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Demand of PMI method for material recognize in various applications

Positive material identification (PMI) is used to recognize and test the different metallic materials depending on their chemical composition in the test. In this post the alloys used are Inconel 625 and stainless steel 316l. The analyses include a field testing by using the PMI analyzers.

As the specifications for materials utilized in the industry are highly specific, the demand for PMI analyses has been rapidly increasing over the years. The regular plant shutdowns for maintenance are less common therefore the materials used remain in service for the longer period.  The different alloys that are hard to differentiate through eyes are used in the individual plants.

When the unit staff replace parts, they should ensure that the new components withstand the engineering standards. Recent damages have risked the life of operators and raised the concern for the demand of accurate and wide PMI checking.

Why identification of application material is needed?

Currently, several major oil firms need that each of pipe, connector and other components of the plant should be measured to verify that materials meet the engineering specifications. The global sourcing is a main factor that demands the PMI. The buyers need look for verified quality materials for their applications.

The methods used for PMI are – X – ray Fluorescence and Optimal emission spectroscopy

X-ray fluorescence

XRF works by subjecting the material in the beam of x- rays that are absorbed by the material’s atoms. Every element present in the Inconel 625 alloy releases X- rays at a specific energy level. By assessing the intensity and characteristic energy of the X- rays, an analyzer is used to offer the results in correspondence to the material used.

Optical Emission Spectroscopy

In this method, the atoms in the material are excited although the excitation energy is received from the a spark made between the material and electrode. The spark energy emits light from the material’s atoms that is then transformed into the spectral pattern. The peak intensity of this spectrum is measured, OES analyzer evaluates the material chemical composition. However it is considered a safe testing technique, the spark creates a tiny burn on the material’s surface.

Benefits and drawback of testing methods

  1. XRF analyzers can be easily used, the sample doesn’t need to be well prepared.
  2. Unlike to traditional methods, the x-rays are produced by small tubes rather isotopes. So these need nominal documentation.
  3. The OES equipments offer endless ability to evaluate the elements of metals.
  4. OES is even a superior method than XRF because of its excellence in assessing the light elements for example aluminium and carbon.
  5. OES is a reliable method to assess the carbon even on site that usually needs samples of silicon or stainless steels.
  6. OES is also used to analyze the aluminium present in aluminium based alloys. In order to maintain the accuracy and precision, argon environment should be used.

Application sectors that demand PMI