Dont want to step on toes MG, the bunchy part has been left out of the boolean op so it can work, but still good advice in modeling. (If you see the bunchy, redo something).

The problem with his model was his seam edge was glancing and intersecting back and forth by just a smidgeon. Yet another thing to notice during the construction phase. I rotated the orinal circle to re-produce the pipe with the seam edge "OUT" of the model.

Here's your file with the bools (add and subtract) I saved all the materials for brian to review. I forgot to save a copy of the original master object, but if you need it brian, you can just merge it from the old file posted.