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Ferrite Content in (Duplex) Steel and Weld Seams

Requirements for steel in industry

Components found in industrial plants โ€“ whether chemical, energy, petrochemical or other โ€“ are often subject to heat, aggressive agents and high pressure. These conditions demand steel types that are extremely corrosion and acid resistant even at high temperatures. When austenitic steels are used, it is important to make sure the ferrite content of the weld seams is within strict norms, because only the optimal ferrite content can ensure the best corrosion protection. For this reason some industries have set standards, specifications and regulations for ferrite content.

Ferrite content in steels and welds

During the welding of joints on e.g. boilers and pipelines made of austenitic steel, the heat causes modifications in the crystal lattice structure which lead to the formation of ferrite. Weld seams that are poor in ferrite do not have as much yield strength, but too much ferrite reduces their fracture toughness, ductility and corrosion resistance, so it is important that the welding process produces just the right amount.

Determining the ferrite content

With duplex steel in particular, the ferrite content in the heat affected zone can easily deviate from the target values, either due to unsuitable filler materials or through incorrect heat input or cooling during the welding. Only onsite spot measurements can provide assurance that the processing did not change the ferrite content at the expense of crucial mechanical or corrosion-resistance properties.

The magnetic induction method

To meet these requirements FISCHER has developed the handheld FERITSCOPEยฎ FMP30 instrument, which measures the ferrite content using the magnetic induction method and displays it either as percent ferrite content or as a WRC (Welding Research Council) ferrite number The FERITSCOPEยฎ FMP30 can be outfitted with a variety of probes in special shapes such as axial, angled or for measuring inside centre holes.

Optimum measurement of ferrite content with the FERITSCOPEยฎ FMP30

The FISCHER FERITSCOPEยฎ FMP30 allows for reliable and precise determination of the ferrite content in percent or as a WRC ferrite number. For further information please contact your local FISCHER representative.

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