And let's say you're using a specific kind of kettle that's made of 3-inch metal. The kettle has a latch on it, that when shut, makes the kettle completely airproof, waterproof, gasproof, etc.
You open the latch until the water starts to boil and steam comes out. Then you shut the latch. What would happen?
-
Pressure would build in the kettle as more the air and water vapour got hotter and expanded, but I doubt there would be a rupture. Perhaps a minute distortion or bulging of the kettle?