unsupported ends of drywall.
I would never "float" drywall 2'. I MIGHT go 12" (prefer nothing over 6" - 8"), depending on the situation. Can you post a pic of the area?? There's usually some way to get some sort of backing in there, even if it's not structural. That will help prevent movement that may cause tape to crack later. If necessary, you could frame out a "column" around the pipes.....
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