If you are talking about a written document, a somewhat obscure term is screed:
screed (n): a long piece of writing, especially one that is boring or expresses an unreasonably strong opinion:
A recent example of its use:
Brown joined the company in 2017, not long before a screed against Google’s diversity efforts written by engineer James Damore went viral.
If not actually angry, a "tirade" should be at least loud and energetic and usually refers to oratory. If the speech was long but dull I would instead use something like monologue, or say the speaker droned on for some length of time. It can be boring (or at least tedious and repetitive), but since that's not included in the definition, you'd have to explicitly add that information.
I managed to get through the text of her speech, which was mostly an interminable tirade against the evils of gluten.
A "harangue" is similarly energetic, and usually is meant to make the listener feel guilty for some misdeed. As with "tirade", if it's boring, you'd have to say so.
After we got home, covered in filth, our father launched a tedious harangue at us about how foolish we were to play around the storm drains after a heavy rain. As if we didn't already know.