Positive Material Identification According to Material Standard

Positive Material Identification
Positive material identification or PMI is a nondestructive test method that is used to examine alloys and other materials to determine the presence of impurity. This is done in order to find out if the material is authentic based on the grade name it bears and to find out whether an alloy possesses unneeded elements. It is a process that shall serve as a gauge whether to accept or reject a material. There is no way that this process will be used to adjust the quality of the material to make it suitable for usage.

Engineers generally push the borderline of the capacity of any material to limits that make it efficient for the purpose and design. Hardly ever does a material come pure as it is typically alloyed or mixed with other elements to make it sturdier and more durable. However, several issues arise and we should take into account that with modification of composition comes the change in material specification. The durability of a material shall be determined by the proportions of the elements present in it. The wrong ratio can render the material futile. To complicate matters, the presence of impurities can limit the usefulness of a material. There is no other way for engineers to find out if a material is going to be suitable for particular purpose than doing methodical tests and it is just one of those standard tests employed to verify aptness of a material.

Positive material identification determines the alloy composition and grade of a material whether it comes with a certificate or not. The objective is to find out whether the grade as mentioned on the label is truthful. The process is generally used for premium metals like precious alloys and stainless steel. Because it is a non destructive test (like dye penetrant inspection or radiography), it is an excellent method of examination without altering the material physically or chemically.

There are usually two ways to carry out positive material inspection and these are x-ray fluorescence and spark emission spectrography. X-ray fluorescence (XRF) is usually more reliable than spark emission spectrography because it leaves no traces on the surface of the material being tested. The x-ray flourescence equipment consists of radioactive sources that emit low voltage x-rays. As the theory speaks, atoms of materials exposed to x-rays become excited and emit energy. The energy emitted by an excited atom is unique. As a result, this method is an effective way of identifying what elements are present in a material. X-ray flourescence does not only detect what elements are present but also determines how much of each element is present.

Much of positive material identification test is done with the use of x-ray flourescence, which is suitable when the integrity of the material being tested should be preserved. Some material analysis require taking a piece of the test subject for laboratory analysis but this is not applicable in many instances. Positive material identification is just one of the many nondestructive testing methods, like acoustic emission, leak detection, and hydrotesting.

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