Corrosion of Ductile Iron Drain Piping

[KenRad]

I have a system of floor drains that serves a cafeteria. All drain piping is ductile iron. This week, we had a P-trap that developed a hole in the side of it, and began to leak over a production line. When we removed the trap and inspected it, there was an area about 2" x 2" that could be pushed in with your finger.

Does anyone have any idea what would cause drain piping to do this? The system is only 15 years old. This particular drain line is 3", and serves a number of softdrink dispensers. To my knowledge, there has never been any drain chemicals put into the system.

Thanks in advance!

---KenRad

 

[pedarrin]

I have seen similar problems with cast iron piping under kitchens. The piping I witnessed was probably 20+ years old.

The question I would ask is why was ductile iron used for drainage piping?

In my neck of the woods, where the International Plumbing Code is used, ductile iron is not an approved material for drainage piping. It is approved for water supply, but not for drainage.

I am not very familiar with the corrosion characteristics of ductile iron to say exactly how it happened. Maybe try the corrosion engineering forum for more information.

That being said, drainage from soft drink dispensers would contain some carbonic acid. This is a fairly weak acid which probably does not contribute much to corrosion, but it might.

Another more likely thing is you might just have rust forming in the piping because you have water with some electrolytes and air in the piping.

My suggestion would be replace all the piping or you might have more of thes problems in the future.

 

[nomad42]

I have heard of this before. Replace with PVC or FRP piping. The carbolic acid will attack and destroy cast iron and ductile iron.

 

[rconner]

I believe ductile iron piping is quite commonly used for drain/waste piping in at least 4" and larger sizes, but I had not before heard of a three inch ductile iron "P-trap". You may wish to confirm that this p-trap is ductile iron. Also, is the piping lined?