Positive Material Identification (PMI)

Last update: Jan 13, 2017

Positive Material Identification (PMI) is a term that refers to the analysis and identification of materials through various nondestructive methods. PMI is able to determine the alloy composition of materials, and is a well-established technique that can either be performed in the field using handheld devices or in a laboratory.

PMI is an effective tool in situations where, for whatever reason, the material certificate for a component has been misplaced, destroyed, or is otherwise missing. It can be used in any situation where there is uncertainty about the material composition of a component.

There are several nondestructive examination (NDE) methods that can be used for PMI. Two of the more popular are X-Ray Fluorescence (XRF) and Optical Emission Spectroscopy (OES).

XRF works by exposing the material to be tested to an X-ray, causing the material to emit its own secondary X-rays in response. The levels of X-rays emitted by any particular material are always consistent based on the composition of that material. Thus by analyzing the secondary X-rays it is possible to determine the chemical composition of any unknown material. However, it should be noted that XRF cannot distinguish between material grades in certain elements such as carbon and silicon, among others.

OES works by exposing the material to an electrical spark and an electrode, often in an atmosphere of Argon. This spark works in a similar way to the X-rays in that it forces the material to emit light, which will differ in color and intensity based on the material that it is emitted from. It tends to offer a more complete view than XRF, and is the only method that can distinguish between levels of carbon in a material. While OES is considered a nondestructive method, it requires grinding the material for surface preparation and the process does cause slight burning on the surface as well.


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Embracing a New Approach to Retroactive PMI
July/August 2016 Inspectioneering Journal
By Brian Wilson at Thermo Fisher Scientific

The instrumentation available to detect inadvertent material substitutions through positive material identification (PMI) has never been more available, portable or powerful than it is today. For one industrial services company, Tacten Industrial, Inc., embracing the latest technological advances in PMI while using rope access to conduct inspections has helped to transform their business. It has found the ideal formula for retroactive PMI that allows its team and its clients to rest assured that they’ve conducted their testing right – the first time.

Advancements in Positive Material Identification Tools Bring Accuracy and Convenience to the Work Site
March/April 2016 Inspectioneering Journal
By Mark Lessard at Thermo Fisher Scientific

In numerous industries that require elemental and material testing, including the oil and gas, power generation, and petrochemical industries, positive material identification (PMI) is at the forefront of any operation. In fact, an increasing number of facilities are adopting a 100% PMI program to ensure that every metal component is made up of exactly the desired chemical composition.

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By Paolo Torrado at Engineering and Inspection Services, LLC.

An issue that arises frequently in the oil and gas industry is poor or missing documentation of pressure vessels. It is common in the industry to repurpose old equipment, bring equipment back into operation after a long period of time out of service, or rerate equipment due to debottlenecking of process units.

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A recent High Temperature Hydrogen Attack (HTHA) failure atarefineryinthestateofWashingtonwasa“wakeupcall” to our industry. On April 2, 2010, the shell of a feed-effluent heat exchanger in the Naphtha Hydrotreating (NHT) unit at the Tesoro Anacortes WA refinery ruptured, ultimately resulting in seven fatalities.

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Unfortunately there is a recurring theme of pressure equipment integrity incidents in the hydrocarbon process industry which has been identified by the API and that is leaks and fires caused by the inadvertent substitution of materials of construction in piping systems - the so called positive materials identification (PMI) incidents.

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