Pin hole on the body of steam trap

[Ashish]

I have installed a steam trap at VAM just one year back. body material is cast steel, now just after one year of operation the body of the steam trap got leaked. its a pin hole and it looks like a perfectly drilled small hole on the body. body is rusted heavily from the inside. still i am surprised by looking the pin hole on the thick metal body. please suggest the reason for this problem