If that's your gas pipe coming through your garage wall into the garage (I have the exact same thing), the gas pipe is very cold (due to being connected to the exteriour) in the winter, but comes into a garage (mygarage is finished, so it is quite warm even in the winter) so, as a result, there is a lot of condensation on the pipe. I cleaned it periodically this past winter and painted it with rustoleum and that's stopped any issues.
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