Ferrite Content Measurement

Ferrite Content Measurement  and its Measurement

Measuring the ferrite content in metal is an important part of ensuring quality and minimizing potential failures. To achieve this, a ferrite scope test is typically used which employs digital technology to quickly and accurately determine the ferrite value. This type of testing is especially useful in industries where high temperatures, aggressive media, and high pressure is common, such as oil and gas, power, and process engineering plants.

The ferrite content of stainless steel welds and duplex steel can be determined with this test. Depending on the application, there is a maximum allowable ferrite content value that should not be exceeded. If the value is too low, hot-cracking or solidification cracks can form in the weldment, while if it is too high, the steel can lose its toughness, ductility, and corrosion resistance. In duplex stainless steel, a lack of ferrite content can weaken welds and promote the growth of stress corrosion cracks.

The ferrite number (FN) or the ferrite percentage (%) is used to determine the success of the test. Reports are generated in accordance with applicable technical specifications (AWS A4.2) and/or customer requirements, including drawings to help readers locate the areas that were examined. With comprehensive testing and inspection services, international quality standards are supported.

Different Techniques 

There are numerous methods for measuring ferrite content, and the method used depends on the application and the level of accuracy sought. Here are some examples of commonly used techniques:

Magnetic Permeability Method: Determines ferrite content by comparing permeability with calibration, based on ferrite’s lower permeability compared to austenite.

X-Ray Diffraction (XRD): Analyzes X-ray diffraction patterns to assess ferrite content based on crystal structure, which necessitates the use of specialized equipment.

Magnetic Saturation Method: Determines ferrite content by measuring magnetic flux density after saturating a sample and comparing it to a calibration curve.

Method of Point Counting: Examines microstructure and counts ferrite phase intersections on a grid to calculate ferrite content percentage.