Help, calcium/efflorescence buildup in conduit

[squirm]

Hello, I have a problem with one of our electrical projects that we did. I was notified after one of the projects we finished a few years ago, there is a efflorescence like build up inside the PVC conduits that are embedded in the duct banks. The build up in the conduit seems to have solidified and we're not sure how to remove it. I'm guessing water is seeping through the concrete ductbank, and carring minerals and salts with it, and then seeping into the conduit. Once there it is evaporting and leaving behind the salts, etc.

The conduits are empty, there are no conductors in them, yet fortunately and thus I'm exploring options on how to desolve it out of the conduits. Has anyone encountered this before? I've search around and haven't found anything! I was hoping to find something on IEEE or similar. Thanks for any input.

 

[eric9822]

That's pretty common where I am. We usually pull a steel brush mandrel through and then followup with a cleaning mandrel.

http://www.rothenbergertools.us/62.html

 

[chris kennedy]

I was notified after one of the projects we finished a few years ago, there is a efflorescence like build up inside the PVC conduits that are embedded in the duct banks.

Did someone E-mail you pictures of these deposits? If so could you share?

Welcome to the Forum.

 

[big john]

This is a constant problem where I work, because minerals seep into any conduit inside the dams. What I do is pour a mixture of 50% water and vinegar down the pipes. The longer you allow it to sit inside the pipe and work it's magic, the better off you are. Do a couple passes with a wire brush to break loose the scale. Then flush the mess out with clean water.

I've never had to do this on an entire duct bank, so the 50/50 mix might not be cost effective. The goal is just to get the water as acidic as possible so it eats away at the calcium.

-John

 

[nicholaaaas]

This is a constant problem where I work, because minerals seep into any conduit inside the dams. What I do is pour a mixture of 50% water and vinegar down the pipes. The longer you allow it to sit inside the pipe and work it's magic, the better off you are. Do a couple passes with a wire brush to break loose the scale. Then flush the mess out with clean water.

I've never had to do this on an entire duct bank, so the 50/50 mix might not be cost effective. The goal is just to get the water as acidic as possible so it eats away at the calcium.

-John

you do that when you have conductors in the conduit?

 

[PetrosA]

I agree that acidity is the solution if it's a calcium deposit. The best first step would be to gather some and test white vinegar on it to make sure it'll dissolve it. If it does, and you have a large volume of deposits and conduit, you may be better off getting food grade citric acid in powder form and mixing that up to pour in. Just for safety you could call the conduit manufacturer and get confirmation that the PVC is acid resistant, but I think you'll be fine with citric acid. There are stronger acids out there that come in bulk industrial packages (Phosphoric, hydrochloric and sulfamic are commonly used for descaling) but with them I would definitely check with the manufacturers of the PVC and wire for compatibility. You would also probably need respirators to use them as they can give off some nasty gases.

 

[LHarrington]

We have used in the past a household cleaner called CLR, which is an acronym for Calcium, Lime and Rust. It typically used in bathrooms to clean hard water stains, calcium build up and lime deposits, but has worked well in this application. It has proven to be save on PVC and metal conduit. It includes many of the ingredients others have suggested.

LHarrington

 

[Data Center Electrician]

Be careful with some of the acids because they will produce Flammable hydrogen gas as a byproduct. If these solids just came out of solution with evaporation you may be able to wash them out with water and pulling a brush through the pipe a couple times. It will be less expensive.

 

[mcclary's electrical]

you do that when you have conductors in the conduit?

How could that be possible?

 

[squirm]

Hello everyone and thank you very much for your replies. I unfortunately do not have any pictures at this time. Currently I am just going by hearsay. The problem stems from a facility located close to a river, where I suspect high hydrostatic pressure is pushing efflorescence/salty ground water through the concrete duct bank, into the conduits. These conduits are empty at this time.

However, here is another question. The above corrections sound reasonable and thank you, is there a method to prevent it? I have heard there is a product that will permeate it's way through concrete and fill the voids and prevent seepage, do you know the name? Whether it actually works or not is another issue I guess. Second question, what would be the consequence of doing nothing? Obviously the conduits will be used sometime in the future, however is there any reasonble conclusion to take care of this issue now? I'd like to draft a response and due to budget issues have to cover all avenues including a do nothing scenario.

This is a very strange issue that I haven't encountered and therefore appreciate everyone's expertise on this. Thank you very much.

 

[chris kennedy]

This is a very strange issue that I haven't encountered and therefore appreciate everyone's expertise on this.

Agreed, this is a bump.

 

[nicholaaaas]

How could that be possible?

that's why i asked. you figure if the problem is in empty conduits it's in conduits wire wires in em too

 

[big john]

you do that when you have conductors in the conduit?

It definitely does happen in pipes with wires in 'em, but 90% of the time when I've had to do this it was because I wanted to remove the conductors that were frozen in the conduit. Then I do a couple passes with the brush before pulling new conductors in.

There've only been a couple of times where I needed to leave wires in, in which case the vinegar/water allowed me to get a snake through the pipe.

As far as the vinegar reacting with the pipe/wires: Vinegar is mild, it doesn't sit in there long, and fresh water flushes the pipe clean. I don't lose sleep over it.

-John

 

[eric9822]

Second question, what would be the consequence of doing nothing?

I have two concrete encased duct banks, 12 each 5" PVC filled with 12.47KV and 4.16KV feeders. All the spare conduits are full of calcium and a salt type buildup. We recently pulled out a 30 year old feeder as part of a capacity increase and I thought we were going to pull the tugger off the floor getting the old feeder to break free. We haven't had any problems other then more work when we need to pull cable.

 

[squirm]

Hello everyone

Hello everyone

Here is a recent picture.

What do you think? (no it's not snow)

 

[squirm]

Another picture

Another picture

 

[steve66]

Wow!!! That's a lot of buildup. Sorry, I don't have any suggestions other than to write off the conduit.

 

[PetrosA]

I don't think that's calcium... It would need to be heated to form that kind of solid or it would need more than a few years to build up to that degree. What's the consistency of that stuff? What kind of soil is around the concrete that the pipe is in? Is there any industry in the area whose runoff would explain it or which might be leaking acidic liquids or gases that could create this in a reaction with the concrete itself? It just seems like too much buildup to be happening naturally.

 

[rcwilson]

My non-technical analysis is the site was visited by the Ghostbuster marshmallow monster . That is some build up! It almost looks like a foaming chemical reaction.

As you surmized, maybe the river water is pushing all of the calcium to the conduit stub up.

Good luck!

 

[don_resqcapt19]

That conduit appears to be PVC coated rigid, normally indicating some type of chemical corrosion issue. I would expect that the buildup is related to the chemicals used in the process.