You can make it worthless by moving all coins to newly generated seed phrase, but if you want to totally destroy evidence you need to use extreme high temperature.
Stainless steel melting point is around 1500°C (or 2800°F), so maybe use propane blowtorch, or throw it away in some metal melting factory like the one from Terminator2 movie 
Another way if you don't have all those option available, is to stamp over X, # or similar characters over all letters and make it unreadable.
I am not sure what acid is reacting with stainless steel so I would not recommend that method.