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Clogged up conduits inside tank foundation

Clogged up conduits inside tank foundation

Clogged up conduits inside tank foundation

(OP)
Hi all. We have been tasked with replacement of old heating cables pulled through conduits embedded in the foundation of storage tanks (for preventing frost heave). However, these conduits (3/4") are ancient and in many places clogged up. Just pulling out those old cables has proven to be impossible. Anyone face something like this before? Any ideas on how to clear this mess up? Thanks in advance.

RE: Clogged up conduits inside tank foundation

You might try connecting to a fairly high pressure water system to try to flush them out, but depending on the existing conduit layout, that could be difficult. It could also be that there is no conduit left as it may have corroded away. If it is concrete encased, you still may be able to clear it out and pull heat tape through the opening in the conduit, but without the metal raceway, I don't think the heat transfer will be a good.

RE: Clogged up conduits inside tank foundation

Sounds like not possible, but what are the details?

Tube material?
Tube ID
Length of Tube?
Cable OD
Type of insulation?
How old is "ancient"?

Might be better in the storage tank forum.


Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Clogged up conduits inside tank foundation

(OP)
Thank you all. Sorry about the late reply. These are SS tubes (3/4" ID) ID about 0.58" length over 20m with just heating cables pulled through them. installed over 40 years ago.

RE: Clogged up conduits inside tank foundation

While this may be obvious on site, from a distance I have to ask:
Are you sure that the conduits are continuous?
Some installations may use direct burial heating cables with lengths of conduit on the ends for mechanical protection.
If continuous, try very high pressure water, left pressurized all day.
If removing the cables is impossible, abandon in place and use directional drilling to install new cables.
Consider perimeter cables installed down to below the frost line, and one or two cables under the tank.
The under tank cable does not have to be in contact with the tank.
If the conduits are electrically continuous, you may be able to use low voltage to drive a current through the conduits and use the conduits as heaters.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

RE: Clogged up conduits inside tank foundation

You are reported as posting from Kuwait.
Is that where the job is?
I wasn't aware that freezing was an issue in Kuwait.
Are you sure that the cables are not cathodic protection?
Kuwait?
Not serious. I've been in Central America and have been reported as located in Virginia.
(I wonder if I am on the Company's radar .)(Common abbreviation of a Spanish translation)

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

RE: Clogged up conduits inside tank foundation

(OP)
Thank you waross for your valuable inputs. Yes these are cryogenic tanks hence the possibility of ground freezing up.
The cables are indeed heating cables pulled through continuous conduits. Yes I am based in ME and I have encountered this exact problem in two other sites in the region (current site being in Iraq). Pressurized water might be the way to go; we will give it a shot anyway.

RE: Clogged up conduits inside tank foundation

What sort of connection can you get onto the tubes? I assume you can get access to both ends so need to leave room for availability of cable at both ends.

Any idea which direction they were installed? Going the same direction as installation might be a good idea.

Some sort of very light oil or maybe bentonite could be better.

But from your data you have a max annulus of 4mm? That's not a lot. But is there any sort of tubing you can find that can squeeze into the gap?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Clogged up conduits inside tank foundation

(OP)
We will try first with the pressurized water and lets see if it produces any results!! Also not all of them are damaged so we will replace wherever it is possible.

RE: Clogged up conduits inside tank foundation

If you could get a small tube in as far as possible and blow out might help with air or water. All the sand and dust and spiders has only come from the outside so it might not be the best to blow all that through the pipe?

Do both ends and then see?

Photos always help.

Of course if your foundation has cracked or settled a bit of you had frost heave in the middle of the slab then the tubes might be crushed or broken?

Kind of curios as to why you're replacing them if they haven't worked for a while? The damage has already been done?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Clogged up conduits inside tank foundation

(OP)
Photos are always difficult as cameras are not allowed; Ill google for similar images though. Cracked conduits in the middle is the nightmare scenario, we are hoping for best. Over time the heat output of the cables have been insufficient; Client wants to replace them with the latest cables.

RE: Clogged up conduits inside tank foundation

If the pipe passes through without bends, and the high pressure water does not work, you may be able to run some type of small sectional drill though the tubes. It would be very time consuming as you would have to keep pulling the drill rods back out to clear the debris.

The last one I worked on did not even use heating cables.... just long lengths of 14AWG copper wire with XHHW insulation connected directly to the power source. In that one, the conduits did to straight across the pad to junction boxes on the outside of the pad at each side.

RE: Clogged up conduits inside tank foundation

It may be time to discuss with the client the possibility of directional drilling and installing oversized conduits.
Seal the ends to prevent the ingress of dirt.
I sometimes see small cavities plugged by insects building nests.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

RE: Clogged up conduits inside tank foundation

ps: I do see small cavities plugged with fine dust. The "insects building nests" is an assumption.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

RE: Clogged up conduits inside tank foundation

(OP)
@resqcapt19 WOW. Its exactly the case here too. Same wire used here; we are gonna replace them with newer models. Did you face difficulty in pulling the new cables?

RE: Clogged up conduits inside tank foundation

(OP)
Installing new conduits is out of the equation. They will build a whole new tank in that case, if it comes to that.

RE: Clogged up conduits inside tank foundation

What's the plan view of the cable layout?

Are they equally spaced across the tank so that some are shorter than others?
Start with the shortest and see what happens.

Then pull one to destruction / yield and then start flushing water / oil etc from the now broken end? At least it will be a lot easier to attach a pipe coupling to and then pull from the other side.

Or at least if you then drill it out some of the cable will be gone.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Clogged up conduits inside tank foundation

@
Dodger_Fan123 We had some difficulty but not a lot. The conduits in the one I worked on were 3/4" rigid conduit and where we could not pull the existing wire out, we were able to force a 1/4" spring steel fish tape through to open it up enough to flow water through. The water was to force out as much debris as possible before replacing the 14 AWG conductors. As I recall the diameter of the tank pad was about 80', but it was 30+ years ago.

RE: Clogged up conduits inside tank foundation

Perhaps I should have said Horizontal drilling.
A couple of years ago, a long distance water main was installed alongside of the highway in front of our home.
They used horizontal drilling for distances of about 1/4 mile.
They are able to hit an access pit 1/4 mile away.
It was cheaper than trenching.
Explore this web-site:
https://www.directional.ca/

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

RE: Clogged up conduits inside tank foundation

One of the issues with directional boring will be thermal contact with the earth. A number of years ago, they did a geothermal project here using directional boring, but did not get the space between the geothermal piping and the bored hole in the earth filled with thermally conductive material. The system did not work very well unit a few years later when the earth around the bore holes had collapsed and provided thermal contact with the piping.

RE: Clogged up conduits inside tank foundation

(OP)
Thank you all for the ideas!

@littleinch

Rough pic attached (its a crude representation in ms paint, sorry!). The only places where we can actually see the cables are the pull boxes located on the foundation edges; rest of the conduits buried in the foundation. its a single run cable starting from jb 1 until the end.

@resqcapt19

We are putting forward to our clients this exact method! We will first try to run a fish wire and see if its gonna work; clear the conduits one by one. We will need tank shutdown so its a while away

@waross

Drilling on the foundation is a no-no since there is a chance to affect structural integrity.


RE: Clogged up conduits inside tank foundation

One thing you could do if you can find a spare length of the same cable is establish what exactly its yield strength is in terms of force and its UTS/ breakage. The vendors will probably have FoS involved but you need to know how much can you pull until you start to go plastic.

Then at least you could try pulling ot the yield force then relaxing and trying the other way, then relaxing and....

A bit of pull / push often works, especially if you can inject or force in some sort of lubricant - water, light oil, drilling fluid.

Clearly those middle runs are the worst but start on the short lines and see what happens.

Is each end a pull box and you can get to them or something else?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Clogged up conduits inside tank foundation

So long as there is enough cable to get a good grip on then that's enough.

Are there three separate cables or one multicore?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Clogged up conduits inside tank foundation

(OP)
One multi core.

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