The properties of duplex and super duplex stainless steels depend upon achieving an optimal balance of austenitic and ferritic microstructures in the product. This can be a useful check of the quality of raw materials and bought-in components, but also where welding has been undertaken as this can significantly alter the original microstructure.
Ferritic microstructures are magnetic, whereas austenitic microstructures are effectively non-magnetic. This property is used by a ferritescope to infer the proportion of ferritic microstructure present underneath the measurement tool. This technique gives immediate results, but with less accuracy than (destructive) microscopy, even though the equipment can be calibrated for measuring different alloys. However, it is an acceptable approach to validate material properties claimed in other test reports.