how can I cap off a 1 1/2

I have leak in one of the one pipe steam system and I would like to cut pipe and cap it. The reason I want to cut pipe is because its very old and will probably do more damage to the system. I want to repair it later but for now I would like to cap it off. My question or questions are is there a metal unthreaded cap , and would a rubber cap work? The pipe is