This is fairly common with metal drain lines, traps, etc. What is uncommon is that you seldom find a pipe like this in full bloom! Most of the time when they get to this stage of bloom they are leaking like a sieve and the section has been replaced.
So if you have metal drain pipes take a look and see if you have a bumper crop of blooms. If you find a pipe that has even the smallest amount of corrosion or discoloration, go ahead and replace that section of pipe. The damage starts from the inside of the pipe and it might not be leaking now but it will be soon, it is only a matter of time.
Oh, and a word to the wise! Do not pick the blooms! If you do you will need a bucket to catch the water that will flow from the vase that was holding that pretty flower!!