I have 20 foot sections of 1-1/2" sched 40 pipes I have to install across the ceiling. I know aligning long sections of pipe well enough for them to thread together can be a real headache. Now I have to do it on the ceiling, these could be several bad days.

How do I align long sections of pipe well enough for them to reliably thread into each other?

You align good quality hangers, first. The pipe will fall in place.

screw the coupling on as tight as you can by hand onto one piece. slide the pipes gently together. unscrew the coupling a turn or two and it should be caught on both pieces. once successful doing this you know you are aligned. back off the coupling, apply pipe dope to each pipe and repeat.

ditto

Quote

Author: Paul48 (CT)
You align good quality hangers, first. The pipe will fall in place.

==============================================

"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638

the problem comes when you rotate the pipe it 'walks' in the hangers thowing it off just slightly.
if you do as i suggested, the only thing turning is the coupling. once you have pipe doped both ends and done the coupling thing again, they will catch a thread and turning the full length will not throw it out of alignment.
ah, the good old days.. packing and pouring bell and spigot cast iron and then running 2 inch galvanized vents with cast iron fittings.