When I was a teenager, I worked at my dad’s machinery business during the summer. One day the foreman gave me the responsibility of pressure testing a kettle. He said to run water into the jacket and build up the pressure SLOWLY. He said, if it sounds like it is going to blow, you must let the water out.
I did as he said and built up the pressure to one and a half times the pressure rating, as instructed. I did not hear anything and I did not see any bulges on the outside, so I thought everything was fine. Then the foreman came by and looked inside the kettle and he was not happy. “You blew this his kettle,” he said. I didn’t realize that kettles do not blow like a tire. They blow INSIDE. The inside of the kettle was all puffed up.
Since that day, I know what a blown kettle looks like.