Replacing our aging Feritscope and need consistent FN measurement on 309L/309Mo stainless overlays on P11, where dilution shifts the austenite/ferrite balance and we’re guarding against hot cracking. Any practical pros/cons on Fischer FMP30 probe options for 6–8 mm beads and small OD pipe, calibration block choices, and reading stability after a 200 °C preheat once the weld cools to ambient?
On 309L overlays I get steadier FN on small OD by using the FMP30’s small-area FGAB1.3 probe and laying a single layer of 25 µm Kapton as a repeatable lift-off when the weld’s just coming down from that “200 °C” preheat, @OP. Calibrate with blocks bracketing your target (I use 5 and 10 FN for P11 dilution), and if readings wander, run a quick demag pass before rechecking; curvature and residual mag are bigger culprits than the probe itself. If your beads are truly “6–8 mm”, keep the probe footprint centered and avoid toe wetting, or it biases low.