Screener confiscates them anyway, because of their "material and appearance."
Because they're not actually a threat, screener leaves them at the checkpoint.
Everyone forgets about them.
Six hours later, the next shift of TSA screeners notices the pipes and -- not being able to explain how they got there and, presumably, because of their "material and appearance" -- calls the police bomb squad to remove the pipes.
TSA does not evacuate the airport, or even close the checkpoint, because -- well, we don't know why.
Bruce's comment: "I don't even know where to begin." Neither do I, but I'm starting to wonder whether Douglas Adams was really joking about the telephone sanitizers and human ancestry.
In any case, it helps to view the world as a gigantic piece of absurd performance art. :)