Clogged up conduits inside tank foundation

[Dodger_Fan123]

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.

 

[Dodger_Fan123]

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.

 

[LittleInch]

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.

 

[Dodger_Fan123]

Pull boxes are small boxes on the edge of the foundation. these are where each conduits starts.

 

[LittleInch]

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.

 

[Dodger_Fan123]

One multi core.