Corrosion in/on Pullboxes, Hubs, Conduit, etc.

[erickench]

Hi everybody, I just completed an inspection of about 50 pull boxes located in the conduit system above the lower roadway of a very high bridge. I took photos and wrote checklists of the whole facility. I found that alot of the pullboxes, hubs, and some conduit threads/ends are corroded. Some of the gaskets were deteriorating and alot of screws were corroded and stripped so that the pullbox could not be opened. What I need is a step by step procedure on how to refurbish this equipment. I'm an engineer, not an electrician. Does anyone have any ideas? Perhaps a link to a website? Would appreciate it.

 

[don_resqcapt19]

From your description, I think you are beyond refurbishment. I would be looking at replacement with either PVC coated rigid, or stainless, or with standard rigid with plans to replace every 10-15 years.

 

[erickench]

This conduit system was installed five years ago. The conduit itself is in pretty good shape. The idea that we have is to perhaps refurbish the pullboxes.

 

[petersonra]

Does it matter any?

It is probably not really fixable. Maybe cover the pull boxes with some kind of tar like substance to stop any further deterioration.

You can't really fix it. It is a gut it and start over kind of thing.

 

[erickench]

Does it matter any?

It is probably not really fixable. Maybe cover the pull boxes with some kind of tar like substance to stop any further deterioration.

You can't really fix it. It is a gut it and start over kind of thing.

Okay some of the boxes are severely corroded and would require replacement. We could just remove the pullbox and replace it with another. Problem is that there would be alot of cutting and splicing of the cables. There was already an accident in one of the pullboxes where the splice overheated and it actually burned through the wrap. When I first saw the photo I thought it was a bad connection. But a bad connection can be caused by either bad crimping or corrosion on the wire ends. But if we increase the number of splices in the system then it would increase the chances of more accidents of this type.

 

[Smart $]

Okay some of the boxes are severely corroded and would require replacement. We could just remove the pullbox and replace it with another. Problem is that there would be alot of cutting and splicing of the cables. There was already an accident in one of the pullboxes where the splice overheated and it actually burned through the wrap. When I first saw the photo I thought it was a bad connection. But a bad connection can be caused by either bad crimping or corrosion on the wire ends. But if we increase the number of splices in the system then it would increase the chances of more accidents of this type.

You are answering your own question.

 

[erickench]

You are answering your own question.

Just trying to see what everyone else thinks.

 

[Smart $]

Just trying to see what everyone else thinks.

Budget will likely be the deciding factor.

Yes, some of the existing system can likely be salvaged... at the expense of integrity. It really is that simple. Putting a price tag on the possible remedies and choosing which remedy is the hard part. In the end sometimes, what started as the lower budget method can end up costing more in the long run though.

 

[pjholguin]

IMHO....it would be advantageous to replace the system with the proper materials, the benefits of doing this will play out in the labor saved. Sometimes, well most of time we tend to look at material cost, and forget the real killer in a budget MANHOURS. The time saved replacing system will be a lot less than trying fix each problem area. The old spend a $1.00 to save $ 0.10. :-(

PJHolguin

Budget will likely be the deciding factor.

Yes, some of the existing system can likely be salvaged... at the expense of integrity. It really is that simple. Putting a price tag on the possible remedies and choosing which remedy is the hard part. In the end sometimes, what started as the lower budget method can end up costing more in the long run though.

 

[Cow]

Go back in with stainless conduit, stainless myers hubs, and stainless enclosures and never work on it again. Anything else is just putting off the rust and corrosion for longer, but it will happen eventually.

 

[erickench]

Go back in with stainless conduit, stainless myers hubs, and stainless enclosures and never work on it again. Anything else is just putting off the rust and corrosion for longer, but it will happen eventually.

The pull boxes are actually conduit bodies. That's where most of the corrosion is.

 

[Cow]

The pull boxes are actually conduit bodies. That's where most of the corrosion is.

What kind of conduit bodies? Form 7? 35? Potmetal aluminum type?

 

[petersonra]

Okay some of the boxes are severely corroded and would require replacement. We could just remove the pullbox and replace it with another. Problem is that there would be alot of cutting and splicing of the cables. There was already an accident in one of the pullboxes where the splice overheated and it actually burned through the wrap. When I first saw the photo I thought it was a bad connection. But a bad connection can be caused by either bad crimping or corrosion on the wire ends. But if we increase the number of splices in the system then it would increase the chances of more accidents of this type.

Your OP never mentioned problems with splices in pull boxes.

There are ways to splice wires that protect the integrity of the wires, even in corrosive environments. Wire nuts or split bolts are not the answer in such an environment.

Is this AL wiring by any chance? That would make the situation worse.

I don't quite understand your "bad crimping" comment. A properly crimped and re-insulated connection is about as corrosion resistant as the wire itself. Are you saying the problem is poor workmanship?

 

[petersonra]

What kind of conduit bodies? Form 7? 35? Potmetal aluminum type?

Why would a bridge spec allow the use of AL conduit bodies?

 

[petersonra]

Go back in with stainless conduit, stainless myers hubs, and stainless enclosures and never work on it again. Anything else is just putting off the rust and corrosion for longer, but it will happen eventually.

One of his posts claimed that splices were failing as well. Changing the conduit to SS won't fix that problem.

 

[erickench]

No the equipment is not aluminum. The conduit bodies are 24 inches long as the conduit itself in 3 inches. I guess it comes down to a decision on whether or not we replace just the conduit bodies or just replace the whole conduit system.

 

[petersonra]

No the equipment is not aluminum. The conduit bodies are 24 inches long as the conduit itself in 3 inches. I guess it comes down to a decision on whether or not we replace just the conduit bodies or just replace the whole conduit system.

I think I would figure out just why the bridge is experiencing so much corrosion. Don't want to be back 5 years from now replacing it again.

 

[gadfly56]

I think I would figure out just why the bridge is experiencing so much corrosion. Don't want to be back 5 years from now replacing it again.

In that vein, I'm not sure that stainless steel is the answer. Eric is in my neck of the woods, and dollars to donuts they are slathering the bridge with salt during the winter. NaCl and stainless don't play well together, you'll get stress crack corrosion. Might need to go to an active protection system.

 

[erickench]

Okay lets suppose that we decide to replace the RMC with PVC coated metal conduit as made by Thomas & Betts. This type of conduit is neither pure metallic or pure PVC. How would you support this conduit? Would you support it at 10 foot intervals as you would with RMC or would you support it in accordance with NEC Table 352.30? The existing conduit system is 3" diameter.

 

[Smart $]

Okay lets suppose that we decide to replace the RMC with PVC coated metal conduit as made by Thomas & Betts. This type of conduit is neither pure metallic or pure PVC. How would you support this conduit? Would you support it at 10 foot intervals as you would with RMC or would you support it in accordance with NEC Table 352.30? The existing conduit system is 3" diameter.

Typically PVC-coated GRC and supported at intervals just like GRC (RMC).