The worst thing that can happen...

[rizmage]

I spent hours building a large refinery and getting everything working and then found that I had an odd number of underground pipes in my inventory.
This can only mean that somewhere in that vast rats maze of pipes, tanks and chemical plants, there is a single down pipe without a matching up pipe, and I can't find the error. Grrrrr !!!

[steinio]

If you take half a stack you end also with an odd number.
Get over it.

[zombieroboninja]

I've personally never used this mod, but it might be helpful for you!
https://mods.factorio.com/mod/Orphan%20Finder

[theolderbeholder]

Build a second refinery, then it is even again