I hear you're not supposed to use plastic pipe for dust collection. Why?
The main reason why PVC pipe is not recommended is the buildup of static electricity and the high risk of explosion.
With a metal dust collection piping system, static electrically won't develop. Elbows and other various fittings are properly designed for conveying dust. The diversity of fittings and accessories will enable you to meet design requirements.
When we create a duct system, the interior should be as obstruction-free as possible. A copper wire will snag chips and curls. In addition, many extraction systems are abrasive, such as the conveying of hardwood chips. This material will wear the copper wire.
While removing the plastic (prior to a metal install) on a Monday after a non-working weekend, I noticed that the pipe still held a charge from the previous Friday's work. As a precaution I put on light duty rubber gloves. I got zapped right through the gloves by the static discharge from a length of pipe connected to the planer, which had been working hard the previous week. A few minutes later I picked up a piece of pipe that had also been connected to the planer and watched as a large spark arced from the pipe to my chest. These shocks were not life-threatening, as the discharge was mostly voltage with little amperage. That said, they made me painfully aware of the potential for static build-up.
You may get away with a plastic system for years, but some day when you are collecting large quantities of fine dust through your new wide-belt sander, disaster may strike. I'd never consider using anything but metal pipe for dust collection.
Comment from contributor A:
In Oregon, if you are an employer, the OSHA rule pertaining to PVC air pipe in your shop is 437-002-0210, which states in part "PVC pipe can only be used for compressed air if it is buried or encased". Employers in other states may have similar codes they are subject to.
I have seen some air pipe burst causing shop damage and narrowly missing the owner. Luckily, no one was injured.