines.

Therefore, the light generated by the discharge can be said to be a collection of the spectral lines generated by the elements in the sample. This light is split by a diffraction grating to extract the emission spectrum for the target elements. The intensity of each emission spectrum depends on the concentration of the element in the sample. Detectors (photomultiplier tubes) measure the presence or absence or presence of the spectrum extracted for each element and the intensity of the spectrum to perform qualitative and quantitative analysis of the elements.

OES is capable of analyzing a wide range of elements from Lithium to Uranium in solid metal examples covering an extensive concentration range, providing low detection limits, high precision, and very high accuracy.The type of samples which can be analyzed using OES include samples from the melt in primary and secondary metal production, and in the metals processing industries bolts, tubes, wires, rods, plates etc.

Even though OES is considered a nondestructive testing method, the sample needs to be prepared with a mechanical sanding device and the spark does leave a small burn on the sample surface that would need to be removed after analysis.

References :


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