@cherrybim Rav Moshe writes in Igros Moshe Y”D Chelek Gimmel, Siman Lamed (from 5713) – that steam should not be used for Hagalah for Pesach. In Igros Moshe Y”D Chelek Alef, Siman Samach (from 5718) he writes that steam should not be used for Hagalah even in a glycerin factory to Kasher from Treif glycerin (seemingly even for the rest of the year) – I think he mentions there (Siman Samach) that if the steam turns to boiling water (212 degrees F), then that water can be used for Hagalah (however, it’s probably not so easy to accomplish this with most electric steamers, especially those that are designed not to leave a mess).