Does it matter what kind of pipe is used for a sink drain?

Question

The drainpipe in our sink broke (corroded right through in several places). Not having the time to find my pipe wrench (much less actually replace the pipe) we called a plumber. The plumber replaced the drainpipe with PVC (under the theory it would be immune from corrosion).

So I got to wondering: Is there any reason to prefer one kind of drainpipe to another? I know that for blackwater lines you need to make sure the urine won't corrode the pipe, but for a kitchen sink does it matter at all? I could even use lead pipes since that water will be treated before anyone drinks it, right?

Answer 1

There are two main factors that determine what is used:

1. Code requirements (as well as the project's specifications)
2. Cost

ABS and PVC are the cheapest, however there can be limitations with their use in larger buildings due to fire code requirements.

Where fire codes requirements limit the use of plastics, either cast-iron or DWV copper is used for the piping above ground switching to either Chrome or Brass p-traps for the sinks. However depending on the authority having jurisdiction (usually the local inspector), PVC or ABS p-traps may be permitted within the sink cabinet.

XFR-PVC is a kind of fire resistant PVC, and does meet flame and smoke spread requirements and, depending on the project, may be allowed to be used instead of Cast-iron or DWV copper where metal is typically required.

Chrome plated metal is also used for wall hung sinks where the p-trap will be left exposed.

Labs that use chemicals and acids typically use either glass or special acid resistant plastic pipe and p-traps.

Answer 2

I think new sink drainpipes are almost all PVC. I recently replaced a corroded metal kitchen sink pipe with PVC, but in the store I noticed that metal downpipes are still available.

In theory PVC should be more resistant to chemicals and rust while metal is more resistant to heat. But most drain cleaners don't contain lye any more and nobody in their right mind dumps 500F fluid into a sink. Rust, however, is still a problem.

Yes, I think the concern with lead is the contamination of incoming water more than outgoing. And plumbers sometimes still do use molten lead to repair old drain tile junctions. But I doubt most municipal water treatment facilities are equipped to extract a high level of heavy metals, so it's probably better to get the lead out anywhere possible.

Answer 3

`As a note, some codes specify you use only PVC or ABS (almost all allow metal). Also because of codes, sometimes there is a stronger availability of one type of plastic or the other, again, so you may want to choose the more common ("regional availability"). One type may be cheaper in your area, as well, another factor. For larger buildings you may be required by code to use metal.

PVC (at least sched. 40 thickness is required):

Lasts "about forever," resists corrosion, cheap. Doesn't sag as much as ABS (on very long horizontal pipes, for instance). Requires both a primer and glue, which is more work to install). Fittings may hold up better. Typically white. Is said to be slightly quieter than ABS. If on rooftop (i.e. vent) might degrade more quickly than ABS. It's rumored to be more brittle than ABS in cold climates (shatter more easily), though typically your sink drain pipes might be exposed to temperature extremes (vents on the roof might though). Temperature rating is max 180 °F (typically high enough for typical drain use). Might be more resistant to chemicals, if it's a laboratory. Might shatter more easily after being exposed to cold a lot.

ABS:

Lasts "about forever," resists corrosion, cheap. Can glue without a primer (faster install/labor). Typically black. Apparently it can deform if left in the sun for short periods of time, though PVC and ABS both become brittle if left in the sun for long, so be careful there, possibly painting vents, etc. Is said to have better impact strength (read "smash it with a hammer") than PVC, though hopefully you're not accidentally smashing pipes anyway. It is said to "continue burning" after the flame is extinguished, therefore sometimes disallowed in commercial buildings. Is said to have worse fittings over time than ABS. Temperature rating -40 °F to 180 °F.

In the end, ABS is "made for" DWV, and works great. PVC also works great. Note that you cannot trivially direct connect (as in glue) ABS to PVC pipes, some codes require a special joining connector, etc. This isn't as big of a deal with sink drains (since you're screwing it into the wall anyway, not gluing it together) but is for normal pipe lines. It may be worth it to "stick with what's already there" (ex: what's in the wall) in case it adds stability. Some people seem to prefer ABS, some PVC. Since the drain is indoors, so few temperature extremes, no long pipes, they'll probably both work under the sink.

Cast Iron:

More fire safe. Less noisy (frequently used for vertical pipes because of that). Can gets lime deposit build-up, etc over time, especially on smaller pipes. You can chrome plate it for looks.

Copper:

More fire safe. Susceptible to chemicals poured down it and corrosion over time causing it to weaken. You can chrome plate it for looks.