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Positive Material Identification (PMI)

Positive material identification (PMI)
Using a handheld scanner, positive material identification (PMI) instantly delivers alloy chemistry and grade ID information.PMI is frequently used to make sure that the parent material in pipes and vessels has the right composition. The equipment was repaired with the right filling material.

Procedure for PMI-Positive Material Identification:

Elements lighter than Sulfur cannot be detected by the X-ray emission analysis due to inherent limitations.  Therefore,  this technique cannot be used to detect Carbon. An optical emission spectroscope may be used to check for all the required elements, including Carbon. The PMI program covers alloy material, pressure-containing components in shop and field fabricated equipment and piping (both base metal and welds), and materials used for repair or replacement of pressure-containing components.

  • 100% PMI testing (each component and weld is tested) shall be performed on all pressure components and welds of alloy materials.PMI testing of weld material shall be performed in the same manner as for the adjacent base metal.
  • One PMI  test for each pressure-containing component. If an assembly contains a number of components (parts), one test is required for each component (part).
  • One test for each pressure-containing weld and weld repair, plus filler metal testing

The elements of the basic alloy materials to be verified shall be in accordance with Table

Basic Alloy Elements to be verified
Carbon-Molybdenum Manganese-Molybdenum, and Chromium-Molybdenum steels  

Chromium and Molybdenum

Nickel Steels Nickel
Regular carbon grade stainless steels Chromium, Nickel and Molybdenum
Low and High carbon stainless steels Chromium, Nickel, Molybdenum, and Carbon
Stabilized stainless steels Chromium, Nickel, Molybdenum, Titanium and Niobium
Nickel-based alloys Nickel, Iron, Copper, Chromium, and Molybdenum
Copper-based alloys Copper, Zinc, and other elements specified in P.O. or SAMS

PMI Testing of Welding Consumables:

In addition to the PMI testing of completed pressure-containing welds, when welding of alloy materials is conducted, one electrode or wire sample from each lot of filler metal shall be positively identified. PMI testing of weld metal (e.g., deposited or undiluted weld “buttons”) is an acceptable alternative to PMI testing of an electrode or wire sample provided; is conducted immediately prior to welding or during the welding process

Optical Emission Spectrograph-OES:

OES otherwise known as Optical Emission Spectrograph is a material analysis method used to find out the Carbon, Phosphorus and Sulphur in addition to the other elements by  PMI XRF Analysis method of material composition. So it is also known as PMI With carbon method. Normally PMI with carbon method is used to find out the chemical composition used in SS 316 L materials and other materials used in oil and gas industry. The principle of the analysis method of SPECTRO’s portable metal analyzer is optical emission spectroscopy(OES) and NITON XLt analyzer is x-ray fluorescence (XRF).The PMI XRF and PMI With carbon equipment shall be always re-calibrated at the job site if the readings observed are abnormal due to severe temperature fluctuations or any other adverse site conditions. Analyzed samples with reference to the job shall be made available for cross-reference and calibration. If sample removal is used, a written procedure for identification and traceability to original material is required. Both inside and outside weld surfaces shall be tested where accessible. PMI XRF  testing of welds shall be done after removal of slag and/or oxide from the weld surface. Surface shall be clean bare metal, free of grease or oil as specified by the instrument manufacturer. Surface shall be clean bare metal, free of grease or oil as specified by the instrument manufacturer.