Nice shot, a little weak tonally. Looks like you applied sharpening after the border, incidentally, whih has produced a haloing effect on the border itself. Better post prodcution could have made this image really pop.
An interesting composition and a square-form works well here. However, the main point in this photo is a hole, not metal. I like this pic but I think it doesn't fit entirely the rules of this competition.
It is the attention to small detail (cropping the adjacent boarder circles to be equal) that really gives this photo its extra bite. Oh and you had me singing the seasame street song *grin*
Without the light at the end of just one pipe this would be quite unexceptional. With that wonderful focal point and the intrigue it provides, it works very well. For me there's quite a tension in wanting to fly through that pipe and look out of the other end...